client: fix typo in selectdata help text

sources: add configurable limits for stratum
Add minstratum and maxstratum directives to specify the minimum and maximum allowed stratum of sources to be selected. The default values are 0 and 15 respectively, allowing all NTP sources and refclocks. Sources that are rejected due to having too large or too small stratum are marked with 'r' in the selection log and selectdata report. This is similar to the "tos floor" and "tos ceiling" settings of ntpd, except that maxstratum is interpreted as one below the ceiling.
2025-12-03 18:25:07 -05:00 · 2025-11-04 14:47:35 +01:00 · 2025-11-04 14:47:35 +01:00 · 2025-11-04 14:47:35 +01:00 · 2025-11-04 14:47:35 +01:00 · 2025-11-04 14:47:35 +01:00
249 changed files with 17905 additions and 5849 deletions
--- a/Makefile.in
+++ b/Makefile.in
@@ -33,9 +33,13 @@ CFLAGS = @CFLAGS@
 CPPFLAGS = @CPPFLAGS@
 LDFLAGS = @LDFLAGS@

+GETDATE_CFLAGS = @GETDATE_CFLAGS@
+
 EXTRA_OBJS = @EXTRA_OBJS@

-OBJS = array.o cmdparse.o conf.o local.o logging.o main.o memory.o \
+OBJS = addrfilt.o array.o clientlog.o cmdparse.o conf.o keys.o leapdb.o \
+       local.o logging.o main.o memory.o nameserv.o nameserv_async.o \
+       ntp_auth.o ntp_core.o ntp_ext.o ntp_io.o ntp_sources.o quantiles.o \
       reference.o regress.o rtc.o samplefilt.o sched.o socket.o sources.o sourcestats.o \
       stubs.o smooth.o sys.o sys_null.o tempcomp.o util.o $(EXTRA_OBJS)

@@ -61,6 +65,8 @@ chronyd : $(OBJS)
 chronyc : $(CLI_OBJS)
 	$(CC) $(CFLAGS) -o chronyc $(CLI_OBJS) $(LDFLAGS) $(LIBS) $(EXTRA_CLI_LIBS)

+getdate.o: CFLAGS += $(GETDATE_CFLAGS)
+
 distclean : clean
 	$(MAKE) -C doc distclean
 	$(MAKE) -C test/unit distclean
--- a/198
+++ b/198
@@ -1,3 +1,192 @@
+New in version 4.8
+==================
+
+Enhancements
+------------
+* Add maxunreach option to limit selection of unreachable sources
+* Add -u option to chronyc to drop root privileges (default chronyc
+  user is set by configure script)
+
+Bug fixes
+---------
+* Hide chronyc socket to mitigate unsafe permissions change
+* Fix refclock extpps option to work on Linux >= 6.15
+* Validate refclock samples for reachability updates
+
+New in version 4.7
+==================
+
+Enhancements
+------------
+* Add opencommands directive to select remote monitoring commands
+* Add interval option to driftfile directive
+* Add waitsynced and waitunsynced options to local directive
+* Add sanity checks for integer values in configuration
+* Add support for systemd Type=notify service
+* Add RTC refclock driver
+* Allow PHC refclock to be specified with network interface name
+* Don't require multiple refclock samples per poll to simplify
+  filter configuration
+* Keep refclock reachable when dropping samples with large delay
+* Improve quantile-based filtering to adapt faster to larger delay
+* Improve logging of selection failures
+* Detect clock interference from other processes
+* Try to reopen message log (-l option) on cyclelogs command
+
+Bug fixes
+---------
+* Fix sourcedir reloading to not multiply sources
+* Fix tracking offset after failed clock step
+
+Removed features
+----------------
+* Drop support for NTS with Nettle < 3.6 and GnuTLS < 3.6.14
+* Drop support for building without POSIX threads
+
+New in version 4.6.1
+====================
+
+Enhancements
+------------
+* Add ntsaeads directive to enable only selected AEAD algorithms for NTS
+
+Workarounds
+-----------
+* Negotiate use of compliant NTS keys with AES-128-GCM-SIV AEAD algorithm
+  (by default the keys are generated differently than in RFC 8915 for
+  compatibility with chrony server and client versions 4.4, 4.5, and 4.6)
+* Switch to compliant NTS keys if first response from server is NTS NAK
+
+New in version 4.6
+==================
+
+Enhancements
+------------
+* Add activate option to local directive to set activation threshold
+* Add ipv4 and ipv6 options to server/pool/peer directive
+* Add kod option to ratelimit directive for server KoD RATE support
+* Add leapseclist directive to read NIST/IERS leap-seconds.list file
+* Add ptpdomain directive to set PTP domain for NTP over PTP
+* Allow disabling pidfile
+* Improve copy server option to accept unsynchronised status instantly
+* Log one selection failure on start
+* Add offset command to modify source offset correction
+* Add timestamp sources to ntpdata report
+
+Bug fixes
+---------
+* Fix crash on sources reload during initstepslew or RTC initialisation
+* Fix source refreshment to not repeat failed name resolving attempts
+
+New in version 4.5
+==================
+
+Enhancements
+------------
+* Add support for AES-GCM-SIV in GnuTLS
+* Add support for corrections from PTP transparent clocks
+* Add support for systemd socket activation
+
+Bug fixes
+---------
+* Fix presend in interleaved mode
+* Fix reloading of modified sources from sourcedir
+
+New in version 4.4
+==================
+
+Enhancements
+------------
+* Add support for AES-GCM-SIV with Nettle >= 3.9 to shorten NTS
+  cookies to avoid some length-specific blocking of NTP on Internet
+* Add support for multiple refclocks using extpps option on one PHC
+* Add maxpoll option to hwtimestamp directive to improve PHC tracking
+  with low packet rates
+* Add hwtstimeout directive to configure timeout for late timestamps
+* Handle late hardware transmit timestamps of NTP requests on all sockets
+* Handle mismatched 32/64-bit time_t in SOCK refclock samples
+* Improve source replacement
+* Log important changes made by command requests (chronyc)
+* Refresh address of NTP sources periodically
+* Request nanosecond kernel RX timestamping on FreeBSD
+* Set DSCP for IPv6 packets
+* Shorten NTS-KE retry interval when network is down
+* Update seccomp filter for musl
+* Warn if loading keys from file with unexpected permissions
+* Warn if source selection fails or falseticker is detected
+* Add selectopts command to modify source-specific selection options
+* Add timestamp sources to serverstats report and make its fields 64-bit
+* Add -e option to chronyc to indicate end of response
+
+New in version 4.3
+==================
+
+Enhancements
+------------
+* Add local option to refclock directive to stabilise system clock
+  with more stable free-running clock (e.g. TCXO, OCXO)
+* Add maxdelayquant option to server/pool/peer directive to replace
+  maxdelaydevratio filter with long-term quantile-based filtering
+* Add selection option to log directive
+* Allow external PPS in PHC refclock without configurable pin
+* Don't accept first interleaved response to minimise error in delay
+* Don't use arc4random on Linux to avoid server performance loss
+* Improve filter option to better handle missing NTP samples
+* Improve stability with hardware timestamping and PHC refclock
+* Update seccomp filter
+
+Bug fixes
+---------
+* Fix waitsync command to reconnect when not getting response
+
+New in version 4.2
+==================
+
+Enhancements
+------------
+* Add support for NTPv4 extension field improving synchronisation
+  stability and resolution of root delay and dispersion (experimental)
+* Add support for NTP over PTP (experimental)
+* Add support for AES-CMAC and hash functions in GnuTLS
+* Improve server interleaved mode to be more reliable and support
+  multiple clients behind NAT
+* Update seccomp filter
+* Add statistics about interleaved mode to serverstats report
+
+Bug fixes
+---------
+* Fix RTC support with 64-bit time_t on 32-bit Linux
+* Fix seccomp filter to work correctly with bind*device directives
+* Suppress kernel adjustments of system clock (dosynctodr) on illumos
+
+Other changes
+-------------
+* Switch Solaris support to illumos
+
+New in version 4.1
+==================
+
+Enhancements
+------------
+* Add support for NTS servers specified by IP address (matching
+  Subject Alternative Name in server certificate)
+* Add source-specific configuration of trusted certificates
+* Allow multiple files and directories with trusted certificates
+* Allow multiple pairs of server keys and certificates
+* Add copy option to server/pool directive
+* Increase PPS lock limit to 40% of pulse interval
+* Perform source selection immediately after loading dump files
+* Reload dump files for addresses negotiated by NTS-KE server
+* Update seccomp filter and add less restrictive level
+* Restart ongoing name resolution on online command
+
+Bug fixes
+---------
+* Fix responding to IPv4 command requests on FreeBSD
+* Fix dump files to not include uncorrected offset
+* Fix initstepslew to accept time from own NTP clients
+* Reset NTP address and port when no longer negotiated by NTS-KE server
+
 New in version 4.0
 ==================

@@ -8,11 +197,13 @@ Enhancements
 * Add authselectmode directive to control selection of unauthenticated sources
 * Add binddevice, bindacqdevice, bindcmddevice directives
 * Add confdir directive to better support fragmented configuration
-* Add sourcedir directive and "reload sources" command to support
-  dynamic NTP sources specified in files
+* Add sourcedir directive and "reload sources" command to support dynamic
+  NTP sources specified in files
+* Add clockprecision directive
 * Add dscp directive to set Differentiated Services Code Point (DSCP)
 * Add -L option to limit log messages by severity
 * Add -p option to print whole configuration with included files
+* Add -U option to allow start under non-root user
 * Allow maxsamples to be set to 1 for faster update with -q/-Q option
 * Avoid replacing NTP sources with sources that have unreachable address
 * Improve pools to repeat name resolution to get "maxsources" sources
@@ -38,6 +229,9 @@ Bug fixes
 Removed features
 ----------------
 * Drop support for RIPEMD keys (RMD128, RMD160, RMD256, RMD320)
+* Drop support for long (non-standard) MACs in NTPv4 packets (chrony 2.x
+  clients using non-MD5/SHA1 keys need to use option "version 3")
+* Drop support for line editing with GNU Readline

 New in version 3.5.1
 ====================
--- a/53
+++ b/53
@@ -12,7 +12,7 @@ a time service to other computers in the network.
 It is designed to perform well in a wide range of conditions, including
 intermittent network connections, heavily congested networks, changing
 temperatures (ordinary computer clocks are sensitive to temperature),
-and systems that do not run continuosly, or run on a virtual machine.
+and systems that do not run continuously, or run on a virtual machine.

 Typical accuracy between two machines synchronised over the Internet is
 within a few milliseconds; on a LAN, accuracy is typically in tens of
@@ -28,7 +28,7 @@ What will chrony run on?
 ========================

 The software is known to work on Linux, FreeBSD, NetBSD, macOS and
-Solaris.  Closely related systems may work too.  Any other system will
+illumos.  Closely related systems may work too.  Any other system will
 likely require a porting exercise.

 How do I set it up?
@@ -47,32 +47,7 @@ Frequently Asked Questions (FAQ).
 The documentation is also available on the chrony web pages, accessible
 through the URL 

-    https://chrony.tuxfamily.org/
-
-Where are new versions announced?
-=================================
-
-There is a low volume mailing list where new versions and other
-important news relating to chrony are announced.  You can join this list
-by sending mail with the subject "subscribe" to
-
-chrony-announce-request@chrony.tuxfamily.org
-
-How can I get support for chrony?
-=================================
-
-There are two other mailing lists relating to chrony.  chrony-users is a
-discussion list for users, e.g. for questions about chrony configuration
-and bug reports.  chrony-dev is a more technical list for developers,
-e.g. for submitting patches and discussing how new features should be
-implemented.  To subscribe to either of these lists, send a message with
-the subject "subscribe" to
-
-chrony-users-request@chrony.tuxfamily.org
-or
-chrony-dev-request@chrony.tuxfamily.org
-
-as applicable.
+    https://chrony-project.org/

 License
 =======
@@ -91,7 +66,7 @@ Acknowledgements
 In writing the chronyd program, extensive use has been made of the NTPv3 (RFC
 1305) and NTPv4 (RFC 5905) specification.  The source code of the xntpd/ntpd
 implementation written by Dennis Fergusson, Lars Mathiesen, David Mills, and
-others, has been used to check the details of the protocol.
+others has been used to check the details of the protocol.

 The following people have provided patches and other major contributions
 to chrony:
@@ -100,19 +75,28 @@ Lonnie Abelbeck <lonnie@abelbeck.com>
 Benny Lyne Amorsen <benny@amorsen.dk>
 Andrew Bishop <amb@gedanken.demon.co.uk>
 Vincent Blut <vincent.debian@free.fr>
+Luca Boccassi <bluca@debian.org>
 Stephan I. Boettcher <stephan@nevis1.columbia.edu>
 David Bohman <debohman@gmail.com>
+Anthony Brandon <anthony@amarulasolutions.com>
 Goswin Brederlow <brederlo@informatik.uni-tuebingen.de>
 Leigh Brown <leigh@solinno.co.uk>
 Erik Bryer <ebryer@spots.ab.ca>
 Jonathan Cameron <jic23@cam.ac.uk>
 Bryan Christianson <bryan@whatroute.net>
 Juliusz Chroboczek <jch@pps.jussieu.fr>
+Paul Donald <newtwen+gitlab@gmail.com>
+Dan Drown <dan-ntp@drown.org>
+Kamil Dudka <kdudka@redhat.com>
 Christian Ehrhardt <christian.ehrhardt@canonical.com>
 Paul Elliott <pelliott@io.com>
 Robert Fairley <rfairley@redhat.com>
+Ahmad Fatoum <a.fatoum@pengutronix.de>
+Andreas Fenkart <extern-afe@mission-embedded.com>
 Stefan R. Filipek <srfilipek@gmail.com>
+Andy Fiddaman <illumos@fiddaman.net>
 Mike Fleetwood <mike@rockover.demon.co.uk>
+Rob Gill <rrobgill@protonmail.com>
 Alexander Gretencord <arutha@gmx.de>
 Andrew Griffiths <agriffit@redhat.com>
 Walter Haidinger <walter.haidinger@gmx.at>
@@ -120,10 +104,12 @@ Juergen Hannken-Illjes <hannken@eis.cs.tu-bs.de>
 John Hasler <john@dhh.gt.org>
 Tjalling Hattink <t.hattink@fugro.nl>
 Liam Hatton <me@liamhatton.com>
+Holger Hoffstätte <holger@applied-asynchrony.com>
 Jachym Holecek <jakym@volny.cz>
 Håkan Johansson <f96hajo@chalmers.se>
 Jim Knoble <jmknoble@pobox.com>
 Antti Jrvinen <costello@iki.fi>
+Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
 Eric Lammerts <eric@lammerts.org>
 Stefan Lucke <stefan@lucke.in-berlin.de>
 Victor Lum <viclum@vanu.com>
@@ -132,15 +118,23 @@ Paul Menzel <paulepanter@users.sourceforge.net>
 Vladimir Michl <vladimir.michl@seznam.cz>
 Victor Moroz <vim@prv.adlum.ru>
 Kalle Olavi Niemitalo  <tosi@stekt.oulu.fi>
+Patrick Oppenlander <patrick.oppenlander@gmail.com>
 Frank Otto <sandwichmacher@web.de>
 Denny Page <dennypage@me.com>
+Rupesh Patel <rupatel@redhat.com>
 Chris Perl <cperl@janestreet.com>
 Gautier PHILIPPON <gautier.philippon@ensimag.grenoble-inp.fr>
 Andreas Piesk <apiesk@virbus.de>
+Shachar Raindel <shacharr@google.com>
+Mike Ryan <msr@hsilop.net>
+Baruch Siach <baruch@tkos.co.il>
+Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
+Foster Snowhill <forst@forstwoof.ru>
 Andreas Steinmetz <ast@domdv.de>
 NAKAMURA Takumi <takumi@ps.sakura.ne.jp>
 Timo Teras <timo.teras@iki.fi>
 Bill Unruh <unruh@physics.ubc.ca>
+Luke Valenta <lvalenta@cloudflare.com>
 Stephen Wadeley <swadeley@redhat.com>
 Bernhard Weiss <lisnablagh@web.de>
 Wolfgang Weisselberg <weissel@netcologne.de>
@@ -148,6 +142,7 @@ Bernhard M. Wiedemann <bwiedemann@suse.de>
 Joachim Wiedorn <ad_debian@joonet.de>
 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
 Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>
+Michael Witten <mfwitten@gmail.com>
 Doug Woodward <dougw@whistler.com>
 Thomas Zajic <zlatko@zlatko.fdns.net>

--- a/array.c
+++ b/array.c
@@ -116,6 +116,21 @@ ARR_AppendElement(ARR_Instance array, void *element)
  memcpy(e, element, array->elem_size);
 }

+void
+ARR_RemoveElement(ARR_Instance array, unsigned int index)
+{
+  void *e, *l;
+
+  e = ARR_GetElement(array, index);
+  l = ARR_GetElement(array, array->used - 1);
+
+  if (e < l)
+    memmove(e, (char *)e + array->elem_size, (char *)l - (char *)e);
+  array->used--;
+
+  realloc_array(array, array->used);
+}
+
 void
 ARR_SetSize(ARR_Instance array, unsigned int size)
 {
--- a/array.h
+++ b/array.h
@@ -47,6 +47,9 @@ extern void *ARR_GetElements(ARR_Instance array);
 /* Add a new element to the end of the array */
 extern void ARR_AppendElement(ARR_Instance array, void *element);

+/* Remove element with given index */
+extern void ARR_RemoveElement(ARR_Instance array, unsigned int index);
+
 /* Set the size of the array */
 extern void ARR_SetSize(ARR_Instance array, unsigned int size);

--- a/candm.h
+++ b/candm.h
@@ -37,7 +37,6 @@
 #define DEFAULT_CANDM_PORT 323

 /* Request codes */
-#define REQ_NULL 0
 #define REQ_ONLINE 1
 #define REQ_OFFLINE 2
 #define REQ_BURST 3
@@ -108,7 +107,11 @@
 #define REQ_CLIENT_ACCESSES_BY_INDEX3 68
 #define REQ_SELECT_DATA 69
 #define REQ_RELOAD_SOURCES 70
-#define N_REQUEST_TYPES 71
+#define REQ_DOFFSET2 71
+#define REQ_MODIFY_SELECTOPTS 72
+#define REQ_MODIFY_OFFSET 73
+#define REQ_LOCAL3 74
+#define N_REQUEST_TYPES 75

 /* Structure used to exchange timespecs independent of time_t size */
 typedef struct {
@@ -120,6 +123,12 @@ typedef struct {
 /* This is used in tv_sec_high for 32-bit timestamps */
 #define TV_NOHIGHSEC 0x7fffffff

+/* Structure for 64-bit integers (not requiring 64-bit alignment) */
+typedef struct {
+  uint32_t high;
+  uint32_t low;
+} Integer64;
+
 /* 32-bit floating-point format consisting of 7-bit signed exponent
   and 25-bit signed coefficient without hidden bit.
   The result is calculated as: 2^(exp - 25) * coef */
@@ -213,11 +222,6 @@ typedef struct {
  int32_t EOR;
 } REQ_Modify_Makestep;

-typedef struct {
-  Timespec ts;
-  int32_t EOR;
-} REQ_Logon;
-
 typedef struct {
  Timespec ts;
  int32_t EOR;
@@ -228,6 +232,9 @@ typedef struct {
  int32_t stratum;
  Float distance;
  int32_t orphan;
+  Float activate;
+  Float wait_synced;
+  Float wait_unsynced;
  int32_t EOR;
 } REQ_Local;

@@ -268,6 +275,11 @@ typedef struct {
 #define REQ_ADDSRC_INTERLEAVED 0x80
 #define REQ_ADDSRC_BURST 0x100
 #define REQ_ADDSRC_NTS 0x200
+#define REQ_ADDSRC_COPY 0x400
+#define REQ_ADDSRC_EF_EXP_MONO_ROOT 0x800
+#define REQ_ADDSRC_EF_EXP_NET_CORRECTION 0x1000
+#define REQ_ADDSRC_IPV4 0x2000
+#define REQ_ADDSRC_IPV6 0x4000

 typedef struct {
  uint32_t type;
@@ -292,7 +304,9 @@ typedef struct {
  Float offset;
  uint32_t flags;
  int32_t filter_length;
-  uint32_t reserved[3];
+  uint32_t cert_set;
+  Float max_delay_quant;
+  int32_t max_unreach;
  int32_t EOR;
 } REQ_NTP_Source;

@@ -307,8 +321,7 @@ typedef struct {
 } REQ_Dfreq;

 typedef struct {
-  int32_t sec;
-  int32_t usec;
+  Float doffset;
  int32_t EOR;
 } REQ_Doffset;

@@ -367,6 +380,22 @@ typedef struct {
  int32_t EOR;
 } REQ_SelectData;

+/* Mask and options reuse the REQ_ADDSRC flags */
+typedef struct {
+  IPAddr address;
+  uint32_t ref_id;
+  uint32_t mask;
+  uint32_t options;
+  int32_t EOR;
+} REQ_Modify_SelectOpts;
+
+typedef struct {
+  IPAddr address;
+  uint32_t ref_id;
+  Float new_offset;
+  int32_t EOR;
+} REQ_Modify_Offset;
+
 /* ================================================== */

 #define PKT_TYPE_CMD_REQUEST 1
@@ -403,7 +432,7 @@ typedef struct {
   domain socket.

   Version 6 (no authentication) : changed format of client accesses by index
-   (using new request/reply types) and manual timestamp, added new fields and
+   (two times), delta offset, and manual timestamp, added new fields and
   flags to NTP source request and report, made length of manual list constant,
   added new commands: authdata, ntpdata, onoffline, refresh, reset,
   selectdata, serverstats, shutdown, sourcename
@@ -453,7 +482,6 @@ typedef struct {
    REQ_Modify_Polltarget modify_polltarget;
    REQ_Modify_Maxupdateskew modify_maxupdateskew;
    REQ_Modify_Makestep modify_makestep;
-    REQ_Logon logon;
    REQ_Settime settime;
    REQ_Local local;
    REQ_Manual manual;
@@ -473,6 +501,8 @@ typedef struct {
    REQ_NTPSourceName ntp_source_name;
    REQ_AuthData auth_data;
    REQ_SelectData select_data;
+    REQ_Modify_SelectOpts modify_select_opts;
+    REQ_Modify_Offset modify_offset;
  } data; /* Command specific parameters */

  /* Padding used to prevent traffic amplification.  It only defines the
@@ -481,13 +511,6 @@ typedef struct {

 } CMD_Request;

-/* ================================================== */
-/* Authority codes for command types */
-
-#define PERMIT_OPEN 0
-#define PERMIT_LOCAL 1
-#define PERMIT_AUTH 2
-
 /* ================================================== */

 /* Reply codes */
@@ -514,7 +537,10 @@ typedef struct {
 #define RPY_CLIENT_ACCESSES_BY_INDEX3 21
 #define RPY_SERVER_STATS2 22
 #define RPY_SELECT_DATA 23
-#define N_REPLY_TYPES 24
+#define RPY_SERVER_STATS3 24
+#define RPY_SERVER_STATS4 25
+#define RPY_NTP_DATA2 26
+#define N_REPLY_TYPES 27

 /* Status codes */
 #define STT_SUCCESS 0
@@ -527,8 +553,7 @@ typedef struct {
 #define STT_BADSUBNET 7
 #define STT_ACCESSALLOWED 8
 #define STT_ACCESSDENIED 9
-/* Deprecated */
-#define STT_NOHOSTACCESS 10
+#define STT_NOHOSTACCESS 10 /* Deprecated */
 #define STT_SOURCEALREADYKNOWN 11
 #define STT_TOOMANYSOURCES 12
 #define STT_NORTC 13
@@ -553,12 +578,12 @@ typedef struct {
 #define RPY_SD_MD_PEER   1
 #define RPY_SD_MD_REF    2

-#define RPY_SD_ST_SYNC 0
-#define RPY_SD_ST_UNREACH 1
+#define RPY_SD_ST_SELECTED 0
+#define RPY_SD_ST_NONSELECTABLE 1
 #define RPY_SD_ST_FALSETICKER 2
 #define RPY_SD_ST_JITTERY 3
-#define RPY_SD_ST_CANDIDATE 4
-#define RPY_SD_ST_OUTLIER 5
+#define RPY_SD_ST_UNSELECTED 4
+#define RPY_SD_ST_SELECTABLE 5

 typedef struct {
  IPAddr ip_addr;
@@ -650,14 +675,24 @@ typedef struct {
 } RPY_ClientAccessesByIndex;

 typedef struct {
-  uint32_t ntp_hits;
-  uint32_t nke_hits;
-  uint32_t cmd_hits;
-  uint32_t ntp_drops;
-  uint32_t nke_drops;
-  uint32_t cmd_drops;
-  uint32_t log_drops;
-  uint32_t ntp_auth_hits;
+  Integer64 ntp_hits;
+  Integer64 nke_hits;
+  Integer64 cmd_hits;
+  Integer64 ntp_drops;
+  Integer64 nke_drops;
+  Integer64 cmd_drops;
+  Integer64 log_drops;
+  Integer64 ntp_auth_hits;
+  Integer64 ntp_interleaved_hits;
+  Integer64 ntp_timestamps;
+  Integer64 ntp_span_seconds;
+  Integer64 ntp_daemon_rx_timestamps;
+  Integer64 ntp_daemon_tx_timestamps;
+  Integer64 ntp_kernel_rx_timestamps;
+  Integer64 ntp_kernel_tx_timestamps;
+  Integer64 ntp_hw_rx_timestamps;
+  Integer64 ntp_hw_tx_timestamps;
+  Integer64 reserved[4];
  int32_t EOR;
 } RPY_ServerStats;

@@ -727,6 +762,11 @@ typedef struct {
  uint32_t total_tx_count;
  uint32_t total_rx_count;
  uint32_t total_valid_count;
+  uint32_t total_good_count;
+  uint32_t total_kernel_tx_ts;
+  uint32_t total_kernel_rx_ts;
+  uint32_t total_hw_tx_ts;
+  uint32_t total_hw_rx_ts;
  uint32_t reserved[4];
  int32_t EOR;
 } RPY_NTPData;
@@ -764,7 +804,8 @@ typedef struct {
  IPAddr ip_addr;
  uint8_t state_char;
  uint8_t authentication;
-  uint8_t pad[2];
+  uint8_t leap;
+  uint8_t pad;
  uint16_t conf_options;
  uint16_t eff_options;
  uint32_t last_sample_ago;
--- a/client.c
+++ b/client.c
--- a/clientlog.c
+++ b/clientlog.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009, 2015-2017
+ * Copyright (C) Miroslav Lichvar  2009, 2015-2017, 2021, 2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -38,6 +38,7 @@
 #include "array.h"
 #include "clientlog.h"
 #include "conf.h"
+#include "local.h"
 #include "memory.h"
 #include "ntp.h"
 #include "reports.h"
@@ -55,8 +56,6 @@ typedef struct {
  int8_t rate[MAX_SERVICES];
  int8_t ntp_timeout_rate;
  uint8_t drop_flags;
-  NTP_int64 ntp_rx_ts;
-  NTP_int64 ntp_tx_ts;
 } Record;

 /* Hash table of records, there is a fixed number of records per slot */
@@ -118,23 +117,72 @@ static int token_shift[MAX_SERVICES];

 static int leak_rate[MAX_SERVICES];

+/* Rates at which responses requesting clients to reduce their rate
+   (e.g. NTP KoD RATE) are randomly allowed (in log2, but 0 means disabled) */
+
+#define MIN_KOD_RATE 0
+#define MAX_KOD_RATE 4
+
+static int kod_rate[MAX_SERVICES];
+
 /* Limit intervals in log2 */
 static int limit_interval[MAX_SERVICES];

 /* Flag indicating whether facility is turned on or not */
 static int active;

+/* RX and TX timestamp saved for clients using interleaved mode */
+typedef struct {
+  uint64_t rx_ts;
+  uint8_t flags;
+  uint8_t tx_ts_source;
+  uint16_t slew_epoch;
+  int32_t tx_ts_offset;
+} NtpTimestamps;
+
+/* Flags for NTP timestamps */
+#define NTPTS_DISABLED 1
+#define NTPTS_VALID_TX 2
+
+/* RX->TX map using a circular buffer with ordered timestamps */
+typedef struct {
+  ARR_Instance timestamps;
+  uint32_t first;
+  uint32_t size;
+  uint32_t max_size;
+  uint32_t cached_index;
+  uint64_t cached_rx_ts;
+  uint16_t slew_epoch;
+  double slew_offset;
+} NtpTimestampMap;
+
+static NtpTimestampMap ntp_ts_map;
+
+/* Maximum interval of NTP timestamps in future after a backward step */
+#define NTPTS_FUTURE_LIMIT (1LL << 32) /* 1 second */
+
+/* Maximum number of timestamps moved in the array to insert a new timestamp */
+#define NTPTS_INSERT_LIMIT 64
+
+/* Maximum expected value of the timestamp source */
+#define MAX_NTP_TS NTP_TS_HARDWARE
+
 /* Global statistics */
-static uint32_t total_hits[MAX_SERVICES];
-static uint32_t total_drops[MAX_SERVICES];
-static uint32_t total_ntp_auth_hits;
-static uint32_t total_record_drops;
+static uint64_t total_hits[MAX_SERVICES];
+static uint64_t total_drops[MAX_SERVICES];
+static uint64_t total_ntp_auth_hits;
+static uint64_t total_ntp_interleaved_hits;
+static uint64_t total_record_drops;
+static uint64_t total_ntp_rx_timestamps[MAX_NTP_TS + 1];
+static uint64_t total_ntp_tx_timestamps[MAX_NTP_TS + 1];

 #define NSEC_PER_SEC 1000000000U

 /* ================================================== */

 static int expand_hashtable(void);
+static void handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
+                        double doffset, LCL_ChangeType change_type, void *anything);

 /* ================================================== */

@@ -169,7 +217,7 @@ compare_total_hits(Record *x, Record *y)
 static Record *
 get_record(IPAddr *ip)
 {
-  uint32_t last_hit, oldest_hit = 0;
+  uint32_t last_hit = 0, oldest_hit = 0;
  Record *record, *oldest_record;
  unsigned int first, i, j;

@@ -217,20 +265,15 @@ get_record(IPAddr *ip)
  }

  record->ip_addr = *ip;
-  for (i = 0; i < MAX_SERVICES; i++)
+  for (i = 0; i < MAX_SERVICES; i++) {
    record->last_hit[i] = INVALID_TS;
-  for (i = 0; i < MAX_SERVICES; i++)
    record->hits[i] = 0;
-  for (i = 0; i < MAX_SERVICES; i++)
    record->drops[i] = 0;
-  for (i = 0; i < MAX_SERVICES; i++)
    record->tokens[i] = max_tokens[i];
-  for (i = 0; i < MAX_SERVICES; i++)
    record->rate[i] = INVALID_RATE;
+  }
  record->ntp_timeout_rate = INVALID_RATE;
  record->drop_flags = 0;
-  UTI_ZeroNtp64(&record->ntp_rx_ts);
-  UTI_ZeroNtp64(&record->ntp_tx_ts);

  return record;
 }
@@ -316,18 +359,19 @@ set_bucket_params(int interval, int burst, uint16_t *max_tokens,
 void
 CLG_Initialise(void)
 {
-  int i, interval, burst, lrate;
+  int i, interval, burst, lrate, krate, slots2;

  for (i = 0; i < MAX_SERVICES; i++) {
    max_tokens[i] = 0;
    tokens_per_hit[i] = 0;
    token_shift[i] = 0;
    leak_rate[i] = 0;
+    kod_rate[i] = 0;
    limit_interval[i] = MIN_LIMIT_INTERVAL;

    switch (i) {
      case CLG_NTP:
-        if (!CNF_GetNTPRateLimit(&interval, &burst, &lrate))
+        if (!CNF_GetNTPRateLimit(&interval, &burst, &lrate, &krate))
          continue;
        break;
      case CLG_NTSKE:
@@ -344,6 +388,7 @@ CLG_Initialise(void)

    set_bucket_params(interval, burst, &max_tokens[i], &tokens_per_hit[i], &token_shift[i]);
    leak_rate[i] = CLAMP(MIN_LEAK_RATE, lrate, MAX_LEAK_RATE);
+    kod_rate[i] = CLAMP(MIN_KOD_RATE, krate, MAX_KOD_RATE);
    limit_interval[i] = CLAMP(MIN_LIMIT_INTERVAL, interval, MAX_LIMIT_INTERVAL);
  }

@@ -359,9 +404,13 @@ CLG_Initialise(void)
  /* Calculate the maximum number of slots that can be allocated in the
     configured memory limit.  Take into account expanding of the hash
     table where two copies exist at the same time. */
-  max_slots = CNF_GetClientLogLimit() / (sizeof (Record) * SLOT_SIZE * 3 / 2);
+  max_slots = CNF_GetClientLogLimit() /
+              ((sizeof (Record) + sizeof (NtpTimestamps)) * SLOT_SIZE * 3 / 2);
  max_slots = CLAMP(MIN_SLOTS, max_slots, MAX_SLOTS);
-  DEBUG_LOG("Max records %u", 1U << ((int)round(log(max_slots) / log(2)) + SLOT_BITS));
+  for (slots2 = 0; 1U << (slots2 + 1) <= max_slots; slots2++)
+    ;
+
+  DEBUG_LOG("Max records %u", 1U << (slots2 + SLOT_BITS));

  slots = 0;
  records = NULL;
@@ -370,6 +419,17 @@ CLG_Initialise(void)

  UTI_GetRandomBytes(&ts_offset, sizeof (ts_offset));
  ts_offset %= NSEC_PER_SEC / (1U << TS_FRAC);
+
+  ntp_ts_map.timestamps = NULL;
+  ntp_ts_map.first = 0;
+  ntp_ts_map.size = 0;
+  ntp_ts_map.max_size = 1U << (slots2 + SLOT_BITS);
+  ntp_ts_map.cached_index = 0;
+  ntp_ts_map.cached_rx_ts = 0ULL;
+  ntp_ts_map.slew_epoch = 0;
+  ntp_ts_map.slew_offset = 0.0;
+
+  LCL_AddParameterChangeHandler(handle_slew, NULL);
 }

 /* ================================================== */
@@ -381,6 +441,10 @@ CLG_Finalise(void)
    return;

  ARR_DestroyInstance(records);
+  if (ntp_ts_map.timestamps)
+    ARR_DestroyInstance(ntp_ts_map.timestamps);
+
+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
 }

 /* ================================================== */
@@ -522,28 +586,28 @@ CLG_LogServiceAccess(CLG_Service service, IPAddr *client, struct timespec *now)
 /* ================================================== */

 static int
-limit_response_random(int leak_rate)
+limit_response_random(int rate)
 {
  static uint32_t rnd;
  static int bits_left = 0;
  int r;

-  if (bits_left < leak_rate) {
+  if (bits_left < rate) {
    UTI_GetRandomBytes(&rnd, sizeof (rnd));
    bits_left = 8 * sizeof (rnd);
  }

-  /* Return zero on average once per 2^leak_rate */
-  r = rnd % (1U << leak_rate) ? 1 : 0;
-  rnd >>= leak_rate;
-  bits_left -= leak_rate;
+  /* Return zero on average once per 2^rate */
+  r = rnd % (1U << rate) ? 1 : 0;
+  rnd >>= rate;
+  bits_left -= rate;

  return r;
 }

 /* ================================================== */

-int
+CLG_Limit
 CLG_LimitServiceRate(CLG_Service service, int index)
 {
  Record *record;
@@ -552,14 +616,14 @@ CLG_LimitServiceRate(CLG_Service service, int index)
  check_service_number(service);

  if (tokens_per_hit[service] == 0)
-    return 0;
+    return CLG_PASS;

  record = ARR_GetElement(records, index);
  record->drop_flags &= ~(1U << service);

  if (record->tokens[service] >= tokens_per_hit[service]) {
    record->tokens[service] -= tokens_per_hit[service];
-    return 0;
+    return CLG_PASS;
  }

  drop = limit_response_random(leak_rate[service]);
@@ -575,34 +639,31 @@ CLG_LimitServiceRate(CLG_Service service, int index)

  if (!drop) {
    record->tokens[service] = 0;
-    return 0;
+    return CLG_PASS;
+  }
+
+  if (kod_rate[service] > 0 && !limit_response_random(kod_rate[service])) {
+    return CLG_KOD;
  }

  record->drop_flags |= 1U << service;
  record->drops[service]++;
  total_drops[service]++;

-  return 1;
+  return CLG_DROP;
 }

 /* ================================================== */

 void
-CLG_LogAuthNtpRequest(void)
+CLG_UpdateNtpStats(int auth, NTP_Timestamp_Source rx_ts_src, NTP_Timestamp_Source tx_ts_src)
 {
-  total_ntp_auth_hits++;
-}
-
-/* ================================================== */
-
-void CLG_GetNtpTimestamps(int index, NTP_int64 **rx_ts, NTP_int64 **tx_ts)
-{
-  Record *record;
-
-  record = ARR_GetElement(records, index);
-
-  *rx_ts = &record->ntp_rx_ts;
-  *tx_ts = &record->ntp_tx_ts;
+  if (auth)
+    total_ntp_auth_hits++;
+  if (rx_ts_src >= 0 && rx_ts_src <= MAX_NTP_TS)
+    total_ntp_rx_timestamps[rx_ts_src]++;
+  if (tx_ts_src >= 0 && tx_ts_src <= MAX_NTP_TS)
+    total_ntp_tx_timestamps[tx_ts_src]++;
 }

 /* ================================================== */
@@ -615,6 +676,336 @@ CLG_GetNtpMinPoll(void)

 /* ================================================== */

+static NtpTimestamps *
+get_ntp_tss(uint32_t index)
+{
+  return ARR_GetElement(ntp_ts_map.timestamps,
+                        (ntp_ts_map.first + index) & (ntp_ts_map.max_size - 1));
+}
+
+/* ================================================== */
+
+static int
+find_ntp_rx_ts(uint64_t rx_ts, uint32_t *index)
+{
+  uint64_t rx_x, rx_lo, rx_hi, step;
+  uint32_t i, x, lo, hi;
+
+  if (ntp_ts_map.cached_rx_ts == rx_ts && rx_ts != 0ULL) {
+    *index = ntp_ts_map.cached_index;
+    return 1;
+  }
+
+  if (ntp_ts_map.size == 0) {
+    *index = 0;
+    return 0;
+  }
+
+  lo = 0;
+  hi = ntp_ts_map.size - 1;
+  rx_lo = get_ntp_tss(lo)->rx_ts;
+  rx_hi = get_ntp_tss(hi)->rx_ts;
+
+  /* Check for ts < lo before ts > hi to trim timestamps from "future" later
+     if both conditions are true to not break the order of the endpoints.
+     Compare timestamps by their difference to allow adjacent NTP eras. */
+  if ((int64_t)(rx_ts - rx_lo) < 0) {
+    *index = 0;
+    return 0;
+  } else if ((int64_t)(rx_ts - rx_hi) > 0) {
+    *index = ntp_ts_map.size;
+    return 0;
+  }
+
+  /* Perform a combined linear interpolation and binary search */
+
+  for (i = 0; ; i++) {
+    if (rx_ts == rx_hi) {
+      *index = ntp_ts_map.cached_index = hi;
+      ntp_ts_map.cached_rx_ts = rx_ts;
+      return 1;
+    } else if (rx_ts == rx_lo) {
+      *index = ntp_ts_map.cached_index = lo;
+      ntp_ts_map.cached_rx_ts = rx_ts;
+      return 1;
+    } else if (lo + 1 == hi) {
+      *index = hi;
+      return 0;
+    }
+
+    if (hi - lo > 3 && i % 2 == 0) {
+      step = (rx_hi - rx_lo) / (hi - lo);
+      if (step == 0)
+        step = 1;
+      x = lo + (rx_ts - rx_lo) / step;
+    } else {
+      x = lo + (hi - lo) / 2;
+    }
+
+    if (x <= lo)
+      x = lo + 1;
+    else if (x >= hi)
+      x = hi - 1;
+
+    rx_x = get_ntp_tss(x)->rx_ts;
+
+    if ((int64_t)(rx_x - rx_ts) <= 0) {
+      lo = x;
+      rx_lo = rx_x;
+    } else {
+      hi = x;
+      rx_hi = rx_x;
+    }
+  }
+}
+
+/* ================================================== */
+
+static uint64_t
+ntp64_to_int64(NTP_int64 *ts)
+{
+  return (uint64_t)ntohl(ts->hi) << 32 | ntohl(ts->lo);
+}
+
+/* ================================================== */
+
+static void
+int64_to_ntp64(uint64_t ts, NTP_int64 *ntp_ts)
+{
+  ntp_ts->hi = htonl(ts >> 32);
+  ntp_ts->lo = htonl(ts);
+}
+
+/* ================================================== */
+
+static uint32_t
+push_ntp_tss(uint32_t index)
+{
+  if (ntp_ts_map.size < ntp_ts_map.max_size) {
+    ntp_ts_map.size++;
+  } else {
+    ntp_ts_map.first = (ntp_ts_map.first + 1) % (ntp_ts_map.max_size);
+    if (index > 0)
+      index--;
+  }
+
+  return index;
+}
+
+/* ================================================== */
+
+static void
+set_ntp_tx(NtpTimestamps *tss, NTP_int64 *rx_ts, struct timespec *tx_ts,
+           NTP_Timestamp_Source tx_src)
+{
+  struct timespec ts;
+
+  if (!tx_ts) {
+    tss->flags &= ~NTPTS_VALID_TX;
+    return;
+  }
+
+  UTI_Ntp64ToTimespec(rx_ts, &ts);
+  UTI_DiffTimespecs(&ts, tx_ts, &ts);
+
+  if (ts.tv_sec < -2 || ts.tv_sec > 1) {
+    tss->flags &= ~NTPTS_VALID_TX;
+    return;
+  }
+
+  tss->tx_ts_offset = (int32_t)ts.tv_nsec + (int32_t)ts.tv_sec * (int32_t)NSEC_PER_SEC;
+  tss->flags |= NTPTS_VALID_TX;
+  tss->tx_ts_source = tx_src;
+}
+
+/* ================================================== */
+
+static void
+get_ntp_tx(NtpTimestamps *tss, struct timespec *tx_ts, NTP_Timestamp_Source *tx_src)
+{
+  int32_t offset = tss->tx_ts_offset;
+  NTP_int64 ntp_ts;
+
+  if (tss->flags & NTPTS_VALID_TX) {
+    int64_to_ntp64(tss->rx_ts, &ntp_ts);
+    UTI_Ntp64ToTimespec(&ntp_ts, tx_ts);
+    if (offset >= (int32_t)NSEC_PER_SEC) {
+      offset -= NSEC_PER_SEC;
+      tx_ts->tv_sec++;
+    }
+    tx_ts->tv_nsec += offset;
+    UTI_NormaliseTimespec(tx_ts);
+  } else {
+    UTI_ZeroTimespec(tx_ts);
+  }
+
+  *tx_src = tss->tx_ts_source;
+}
+
+/* ================================================== */
+
+void
+CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts, NTP_Timestamp_Source tx_src)
+{
+  NtpTimestamps *tss;
+  uint32_t i, index;
+  uint64_t rx;
+
+  if (!active)
+    return;
+
+  /* Allocate the array on first use */
+  if (!ntp_ts_map.timestamps) {
+    ntp_ts_map.timestamps = ARR_CreateInstance(sizeof (NtpTimestamps));
+    ARR_SetSize(ntp_ts_map.timestamps, ntp_ts_map.max_size);
+  }
+
+  rx = ntp64_to_int64(rx_ts);
+
+  if (rx == 0ULL)
+    return;
+
+  /* Disable the RX timestamp if it already exists to avoid responding
+     with a wrong TX timestamp */
+  if (find_ntp_rx_ts(rx, &index)) {
+    get_ntp_tss(index)->flags |= NTPTS_DISABLED;
+    return;
+  }
+
+  assert(index <= ntp_ts_map.size);
+
+  if (index == ntp_ts_map.size) {
+    /* Increase the size or drop the oldest timestamp to make room for
+       the new timestamp */
+    index = push_ntp_tss(index);
+  } else {
+    /* Trim timestamps in distant future after backward step */
+    while (index < ntp_ts_map.size &&
+           get_ntp_tss(ntp_ts_map.size - 1)->rx_ts - rx > NTPTS_FUTURE_LIMIT)
+      ntp_ts_map.size--;
+
+    /* Insert the timestamp if it is close to the latest timestamp.
+       Otherwise, replace the closest older or the oldest timestamp. */
+    if (index + NTPTS_INSERT_LIMIT >= ntp_ts_map.size) {
+      index = push_ntp_tss(index);
+      for (i = ntp_ts_map.size - 1; i > index; i--)
+        *get_ntp_tss(i) = *get_ntp_tss(i - 1);
+    } else {
+      if (index > 0)
+        index--;
+    }
+  }
+
+  ntp_ts_map.cached_index = index;
+  ntp_ts_map.cached_rx_ts = rx;
+
+  tss = get_ntp_tss(index);
+  tss->rx_ts = rx;
+  tss->flags = 0;
+  tss->slew_epoch = ntp_ts_map.slew_epoch;
+  set_ntp_tx(tss, rx_ts, tx_ts, tx_src);
+
+  DEBUG_LOG("Saved RX+TX index=%"PRIu32" first=%"PRIu32" size=%"PRIu32,
+            index, ntp_ts_map.first, ntp_ts_map.size);
+}
+
+/* ================================================== */
+
+static void
+handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
+            double doffset, LCL_ChangeType change_type, void *anything)
+{
+  /* Drop all timestamps on unknown step */
+  if (change_type == LCL_ChangeUnknownStep) {
+    ntp_ts_map.size = 0;
+    ntp_ts_map.cached_rx_ts = 0ULL;
+  }
+
+  ntp_ts_map.slew_epoch++;
+  ntp_ts_map.slew_offset = doffset;
+}
+
+/* ================================================== */
+
+void
+CLG_UndoNtpTxTimestampSlew(NTP_int64 *rx_ts, struct timespec *tx_ts)
+{
+  uint32_t index;
+
+  if (!ntp_ts_map.timestamps)
+    return;
+
+  if (!find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
+    return;
+
+  /* If the RX timestamp was captured before the last correction of the clock,
+     remove the adjustment from the TX timestamp */
+  if ((uint16_t)(get_ntp_tss(index)->slew_epoch + 1U) == ntp_ts_map.slew_epoch)
+    UTI_AddDoubleToTimespec(tx_ts, ntp_ts_map.slew_offset, tx_ts);
+}
+
+/* ================================================== */
+
+void
+CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                         NTP_Timestamp_Source tx_src)
+{
+  uint32_t index;
+
+  if (!ntp_ts_map.timestamps)
+    return;
+
+  if (!find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
+    return;
+
+  set_ntp_tx(get_ntp_tss(index), rx_ts, tx_ts, tx_src);
+}
+
+/* ================================================== */
+
+int
+CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                      NTP_Timestamp_Source *tx_src)
+{
+  NtpTimestamps *tss;
+  uint32_t index;
+
+  if (!ntp_ts_map.timestamps)
+    return 0;
+
+  if (!find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
+    return 0;
+
+  tss = get_ntp_tss(index);
+
+  if (tss->flags & NTPTS_DISABLED)
+    return 0;
+
+  get_ntp_tx(tss, tx_ts, tx_src);
+
+  return 1;
+}
+
+/* ================================================== */
+
+void
+CLG_DisableNtpTimestamps(NTP_int64 *rx_ts)
+{
+  uint32_t index;
+
+  if (!ntp_ts_map.timestamps)
+    return;
+
+  if (find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
+    get_ntp_tss(index)->flags |= NTPTS_DISABLED;
+
+  /* This assumes the function is called only to prevent multiple
+     interleaved responses to the same timestamp */
+  total_ntp_interleaved_hits++;
+}
+
+/* ================================================== */
+
 int
 CLG_GetNumberOfIndices(void)
 {
@@ -717,4 +1108,15 @@ CLG_GetServerStatsReport(RPT_ServerStatsReport *report)
  report->cmd_drops = total_drops[CLG_CMDMON];
  report->log_drops = total_record_drops;
  report->ntp_auth_hits = total_ntp_auth_hits;
+  report->ntp_interleaved_hits = total_ntp_interleaved_hits;
+  report->ntp_timestamps = ntp_ts_map.size;
+  report->ntp_span_seconds = ntp_ts_map.size > 1 ?
+                             (get_ntp_tss(ntp_ts_map.size - 1)->rx_ts -
+                              get_ntp_tss(0)->rx_ts) >> 32 : 0;
+  report->ntp_daemon_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_DAEMON];
+  report->ntp_daemon_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_DAEMON];
+  report->ntp_kernel_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_KERNEL];
+  report->ntp_kernel_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_KERNEL];
+  report->ntp_hw_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_HARDWARE];
+  report->ntp_hw_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_HARDWARE];
 }
--- a/clientlog.h
+++ b/clientlog.h
@@ -37,15 +37,31 @@ typedef enum {
  CLG_CMDMON,
 } CLG_Service;

+typedef enum {
+  CLG_PASS = 0,
+  CLG_DROP,
+  CLG_KOD,
+} CLG_Limit;
+
 extern void CLG_Initialise(void);
 extern void CLG_Finalise(void);
 extern int CLG_GetClientIndex(IPAddr *client);
 extern int CLG_LogServiceAccess(CLG_Service service, IPAddr *client, struct timespec *now);
-extern int CLG_LimitServiceRate(CLG_Service service, int index);
-extern void CLG_LogAuthNtpRequest(void);
-extern void CLG_GetNtpTimestamps(int index, NTP_int64 **rx_ts, NTP_int64 **tx_ts);
+extern CLG_Limit CLG_LimitServiceRate(CLG_Service service, int index);
+extern void CLG_UpdateNtpStats(int auth, NTP_Timestamp_Source rx_ts_src,
+                               NTP_Timestamp_Source tx_ts_src);
 extern int CLG_GetNtpMinPoll(void);

+/* Functions to save and retrieve timestamps for server interleaved mode */
+extern void CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                  NTP_Timestamp_Source tx_src);
+extern void CLG_UndoNtpTxTimestampSlew(NTP_int64 *rx_ts, struct timespec *tx_ts);
+extern void CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                     NTP_Timestamp_Source tx_src);
+extern int CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                 NTP_Timestamp_Source *tx_src);
+extern void CLG_DisableNtpTimestamps(NTP_int64 *rx_ts);
+
 /* And some reporting functions, for use by chronyc. */

 extern int CLG_GetNumberOfIndices(void);
--- a/cmac_gnutls.c
+++ b/cmac_gnutls.c
@@ -0,0 +1,189 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2021
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  CMAC using the GnuTLS library
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include <gnutls/crypto.h>
+
+#include "cmac.h"
+#include "hash.h"
+#include "logging.h"
+#include "memory.h"
+
+struct CMC_Instance_Record {
+  gnutls_mac_algorithm_t algorithm;
+  gnutls_hmac_hd_t mac;
+};
+
+/* ================================================== */
+
+static int instance_counter = 0;
+static int gnutls_initialised = 0;
+
+/* ================================================== */
+
+static void
+init_gnutls(void)
+{
+  int r;
+
+  if (gnutls_initialised)
+    return;
+
+  r = gnutls_global_init();
+  if (r < 0)
+    LOG_FATAL("Could not initialise %s : %s", "gnutls", gnutls_strerror(r));
+
+  DEBUG_LOG("Initialised");
+  gnutls_initialised = 1;
+}
+
+/* ================================================== */
+
+static void
+deinit_gnutls(void)
+{
+  assert(gnutls_initialised);
+  gnutls_global_deinit();
+  gnutls_initialised = 0;
+  DEBUG_LOG("Deinitialised");
+}
+
+/* ================================================== */
+
+static gnutls_mac_algorithm_t
+get_mac_algorithm(CMC_Algorithm algorithm)
+{
+  switch (algorithm) {
+    case CMC_AES128:
+      return GNUTLS_MAC_AES_CMAC_128;
+    case CMC_AES256:
+      return GNUTLS_MAC_AES_CMAC_256;
+    default:
+      return GNUTLS_MAC_UNKNOWN;
+  }
+}
+
+/* ================================================== */
+
+int
+CMC_GetKeyLength(CMC_Algorithm algorithm)
+{
+  gnutls_mac_algorithm_t malgo = get_mac_algorithm(algorithm);
+  int len;
+
+  if (malgo == GNUTLS_MAC_UNKNOWN)
+    return 0;
+
+  len = gnutls_hmac_get_key_size(malgo);
+
+  if (len < 0)
+    return 0;
+
+  return len;
+}
+
+/* ================================================== */
+
+CMC_Instance
+CMC_CreateInstance(CMC_Algorithm algorithm, const unsigned char *key, int length)
+{
+  gnutls_hmac_hd_t handle;
+  CMC_Instance inst;
+
+  int r;
+
+  if (instance_counter == 0)
+    init_gnutls();
+
+  if (length <= 0 || length != CMC_GetKeyLength(algorithm))
+    goto error;
+
+  r = gnutls_hmac_init(&handle, get_mac_algorithm(algorithm), key, length);
+  if (r < 0) {
+    DEBUG_LOG("Could not initialise %s : %s", "mac", gnutls_strerror(r));
+    goto error;
+  }
+
+  inst = MallocNew(struct CMC_Instance_Record);
+  inst->algorithm = get_mac_algorithm(algorithm);
+  inst->mac = handle;
+
+  instance_counter++;
+
+  return inst;
+
+error:
+  if (instance_counter == 0)
+    deinit_gnutls();
+  return NULL;
+}
+
+/* ================================================== */
+
+int
+CMC_Hash(CMC_Instance inst, const void *in, int in_len, unsigned char *out, int out_len)
+{
+  unsigned char buf[MAX_HASH_LENGTH];
+  int hash_len;
+
+  if (in_len < 0 || out_len < 0)
+    return 0;
+
+  hash_len = gnutls_hmac_get_len(inst->algorithm);
+
+  if (out_len > hash_len)
+    out_len = hash_len;
+
+  if (hash_len > sizeof (buf))
+    return 0;
+
+  if (gnutls_hmac(inst->mac, in, in_len) < 0) {
+    /* Reset the state */
+    gnutls_hmac_output(inst->mac, buf);
+    return 0;
+  }
+
+  gnutls_hmac_output(inst->mac, buf);
+  memcpy(out, buf, out_len);
+
+  return out_len;
+}
+
+/* ================================================== */
+
+void
+CMC_DestroyInstance(CMC_Instance inst)
+{
+  gnutls_hmac_deinit(inst->mac, NULL);
+  Free(inst);
+
+  instance_counter--;
+  if (instance_counter == 0)
+    deinit_gnutls();
+}
--- a/cmdmon.c
+++ b/cmdmon.c
--- a/cmdparse.c
+++ b/cmdparse.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2013-2014, 2016
+ * Copyright (C) Miroslav Lichvar  2013-2014, 2016, 2021, 2025
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -39,12 +39,19 @@

 /* ================================================== */

-int
+#define SSCANF_IN_RANGE(s, f, x, n, min, max) \
+  (sscanf((s), (f), (x), (n)) == 1 && *(x) >= (min) && *(x) <= (max))
+
+/* ================================================== */
+
+CPS_Status
 CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
 {
  char *hostname, *cmd;
-  int n;
+  uint32_t ef_type;
+  int n, sel_option;
  
+  src->family = IPADDR_UNSPEC;
  src->port = SRC_DEFAULT_PORT;
  src->params.minpoll = SRC_DEFAULT_MINPOLL;
  src->params.maxpoll = SRC_DEFAULT_MAXPOLL;
@@ -59,15 +66,20 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  src->params.max_sources = SRC_DEFAULT_MAXSOURCES;
  src->params.min_samples = SRC_DEFAULT_MINSAMPLES;
  src->params.max_samples = SRC_DEFAULT_MAXSAMPLES;
+  src->params.max_unreach = SRC_DEFAULT_MAXUNREACH;
  src->params.filter_length = 0;
  src->params.interleaved = 0;
  src->params.sel_options = 0;
  src->params.nts = 0;
  src->params.nts_port = SRC_DEFAULT_NTSPORT;
+  src->params.copy = 0;
+  src->params.ext_fields = 0;
  src->params.authkey = INACTIVE_AUTHKEY;
+  src->params.cert_set = SRC_DEFAULT_CERTSET;
  src->params.max_delay = SRC_DEFAULT_MAXDELAY;
  src->params.max_delay_ratio = SRC_DEFAULT_MAXDELAYRATIO;
  src->params.max_delay_dev_ratio = SRC_DEFAULT_MAXDELAYDEVRATIO;
+  src->params.max_delay_quant = 0.0;
  src->params.min_delay = 0.0;
  src->params.asymmetry = SRC_DEFAULT_ASYMMETRY;
  src->params.offset = 0.0;
@@ -76,7 +88,7 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  line = CPS_SplitWord(line);

  if (!*hostname)
-    return 0;
+    return CPS_MissingArgument;

  src->name = hostname;

@@ -90,122 +102,255 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
      src->params.auto_offline = 1;
    } else if (!strcasecmp(cmd, "burst")) {
      src->params.burst = 1;
+    } else if (!strcasecmp(cmd, "copy")) {
+      src->params.copy = 1;
    } else if (!strcasecmp(cmd, "iburst")) {
      src->params.iburst = 1;
    } else if (!strcasecmp(cmd, "offline")) {
      src->params.connectivity = SRC_OFFLINE;
-    } else if (!strcasecmp(cmd, "noselect")) {
-      src->params.sel_options |= SRC_SELECT_NOSELECT;
-    } else if (!strcasecmp(cmd, "prefer")) {
-      src->params.sel_options |= SRC_SELECT_PREFER;
-    } else if (!strcasecmp(cmd, "require")) {
-      src->params.sel_options |= SRC_SELECT_REQUIRE;
-    } else if (!strcasecmp(cmd, "trust")) {
-      src->params.sel_options |= SRC_SELECT_TRUST;
+    } else if (!strcasecmp(cmd, "certset")) {
+      if (sscanf(line, "%"SCNu32"%n", &src->params.cert_set, &n) != 1)
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "key")) {
      if (sscanf(line, "%"SCNu32"%n", &src->params.authkey, &n) != 1 ||
          src->params.authkey == INACTIVE_AUTHKEY)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "asymmetry")) {
      if (sscanf(line, "%lf%n", &src->params.asymmetry, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "extfield")) {
+      if (sscanf(line, "%"SCNx32"%n", &ef_type, &n) != 1)
+        return CPS_InvalidValue;
+      switch (ef_type) {
+        case NTP_EF_EXP_MONO_ROOT:
+          src->params.ext_fields |= NTP_EF_FLAG_EXP_MONO_ROOT;
+          break;
+        case NTP_EF_EXP_NET_CORRECTION:
+          src->params.ext_fields |= NTP_EF_FLAG_EXP_NET_CORRECTION;
+          break;
+        default:
+          return CPS_InvalidValue;
+      }
    } else if (!strcasecmp(cmd, "filter")) {
-      if (sscanf(line, "%d%n", &src->params.filter_length, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.filter_length, &n, 0, INT_MAX))
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "ipv4")) {
+      src->family = IPADDR_INET4;
+    } else if (!strcasecmp(cmd, "ipv6")) {
+      src->family = IPADDR_INET6;
    } else if (!strcasecmp(cmd, "maxdelay")) {
      if (sscanf(line, "%lf%n", &src->params.max_delay, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "maxdelayratio")) {
      if (sscanf(line, "%lf%n", &src->params.max_delay_ratio, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "maxdelaydevratio")) {
      if (sscanf(line, "%lf%n", &src->params.max_delay_dev_ratio, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "maxdelayquant")) {
+      if (sscanf(line, "%lf%n", &src->params.max_delay_quant, &n) != 1)
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "maxpoll")) {
-      if (sscanf(line, "%d%n", &src->params.maxpoll, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.maxpoll, &n, -32, 32))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "maxsamples")) {
-      if (sscanf(line, "%d%n", &src->params.max_samples, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.max_samples, &n, 0, INT_MAX))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "maxsources")) {
-      if (sscanf(line, "%d%n", &src->params.max_sources, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.max_sources, &n, 1, INT_MAX))
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "maxunreach")) {
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.max_unreach, &n, 0, INT_MAX))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "mindelay")) {
      if (sscanf(line, "%lf%n", &src->params.min_delay, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "minpoll")) {
      if (sscanf(line, "%d%n", &src->params.minpoll, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "minsamples")) {
-      if (sscanf(line, "%d%n", &src->params.min_samples, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.min_samples, &n, 0, INT_MAX))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "minstratum")) {
-      if (sscanf(line, "%d%n", &src->params.min_stratum, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.min_stratum, &n, 0, NTP_MAX_STRATUM))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "nts")) {
      src->params.nts = 1;
    } else if (!strcasecmp(cmd, "ntsport")) {
-      if (sscanf(line, "%d%n", &src->params.nts_port, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.nts_port, &n, 0, 65535))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "offset")) {
      if (sscanf(line, "%lf%n", &src->params.offset, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "port")) {
-      if (sscanf(line, "%d%n", &src->port, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->port, &n, 0, 65535))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "polltarget")) {
-      if (sscanf(line, "%d%n", &src->params.poll_target, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.poll_target, &n, 1, INT_MAX))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "presend")) {
-      if (sscanf(line, "%d%n", &src->params.presend_minpoll, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.presend_minpoll, &n, -32, 32))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "version")) {
-      if (sscanf(line, "%d%n", &src->params.version, &n) != 1)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", &src->params.version, &n, 1, NTP_VERSION))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "xleave")) {
      src->params.interleaved = 1;
+    } else if ((sel_option = CPS_GetSelectOption(cmd)) != 0) {
+      src->params.sel_options |= sel_option;
    } else {
-      return 0;
+      return CPS_InvalidOption;
    }
  }

-  return 1;
+  return CPS_Success;
 }

 /* ================================================== */

 int
-CPS_ParseLocal(char *line, int *stratum, int *orphan, double *distance)
+CPS_GetSelectOption(char *option)
+{
+  if (!strcasecmp(option, "noselect")) {
+    return SRC_SELECT_NOSELECT;
+  } else if (!strcasecmp(option, "prefer")) {
+    return SRC_SELECT_PREFER;
+  } else if (!strcasecmp(option, "require")) {
+    return SRC_SELECT_REQUIRE;
+  } else if (!strcasecmp(option, "trust")) {
+    return SRC_SELECT_TRUST;
+  }
+  return 0;
+}
+
+/* ================================================== */
+
+int
+CPS_ParseAllowDeny(char *line, int *all, IPAddr *ip, int *subnet_bits)
+{
+  char *p, *net, *slash;
+  uint32_t a, b, c;
+  int bits, len, n;
+
+  p = CPS_SplitWord(line);
+
+  if (strcmp(line, "all") == 0) {
+    *all = 1;
+    net = p;
+    p = CPS_SplitWord(p);
+  } else {
+    *all = 0;
+    net = line;
+  }
+
+  /* Make sure there are no other arguments */
+  if (*p)
+    return 0;
+
+  /* No specified address or network means all IPv4 and IPv6 addresses */
+  if (!*net) {
+    ip->family = IPADDR_UNSPEC;
+    *subnet_bits = 0;
+    return 1;
+  }
+
+  slash = strchr(net, '/');
+  if (slash) {
+    if (sscanf(slash + 1, "%d%n", &bits, &len) != 1 || slash[len + 1] || bits < 0)
+      return 0;
+    *slash = '\0';
+  } else {
+    bits = -1;
+  }
+
+  if (UTI_StringToIP(net, ip)) {
+    if (bits >= 0)
+      *subnet_bits = bits;
+    else
+      *subnet_bits = ip->family == IPADDR_INET6 ? 128 : 32;
+    return 1;
+  }
+
+  /* Check for a shortened IPv4 network notation using only 1, 2, or 3 decimal
+     numbers.  This is different than the numbers-and-dots notation accepted
+     by inet_aton()! */
+
+  a = b = c = 0;
+  n = sscanf(net, "%"PRIu32"%n.%"PRIu32"%n.%"PRIu32"%n", &a, &len, &b, &len, &c, &len);
+
+  if (n > 0 && !net[len]) {
+    if (a > 255 || b > 255 || c > 255)
+      return 0;
+
+    ip->family = IPADDR_INET4;
+    ip->addr.in4 = (a << 24) | (b << 16) | (c << 8);
+
+    if (bits >= 0)
+      *subnet_bits = bits;
+    else
+      *subnet_bits = n * 8;
+
+    return 1;
+  }
+
+  /* The last possibility is a hostname */
+  if (bits < 0 && DNS_Name2IPAddress(net, ip, 1) == DNS_Success) {
+    *subnet_bits = ip->family == IPADDR_INET6 ? 128 : 32;
+    return 1;
+  }
+
+  return 0;
+}
+
+/* ================================================== */
+
+CPS_Status
+CPS_ParseLocal(char *line, int *stratum, int *orphan, double *distance, double *activate,
+               double *wait_synced, double *wait_unsynced)
 {
  int n;
  char *cmd;

  *stratum = 10;
  *distance = 1.0;
+  *activate = 0.0;
  *orphan = 0;
+  *wait_synced = 0;
+  *wait_unsynced = -1.0;

  while (*line) {
    cmd = line;
    line = CPS_SplitWord(line);

    if (!strcasecmp(cmd, "stratum")) {
-      if (sscanf(line, "%d%n", stratum, &n) != 1 ||
-          *stratum >= NTP_MAX_STRATUM || *stratum <= 0)
-        return 0;
+      if (!SSCANF_IN_RANGE(line, "%d%n", stratum, &n, 1, NTP_MAX_STRATUM - 1))
+        return CPS_InvalidValue;
    } else if (!strcasecmp(cmd, "orphan")) {
      *orphan = 1;
      n = 0;
    } else if (!strcasecmp(cmd, "distance")) {
      if (sscanf(line, "%lf%n", distance, &n) != 1)
-        return 0;
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "activate")) {
+      if (sscanf(line, "%lf%n", activate, &n) != 1)
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "waitsynced")) {
+      if (sscanf(line, "%lf%n", wait_synced, &n) != 1)
+        return CPS_InvalidValue;
+    } else if (!strcasecmp(cmd, "waitunsynced")) {
+      if (sscanf(line, "%lf%n", wait_unsynced, &n) != 1)
+        return CPS_InvalidValue;
    } else {
-      return 0;
+      return CPS_InvalidOption;
    }

    line += n;
  }

-  return 1;
+  if (*wait_unsynced < 0.0)
+    *wait_unsynced = *orphan ? 300 : 0.0;
+
+  return CPS_Success;
 }

 /* ================================================== */
@@ -294,3 +439,19 @@ CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key)

  return 1;
 }
+
+/* ================================================== */
+
+int
+CPS_ParseRefid(char *line, uint32_t *ref_id)
+{
+  int i;
+
+  for (i = *ref_id = 0; line[i] && !isspace((unsigned char)line[i]); i++) {
+    if (i >= 4)
+      return 0;
+    *ref_id |= (uint32_t)line[i] << (24 - i * 8);
+  }
+
+  return i;
+}
--- a/cmdparse.h
+++ b/cmdparse.h
@@ -30,17 +30,32 @@
 #include "srcparams.h"
 #include "addressing.h"

+typedef enum {
+  CPS_Success,
+  CPS_InvalidValue,
+  CPS_InvalidOption,
+  CPS_MissingArgument,
+} CPS_Status;
+
 typedef struct {
  char *name;
+  int family;
  int port;
  SourceParameters params;
 } CPS_NTP_Source;

 /* Parse a command to add an NTP server or peer */
-extern int CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src);
+extern CPS_Status CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src);
+  
+/* Get an NTP/refclock select option */
+extern int CPS_GetSelectOption(char *option);
+
+/* Parse a command to allow/deny access */
+extern int CPS_ParseAllowDeny(char *line, int *all, IPAddr *ip, int *subnet_bits);

 /* Parse a command to enable local reference */
-extern int CPS_ParseLocal(char *line, int *stratum, int *orphan, double *distance);
+extern CPS_Status CPS_ParseLocal(char *line, int *stratum, int *orphan, double *distance,
+                                 double *activate, double *wait_synced, double *wait_unsynced);

 /* Remove extra white-space and comments */
 extern void CPS_NormalizeLine(char *line);
@@ -51,4 +66,7 @@ extern char *CPS_SplitWord(char *line);
 /* Parse a key from keyfile */
 extern int CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key);

+/* Parse a refclock reference ID (returns number of characters) */
+extern int CPS_ParseRefid(char *line, uint32_t *ref_id);
+
 #endif /* GOT_CMDPARSE_H */
--- a/conf.c
+++ b/conf.c
--- a/conf.h
+++ b/conf.h
@@ -29,6 +29,7 @@
 #define GOT_CONF_H

 #include "addressing.h"
+#include "array.h"
 #include "reference.h"
 #include "sources.h"

@@ -44,6 +45,8 @@ extern void CNF_ParseLine(const char *filename, int number, char *line);

 extern void CNF_CreateDirs(uid_t uid, gid_t gid);

+extern void CNF_CheckReadOnlyAccess(void);
+
 extern void CNF_AddInitSources(void);
 extern void CNF_AddSources(void);
 extern void CNF_AddBroadcasts(void);
@@ -53,11 +56,12 @@ extern void CNF_ReloadSources(void);

 extern int CNF_GetAcquisitionPort(void);
 extern int CNF_GetNTPPort(void);
-extern char *CNF_GetDriftFile(void);
+extern char *CNF_GetDriftFile(int *interval);
 extern char *CNF_GetLogDir(void);
 extern char *CNF_GetDumpDir(void);
 extern int CNF_GetLogBanner(void);
 extern int CNF_GetLogMeasurements(int *raw);
+extern int CNF_GetLogSelection(void);
 extern int CNF_GetLogStatistics(void);
 extern int CNF_GetLogTracking(void);
 extern int CNF_GetLogRtc(void);
@@ -66,6 +70,7 @@ extern int CNF_GetLogTempComp(void);
 extern char *CNF_GetKeysFile(void);
 extern char *CNF_GetRtcFile(void);
 extern int CNF_GetManualEnabled(void);
+extern ARR_Instance CNF_GetOpenCommands(void);
 extern int CNF_GetCommandPort(void);
 extern int CNF_GetRtcOnUtc(void);
 extern int CNF_GetRtcSync(void);
@@ -88,6 +93,7 @@ extern char *CNF_GetNtpSigndSocket(void);
 extern char *CNF_GetPidFile(void);
 extern REF_LeapMode CNF_GetLeapSecMode(void);
 extern char *CNF_GetLeapSecTimezone(void);
+extern char *CNF_GetLeapSecList(void);

 /* Value returned in ppm, as read from file */
 extern double CNF_GetMaxUpdateSkew(void);
@@ -95,22 +101,26 @@ extern double CNF_GetMaxClockError(void);
 extern double CNF_GetMaxDrift(void);
 extern double CNF_GetCorrectionTimeRatio(void);
 extern double CNF_GetMaxSlewRate(void);
+extern double CNF_GetClockPrecision(void);

 extern SRC_AuthSelectMode CNF_GetAuthSelectMode(void);
 extern double CNF_GetMaxDistance(void);
 extern double CNF_GetMaxJitter(void);
+extern int CNF_GetMaxStratum(void);
+extern int CNF_GetMinStratum(void);
 extern double CNF_GetReselectDistance(void);
 extern double CNF_GetStratumWeight(void);
 extern double CNF_GetCombineLimit(void);

-extern int CNF_AllowLocalReference(int *stratum, int *orphan, double *distance);
+extern int CNF_AllowLocalReference(int *stratum, int *orphan, double *distance, double *activate,
+                                   double *wait_synced, double *wait_unsynced);

 extern void CNF_SetupAccessRestrictions(void);

 extern int CNF_GetSchedPriority(void);
 extern int CNF_GetLockMemory(void);

-extern int CNF_GetNTPRateLimit(int *interval, int *burst, int *leak);
+extern int CNF_GetNTPRateLimit(int *interval, int *burst, int *leak, int *kod);
 extern int CNF_GetNtsRateLimit(int *interval, int *burst, int *leak);
 extern int CNF_GetCommandRateLimit(int *interval, int *burst, int *leak);
 extern void CNF_GetSmooth(double *max_freq, double *max_wander, int *leap_only);
@@ -133,12 +143,14 @@ typedef enum {
  CNF_HWTS_RXFILTER_ANY,
  CNF_HWTS_RXFILTER_NONE,
  CNF_HWTS_RXFILTER_NTP,
+  CNF_HWTS_RXFILTER_PTP,
  CNF_HWTS_RXFILTER_ALL,
 } CNF_HwTs_RxFilter;

 typedef struct {
  char *name;
  int minpoll;
+  int maxpoll;
  int min_samples;
  int max_samples;
  int nocrossts;
@@ -149,17 +161,23 @@ typedef struct {
 } CNF_HwTsInterface;

 extern int CNF_GetHwTsInterface(unsigned int index, CNF_HwTsInterface **iface);
+extern double CNF_GetHwTsTimeout(void);

+extern int CNF_GetPtpPort(void);
+extern int CNF_GetPtpDomain(void);
+
+extern int CNF_GetRefresh(void);
+
+extern ARR_Instance CNF_GetNtsAeads(void);
 extern char *CNF_GetNtsDumpDir(void);
 extern char *CNF_GetNtsNtpServer(void);
-extern char *CNF_GetNtsServerCertFile(void);
-extern char *CNF_GetNtsServerKeyFile(void);
+extern int CNF_GetNtsServerCertAndKeyFiles(const char ***certs, const char ***keys);
 extern int CNF_GetNtsServerPort(void);
 extern int CNF_GetNtsServerProcesses(void);
 extern int CNF_GetNtsServerConnections(void);
 extern int CNF_GetNtsRefresh(void);
 extern int CNF_GetNtsRotate(void);
-extern char *CNF_GetNtsTrustedCertFile(void);
+extern int CNF_GetNtsTrustedCertsPaths(const char ***paths, uint32_t **ids);
 extern int CNF_GetNoSystemCert(void);
 extern int CNF_GetNoCertTimeCheck(void);

--- a/292
+++ b/292
@@ -5,7 +5,7 @@
 #
 # Copyright (C) Richard P. Curnow  1997-2003
 # Copyright (C) Bryan Christianson  2016
-# Copyright (C) Miroslav Lichvar  2009, 2012-2018
+# Copyright (C) Miroslav Lichvar  2009, 2012-2022
 # Copyright (C) Stefan R. Filipek  2019
 #
 # =======================================================================
@@ -33,13 +33,13 @@ test_code () {
    echo "int main(int argc, char **argv) {"
    echo "$code"
    echo "return 0; }"
-  ) > docheck.c
+  ) > conftest.c

-  echo "docheck.c:" >> config.log
-  cat docheck.c >> config.log
-  echo $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o docheck docheck.c $ldflags \
+  echo "conftest.c:" >> config.log
+  cat conftest.c >> config.log
+  echo $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o conftest conftest.c $ldflags \
    $MYLDFLAGS >> config.log
-  $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o docheck docheck.c $ldflags \
+  $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o conftest conftest.c $ldflags \
    $MYLDFLAGS >> config.log 2>&1

  if [ $? -eq 0 ]
@@ -50,7 +50,7 @@ test_code () {
    echo "No"
    result=1
  fi
-  rm -f docheck.c docheck
+  rm -f conftest.c conftest
  echo >> config.log
  return $result
 }
@@ -108,19 +108,14 @@ for instance \`--prefix=$HOME'.

 For better control, use the options below.
  --disable-readline     Disable line editing support
-  --without-readline     Don't use GNU readline even if it is available
  --without-editline     Don't use editline even if it is available
-  --with-readline-includes=DIR Specify where readline include directory is
-  --with-readline-library=DIR Specify where readline lib directory is
-  --with-ncurses-library=DIR Specify where ncurses lib directory is
  --disable-sechash      Disable support for hashes other than MD5
  --without-nettle       Don't use nettle even if it is available
+  --without-gnutls       Don't use gnutls even if it is available
  --without-nss          Don't use NSS even if it is available
  --without-tomcrypt     Don't use libtomcrypt even if it is available
  --disable-nts          Disable NTS support
-  --without-gnutls       Don't use gnutls even if it is available
  --disable-cmdmon       Disable command and monitoring support
-  --disable-ntp          Disable NTP support
  --disable-refclock     Disable reference clock support
  --disable-phc          Disable PHC refclock driver
  --disable-pps          Disable PPS refclock driver
@@ -130,14 +125,15 @@ For better control, use the options below.
  --without-libcap       Don't use libcap even if it is available
  --enable-scfilter      Enable support for system call filtering
  --without-seccomp      Don't use seccomp even if it is available
-  --disable-asyncdns     Disable asynchronous name resolving
  --disable-forcednsretry Don't retry on permanent DNS error
+  --without-aes-gcm-siv  Don't use AES-GCM-SIV for NTS even if it is available
  --without-clock-gettime Don't use clock_gettime() even if it is available
  --disable-timestamping Disable support for SW/HW timestamping
  --enable-ntp-signd     Enable support for MS-SNTP authentication in Samba
  --with-ntp-era=SECONDS Specify earliest assumed NTP time in seconds
                         since 1970-01-01 [50*365 days ago]
  --with-user=USER       Specify default chronyd user [root]
+  --with-chronyc-user=USER Specify default chronyc user [root]
  --with-hwclockfile=PATH Specify default path to hwclock(8) adjtime file
  --with-pidfile=PATH    Specify default pidfile [/var/run/chrony/chronyd.pid]
  --with-rtcdevice=PATH  Specify default path to RTC device [/dev/rtc]
@@ -222,10 +218,8 @@ EXTRA_CLI_OBJECTS=""

 feat_debug=0
 feat_cmdmon=1
-feat_ntp=1
 feat_refclock=1
 feat_readline=1
-try_readline=1
 try_editline=1
 feat_sechash=1
 try_nettle=1
@@ -241,25 +235,23 @@ try_clockctl=0
 feat_scfilter=0
 try_seccomp=-1
 priv_ops=""
-readline_lib=""
-readline_inc=""
-ncurses_lib=""
 feat_ipv6=1
 feat_phc=1
 try_phc=0
 feat_pps=1
 try_setsched=0
 try_lockmem=0
-feat_asyncdns=1
 feat_forcednsretry=1
+try_aes_gcm_siv=1
 try_clock_gettime=1
+try_arc4random=1
 try_recvmmsg=1
 feat_timestamping=1
 try_timestamping=0
 feat_ntp_signd=0
 ntp_era_split=""
-use_pthread=0
 default_user="root"
+default_chronyc_user="root"
 default_hwclockfile=""
 default_pidfile="/var/run/chrony/chronyd.pid"
 default_rtcdevice="/dev/rtc"
@@ -274,21 +266,9 @@ do
    --disable-readline )
      feat_readline=0
    ;;
-    --without-readline )
-      try_readline=0
-    ;;
    --without-editline )
      try_editline=0
    ;;
-    --with-readline-library=* )
-      readline_lib=-L`echo $option | sed -e 's/^.*=//;'`
-    ;;
-    --with-readline-includes=* )
-      readline_inc=-I`echo $option | sed -e 's/^.*=//;'`
-    ;;
-    --with-ncurses-library=* )
-      ncurses_lib=-L`echo $option | sed -e 's/^.*=//;'`
-    ;;
    --prefix=* | --install_prefix=* )
      SETPREFIX=`echo $option | sed -e 's/[^=]*=//;'`
    ;;
@@ -325,9 +305,6 @@ do
    --disable-cmdmon)
      feat_cmdmon=0
    ;;
-    --disable-ntp)
-      feat_ntp=0
-    ;;
    --disable-refclock)
      feat_refclock=0
    ;;
@@ -358,12 +335,12 @@ do
    --without-seccomp)
      try_seccomp=0
    ;;
-    --disable-asyncdns)
-      feat_asyncdns=0
-    ;;
    --disable-forcednsretry)
      feat_forcednsretry=0
    ;;
+    --without-aes-gcm-siv)
+      try_aes_gcm_siv=0
+    ;;
    --without-clock-gettime)
      try_clock_gettime=0
    ;;
@@ -379,6 +356,9 @@ do
    --with-user=* )
      default_user=`echo $option | sed -e 's/^.*=//;'`
    ;;
+    --with-chronyc-user=* )
+      default_chronyc_user=`echo $option | sed -e 's/^.*=//;'`
+    ;;
    --with-hwclockfile=* )
      default_hwclockfile=`echo $option | sed -e 's/^.*=//;'`
    ;;
@@ -441,6 +421,7 @@ case $OPERATINGSYSTEM in
        try_setsched=1
        try_lockmem=1
        try_phc=1
+        try_arc4random=0
        add_def LINUX
        echo "Configuring for " $SYSTEM
    ;;
@@ -487,7 +468,7 @@ case $OPERATINGSYSTEM in
    ;;
    SunOS)
        EXTRA_OBJECTS="sys_generic.o sys_solaris.o sys_timex.o sys_posix.o"
-        LIBS="$LIBS -lsocket -lnsl -lresolv"
+        LIBS="$LIBS -lsocket -lnsl -lkvm -lelf -lresolv"
        try_setsched=1
        try_lockmem=1
        add_def SOLARIS
@@ -499,7 +480,7 @@ case $OPERATINGSYSTEM in
          add_def FEAT_PRIVDROP
          priv_ops="ADJUSTTIMEX SETTIME BINDSOCKET"
        fi
-        echo "Configuring for Solaris (" $SYSTEM "SunOS version" $VERSION ")" 
+        echo "Configuring for illumos (" $SYSTEM "SunOS version" $VERSION ")"
    ;;                                                                        
    * )
        echo "error: $SYSTEM is not supported (yet?)"
@@ -517,27 +498,15 @@ if [ $feat_cmdmon = "1" ]; then
  EXTRA_OBJECTS="$EXTRA_OBJECTS cmdmon.o manual.o pktlength.o"
 fi

-if [ $feat_ntp = "1" ]; then
-  add_def FEAT_NTP
-  EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_auth.o ntp_core.o ntp_ext.o ntp_io.o ntp_sources.o"
-  if [ $feat_ntp_signd = "1" ]; then
-    add_def FEAT_SIGND
-    EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_signd.o"
-  fi
-else
-  feat_asyncdns=0
-  feat_timestamping=0
-fi
-
-if [ "$feat_cmdmon" = "1" ] || [ $feat_ntp = "1" ]; then
-  EXTRA_OBJECTS="$EXTRA_OBJECTS addrfilt.o clientlog.o keys.o nameserv.o"
-else
-  feat_ipv6=0
+if [ $feat_ntp_signd = "1" ]; then
+  add_def FEAT_SIGND
+  EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_signd.o"
 fi

 if [ $feat_refclock = "1" ]; then
  add_def FEAT_REFCLOCK
-  EXTRA_OBJECTS="$EXTRA_OBJECTS refclock.o refclock_phc.o refclock_pps.o refclock_shm.o refclock_sock.o"
+  EXTRA_OBJECTS="$EXTRA_OBJECTS refclock.o refclock_phc.o refclock_pps.o \
+    refclock_rtc.o refclock_shm.o refclock_sock.o"
 fi

 MYCC="$CC"
@@ -583,6 +552,13 @@ if [ "x$MYCFLAGS" = "x" ]; then
  fi
 fi

+TESTCFLAGS="-fwrapv"
+if test_code '-fwrapv' '' "$TESTCFLAGS" '' ''; then
+  GETDATE_CFLAGS="-fwrapv"
+else
+  GETDATE_CFLAGS=""
+fi
+
 if [ "x$MYCC" = "xgcc" ] || [ "x$MYCC" = "xclang" ]; then
  MYCFLAGS="$MYCFLAGS -Wmissing-prototypes -Wall"
 fi
@@ -675,14 +651,30 @@ then
  fi
 fi

+if ! test_code 'O_NOFOLLOW flag' 'sys/types.h sys/stat.h fcntl.h' '' "$LIBS" \
+  'return open("/dev/null", O_NOFOLLOW);'
+then
+  if test_code 'O_NOFOLLOW flag with _GNU_SOURCE' 'sys/types.h sys/stat.h fcntl.h' \
+    '-D_GNU_SOURCE' "$LIBS" \
+    'return open("/dev/null", O_NOFOLLOW);'
+  then
+    add_def _GNU_SOURCE
+  else
+    echo "error: open() does not support O_NOFOLLOW flag"
+    exit 1
+  fi
+fi
+
 if [ $try_clock_gettime = "1" ]; then
-  if test_code 'clock_gettime()' 'time.h' '' '' \
-    'clock_gettime(CLOCK_REALTIME, NULL);'
+  if test_code 'clock_gettime()' 'time.h' '' '' '
+    struct timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);'
  then
    add_def HAVE_CLOCK_GETTIME
  else
-    if test_code 'clock_gettime() in -lrt' 'time.h' '' '-lrt' \
-      'clock_gettime(CLOCK_REALTIME, NULL);'
+    if test_code 'clock_gettime() in -lrt' 'time.h' '' '-lrt' '
+      struct timespec ts;
+      clock_gettime(CLOCK_REALTIME, &ts);'
    then
      add_def HAVE_CLOCK_GETTIME
      EXTRA_LIBS="$EXTRA_LIBS -lrt"
@@ -690,30 +682,37 @@ if [ $try_clock_gettime = "1" ]; then
  fi
 fi

-if test_code 'getaddrinfo()' 'sys/types.h sys/socket.h netdb.h' '' "$LIBS" \
+if ! test_code 'getaddrinfo()' 'sys/types.h sys/socket.h netdb.h' '' "$LIBS" \
  'return getaddrinfo(0, 0, 0, 0);'
 then
-  add_def HAVE_GETADDRINFO
+  echo "error: getaddrinfo() not found"
+  exit 1
 fi

-if [ $feat_asyncdns = "1" ] && \
-  test_code 'pthread' 'pthread.h' '-pthread' '' '
-    pthread_t thread;
-    return (int)pthread_create(&thread, NULL, (void *)1, NULL);'
+if test_code 'pthread' 'pthread.h' '-pthread' '' '
+  pthread_t thread;
+  return (int)pthread_create(&thread, NULL, (void *)1, NULL);'
 then
-  add_def FEAT_ASYNCDNS
  add_def USE_PTHREAD_ASYNCDNS
-  EXTRA_OBJECTS="$EXTRA_OBJECTS nameserv_async.o"
-  use_pthread=1
+  MYCFLAGS="$MYCFLAGS -pthread"
+else
+  echo "error: pthread_create() not found"
+  exit 1
 fi

-if test_code 'arc4random_buf()' 'stdlib.h' '' '' 'arc4random_buf(NULL, 0);'; then
+if [ $try_arc4random = "1" ] && \
+  test_code 'arc4random_buf()' 'stdlib.h' '' '' '
+    char c;
+    arc4random_buf(&c, 1);'
+then
  add_def HAVE_ARC4RANDOM
-fi
-
-if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' \
-    'return getrandom(NULL, 256, 0);'; then
-  add_def HAVE_GETRANDOM
+else
+  if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' '
+    char c;
+    return getrandom(&c, 1, 0);'
+  then
+    add_def HAVE_GETRANDOM
+  fi
 fi

 RECVMMSG_CODE='
@@ -804,11 +803,12 @@ if [ $feat_scfilter = "1" ] && [ $try_seccomp = "1" ] && \
    'seccomp_init(SCMP_ACT_KILL);'
 then
  add_def FEAT_SCFILTER
-  # NAME2IPADDRESS shouldn't be enabled with other operations as the helper
-  # process works on one request at the time and the async resolver could
-  # block the main thread
+  # NAME2IPADDRESS shouldn't be enabled together with a privops operation
+  # used by the main thread as the helper process works on one request at
+  # a time and the async resolver would block the main thread
  priv_ops="NAME2IPADDRESS RELOADDNS"
  EXTRA_LIBS="$EXTRA_LIBS -lseccomp"
+  EXTRA_OBJECTS="$EXTRA_OBJECTS sys_linux_scmp.o"
 fi

 if [ "x$priv_ops" != "x" ]; then
@@ -846,7 +846,6 @@ if [ $try_setsched = "1" ] && \
     pthread_setschedparam(pthread_self(), SCHED_FIFO, &sched);'
 then
  add_def HAVE_PTHREAD_SETSCHEDPARAM
-  use_pthread=1
 fi

 if [ $try_lockmem = "1" ] && \
@@ -876,37 +875,11 @@ fi
 READLINE_LINK=""
 if [ $feat_readline = "1" ]; then
  if [ $try_editline = "1" ]; then
-    if test_code editline 'stdio.h editline/readline.h' \
-      "$readline_inc" "$readline_lib -ledit" \
+    if test_code editline 'stdio.h editline/readline.h' '' '-ledit' \
      'add_history(readline("prompt"));'
    then
      add_def FEAT_READLINE
-      add_def USE_EDITLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib -ledit"
-    fi
-  fi
-
-  if [ "x$READLINE_LINK" = "x" ] && [ $try_readline = "1" ]; then
-    if test_code readline 'stdio.h readline/readline.h readline/history.h' \
-      "$readline_inc" "$readline_lib -lreadline" \
-      'add_history(readline("prompt"));'
-    then
-      add_def FEAT_READLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib -lreadline"
-    fi
-  fi
-
-  if [ "x$READLINE_LINK" = "x" ] && [ $try_readline = "1" ]; then
-    if test_code 'readline with -lncurses' \
-      'stdio.h readline/readline.h readline/history.h' \
-      "$readline_inc" "$readline_lib $ncurses_lib -lreadline -lncurses" \
-      'add_history(readline("prompt"));'
-    then
-      add_def FEAT_READLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib $ncurses_lib -lreadline -lncurses"
+      READLINE_LINK="-ledit"
    fi
  fi

@@ -926,15 +899,46 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nettle = "1" ];
    HASH_OBJ="hash_nettle.o"
    HASH_LINK="$test_link"
    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
+    add_def HAVE_NETTLE
    add_def FEAT_SECHASH

    if test_code 'CMAC in nettle' 'nettle/cmac.h' "$test_cflags" "$test_link" \
-      'cmac128_update(NULL, NULL, NULL, 0, NULL);'
+      'cmac128_update((void *)1, (void *)2, (void *)3, 1, (void *)4);'
    then
      add_def HAVE_CMAC
      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_nettle.o"
      EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS cmac_nettle.o"
    fi
+
+    if test_code 'nettle_memeql_sec()' 'nettle/memops.h' \
+      "$test_cflags" "$test_link" \
+      'return nettle_memeql_sec("", "", 0);'
+    then
+      add_def HAVE_NETTLE_MEMEQL
+    fi
+  fi
+fi
+
+if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_gnutls = "1" ]; then
+  test_cflags="`pkg_config --cflags gnutls`"
+  test_link="`pkg_config --libs gnutls`"
+  if test_code 'gnutls' 'gnutls/crypto.h' \
+    "$test_cflags" "$test_link" '
+      return gnutls_hash((void *)1, (void *)2, 1);'
+  then
+    HASH_OBJ="hash_gnutls.o"
+    HASH_LINK="$test_link"
+    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
+    add_def HAVE_GNUTLS
+    add_def FEAT_SECHASH
+
+    if test_code 'CMAC in gnutls' 'gnutls/crypto.h' "$test_cflags" "$test_link" \
+      'return gnutls_hmac_init((void *)1, GNUTLS_MAC_AES_CMAC_128, (void *)2, 0);'
+    then
+      add_def HAVE_CMAC
+      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_gnutls.o"
+      EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS cmac_gnutls.o"
+    fi
  fi
 fi

@@ -954,7 +958,7 @@ fi

 if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_tomcrypt = "1" ]; then
  if test_code 'tomcrypt' 'tomcrypt.h' '-I/usr/include/tomcrypt' '-ltomcrypt' \
-    'hash_memory_multi(find_hash("md5"), NULL, NULL, NULL, 0, NULL, 0);'
+    'hash_memory_multi(find_hash("md5"), (void *)1, (void *)2, (void *)3, 1, (void *)4, 1);'
  then
    HASH_OBJ="hash_tomcrypt.o"
    HASH_LINK="-ltomcrypt"
@@ -967,41 +971,58 @@ EXTRA_OBJECTS="$EXTRA_OBJECTS $HASH_OBJ"
 EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS $HASH_OBJ"
 LIBS="$LIBS $HASH_LINK"

-if [ $feat_ntp = "1" ] && [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
-  test_cflags="`pkg_config --cflags gnutls`"
-  test_link="`pkg_config --libs gnutls`"
-  if test_code 'gnutls' 'gnutls/gnutls.h' \
-    "$test_cflags" "$test_link" '
-      return gnutls_init(NULL, 0) +
-        gnutls_priority_init2(NULL, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
-        gnutls_prf_rfc5705(NULL, 0, "", 0, "", 16, NULL);'
+if [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
+  if [ "$HASH_OBJ" = "hash_gnutls.o" ]; then
+    test_cflags=""
+    test_link=""
+  else
+    test_cflags="`pkg_config --cflags gnutls`"
+    test_link="`pkg_config --libs gnutls`"
+  fi
+  if test_code 'TLS1.3 in gnutls' 'gnutls/gnutls.h' \
+    "$test_cflags" "$test_link $LIBS" '
+      return gnutls_init((void *)1, 0) + GNUTLS_TLS1_3 +
+        gnutls_priority_init2((void *)1, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
+        gnutls_prf_rfc5705((void *)1, 0, "", 0, "", 16, (void *)2);'
  then
-    if test_code 'SIV in nettle' \
+    if [ $try_nettle = "1" ] && test_code 'AES-SIV-CMAC in nettle' \
      'nettle/siv-cmac.h' "" "$LIBS" \
-      'siv_cmac_aes128_set_key(NULL, NULL);'
+      'siv_cmac_aes128_set_key((void *)1, (void *)2);'
    then
      EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
      add_def HAVE_SIV
-      add_def HAVE_NETTLE_SIV_CMAC
+      if [ $try_aes_gcm_siv = "1" ] && test_code 'AES-GCM-SIV in nettle' \
+        'nettle/siv-gcm.h' "" "$LIBS" \
+        'siv_gcm_aes128_encrypt_message((void *)1, 0, NULL, 0, (void *)2, 16, (void *)3,
+                                        (void *)4);'
+      then
+        add_def HAVE_NETTLE_SIV_GCM
+      fi
    else
-      if test_code 'SIV in gnutls' 'gnutls/gnutls.h' \
-        "$test_cflags" "$test_link" '
-          return gnutls_aead_cipher_init(NULL, GNUTLS_CIPHER_AES_128_SIV, NULL);'
+      if test_code 'AES-SIV-CMAC in gnutls' 'gnutls/crypto.h' \
+        "$test_cflags" "$test_link $LIBS" '
+          return gnutls_aead_cipher_init((void *)1, GNUTLS_CIPHER_AES_128_SIV, (void *)2);'
      then
        EXTRA_OBJECTS="$EXTRA_OBJECTS siv_gnutls.o"
        add_def HAVE_SIV
-      else
-        if test_code 'AES128 in nettle' 'nettle/aes.h' '' "$LIBS" \
-          'aes128_set_encrypt_key(NULL, NULL);'
+        if [ $try_aes_gcm_siv = "1" ] && test_code 'AES-GCM-SIV in gnutls' \
+          'gnutls/crypto.h' "$test_cflags" "$test_link $LIBS" '
+            return gnutls_aead_cipher_init((void *)1, GNUTLS_CIPHER_AES_128_SIV_GCM,
+                                           (void *)2);'
        then
-          EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
-          add_def HAVE_SIV
+          add_def HAVE_GNUTLS_SIV_GCM
+        fi
+        if test_code 'gnutls_aead_cipher_set_key()' 'gnutls/crypto.h' \
+          "$test_cflags" "$test_link $LIBS" '
+            return gnutls_aead_cipher_set_key((void *)1, (void *)2);'
+        then
+          add_def HAVE_GNUTLS_AEAD_CIPHER_SET_KEY
        fi
      fi
    fi

    if grep '#define HAVE_SIV' config.h > /dev/null; then
-      EXTRA_OBJECTS="$EXTRA_OBJECTS nts_ke_client.o nts_ke_server.o nts_ke_session.o"
+      EXTRA_OBJECTS="$EXTRA_OBJECTS nts_ke_client.o nts_ke_server.o nts_ke_session.o tls_gnutls.o"
      EXTRA_OBJECTS="$EXTRA_OBJECTS nts_ntp_auth.o nts_ntp_client.o nts_ntp_server.o"
      LIBS="$LIBS $test_link"
      MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
@@ -1010,10 +1031,6 @@ if [ $feat_ntp = "1" ] && [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
  fi
 fi

-if [ $use_pthread = "1" ]; then
-  MYCFLAGS="$MYCFLAGS -pthread"
-fi
-
 SYSCONFDIR=/etc
 if [ "x$SETSYSCONFDIR" != "x" ]; then
  SYSCONFDIR=$SETSYSCONFDIR
@@ -1074,12 +1091,13 @@ add_def DEFAULT_HWCLOCK_FILE "\"$default_hwclockfile\""
 add_def DEFAULT_PID_FILE "\"$default_pidfile\""
 add_def DEFAULT_RTC_DEVICE "\"$default_rtcdevice\""
 add_def DEFAULT_USER "\"$default_user\""
+add_def DEFAULT_CHRONYC_USER "\"$default_chronyc_user\""
 add_def DEFAULT_COMMAND_SOCKET "\"$CHRONYRUNDIR/chronyd.sock\""
 add_def MAIL_PROGRAM "\"$mail_program\""

 common_features="`get_features SECHASH IPV6 DEBUG`"
 chronyc_features="`get_features READLINE`"
-chronyd_features="`get_features CMDMON NTP REFCLOCK RTC PRIVDROP SCFILTER SIGND ASYNCDNS NTS`"
+chronyd_features="`get_features CMDMON REFCLOCK RTC PRIVDROP SCFILTER SIGND NTS`"
 add_def CHRONYC_FEATURES "\"$chronyc_features $common_features\""
 add_def CHRONYD_FEATURES "\"$chronyd_features $common_features\""
 echo "Features : $chronyd_features $chronyc_features $common_features"
@@ -1101,6 +1119,7 @@ do
          s%@CFLAGS@%${MYCFLAGS}%;\
          s%@CPPFLAGS@%${MYCPPFLAGS}%;\
          s%@LDFLAGS@%${MYLDFLAGS}%;\
+          s%@GETDATE_CFLAGS@%${GETDATE_CFLAGS}%;\
          s%@LIBS@%${LIBS}%;\
          s%@EXTRA_LIBS@%${EXTRA_LIBS}%;\
          s%@EXTRA_CLI_LIBS@%${EXTRA_CLI_LIBS}%;\
@@ -1116,6 +1135,7 @@ do
          s%@DEFAULT_PID_FILE@%${default_pidfile}%;\
          s%@DEFAULT_RTC_DEVICE@%${default_rtcdevice}%;\
          s%@DEFAULT_USER@%${default_user}%;\
+          s%@DEFAULT_CHRONYC_USER@%${default_chronyc_user}%;\
          s%@CHRONY_VERSION@%${CHRONY_VERSION}%;" \
          < ${f}.in > $f
 done
--- a/contrib/bryan_christianson_1/README.txt
+++ b/contrib/bryan_christianson_1/README.txt
@@ -60,8 +60,8 @@ Support files
 Dates and sizes may differ
 -rw-r--r--  1 yourname  staff  2084  4 Aug 22:54 README.txt
 -rwxr-xr-x  1 yourname  staff   676  4 Aug 21:18 chronylogrotate.sh
-rw-r--r--  1 yourname  staff   543 18 Jul 20:10 org.tuxfamily.chronyc.plist
-rw-r--r--  1 yourname  staff   511 19 Jun 18:30 org.tuxfamily.chronyd.plist
+-rw-r--r--  1 yourname  staff   543 18 Jul 20:10 org.chrony-project.chronyc.plist
+-rw-r--r--  1 yourname  staff   511 19 Jun 18:30 org.chrony-project.chronyd.plist

 If you have used chrony support directories other than those suggested, you
 will need to edit each file and make the appropriate changes.
@@ -83,21 +83,21 @@ sudo chmod +x /usr/local/bin/chronylogrotate.sh
 sudo chown root:wheel /usr/local/bin/chronylogrotate.sh


-2. org.tuxfamily.chronyc.plist
+2. org.chrony-project.chronyc.plist
 This file is the launchd plist that runs logrotation each day. You may
 wish to edit this file to change the time of day at which the rotation
 will run, currently 04:05 am

-sudo cp org.tuxfamily.chronyc.plist /Library/LaunchDaemons
-sudo chown root:wheel /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
-sudo chmod 0644 /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
-sudo launchctl load -w /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
+sudo cp org.chrony-project.chronyc.plist /Library/LaunchDaemons
+sudo chown root:wheel /Library/LaunchDaemons/org.chrony-project.chronyc.plist
+sudo chmod 0644 /Library/LaunchDaemons/org.chrony-project.chronyc.plist
+sudo launchctl load -w /Library/LaunchDaemons/org.chrony-project.chronyc.plist


-3. org.tuxfamily.chronyd.plist
+3. org.chrony-project.chronyd.plist
 This file is the launchd plist that runs chronyd when the Macintosh starts.

-sudo cp org.tuxfamily.chronyd.plist /Library/LaunchDaemons
-sudo chown root:wheel /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
-sudo chmod 0644 /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
-sudo launchctl load -w /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
+sudo cp org.chrony-project.chronyd.plist /Library/LaunchDaemons
+sudo chown root:wheel /Library/LaunchDaemons/org.chrony-project.chronyd.plist
+sudo chmod 0644 /Library/LaunchDaemons/org.chrony-project.chronyd.plist
+sudo launchctl load -w /Library/LaunchDaemons/org.chrony-project.chronyd.plist
--- a/contrib/bryan_christianson_1/org.chrony-project.chronyc.plist
+++ b/contrib/bryan_christianson_1/org.chrony-project.chronyc.plist
@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
 	<key>Label</key>
-	<string>org.tuxfamily.logrotate</string>
+	<string>org.chrony-project.logrotate</string>
 	<key>KeepAlive</key>
 	<false/>
 	<key>ProgramArguments</key>
--- a/contrib/bryan_christianson_1/org.chrony-project.chronyd.plist
+++ b/contrib/bryan_christianson_1/org.chrony-project.chronyd.plist
@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
 	<key>Label</key>
-	<string>org.tuxfamily.chronyd</string>
+	<string>org.chrony-project.chronyd</string>
 	<key>Program</key>
 	<string>/usr/local/sbin/chronyd</string>
 	<key>ProgramArguments</key>
--- a/doc/Makefile.in
+++ b/doc/Makefile.in
@@ -17,6 +17,7 @@ CHRONYRUNDIR = @CHRONYRUNDIR@
 CHRONYVARDIR = @CHRONYVARDIR@
 CHRONY_VERSION = @CHRONY_VERSION@
 DEFAULT_USER = @DEFAULT_USER@
+DEFAULT_CHRONYC_USER = @DEFAULT_CHRONYC_USER@
 DEFAULT_HWCLOCK_FILE = @DEFAULT_HWCLOCK_FILE@
 DEFAULT_PID_FILE = @DEFAULT_PID_FILE@
 DEFAULT_RTC_DEVICE = @DEFAULT_RTC_DEVICE@
@@ -29,6 +30,7 @@ SED_COMMANDS = "s%\@SYSCONFDIR\@%$(SYSCONFDIR)%g;\
 	       s%\@DEFAULT_PID_FILE\@%$(DEFAULT_PID_FILE)%g;\
 	       s%\@DEFAULT_RTC_DEVICE\@%$(DEFAULT_RTC_DEVICE)%g;\
 	       s%\@DEFAULT_USER\@%$(DEFAULT_USER)%g;\
+	       s%\@DEFAULT_CHRONYC_USER\@%$(DEFAULT_CHRONYC_USER)%g;\
 	       s%\@CHRONYRUNDIR\@%$(CHRONYRUNDIR)%g;\
 	       s%\@CHRONYVARDIR\@%$(CHRONYVARDIR)%g;"

--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
--- a/doc/chronyc.adoc
+++ b/doc/chronyc.adoc
@@ -2,7 +2,7 @@
 //
 // Copyright (C) Richard P. Curnow  1997-2003
 // Copyright (C) Stephen Wadeley  2016
-// Copyright (C) Miroslav Lichvar  2009-2017
+// Copyright (C) Miroslav Lichvar  2009-2017, 2019-2025
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -39,7 +39,7 @@ running.
 If no commands are specified on the command line, *chronyc* will expect input
 from the user. The prompt _chronyc>_ will be displayed when it is being run
 from a terminal. If *chronyc*'s input or output are redirected from or to a file,
-the prompt is not shown.
+the prompt will not be shown.

 There are two ways *chronyc* can access *chronyd*. One is the Internet
 Protocol (IPv4 or IPv6) and the other is a Unix domain socket, which is
@@ -50,7 +50,7 @@ running under a non-root user), it will try to connect to 127.0.0.1 and then
 ::1.

 Only the following monitoring commands, which do not affect the behaviour of
-*chronyd*, are allowed from the network: *activity*, *manual list*,
+*chronyd*, are allowed from the network by default: *activity*, *manual list*,
 *rtcdata*, *smoothing*, *sourcename*, *sources*, *sourcestats*, *tracking*,
 *waitsync*. The
 set of hosts from which *chronyd* will accept these commands can be configured
@@ -58,11 +58,12 @@ with the <<chrony.conf.adoc#cmdallow,*cmdallow*>> directive in the *chronyd*'s
 configuration file or the <<cmdallow,*cmdallow*>> command in *chronyc*. By
 default, the commands are accepted only from localhost (127.0.0.1 or ::1).

-All other commands are allowed only through the Unix domain socket. When sent
+Other monitoring commands can be enabled for network access by the
+<<chrony.conf.adoc#opencommands,*opencommands*>> directive. Monitoring commands
+with disabled network access and commands that affect the behaviour of
+*chronyd* are allowed only through the Unix domain socket. If they are sent
 over the network, *chronyd* will respond with a '`Not authorised`' error, even
-if it is from localhost. In chrony versions before 2.2 they were allowed
-from the network if they were authenticated with a password, but that is no
-longer supported.
+if it is from localhost.

 Having full access to *chronyd* via *chronyc* is more or less equivalent to
 being able to modify the *chronyd*'s configuration file and restart it.
@@ -80,11 +81,10 @@ This option disables resolving of IP addresses to hostnames, e.g. to avoid slow
 DNS lookups. Long addresses will not be truncated to fit into the column.

 *-N*::
-This option enables printing of the original names of NTP sources that were
-specified in the configuration file, or *chronyc* commands, and are internally
-used by *chronyd*. Without the *-n* and *-N* option, the names of NTP sources
-are obtained from reverse DNS lookups and can be different from the original
-names.
+This option enables printing of original hostnames or IP addresses of NTP
+sources that were specified in the configuration file, or *chronyc* commands.
+Without the *-n* and *-N* option, the printed hostnames are obtained from
+reverse DNS lookups and can be different from the specified hostnames.

 *-c*::
 This option enables printing of reports in a comma-separated values (CSV)
@@ -92,6 +92,10 @@ format. Reverse DNS lookups will be disabled, time will be printed as number of
 seconds since the epoch, and values in seconds will not be converted to other
 units.

+*-e*::
+With this option each *chronyc* response will end with a line containing a
+single dot.
+
 *-d*::
 This option enables printing of debugging messages if *chronyc* was compiled
 with debugging support.
@@ -102,28 +106,42 @@ With this option multiple commands can be specified. Each argument will be
 interpreted as a whole command.

 *-h* _host_::
-This option allows the user to specify which host (or comma-separated list of
-addresses) running the *chronyd* program is to be contacted. This allows for
-remote monitoring, without having to connect over SSH to the other host first.
+This option specifies the host to be contacted by *chronyc*. It can be
+specified with a hostname, IP address, or path to the local Unix domain socket.
+Multiple values can be specified as a comma-separated list to provide a
+fallback.
 +
-The default is to contact *chronyd* running on the same host where
-*chronyc* is being run.
+The default value is _@CHRONYRUNDIR@/chronyd.sock,127.0.0.1,::1_, i.e. the host
+where *chronyc* is being run. First, it tries to connect to the Unix domain
+socket and if that fails (e.g. due to running under a non-root user), it
+will try to connect to 127.0.0.1 and then ::1.

 *-p* _port_::
 This option allows the user to specify the UDP port number which the target
 *chronyd* is using for its monitoring connections. This defaults to 323; there
 would rarely be a need to change this.

+*-u* _user_::
+This option sets the name of the user to which *chronyc* will switch when it is
+started under the root user in order to drop its privileges. *chronyc* will not
+try to change its identity if the option is set to _root_, or the effective
+user ID of the started process is not 0. The compiled-in default value is
+_@DEFAULT_CHRONYC_USER@_.
+
 *-f* _file_::
 This option is ignored and is provided only for compatibility.

 *-a*::
 This option is ignored and is provided only for compatibility.

-*-v*::
+*-v*, *--version*::
 With this option *chronyc* displays its version number on the terminal and
 exits.

+*--help*::
+With this option *chronyc* displays a help message on the terminal and
+exits.
+
 == COMMANDS

 This section describes each of the commands available within the *chronyc*
@@ -136,7 +154,7 @@ The *tracking* command displays parameters about the system's clock
 performance. An example of the output is shown below.
 +
 ----
-Reference ID    : CB00710F (foo.example.net)
+Reference ID    : CB00710F (ntp1.example.net)
 Stratum         : 3
 Ref time (UTC)  : Fri Jan 27 09:49:17 2017
 System time     : 0.000006523 seconds slow of NTP time
@@ -170,23 +188,29 @@ with an IPv4 address.
 *Stratum*:::
 The stratum indicates how many hops away from a computer with an attached
 reference clock we are. Such a computer is a stratum-1 computer, so the
-computer in the example is two hops away (i.e. _foo.example.net_ is a
+computer in the example is two hops away (i.e. _ntp1.example.net_ is a
 stratum-2 and is synchronised from a stratum-1).
 *Ref time*:::
 This is the time (UTC) at which the last measurement from the reference
 source was processed.
 *System time*:::
-In normal operation, *chronyd* by default never steps the system clock, because
-any jump in the time can have adverse consequences for certain application
-programs. Instead, any error in the system clock is corrected by slightly
-speeding up or slowing down the system clock until the error has been removed,
-and then returning to the system clock's normal speed. A consequence of this is
-that there will be a period when the system clock (as read by other programs)
-will be different from *chronyd*'s estimate of the current true time (which it
-reports to NTP clients when it is operating in server mode). The value reported
-on this line is the difference due to this effect.
+This is the current offset between the NTP clock and system clock. The NTP
+clock is a software (virtual) clock maintained by *chronyd*, which is
+synchronised to the configured time sources and provides time to NTP clients.
+The system clock is synchronised to the NTP clock. To avoid steps in the
+system time, which might have adverse consequences for certain applications,
+the system clock is normally corrected only by speeding up or slowing down (up
+to the rate configured by the <<chrony.conf.adoc#maxslewrate,*maxslewrate*>>
+directive). If the offset is too large, this correction will take a very long
+time. A step can be forced by the <<makestep,*makestep*>> command, or the
+<<chrony.conf.adoc#makestep,*makestep*>> directive in the configuration file.
+
+Note that all other offsets reported by *chronyc* and most offsets in the log
+files are relative to the NTP clock, not the system clock.
 *Last offset*:::
-This is the estimated local offset on the last clock update.
+This is the estimated local offset on the last clock update. A positive value
+indicates the local time (as previously estimated true time) was ahead of the
+time sources.
 *RMS offset*:::
 This is a long-term average of the offset value.
 *Frequency*:::
@@ -307,8 +331,8 @@ extra caption lines are shown as a reminder of the meanings of the columns.
 MS Name/IP address         Stratum Poll Reach LastRx Last sample
 ===============================================================================
 #* GPS0                          0   4   377    11   -479ns[ -621ns] +/-  134ns
-^? foo.example.net               2   6   377    23   -923us[ -924us] +/-   43ms
-^+ bar.example.net               1   6   377    21  -2629us[-2619us] +/-   86ms
+^? ntp1.example.net              2   6   377    23   -923us[ -924us] +/-   43ms
+^+ ntp2.example.net              1   6   377    21  -2629us[-2619us] +/-   86ms
 ----
 +
 The columns are as follows:
@@ -317,18 +341,23 @@ The columns are as follows:
 This indicates the mode of the source. _^_ means a server, _=_ means a peer
 and _#_ indicates a locally connected reference clock.
 *S*:::
-This column indicates the state of the source.
-* _*_ indicates the source to which *chronyd* is currently synchronised.
-* _+_ indicates acceptable sources which are combined with the selected
-  source.
-* _-_ indicates acceptable sources which are excluded by the combining
-  algorithm.
-* _?_ indicates sources to which connectivity has been lost or whose packets
-  do not pass all tests. It is also shown at start-up, until at least 3 samples
-  have been gathered from it.
-* _x_ indicates a clock which *chronyd* thinks is a falseticker (i.e. its
-  time is inconsistent with a majority of other sources).
+This column indicates the selection state of the source.
+* _*_ indicates the best source which is currently selected for
+  synchronisation.
+* _+_ indicates other sources selected for synchronisation, which are combined
+  with the best source.
+* _-_ indicates a source which is considered to be selectable for
+  synchronisation, but not currently selected.
+* _x_ indicates a source which *chronyd* thinks is a falseticker (i.e. its
+  time is inconsistent with a majority of other sources, or sources specified
+  with the *trust* option).
 * _~_ indicates a source whose time appears to have too much variability.
+* _?_ indicates a source which is not considered to be selectable for
+  synchronisation for other reasons (e.g. unreachable, not synchronised, or
+  does not have enough measurements).
+{blank}:::
+The <<selectdata,*selectdata*>> command can be used to get more details about
+the selection state.
 *Name/IP address*:::
 This shows the name or the IP address of the source, or reference ID for reference
 clocks.
@@ -345,9 +374,12 @@ a measurement is being made every 64 seconds. *chronyd* automatically varies
 the polling rate in response to prevailing conditions.
 *Reach*:::
 This shows the source's reachability register printed as an octal number. The
-register has 8 bits and is updated on every received or missed packet from
-the source. A value of 377 indicates that a valid reply was received for all
-from the last eight transmissions.
+register has 8 bits. It is shifted to left by one bit with each poll and it is
+updated by 1 when a valid NTP response, or just a sample in case of a reference
+clock, is received from the source. A value of 377 indicates that a valid
+response or sample was received for all of the last 8 polls. Note that samples
+can be dropped if they are not considered good enough for synchronisation, but
+the reachability register will still have 1s for their polls.
 *LastRx*:::
 This column shows how long ago the last good sample (which is shown in the next
 column) was received from the source. Measurements that failed some tests are
@@ -360,9 +392,9 @@ offset. This can be suffixed by _ns_ (indicating nanoseconds), _us_
 (indicating microseconds), _ms_ (indicating milliseconds), or _s_ (indicating
 seconds). The number to the left of the square brackets shows the original
 measurement, adjusted to allow for any slews applied to the local clock
-since. The number following the _+/-_ indicator shows the margin of error in
-the measurement. Positive offsets indicate that the local clock is ahead of
-the source.
+since. Positive offsets indicate that the local clock is ahead of the source.
+The number following the _+/-_ indicator shows the margin of error in the
+measurement (NTP root distance).

 [[sourcestats]]*sourcestats* [*-a*] [*-v*]::
 The *sourcestats* command displays information about the drift rate and offset
@@ -381,7 +413,7 @@ An example report is:
 ----
 Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
 ===============================================================================
-foo.example.net            11   5   46m     -0.001      0.045      1us    25us
+ntp1.example.net           11   5   46m     -0.001      0.045      1us    25us
 ----
 +
 The columns are as follows:
@@ -423,11 +455,11 @@ lines are shown as a reminder of the meanings of the columns.
 An example of the output is shown below.
 +
 ----
-S Name/IP Address        Auth COpts EOpts Last Score     Interval   
-====================================================================
-D foo.example.net           Y ----- --TR-    4   1.0   -61ms   +62ms
-* bar.example.net           N ----- -----    0   1.0 -6846us +7305us
-+ baz.example.net           N ----- -----   10   1.0 -7381us +7355us
+S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
+=======================================================================
+D ntp1.example.net          Y ----- --TR-    4   1.0   -61ms   +62ms  N
+* ntp2.example.net          N ----- -----    0   1.0 -6846us +7305us  N
+ ntp3.example.net          N ----- -----   10   1.0 -7381us +7355us  N
 ----
 +
 The columns are as follows:
@@ -441,12 +473,17 @@ The following states indicate the source is not considered selectable for
 synchronisation:
 * _N_ - has the *noselect* option.
 * _M_ - does not have enough measurements.
+* _s_ - is not synchronised.
+* _r_ - has a stratum outside of the allowed range (configured by the
+        <<chrony.conf.adoc#minstratum,*minstratum*>> and
+        <<chrony.conf.adoc#maxstratum,*maxstratum*>> directives).
 * _d_ - has a root distance larger than the maximum distance (configured by the
        <<chrony.conf.adoc#maxdistance,*maxdistance*>> directive).
 * _~_ - has a jitter larger than the maximum jitter (configured by the
        <<chrony.conf.adoc#maxjitter,*maxjitter*>> directive).
 * _w_ - waits for other sources to get out of the _M_ state.
-* _S_ - has older measurements than other sources.
+* _S_ - has only measurements older than reachable sources, or is unreachable
+        for too many polls (configured by the *maxunreach* option).
 * _O_ - has a stratum equal or larger than the orphan stratum (configured by
        the <<chrony.conf.adoc#local,*local*>> directive).
 * _T_ - does not fully agree with sources that have the *trust* option.
@@ -472,7 +509,7 @@ local clock:
 This column shows the name or IP address of the source if it is an NTP server,
 or the reference ID if it is a reference clock.
 *Auth*:::
-This column indicites whether an authentication mechanism is enabled for the
+This column indicates whether an authentication mechanism is enabled for the
 source. _Y_ means yes and _N_ means no.
 *COpts*:::
 This column displays the configured selection options of the source.
@@ -484,8 +521,8 @@ This column displays the configured selection options of the source.
 This column displays the current effective selection options of the source,
 which can be different from the configured options due to the authentication
 selection mode (configured by the
-<<chrony.conf.adoc#authselmode,*authselmode*>> directive). The symbols are the
-same as in the *COpts* column.
+<<chrony.conf.adoc#authselectmode,*authselectmode*>> directive). The symbols
+are the same as in the *COpts* column.
 *Last*:::
 This column displays how long ago was the last measurement of the source made
 when the selection was performed.
@@ -499,6 +536,29 @@ be reselected and the scores will be reset to 1.
 This column displays the lower and upper endpoint of the interval which was
 expected to contain the true offset of the local clock considering the root
 distance at the time of the selection.
+*Leap*:::
+This column displays the current leap status of the source.
+* _N_ indicates the normal status (no leap second).
+* _+_ indicates that a leap second will be inserted at the end of the month.
+* _-_ indicates that a leap second will be deleted at the end of the month.
+* _?_ indicates the unknown status (i.e. no valid measurement was made).
+
+[[selectopts]]*selectopts* _address|refid_ [_+|-option_]...::
+The *selectopts* command modifies the configured selection options of an NTP
+source specified by IP address (or the _ID#XXXXXXXXXX_ identifier used for
+unknown addresses), or a reference clock specified by reference ID as a string.
+
+The selection options can be added with the *+* symbol or removed with the *-*
+symbol. The *selectdata* command can be used to verify the configuration. The
+modified options will be applied in the next source selection, e.g. when a new
+measurement is made, or the *reselect* command is executed.
+
+An example of using this command is shown below.
+
+----
+selectopts 1.2.3.4 -noselect +prefer
+selectopts GPS +trust
+----

 [[reselect]]*reselect*::
 To avoid excessive switching between sources, *chronyd* can stay synchronised
@@ -513,6 +573,13 @@ The *reselectdist* command sets the reselection distance. It is equivalent to
 the <<chrony.conf.adoc#reselectdist,*reselectdist*>> directive in the
 configuration file.

+[[offset]]*offset* _address|refid_ _offset_::
+The *offset* command modifies the offset correction of an NTP source specified
+by IP address (or the _ID#XXXXXXXXXX_ identifier used for unknown addresses),
+or a reference clock specified by reference ID as a string. It is equivalent to
+the *offset* option in the <<chrony.conf.adoc#server,*server*>> or
+<<chrony.conf.adoc#refclock,*refclock*>> directive respectively.
+
 === NTP sources

 [[activity]]*activity*::
@@ -549,9 +616,9 @@ shown below.
 ----
 Name/IP address             Mode KeyID Type KLen Last Atmp  NAK Cook CLen
 =========================================================================
-foo.example.net              NTS     1   15  256 135m    0    0    8  100
-bar.example.net               SK    30   13  128    -    0    0    0    0
-baz.example.net                -     0    0    0    -    0    0    0    0
+ntp1.example.net             NTS     1   15  256 135m    0    0    8  100
+ntp2.example.net              SK    30   13  128    -    0    0    0    0
+ntp3.example.net               -     0    0    0    -    0    0    0    0
 ----
 +
 The columns are as follows:
@@ -588,6 +655,7 @@ be reported:
 * 13: AES128
 * 14: AES256
 * 15: AEAD-AES-SIV-CMAC-256
+* 30: AEAD-AES-128-GCM-SIV
 *KLen*:::
 This column shows the length of the key in bits.
 *Last*:::
@@ -644,6 +712,11 @@ RX timestamping : Kernel
 Total TX        : 24
 Total RX        : 24
 Total valid RX  : 24
+Total good RX   : 22
+Total kernel TX : 24
+Total kernel RX : 24
+Total HW TX     : 0
+Total HW RX     : 0
 ----
 +
 The fields are explained as follows:
@@ -681,7 +754,8 @@ packets sent to the source is more variable than the delay of packets sent
 from the source back.
 *NTP tests*:::
 Results of RFC 5905 tests 1 through 3, 5 through 7, and tests for maximum
-delay, delay ratio, delay dev ratio, and synchronisation loop.
+delay, delay ratio, delay dev ratio (or delay quantile), and synchronisation
+loop.
 *Interleaved*:::
 This shows if the response was in the interleaved mode.
 *Authenticated*:::
@@ -696,7 +770,22 @@ The number of packets sent to the source.
 *Total RX*:::
 The number of all packets received from the source.
 *Total valid RX*:::
-The number of valid packets received from the source.
+The number of packets which passed the first two groups of NTP tests.
+*Total good RX*:::
+The number of packets which passed all three groups of NTP tests, i.e. the NTP
+measurement was accepted.
+*Total kernel TX*:::
+The number of packets sent to the source for which a timestamp was captured by
+the kernel.
+*Total kernel RX*:::
+The number of packets received from the source for which a timestamp was
+captured by the kernel.
+*Total HW TX*:::
+The number of packets sent to the source for which a timestamp was captured by
+the NIC.
+*Total HW RX*:::
+The number of packets received from the source for which a timestamp was
+captured by the NIC.

 [[add_peer]]*add peer* _name_ [_option_]...::
 The *add peer* command allows a new NTP peer to be added whilst
@@ -709,7 +798,7 @@ parameters and options is identical to that for the
 An example of using this command is shown below.
 +
 ----
-add peer foo.example.net minpoll 6 maxpoll 10 key 25
+add peer ntp1.example.net minpoll 6 maxpoll 10 key 25
 ----

 [[add_pool]]*add pool* _name_ [_option_]...::
@@ -723,7 +812,7 @@ directive in the configuration file.
 An example of using this command is shown below:
 +
 ----
-add pool foo.example.net maxsources 3 iburst
+add pool ntp1.example.net maxsources 3 iburst
 ----

 [[add_server]]*add server* _name_ [_option_]...::
@@ -737,7 +826,7 @@ directive in the configuration file.
 An example of using this command is shown below:
 +
 ----
-add server foo.example.net minpoll 6 maxpoll 10 key 25
+add server ntp1.example.net minpoll 6 maxpoll 10 key 25
 ----

 [[delete]]*delete* _address_::
@@ -813,7 +902,7 @@ IPv6 addresses have first 48 bits equal to _2001:db8:789a_.
 Example of the three-argument form of the command is:
 +
 ----
-burst 2/10 foo.example.net
+burst 2/10 ntp1.example.net
 ----

 [[maxdelay]]*maxdelay* _address_ _delay_::
@@ -879,7 +968,7 @@ uses an IP address or a hostname. These forms are illustrated below.
 offline
 offline 255.255.255.0/1.2.3.0
 offline 2001:db8:789a::/48
-offline foo.example.net
+offline ntp1.example.net
 ----
 +
 The second form means that the *offline* command is to be applied to any source
@@ -921,17 +1010,26 @@ current set of sources. It is equivalent to the *polltarget* option in the

 [[refresh]]*refresh*::
 The *refresh* command can be used to force *chronyd* to resolve the names of
-configured sources to IP addresses again, e.g. after suspending and resuming
-the machine in a different network.
+configured NTP sources to IP addresses again and replace any addresses missing
+in the list of resolved addresses.
 +
-Sources that stop responding will be replaced with newly resolved addresses
-automatically after 8 polling intervals, but this command can still be useful
-to replace them immediately and not wait until they are marked as unreachable.
+Sources that stop responding are replaced with newly resolved addresses
+automatically after 8 polling intervals. This command can be used to replace
+them immediately, e.g. after suspending and resuming the machine in a different
+network.
+
+Note that with pools which have more than 16 addresses, or not all IPv4 or IPv6
+addresses are included in a single DNS response (e.g. pool.ntp.org), this
+command might replace the addresses even if they are still in the pool.

 [[reload]]*reload* *sources*::
 The *reload sources* command causes *chronyd* to re-read all _*.sources_ files
 from the directories specified by the
 <<chrony.conf.adoc#sourcedir,*sourcedir*>> directive.
+
+Note that modified sources (e.g. specified with a new option) are not modified
+in memory. They are removed and added again, which causes them to lose old
+measurements and reset the selection state.

 [[sourcename]]*sourcename* _address_::
 The *sourcename* command prints the original hostname or address that was
@@ -1040,7 +1138,7 @@ particular host.
 Examples of use, showing a named host and a numeric IP address, are as follows:
 +
 ----
-accheck foo.example.net
+accheck ntp1.example.net
 accheck 1.2.3.4
 accheck 2001:db8::1
 ----
@@ -1067,7 +1165,7 @@ An example of the output is:
 Hostname                      NTP   Drop Int IntL Last     Cmd   Drop Int  Last
 ===============================================================================
 localhost                       2      0   2   -   133      15      0  -1     7
-foo.example.net                12      0   6   -    23       0      0   -     -
+ntp1.example.net               12      0   6   -    23       0      0   -     -
 ----
 +
 Each row shows the data for a single host. Only hosts that have passed the host
@@ -1093,13 +1191,9 @@ The columns are as follows:
  received/accepted.

 [[serverstats]]*serverstats*::
-The *serverstats* command displays how many valid NTP and command requests, and
-NTS-KE connections, *chronyd* operating as a server received from clients, and
-how many of them were dropped due to rate limiting. It also displays how many
-client log records were dropped due to the memory limit configured by the
-<<chrony.conf.adoc#clientloglimit,*clientloglimit*>> directive and how many of
-the NTP requests (from those which were not dropped) were authenticated. An
-example of the output is shown below.
+The *serverstats* command displays NTP and command server statistics.
+
+An example of the output is shown below.
 +
 ----
 NTP packets received       : 1598
@@ -1110,7 +1204,67 @@ Client log records dropped : 0
 NTS-KE connections accepted: 3
 NTS-KE connections dropped : 0
 Authenticated NTP packets  : 189
+Interleaved NTP packets    : 43
+NTP timestamps held        : 44
+NTP timestamp span         : 120
+NTP daemon RX timestamps   : 0
+NTP daemon TX timestamps   : 1537
+NTP kernel RX timestamps   : 1590
+NTP kernel TX timestamps   : 43
+NTP hardware RX timestamps : 0
+NTP hardware TX timestamps : 0
 ----
+
+The fields have the following meaning:
+
+*NTP packets received*:::
+The number of valid NTP requests received by the server.
+*NTP packets dropped*:::
+The number of NTP requests dropped by the server due to rate limiting
+(configured by the <<chrony.conf.adoc#ratelimit,*ratelimit*>> directive).
+*Command packets received*:::
+The number of command requests received by the server.
+*Command packets dropped*:::
+The number of command requests dropped by the server due to rate limiting
+(configured by the <<chrony.conf.adoc#cmdratelimit,*cmdratelimit*>> directive).
+*Client log records dropped*:::
+The number of client log records dropped by the server to limit the memory use
+(configured by the <<chrony.conf.adoc#clientloglimit,*clientloglimit*>>
+directive).
+*NTS-KE connections accepted*:::
+The number of NTS-KE connections accepted by the server.
+*NTS-KE connections dropped*:::
+The number of NTS-KE connections dropped by the server due to rate limiting
+(configured by the <<chrony.conf.adoc#ntsratelimit,*ntsratelimit*>> directive).
+*Authenticated NTP packets*:::
+The number of received NTP requests that were authenticated (with a symmetric
+key or NTS).
+*Interleaved NTP packets*:::
+The number of received NTP requests that were detected to be in the interleaved
+mode.
+*NTP timestamps held*:::
+The number of pairs of receive and transmit timestamps that the server is
+currently holding in memory for clients using the interleaved mode.
+*NTP timestamp span*:::
+The interval (in seconds) covered by the currently held NTP timestamps.
+*NTP daemon RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+daemon.
+*NTP daemon TX timestamps*:::
+The number of NTP responses which included a transmit timestamp captured by the
+daemon.
+*NTP kernel RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+kernel.
+*NTP kernel TX timestamps*:::
+The number of NTP responses (in the interleaved mode) which included a transmit
+timestamp captured by the kernel.
+*NTP hardware RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+NIC.
+*NTP hardware TX timestamps*:::
+The number of NTP responses (in the interleaved mode) which included a transmit
+timestamp captured by the NIC.

 [[allow]]*allow* [*all*] [_subnet_]::
 The effect of the allow command is identical to the
@@ -1119,11 +1273,8 @@ The effect of the allow command is identical to the
 The syntax is illustrated in the following examples:
 +
 ----
-allow foo.example.net
-allow all 1.2
-allow 3.4.5
-allow 6.7.8/22
-allow 6.7.8.9/22
+allow 1.2.3.4
+allow all 3.4.5.0/24
 allow 2001:db8:789a::/48
 allow 0/0
 allow ::/0
@@ -1138,11 +1289,8 @@ The effect of the allow command is identical to the
 The syntax is illustrated in the following examples:
 +
 ----
-deny foo.example.net
-deny all 1.2
-deny 3.4.5
-deny 6.7.8/22
-deny 6.7.8.9/22
+deny 1.2.3.4
+deny all 3.4.5.0/24
 deny 2001:db8:789a::/48
 deny 0/0
 deny ::/0
@@ -1155,8 +1303,8 @@ deny all
 *local* *off*::
 The *local* command allows *chronyd* to be told that it is to appear as a
 reference source, even if it is not itself properly synchronised to an external
-source. (This can be used on isolated networks, to allow one computer to be a
-master time server with the other computers slaving to it.)
+source. This can be used on isolated networks, to allow a computer to be the
+primary time server for other computers.
 +
 The first form enables the local reference mode on the host. The syntax is
 identical to the <<chrony.conf.adoc#local,*local*>> directive in the
@@ -1217,7 +1365,7 @@ used to check whether monitoring access is permitted from a named host.
 Examples of use are as follows:
 +
 ----
-cmdaccheck foo.example.net
+cmdaccheck ntp1.example.net
 cmdaccheck 1.2.3.4
 cmdaccheck 2001:db8::1
 ----
@@ -1328,11 +1476,15 @@ purged. An example of how to do this is shown below.
 ----
 # mv /var/log/chrony/measurements.log /var/log/chrony/measurements1.log
 # chronyc cyclelogs
-# ls -l /var/log/chrony
-rw-r--r--   1 root     root            0 Jun  8 18:17 measurements.log
-rw-r--r--   1 root     root        12345 Jun  8 18:17 measurements1.log
-# rm -f measurements1.log
+# rm /var/log/chrony/measurements1.log
 ----
+
+Note that log files enabled by the *log* directive are opened when the first
+entry is made. The message log file specified by the *chronyd*'s *-l* option is
+opened early on start and closed on the *cyclelogs* command only if opening of
+the new file succeeds to avoid losing messages. If *chronyd* is configured to
+drop root privileges and the directory containing the log file is not writable
+for the specified user, *chronyd* will not be able to open the file again.

 [[dump]]*dump*::
 The *dump* command causes *chronyd* to write its current history of
@@ -1356,7 +1508,9 @@ The *reset sources* command causes *chronyd* to drop all measurements and
 switch to the unsynchronised state. This command can help *chronyd* with
 recovery when the measurements are known to be no longer valid or accurate,
 e.g. due to moving the computer to a different network, or resuming the
-computer from a low-power state (which resets the system clock).
+computer from a low-power state (which resets the system clock). *chronyd* will
+drop the measurements automatically when it detects the clock has made an
+unexpected jump, but the detection is not completely reliable.

 [[shutdown]]*shutdown*::
 The *shutdown* command causes *chronyd* to exit. This is equivalent to sending
@@ -1423,7 +1577,13 @@ keygen 73 SHA1 256
 +
 which generates a 256-bit SHA1 key with number 73. The printed line should
 then be securely transferred and added to the key files on both server and
-client, or peers.
+client, or peers. A different key should be generated for each client or peer.
+
+An example using the AES128 cipher is:
+
+----
+keygen 151 AES128
+----

 [[exit]]*exit*::
 [[quit]]*quit*::
@@ -1439,7 +1599,7 @@ The *help* command displays a summary of the commands and their arguments.
 == BUGS

 For instructions on how to report bugs, please visit
-https://chrony.tuxfamily.org/.
+https://chrony-project.org/.

 == AUTHORS

--- a/doc/chronyd.adoc
+++ b/doc/chronyd.adoc
@@ -55,7 +55,7 @@ IPv6 sockets will be created.

 *-f* _file_::
 This option can be used to specify an alternate location for the configuration
-file. The default value is _@SYSCONFDIR@/chrony.conf_.
+file. The compiled-in default value is _@SYSCONFDIR@/chrony.conf_.

 *-n*::
 When run in this mode, the program will not detach itself from the terminal.
@@ -72,9 +72,9 @@ terminal.

 *-L* _level_::
 This option specifies the minimum severity level of messages to be written to
-the log file, syslog, or terminal. The following levels can be specified:
-0 (informational), 1 (warning), 2 (non-fatal error), and 3 (fatal error). The
-default value is 0.
+the log file, syslog, or terminal. The following levels can be specified: -1
+(debug, if compiled with enabled support for debugging), 0 (informational), 1
+(warning), 2 (non-fatal error), and 3 (fatal error). The default value is 0.

 *-p*::
 When run in this mode, *chronyd* will print the configuration and exit. It will
@@ -88,8 +88,10 @@ will not detach from the terminal.

 *-Q*::
 This option is similar to the *-q* option, except it only prints the offset
-without making any corrections of the clock and it allows *chronyd* to be
-started without root privileges.
+without making any corrections of the clock and disables server ports to allow
+*chronyd* to be started without root privileges, assuming the configuration
+does not have any directives which would require them (e.g. *refclock*,
+*hwtimestamp*, *rtcfile*, etc).

 *-r*::
 This option will try to reload and then delete files containing sample
@@ -100,7 +102,7 @@ directive in the configuration file. This option is useful if you want to stop
 and restart *chronyd* briefly for any reason, e.g. to install a new version.
 However, it should be used only on systems where the kernel can maintain clock
 compensation whilst not under *chronyd*'s control (i.e. Linux, FreeBSD, NetBSD,
-Solaris, and macOS 10.13 or later).
+illumos, and macOS 10.13 or later).

 *-R*::
 When this option is used, the <<chrony.conf.adoc#initstepslew,*initstepslew*>>
@@ -137,51 +139,92 @@ running, but still allow it to adjust the frequency of the system clock.
 *-u* _user_::
 This option sets the name of the system user to which *chronyd* will switch
 after start in order to drop root privileges. It overrides the
-<<chrony.conf.adoc#user,*user*>> directive. The default value is
+<<chrony.conf.adoc#user,*user*>> directive. The compiled-in default value is
 _@DEFAULT_USER@_.
 +
 On Linux, *chronyd* needs to be compiled with support for the *libcap* library.
-On macOS, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
+On macOS, FreeBSD, NetBSD, and illumos *chronyd* forks into two processes.
 The child process retains root privileges, but can only perform a very limited
 range of privileged system calls on behalf of the parent.

+*-U*::
+This option disables a check for root privileges to allow *chronyd* to be
+started under a non-root user, assuming the process will have all capabilities
+(e.g. provided by the service manager) and access to all files, directories,
+and devices, needed to operate correctly in the specified configuration. Note
+that different capabilities might be needed with different configurations and
+different Linux kernel versions. Starting *chronyd* under a non-root user is
+not recommended when the configuration is not known, or at least limited to
+specific directives.
+
 *-F* _level_::
-This option configures a system call filter when *chronyd* is compiled with
-support for the Linux secure computing (seccomp) facility. In level 1 the
-process is killed when a forbidden system call is made, in level -1 the SIGSYS
-signal is thrown instead and in level 0 the filter is disabled. The default
-value is 0.
+This option configures system call filters loaded by *chronyd* processes if it
+was compiled with support for the Linux secure computing (seccomp) facility.
+Three levels are defined: 0, 1, 2. The filters are disabled at level 0. At
+levels 1 and 2, *chronyd* will be killed if it makes a system call which is
+blocked by the filters. The level can be specified as a negative number to
+trigger the SIGSYS signal instead of SIGKILL, which can be useful for
+debugging. The default value is 0.
 +
-It's recommended to enable the filter only when it's known to work on the
-version of the system where *chrony* is installed as the filter needs to allow
-also system calls made from libraries that *chronyd* is using (e.g. libc) and
-different versions or implementations of the libraries may make different
-system calls. If the filter is missing some system call, *chronyd* could be
-killed even in normal operation.
+At level 1, the filters allow only selected system calls that are normally
+expected to be made by *chronyd*. Other system calls are blocked. This level is
+recommended only if it is known to work on the version of the system where
+*chrony* is installed. The filters need to allow also system calls made by
+libraries that *chronyd* is using (e.g. libc), but different versions or
+implementations of the libraries might make different system calls. If the
+filters are missing a system call, *chronyd* could be killed even in normal
+operation.
+
+At level 2, the filters block only a small number of specific system calls
+(e.g. fork and exec). This approach should avoid false positives, but the
+protection of the system against a compromised *chronyd* process is much more
+limited.
+
+The filters cannot be enabled with the *mailonchange* directive.

 *-P* _priority_::
-On Linux, this option will select the SCHED_FIFO real-time scheduler at the
-specified priority (which must be between 0 and 100). On macOS, this option
-must have either a value of 0 to disable the thread time
-constraint policy or 1 for the policy to be enabled. Other systems do not
+On Linux, FreeBSD, NetBSD, and illumos this option will select the SCHED_FIFO
+real-time scheduler at the specified priority (which must be between 0 and
+100). On macOS, this option must have either a value of 0 to disable the thread
+time constraint policy or 1 for the policy to be enabled. Other systems do not
 support this option. The default value is 0.

 *-m*::
 This option will lock *chronyd* into RAM so that it will never be paged out.
-This mode is only supported on Linux.
+This mode is only supported on Linux, FreeBSD, NetBSD, and illumos.

 *-x*::
 This option disables the control of the system clock. *chronyd* will not try to
 make any adjustments of the clock. It will assume the clock is free running and
 still track its offset and frequency relative to the estimated true time. This
-option allows *chronyd* to run without the capability to adjust or set the
-system clock (e.g. in some containers) in order to operate as an NTP server. It
-is not recommended to run *chronyd* (with or without *-x*) when another process
-is controlling the system clock.
+option allows *chronyd* to be started without the capability to adjust or set
+the system clock (e.g. in some containers) to operate as an NTP server.

-*-v*::
+*-v*, *--version*::
 With this option *chronyd* will print version number to the terminal and exit.

+*-h*, *--help*::
+With this option *chronyd* will print a help message to the terminal and exit.
+
+== ENVIRONMENT VARIABLES
+
+*LISTEN_FDS*::
+On Linux systems, the systemd service manager may pass file descriptors for
+pre-initialised sockets to *chronyd*. The service manager allocates and binds
+the file descriptors, and passes a copy to each spawned instance of the
+service. This allows for zero-downtime service restarts as the sockets buffer
+client requests until the service is able to handle them. The service manager
+sets the LISTEN_FDS environment variable to the number of passed file
+descriptors.
+
+*NOTIFY_SOCKET*::
+The systemd service manager sets this variable for services of the *notify*
+type. *chronyd* sends a message to this socket when it it is fully initialised
+and ready to accept commands (e.g. from *chronyc*), with the clock already set
+if using the *-s* option or *initstepslew* directive. It is an alternative to
+the *forking* service type, which does not need the PID file. *chronyd* needs
+to be started with the *-n* or *-d* option to not fork.
+
 == FILES

 _@SYSCONFDIR@/chrony.conf_
@@ -193,7 +236,7 @@ _@SYSCONFDIR@/chrony.conf_
 == BUGS

 For instructions on how to report bugs, please visit
-https://chrony.tuxfamily.org/.
+https://chrony-project.org/.

 == AUTHORS

--- a/doc/contributing.adoc
+++ b/doc/contributing.adoc
@@ -0,0 +1,74 @@
+// This file is part of chrony
+//
+// Copyright (C) Miroslav Lichvar  2024
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of version 2 of the GNU General Public License as
+// published by the Free Software Foundation.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+= Contributing
+
+== Patches
+
+The source code of `chrony` is maintained in a git repository at
+https://gitlab.com/chrony/chrony. Patches can be submitted to the `chrony-dev`
+mailing list, or as a merge request on gitlab. Before spending a lot of time
+implementing a new major feature, it is recommended to ask on the mailing list
+for comments about its design and whether such feature fits the goals of the
+project.
+
+Each commit should be a self-contained logical change, which does not break
+the build or tests. New functionality and fixed bugs should be covered by a new
+test or an extended existing test in the test suite. The test can be included
+in the same commit or added as a separate commit. The same rule applies to
+documentation. All command-line options, configuration directives, and
+`chronyc` commands should be documented.
+
+The most important tests can be executed by running `make check` or `make
+quickcheck`. The unit and system tests run on all supported systems. The system
+tests require root privileges. The simulation tests run only on Linux and
+require https://gitlab.com/chrony/clknetsim[clknetsim] to be compiled in the
+directory containing the tests, but they are executed with a merge request on
+gitlab.
+
+The commit message should explain any non-trivial changes, e.g. what problem is
+the commit solving and how. The commit subject (first line of the message)
+should be written in an imperative form, prefixed with the component name if it
+is not a more general change, starting in lower case, and no period at the end.
+See the git log for examples.
+
+Simpler code is better. Less code is better. Security is a top priority.
+
+Assertions should catch only bugs in the `chrony` code. Unexpected values in
+external input (e.g. anything received from network) must be handled correctly
+without crashing and memory corruption. Fuzzing support is available at
+https://gitlab.com/chrony/chrony-fuzz. The fuzzing coverage is checked by the
+project maintainer before each release.
+
+The code should mostly be self-documenting. Comments should explain the
+less obvious things.
+
+== Coding style
+
+The code uses two spaces for indentation. No tabs. The line length should
+normally not exceed 95 characters. Too much indentation indicates the code will
+not be very readable.
+
+Function names are in an imperative form. Names of static functions use
+lowercase characters and underscores. Public functions, structures, typedefs
+are in CamelCase with a prefix specific to the module (e.g. LCL - local, NCR
+- NTP core, NKS - NTS-KE server, SST - sourcestats).
+
+Function names are not followed by space, but keywords of the language (e.g.
+`if`, `for`, `while`, `sizeof`) are followed by space.
+
+Have a look at the existing code to get a better idea what is expected.
--- a/doc/faq.adoc
+++ b/doc/faq.adoc
--- a/doc/installation.adoc
+++ b/doc/installation.adoc
@@ -27,7 +27,7 @@ The following libraries with their development files, and programs, are needed
 to enable optional features:

 * pkg-config: detection of development libraries
-* Nettle, NSS, or LibTomCrypt: secure hash functions (`SECHASH`)
+* Nettle, GnuTLS, NSS, or LibTomCrypt: secure hash functions (`SECHASH`)
 * libcap: dropping root privileges on Linux (`DROPROOT`)
 * libseccomp: system call filter on Linux (`SCFILTER`)
 * GnuTLS and Nettle: Network Time Security (`NTS`)
@@ -85,22 +85,15 @@ will be built with support for dropping root privileges. On other systems no
 extra library is needed. The default user which `chronyd` should run as can be
 specified with the `--with-user` option of the `configure` script.

-If development files for the POSIX threads library are available, `chronyd`
-will be built with support for asynchronous resolving of hostnames specified in
-the `server`, `peer`, and `pool` directives. This allows `chronyd` operating as
-a server to respond to client requests when resolving a hostname. If you don't
-want to enable the support, specify the `--disable-asyncdns` flag to
-`configure`.
-
 If development files for the https://www.lysator.liu.se/~nisse/nettle/[Nettle],
 https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS[NSS], or
-http://www.libtom.net/LibTomCrypt/[libtomcrypt] library are available,
+https://www.libtom.net/LibTomCrypt/[libtomcrypt] library are available,
 `chronyd` will be built with support for other cryptographic hash functions
 than MD5, which can be used for NTP authentication with a symmetric key. If you
 don't want to enable the support, specify the `--disable-sechash` flag to
 `configure`.

-If development files for the editline or readline library are available,
+If development files for the editline library are available,
 `chronyc` will be built with line editing support. If you don't want this,
 specify the `--disable-readline` flag to `configure`.

@@ -170,43 +163,6 @@ https://github.com/seccomp/libseccomp[libseccomp] library and the
 the kernel attack surface and possibly prevent kernel exploits from `chronyd`
 if it is compromised.

-== Support for line editing libraries
-
-`chronyc` can be built with support for line editing, this allows you to use
-the cursor keys to replay and edit old commands. Two libraries are supported
-which provide such functionality, editline and GNU readline.
-
-Please note that readline since version 6.0 is licensed under GPLv3+ which is
-incompatible with chrony's license GPLv2. You should use editline instead if
-you don't want to use older readline versions.
-
-The `configure` script will automatically enable the line editing support if
-one of the supported libraries is available. If they are both available, the
-editline library will be used.
-
-If you don't want to use it (in which case `chronyc` will use a minimal command
-line interface), invoke `configure` like this:
-
----
-./configure --disable-readline other-options...
----
-
-If you have editline, readline or ncurses installed in locations that aren't
-normally searched by the compiler and linker, you need to use extra options:
-
-`--with-readline-includes=directory_name`::
-  This defines the name of the directory above the one where `readline.h` is.
-  `readline.h` is assumed to be in `editline` or `readline` subdirectory of the
-  named directory.
-
-`--with-readline-library=directory_name`::
-  This defines the directory containing the `libedit.a` or `libedit.so` file,
-  or `libreadline.a` or `libreadline.so` file.
-
-`--with-ncurses-library=directory_name`::
-  This defines the directory containing the `libncurses.a` or `libncurses.so`
-  file.
-
 == Extra options for package builders

 The `configure` and `make` procedures have some extra options that may be
--- a/examples/chrony-wait.service
+++ b/examples/chrony-wait.service
@@ -8,11 +8,39 @@ Wants=time-sync.target

 [Service]
 Type=oneshot
-# Wait up to ~10 minutes for chronyd to synchronize and the remaining
-# clock correction to be less than 0.1 seconds
-ExecStart=/usr/bin/chronyc -h 127.0.0.1,::1 waitsync 600 0.1 0.0 1
+# Wait for chronyd to update the clock and the remaining
+# correction to be less than 0.1 seconds
+ExecStart=/usr/bin/chronyc -h 127.0.0.1,::1 waitsync 0 0.1 0.0 1
+# Wait for at most 3 minutes
+TimeoutStartSec=180
 RemainAfterExit=yes
 StandardOutput=null

+CapabilityBoundingSet=
+DevicePolicy=closed
+DynamicUser=yes
+IPAddressAllow=localhost
+IPAddressDeny=any
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+PrivateDevices=yes
+PrivateUsers=yes
+ProtectClock=yes
+ProtectControlGroups=yes
+ProtectHome=yes
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectProc=invisible
+ProtectSystem=strict
+RestrictAddressFamilies=AF_INET AF_INET6
+RestrictNamespaces=yes
+RestrictRealtime=yes
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallFilter=~@privileged @resources
+UMask=0777
+
 [Install]
 WantedBy=multi-user.target
--- a/examples/chrony.conf.example1
+++ b/examples/chrony.conf.example1
@@ -1,4 +1,4 @@
-# Use public NTP servers from the pool.ntp.org project.
+# Use four public NTP servers from the pool.ntp.org project.
 pool pool.ntp.org iburst

 # Record the rate at which the system clock gains/losses time.
--- a/examples/chrony.conf.example2
+++ b/examples/chrony.conf.example2
@@ -1,5 +1,10 @@
-# Use public servers from the pool.ntp.org project.
-# Please consider joining the pool (http://www.pool.ntp.org/join.html).
+# Note: The general recommendation for an NTP client is to have at least
+# three NTP servers to be able to detect one server providing incorrect
+# time (falseticker).
+
+# Use four public NTP servers from the pool.ntp.org project. If this
+# host has a static public IP address, please consider joining the pool:
+# https://www.ntppool.org/join.html
 pool pool.ntp.org iburst

 # Record the rate at which the system clock gains/losses time.
@@ -37,8 +42,8 @@ ntsdumpdir /var/lib/chrony
 # Insert/delete leap seconds by slewing instead of stepping.
 #leapsecmode slew

-# Get TAI-UTC offset and leap seconds from the system tz database.
-#leapsectz right/UTC
+# Set the TAI-UTC offset of the system clock.
+#leapseclist /usr/share/zoneinfo/leap-seconds.list

 # Specify directory for log files.
 logdir /var/log/chrony
--- a/examples/chrony.conf.example3
+++ b/examples/chrony.conf.example3
@@ -21,15 +21,17 @@
 #######################################################################
 ### SPECIFY YOUR NTP SERVERS
 # Most computers using chrony will send measurement requests to one or
-# more 'NTP servers'.  You will probably find that your Internet Service
+# more NTP servers.  The general recommendation is to have at least
+# three NTP servers to be able to detect one server providing incorrect
+# time (falseticker).  You will probably find that your Internet Service
 # Provider or company have one or more NTP servers that you can specify.
 # Failing that, there are a lot of public NTP servers.  There is a list
-# you can access at http://support.ntp.org/bin/view/Servers/WebHome or
+# you can access at https://support.ntp.org/bin/view/Servers/WebHome or
 # you can use servers from the pool.ntp.org project.

-! server foo.example.net iburst
-! server bar.example.net iburst
-! server baz.example.net iburst
+! server ntp1.example.net iburst
+! server ntp2.example.net iburst
+! server ntp3.example.net iburst

 ! pool pool.ntp.org iburst
 
@@ -99,8 +101,8 @@ ntsdumpdir /var/lib/chrony
 # and edit the following lines to specify the locations of the certificate and
 # key.

-! ntsservercert /etc/.../foo.example.net.crt
-! ntsserverkey /etc/.../foo.example.net.key
+! ntsservercert /etc/.../nts-server.crt
+! ntsserverkey /etc/.../nts-server.key

 # chronyd can save the measurement history for the servers to files when
 # it exits.  This is useful in 2 situations:
@@ -126,11 +128,11 @@ ntsdumpdir /var/lib/chrony

 ! pidfile /var/run/chrony/chronyd.pid

-# If the system timezone database is kept up to date and includes the
-# right/UTC timezone, chronyd can use it to determine the current
-# TAI-UTC offset and when will the next leap second occur.
+# The system timezone database usually comes with a list of leap seconds and
+# corresponding TAI-UTC offsets.  chronyd can use it to set the offset of the
+# system TAI clock and have an additional source of leap seconds.

-! leapsectz right/UTC
+! leapseclist /usr/share/zoneinfo/leap-seconds.list

 #######################################################################
 ### INITIAL CLOCK CORRECTION
@@ -238,7 +240,7 @@ ntsdumpdir /var/lib/chrony
 # several people, you need to set up a mailing list or sendmail alias
 # for them and use the address of that.)

-! mailonchange wibble@foo.example.net 0.5
+! mailonchange wibble@example.net 0.5

 #######################################################################
 ### COMMAND ACCESS
--- a/examples/chrony.keys.example
+++ b/examples/chrony.keys.example
@@ -11,3 +11,5 @@
 #1 MD5 AVeryLongAndRandomPassword
 #2 MD5 HEX:12114855C7931009B4049EF3EFC48A139C3F989F
 #3 SHA1 HEX:B2159C05D6A219673A3B7E896B6DE07F6A440995
+#4 AES128 HEX:2DA837C4B6573748CA692B8C828E4891
+#5 AES256 HEX:2666B8099BFF2D5BA20876121788ED24D2BE59111B8FFB562F0F56AE6EC7246E
--- a/examples/chrony.nm-dispatcher.dhcp
+++ b/examples/chrony.nm-dispatcher.dhcp
@@ -1,8 +1,7 @@
 #!/bin/sh
 # This is a NetworkManager dispatcher script for chronyd to update
-# its NTP sources passed from DHCP options. Note that this script is
-# specific to NetworkManager-dispatcher due to use of the
-# DHCP4_NTP_SERVERS environment variable.
+# its NTP sources with servers from DHCP options passed by NetworkManager
+# in the DHCP4_NTP_SERVERS and DHCP6_DHCP6_NTP_SERVERS environment variables.

 export LC_ALL=C

@@ -10,17 +9,23 @@ interface=$1
 action=$2

 chronyc=/usr/bin/chronyc
-default_server_options=iburst
+server_options=iburst
 server_dir=/var/run/chrony-dhcp

 dhcp_server_file=$server_dir/$interface.sources
-# DHCP4_NTP_SERVERS is passed from DHCP options by NetworkManager.
-nm_dhcp_servers=$DHCP4_NTP_SERVERS
+dhcp_ntp_servers="$DHCP4_NTP_SERVERS $DHCP6_DHCP6_NTP_SERVERS"

 add_servers_from_dhcp() {
    rm -f "$dhcp_server_file"
-    for server in $nm_dhcp_servers; do
-        echo "server $server $default_server_options" >> "$dhcp_server_file"
+    for server in $dhcp_ntp_servers; do
+        # Check for invalid characters (from the DHCPv6 NTP FQDN suboption)
+        len1=$(printf '%s' "$server" | wc -c)
+        len2=$(printf '%s' "$server" | tr -d -c 'A-Za-z0-9:.-' | wc -c)
+        if [ "$len1" -ne "$len2" ] || [ "$len2" -lt 1 ] || [ "$len2" -gt 255 ]; then
+          continue
+        fi
+
+        printf 'server %s %s\n' "$server" "$server_options" >> "$dhcp_server_file"
    done
    $chronyc reload sources > /dev/null 2>&1 || :
 }
@@ -34,10 +39,11 @@ clear_servers_from_dhcp() {

 mkdir -p $server_dir

-if [ "$action" = "up" ] || [ "$action" = "dhcp4-change" ]; then
-    add_servers_from_dhcp
-elif [ "$action" = "down" ]; then
-    clear_servers_from_dhcp
-fi
+case "$action" in
+    up|dhcp4-change|dhcp6-change)
+        add_servers_from_dhcp;;
+    down)
+        clear_servers_from_dhcp;;
+esac

 exit 0
--- a/examples/chrony.nm-dispatcher.onoffline
+++ b/examples/chrony.nm-dispatcher.onoffline
@@ -7,8 +7,20 @@ export LC_ALL=C

 chronyc=/usr/bin/chronyc

-# For NetworkManager consider only up/down events
-[ $# -ge 2 ] && [ "$2" != "up" ] && [ "$2" != "down" ] && exit 0
+# For NetworkManager consider only selected events
+if [ $# -ge 2 ]; then
+    case "$2" in
+        up|down|connectivity-change)
+            ;;
+        dhcp4-change|dhcp6-change)
+            # Actions "up" and "connectivity-change" in some cases do not
+            # guarantee that the interface has a route (e.g. a bond).
+            # dhcp(x)-change handles at least cases that use DHCP.
+            ;;
+        *)
+            exit 0;;
+    esac
+fi

 # Note: for networkd-dispatcher routable.d ~= on and off.d ~= off

--- a/examples/chronyd-restricted.service
+++ b/examples/chronyd-restricted.service
@@ -0,0 +1,59 @@
+# This is a more restricted version of the chronyd service intended for
+# minimal NTP/NTS client configurations. The daemon is started without root
+# privileges and is allowed to write only to its own runtime, state, and log
+# directories. It cannot bind to privileged ports in order to operate as an
+# NTP server, or provide monitoring access over IPv4/IPv6. It cannot use
+# reference clocks, HW timestamping, RTC tracking, and other features.
+[Unit]
+Description=NTP client (restricted)
+Documentation=man:chronyd(8) man:chrony.conf(5)
+After=chronyd.service ntpdate.service sntp.service ntpd.service
+Conflicts=chronyd.service ntpd.service systemd-timesyncd.service
+ConditionCapability=CAP_SYS_TIME
+
+[Service]
+Type=notify
+PIDFile=/run/chrony/chronyd.pid
+Environment="OPTIONS="
+EnvironmentFile=-/etc/sysconfig/chronyd
+ExecStart=/usr/sbin/chronyd -n -U $OPTIONS
+
+User=chrony
+LogsDirectory=chrony
+LogsDirectoryMode=0750
+RuntimeDirectory=chrony
+RuntimeDirectoryMode=0750
+RuntimeDirectoryPreserve=restart
+StateDirectory=chrony
+StateDirectoryMode=0750
+
+AmbientCapabilities=CAP_SYS_TIME
+CapabilityBoundingSet=CAP_SYS_TIME
+DevicePolicy=closed
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
+PrivateDevices=yes
+PrivateTmp=yes
+# This breaks adjtimex()
+#PrivateUsers=yes
+ProtectControlGroups=yes
+ProtectHome=yes
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectProc=invisible
+ProtectSystem=strict
+RemoveIPC=yes
+RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+SystemCallArchitectures=native
+SystemCallFilter=~@cpu-emulation @debug @module @mount @obsolete @raw-io
+SystemCallFilter=~@reboot @resources @swap
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target
--- a/examples/chronyd.service
+++ b/examples/chronyd.service
@@ -6,13 +6,44 @@ Conflicts=ntpd.service systemd-timesyncd.service
 ConditionCapability=CAP_SYS_TIME

 [Service]
-Type=forking
+Type=notify
 PIDFile=/run/chrony/chronyd.pid
+Environment="OPTIONS="
 EnvironmentFile=-/etc/sysconfig/chronyd
-ExecStart=/usr/sbin/chronyd $OPTIONS
+ExecStart=/usr/sbin/chronyd -n $OPTIONS
+
+CapabilityBoundingSet=~CAP_AUDIT_CONTROL CAP_AUDIT_READ CAP_AUDIT_WRITE
+CapabilityBoundingSet=~CAP_BLOCK_SUSPEND CAP_KILL CAP_LEASE CAP_LINUX_IMMUTABLE
+CapabilityBoundingSet=~CAP_MAC_ADMIN CAP_MAC_OVERRIDE CAP_MKNOD CAP_SYS_ADMIN
+CapabilityBoundingSet=~CAP_SYS_BOOT CAP_SYS_CHROOT CAP_SYS_MODULE CAP_SYS_PACCT
+CapabilityBoundingSet=~CAP_SYS_PTRACE CAP_SYS_RAWIO CAP_SYS_TTY_CONFIG CAP_WAKE_ALARM
+DeviceAllow=char-pps rw
+DeviceAllow=char-ptp rw
+DeviceAllow=char-rtc rw
+DevicePolicy=closed
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
 PrivateTmp=yes
+ProtectControlGroups=yes
 ProtectHome=yes
-ProtectSystem=full
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectProc=invisible
+ProtectSystem=strict
+ReadWritePaths=/run /var/lib/chrony -/var/log
+RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
+RestrictNamespaces=yes
+RestrictSUIDSGID=yes
+SystemCallArchitectures=native
+SystemCallFilter=~@cpu-emulation @debug @module @mount @obsolete @raw-io @reboot @swap
+
+# Adjust restrictions for /usr/sbin/sendmail (mailonchange directive)
+NoNewPrivileges=no
+ReadWritePaths=-/var/spool
+RestrictAddressFamilies=AF_NETLINK

 [Install]
 WantedBy=multi-user.target
--- a/getdate.y
+++ b/getdate.y
@@ -448,9 +448,9 @@ o_merid	: /* NULL */
   the same signature as the function definition does. */
 #include "getdate.h"

-extern struct tm	*gmtime ();
-extern struct tm	*localtime ();
-extern time_t		mktime ();
+extern struct tm	*gmtime (const time_t *timep);
+extern struct tm	*localtime (const time_t *timep);
+extern time_t		mktime (struct tm *tm);

 /* Month and day table. */
 static TABLE const MonthDayTable[] = {
@@ -641,16 +641,13 @@ static TABLE const MilitaryTable[] = {

 /* ARGSUSED */
 static int
-yyerror (s)
-     char *s ATTRIBUTE_UNUSED;
+yyerror (char *s ATTRIBUTE_UNUSED)
 {
  return 0;
 }

 static int
-ToHour (Hours, Meridian)
-     int Hours;
-     MERIDIAN Meridian;
+ToHour (int Hours, MERIDIAN Meridian)
 {
  switch (Meridian)
    {
@@ -677,8 +674,7 @@ ToHour (Hours, Meridian)
 }

 static int
-ToYear (Year)
-     int Year;
+ToYear (int Year)
 {
  if (Year < 0)
    Year = -Year;
@@ -694,8 +690,7 @@ ToYear (Year)
 }

 static int
-LookupWord (buff)
-     char *buff;
+LookupWord (char *buff)
 {
  register char *p;
  register char *q;
@@ -912,6 +907,7 @@ get_date (const char *p, const time_t *now)
  yyHour = tmp->tm_hour;
  yyMinutes = tmp->tm_min;
  yySeconds = tmp->tm_sec;
+  memset(&tm, 0, sizeof (tm));
  tm.tm_isdst = tmp->tm_isdst;
  yyMeridian = MER24;
  yyRelSeconds = 0;
--- a/hash.h
+++ b/hash.h
@@ -44,6 +44,7 @@ typedef enum {
  HSH_SHA3_512 = 9,
  HSH_TIGER = 10,
  HSH_WHIRLPOOL = 11,
+  HSH_MD5_NONCRYPTO = 10000, /* For NTPv4 reference ID */
 } HSH_Algorithm;

 extern int HSH_GetHashId(HSH_Algorithm algorithm);
--- a/hash_gnutls.c
+++ b/hash_gnutls.c
@@ -0,0 +1,145 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2021
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Crypto hashing using the GnuTLS library
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include <gnutls/crypto.h>
+
+#include "hash.h"
+#include "logging.h"
+
+struct hash {
+  const HSH_Algorithm algorithm;
+  const gnutls_digest_algorithm_t type;
+  gnutls_hash_hd_t handle;
+};
+
+static struct hash hashes[] = {
+  { HSH_MD5_NONCRYPTO, GNUTLS_DIG_MD5, NULL },
+  { HSH_MD5, GNUTLS_DIG_MD5, NULL },
+  { HSH_SHA1, GNUTLS_DIG_SHA1, NULL },
+  { HSH_SHA256, GNUTLS_DIG_SHA256, NULL },
+  { HSH_SHA384, GNUTLS_DIG_SHA384, NULL },
+  { HSH_SHA512, GNUTLS_DIG_SHA512, NULL },
+  { HSH_SHA3_224, GNUTLS_DIG_SHA3_224, NULL },
+  { HSH_SHA3_256, GNUTLS_DIG_SHA3_256, NULL },
+  { HSH_SHA3_384, GNUTLS_DIG_SHA3_384, NULL },
+  { HSH_SHA3_512, GNUTLS_DIG_SHA3_512, NULL },
+  { 0, 0, NULL }
+};
+
+static int gnutls_initialised = 0;
+
+int
+HSH_GetHashId(HSH_Algorithm algorithm)
+{
+  int id, r;
+
+  if (!gnutls_initialised) {
+    r = gnutls_global_init();
+    if (r < 0)
+      LOG_FATAL("Could not initialise %s : %s", "gnutls", gnutls_strerror(r));
+    gnutls_initialised = 1;
+  }
+
+  for (id = 0; hashes[id].algorithm != 0; id++) {
+    if (hashes[id].algorithm == algorithm)
+      break;
+  }
+
+  if (hashes[id].algorithm == 0)
+    return -1;
+
+  if (hashes[id].handle)
+    return id;
+
+  if (algorithm == HSH_MD5_NONCRYPTO)
+    GNUTLS_FIPS140_SET_LAX_MODE();
+
+  r = gnutls_hash_init(&hashes[id].handle, hashes[id].type);
+
+  if (algorithm == HSH_MD5_NONCRYPTO)
+    GNUTLS_FIPS140_SET_STRICT_MODE();
+
+  if (r < 0) {
+    DEBUG_LOG("Could not initialise %s : %s", "hash", gnutls_strerror(r));
+    hashes[id].handle = NULL;
+    return -1;
+  }
+
+  return id;
+}
+
+int
+HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+         unsigned char *out, int out_len)
+{
+  unsigned char buf[MAX_HASH_LENGTH];
+  gnutls_hash_hd_t handle;
+  int hash_len;
+
+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
+  handle = hashes[id].handle;
+  hash_len = gnutls_hash_get_len(hashes[id].type);
+
+  if (out_len > hash_len)
+    out_len = hash_len;
+
+  if (hash_len > sizeof (buf))
+    return 0;
+
+  if (gnutls_hash(handle, in1, in1_len) < 0 ||
+      (in2 && gnutls_hash(handle, in2, in2_len) < 0)) {
+    /* Reset the state */
+    gnutls_hash_output(handle, buf);
+    return 0;
+  }
+
+  gnutls_hash_output(handle, buf);
+  memcpy(out, buf, out_len);
+
+  return out_len;
+}
+
+void
+HSH_Finalise(void)
+{
+  int i;
+
+  if (!gnutls_initialised)
+    return;
+
+  for (i = 0; hashes[i].algorithm != 0; i++) {
+    if (hashes[i].handle)
+      gnutls_hash_deinit(hashes[i].handle, NULL);
+  }
+
+  gnutls_global_deinit();
+}
--- a/hash_intmd5.c
+++ b/hash_intmd5.c
@@ -39,7 +39,7 @@ int
 HSH_GetHashId(HSH_Algorithm algorithm)
 {
  /* only MD5 is supported */
-  if (algorithm != HSH_MD5)
+  if (algorithm != HSH_MD5 && algorithm != HSH_MD5_NONCRYPTO)
    return -1;

  return 0;
--- a/hash_nettle.c
+++ b/hash_nettle.c
@@ -59,6 +59,9 @@ HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int id, nid;

+  if (algorithm == HSH_MD5_NONCRYPTO)
+    algorithm = HSH_MD5;
+
  for (id = 0; hashes[id].algorithm != 0; id++) {
    if (hashes[id].algorithm == algorithm)
      break;
--- a/hash_nss.c
+++ b/hash_nss.c
@@ -56,6 +56,9 @@ HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int i;

+  if (algorithm == HSH_MD5_NONCRYPTO)
+    algorithm = HSH_MD5;
+
  for (i = 0; hashes[i].algorithm != 0; i++) {
    if (hashes[i].algorithm == algorithm)
      break;
--- a/hash_tomcrypt.c
+++ b/hash_tomcrypt.c
@@ -71,6 +71,9 @@ HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int i, h;

+  if (algorithm == HSH_MD5_NONCRYPTO)
+    algorithm = HSH_MD5;
+
  for (i = 0; hashes[i].algorithm != 0; i++) {
    if (hashes[i].algorithm == algorithm)
      break;
--- a/hwclock.c
+++ b/hwclock.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2018
+ * Copyright (C) Miroslav Lichvar  2016-2018, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +33,7 @@
 #include "local.h"
 #include "logging.h"
 #include "memory.h"
+#include "quantiles.h"
 #include "regress.h"
 #include "util.h"

@@ -43,6 +44,14 @@
 /* Maximum acceptable frequency offset of the clock */
 #define MAX_FREQ_OFFSET (2.0 / 3.0)

+/* Quantiles for filtering readings by delay */
+#define DELAY_QUANT_MIN_K 1
+#define DELAY_QUANT_MAX_K 2
+#define DELAY_QUANT_Q 10
+#define DELAY_QUANT_REPEAT 7
+#define DELAY_QUANT_LARGE_STEP_DELAY 1000
+#define DELAY_QUANT_MIN_STEP 1.0e-9
+
 struct HCL_Instance_Record {
  /* HW and local reference timestamp */
  struct timespec hw_ref;
@@ -64,12 +73,18 @@ struct HCL_Instance_Record {
  /* Minimum interval between samples */
  double min_separation;

+  /* Expected precision of readings */
+  double precision;
+
  /* Flag indicating the offset and frequency values are valid */
  int valid_coefs;

  /* Estimated offset and frequency of HW clock relative to local clock */
  double offset;
  double frequency;
+
+  /* Estimated quantiles of reading delay */
+  QNT_Instance delay_quants;
 };

 /* ================================================== */
@@ -92,7 +107,7 @@ handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
 /* ================================================== */

 HCL_Instance
-HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
+HCL_CreateInstance(int min_samples, int max_samples, double min_separation, double precision)
 {
  HCL_Instance clock;

@@ -110,6 +125,11 @@ HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
  clock->n_samples = 0;
  clock->valid_coefs = 0;
  clock->min_separation = min_separation;
+  clock->precision = precision;
+  clock->delay_quants = QNT_CreateInstance(DELAY_QUANT_MIN_K, DELAY_QUANT_MAX_K,
+                                           DELAY_QUANT_Q, DELAY_QUANT_REPEAT,
+                                           DELAY_QUANT_LARGE_STEP_DELAY,
+                                           DELAY_QUANT_MIN_STEP);

  LCL_AddParameterChangeHandler(handle_slew, clock);

@@ -121,6 +141,7 @@ HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
 void HCL_DestroyInstance(HCL_Instance clock)
 {
  LCL_RemoveParameterChangeHandler(handle_slew, clock);
+  QNT_DestroyInstance(clock->delay_quants);
  Free(clock->y_data);
  Free(clock->x_data);
  Free(clock);
@@ -140,6 +161,102 @@ HCL_NeedsNewSample(HCL_Instance clock, struct timespec *now)

 /* ================================================== */

+int
+HCL_ProcessReadings(HCL_Instance clock, int n_readings, struct timespec tss[][3],
+                    struct timespec *hw_ts, struct timespec *local_ts, double *err,
+                    int *quality)
+{
+  double delay, raw_delay, min_delay, low_delay, high_delay, e, pred_err;
+  double delay_sum, hw_sum, local_sum, local_prec, freq;
+  int i, min_reading, combined;
+  struct timespec ts1, ts2;
+
+  if (n_readings < 1)
+    return 0;
+
+  /* Work out the current correction multiplier needed to get cooked delays */
+  LCL_CookTime(&tss[0][0], &ts1, NULL);
+  LCL_CookTime(&tss[n_readings - 1][2], &ts2, NULL);
+  if (UTI_CompareTimespecs(&tss[0][0], &tss[n_readings - 1][2]) < 0)
+    freq = UTI_DiffTimespecsToDouble(&ts1, &ts2) /
+           UTI_DiffTimespecsToDouble(&tss[0][0], &tss[n_readings - 1][2]);
+  else
+    freq = 1.0;
+
+  for (i = 0; i < n_readings; i++) {
+    delay = freq * UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+
+    if (delay < 0.0) {
+      /* Step in the middle of a reading? */
+      DEBUG_LOG("Bad reading delay=%e", delay);
+      return 0;
+    }
+
+    if (i == 0 || min_delay > delay) {
+      min_delay = delay;
+      min_reading = i;
+    }
+
+    QNT_Accumulate(clock->delay_quants, delay);
+  }
+
+  local_prec = LCL_GetSysPrecisionAsQuantum();
+
+  low_delay = QNT_GetQuantile(clock->delay_quants, QNT_GetMinK(clock->delay_quants)) -
+              QNT_GetMinStep(clock->delay_quants) / 2.0;
+  high_delay = QNT_GetQuantile(clock->delay_quants, QNT_GetMaxK(clock->delay_quants)) +
+               QNT_GetMinStep(clock->delay_quants) / 2.0;
+  low_delay = MIN(low_delay, high_delay);
+  high_delay = MAX(high_delay, low_delay + local_prec);
+
+  /* Combine readings with delay in the expected interval */
+  for (i = combined = 0, delay_sum = hw_sum = local_sum = 0.0; i < n_readings; i++) {
+    raw_delay = UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+    delay = freq * raw_delay;
+
+    if (delay < low_delay || delay > high_delay)
+      continue;
+
+    delay_sum += delay;
+    hw_sum += UTI_DiffTimespecsToDouble(&tss[i][1], &tss[0][1]);
+    local_sum += UTI_DiffTimespecsToDouble(&tss[i][0], &tss[0][0]) + raw_delay / 2.0;
+    combined++;
+  }
+
+  DEBUG_LOG("Combined %d readings lo=%e hi=%e", combined, low_delay, high_delay);
+
+  if (combined > 0) {
+    UTI_AddDoubleToTimespec(&tss[0][1], hw_sum / combined, hw_ts);
+    UTI_AddDoubleToTimespec(&tss[0][0], local_sum / combined, local_ts);
+    *err = MAX(delay_sum / combined / 2.0, clock->precision);
+    *quality = 2;
+    return 1;
+  }
+
+  /* Indicate acceptable quality of the reading with minimum delay if its
+     interval does not contain the current offset predicted from previous
+     samples, or a new sample is needed to get the tracking working */
+
+  *hw_ts = tss[min_reading][1];
+  UTI_AddDoubleToTimespec(&tss[min_reading][0], min_delay / freq / 2.0, local_ts);
+  *err = MAX(min_delay / 2.0, clock->precision);
+
+  pred_err = 0.0;
+  LCL_CookTime(local_ts, &ts1, NULL);
+  if (!HCL_CookTime(clock, hw_ts, &ts2, &e) ||
+      ((pred_err = UTI_DiffTimespecsToDouble(&ts1, &ts2)) > *err)) {
+    *quality = 1;
+  } else {
+    *quality = 0;
+  }
+
+  DEBUG_LOG("Min-delay reading err=%e prerr=%e ql=%d", *err, pred_err, *quality);
+
+  return 1;
+}
+
+/* ================================================== */
+
 void
 HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
                     struct timespec *local_ts, double err)
--- a/hwclock.h
+++ b/hwclock.h
@@ -30,7 +30,7 @@ typedef struct HCL_Instance_Record *HCL_Instance;

 /* Create a new HW clock instance */
 extern HCL_Instance HCL_CreateInstance(int min_samples, int max_samples,
-                                       double min_separation);
+                                       double min_separation, double precision);

 /* Destroy a HW clock instance */
 extern void HCL_DestroyInstance(HCL_Instance clock);
@@ -38,6 +38,15 @@ extern void HCL_DestroyInstance(HCL_Instance clock);
 /* Check if a new sample should be accumulated at this time */
 extern int HCL_NeedsNewSample(HCL_Instance clock, struct timespec *now);

+/* Process new readings of the HW clock in the form of (sys, hw, sys) triplets
+   and produce a sample which can be accumulated by HCL_AccumulateSample().
+   Indicate the quality of the sample relative to already processed samples as
+   a value of 0, 1, or 2, where a sample of quality 0 should normally be
+   dropped. */
+extern int HCL_ProcessReadings(HCL_Instance clock, int n_readings, struct timespec tss[][3],
+                               struct timespec *hw_ts, struct timespec *local_ts, double *err,
+                               int *quality);
+
 /* Accumulate a new sample */
 extern void HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
                                 struct timespec *local_ts, double err);
--- a/keys.c
+++ b/keys.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2012-2016
+ * Copyright (C) Miroslav Lichvar  2012-2016, 2019-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -182,6 +182,9 @@ KEY_Reload(void)
  if (!key_file)
    return;

+  if (!UTI_CheckFilePermissions(key_file, 0771))
+    ;
+
  in = UTI_OpenFile(NULL, key_file, NULL, 'r', 0);
  if (!in) {
    LOG(LOGS_WARN, "Could not open keyfile %s", key_file);
@@ -255,14 +258,13 @@ KEY_Reload(void)
     more careful! */
  qsort(ARR_GetElements(keys), ARR_GetSize(keys), sizeof (Key), compare_keys_by_id);

+  LOG(LOGS_INFO, "Loaded %u symmetric keys", ARR_GetSize(keys));
+
  /* Check for duplicates */
  for (i = 1; i < ARR_GetSize(keys); i++) {
    if (get_key(i - 1)->id == get_key(i)->id)
      LOG(LOGS_WARN, "Detected duplicate key %"PRIu32, get_key(i - 1)->id);
  }
-
-  /* Erase any passwords from stack */
-  memset(line, 0, sizeof (line));
 }

 /* ================================================== */
@@ -400,7 +402,7 @@ check_auth(Key *key, const void *data, int data_len,

  hash_len = generate_auth(key, data, data_len, buf, sizeof (buf));

-  return MIN(hash_len, trunc_len) == auth_len && !memcmp(buf, auth, auth_len);
+  return MIN(hash_len, trunc_len) == auth_len && UTI_IsMemoryEqual(buf, auth, auth_len);
 }

 /* ================================================== */
--- a/leapdb.c
+++ b/leapdb.c
@@ -0,0 +1,272 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2009-2018, 2020, 2022
+ * Copyright (C) Patrick Oppenlander 2023, 2024
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  This module provides leap second information. */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "conf.h"
+#include "leapdb.h"
+#include "logging.h"
+#include "util.h"
+
+/* ================================================== */
+
+/* Source of leap second data */
+enum {
+  SRC_NONE,
+  SRC_TIMEZONE,
+  SRC_LIST,
+} leap_src;
+
+/* Offset between leap-seconds.list timestamp epoch and Unix epoch.
+   leap-seconds.list epoch is 1 Jan 1900, 00:00:00 */
+#define LEAP_SEC_LIST_OFFSET 2208988800
+
+/* ================================================== */
+
+static NTP_Leap
+get_tz_leap(time_t when, int *tai_offset)
+{
+  struct tm stm, *tm;
+  time_t t;
+  char *tz_env, tz_orig[128];
+  NTP_Leap tz_leap = LEAP_Normal;
+
+  tm = gmtime(&when);
+  if (!tm)
+    return tz_leap;
+
+  stm = *tm;
+
+  /* Temporarily switch to the timezone containing leap seconds */
+  tz_env = getenv("TZ");
+  if (tz_env) {
+    if (strlen(tz_env) >= sizeof (tz_orig))
+      return tz_leap;
+    strcpy(tz_orig, tz_env);
+  }
+  setenv("TZ", CNF_GetLeapSecTimezone(), 1);
+  tzset();
+
+  /* Get the TAI-UTC offset, which started at the epoch at 10 seconds */
+  t = mktime(&stm);
+  if (t != -1)
+    *tai_offset = t - when + 10;
+
+  /* Set the time to 23:59:60 and see how it overflows in mktime() */
+  stm.tm_sec = 60;
+  stm.tm_min = 59;
+  stm.tm_hour = 23;
+
+  t = mktime(&stm);
+
+  if (tz_env)
+    setenv("TZ", tz_orig, 1);
+  else
+    unsetenv("TZ");
+  tzset();
+
+  if (t == -1)
+    return tz_leap;
+
+  if (stm.tm_sec == 60)
+    tz_leap = LEAP_InsertSecond;
+  else if (stm.tm_sec == 1)
+    tz_leap = LEAP_DeleteSecond;
+
+  return tz_leap;
+}
+
+/* ================================================== */
+
+static NTP_Leap
+get_list_leap(time_t when, int *tai_offset)
+{
+  FILE *f;
+  char line[1024];
+  NTP_Leap ret_leap = LEAP_Normal;
+  int ret_tai_offset = 0, prev_lsl_tai_offset = 10;
+  int64_t when1900, lsl_updated = 0, lsl_expiry = 0;
+  const char *leap_sec_list = CNF_GetLeapSecList();
+
+  if (!(f = UTI_OpenFile(NULL, leap_sec_list, NULL, 'r', 0))) {
+    LOG(LOGS_ERR, "Failed to open leap seconds list %s", leap_sec_list);
+    goto out;
+  }
+
+  /* Leap second happens at midnight */
+  when = (when / (24 * 3600) + 1) * (24 * 3600);
+
+  /* leap-seconds.list timestamps are relative to 1 Jan 1900, 00:00:00 */
+  when1900 = (int64_t)when + LEAP_SEC_LIST_OFFSET;
+
+  while (fgets(line, sizeof line, f)) {
+    int64_t lsl_when;
+    int lsl_tai_offset;
+    char *p;
+
+    /* Ignore blank lines */
+    for (p = line; *p && isspace((unsigned char)*p); ++p)
+      ;
+    if (!*p)
+      continue;
+
+    if (*line == '#') {
+      /* Update time line starts with #$ */
+      if (line[1] == '$' && sscanf(line + 2, "%"SCNd64, &lsl_updated) != 1)
+        goto error;
+      /* Expiration time line starts with #@ */
+      if (line[1] == '@' && sscanf(line + 2, "%"SCNd64, &lsl_expiry) != 1)
+        goto error;
+      /* Comment or a special comment we don't care about */
+      continue;
+    }
+
+    /* Leap entry */
+    if (sscanf(line, "%"SCNd64" %d", &lsl_when, &lsl_tai_offset) != 2)
+      goto error;
+
+    if (when1900 == lsl_when) {
+      if (lsl_tai_offset > prev_lsl_tai_offset)
+        ret_leap = LEAP_InsertSecond;
+      else if (lsl_tai_offset < prev_lsl_tai_offset)
+        ret_leap = LEAP_DeleteSecond;
+      /* When is rounded to the end of the day, so offset hasn't changed yet! */
+      ret_tai_offset = prev_lsl_tai_offset;
+    } else if (when1900 > lsl_when) {
+      ret_tai_offset = lsl_tai_offset;
+    }
+
+    prev_lsl_tai_offset = lsl_tai_offset;
+  }
+
+  /* Make sure the file looks sensible */
+  if (!feof(f) || !lsl_updated || !lsl_expiry)
+    goto error;
+
+  if (when1900 >= lsl_expiry)
+    LOG(LOGS_WARN, "Leap second list %s needs update", leap_sec_list);
+
+  goto out;
+
+error:
+  if (f)
+    fclose(f);
+  LOG(LOGS_ERR, "Failed to parse leap seconds list %s", leap_sec_list);
+  return LEAP_Normal;
+
+out:
+  if (f)
+    fclose(f);
+  *tai_offset = ret_tai_offset;
+  return ret_leap;
+}
+
+/* ================================================== */
+
+static int
+check_leap_source(NTP_Leap (*src)(time_t when, int *tai_offset))
+{
+  int tai_offset = 0;
+
+  /* Check that the leap second source has good data for Jun 30 2012 and Dec 31 2012 */
+  if (src(1341014400, &tai_offset) == LEAP_InsertSecond && tai_offset == 34 &&
+      src(1356912000, &tai_offset) == LEAP_Normal && tai_offset == 35)
+    return 1;
+
+  return 0;
+}
+
+/* ================================================== */
+
+void
+LDB_Initialise(void)
+{
+  const char *leap_tzname, *leap_sec_list;
+
+  leap_tzname = CNF_GetLeapSecTimezone();
+  if (leap_tzname && !check_leap_source(get_tz_leap)) {
+    LOG(LOGS_WARN, "Timezone %s failed leap second check, ignoring", leap_tzname);
+    leap_tzname = NULL;
+  }
+
+  leap_sec_list = CNF_GetLeapSecList();
+  if (leap_sec_list && !check_leap_source(get_list_leap)) {
+    LOG(LOGS_WARN, "Leap second list %s failed check, ignoring", leap_sec_list);
+    leap_sec_list = NULL;
+  }
+
+  if (leap_sec_list) {
+    LOG(LOGS_INFO, "Using leap second list %s", leap_sec_list);
+    leap_src = SRC_LIST;
+  } else if (leap_tzname) {
+    LOG(LOGS_INFO, "Using %s timezone to obtain leap second data", leap_tzname);
+    leap_src = SRC_TIMEZONE;
+  }
+}
+
+/* ================================================== */
+
+NTP_Leap
+LDB_GetLeap(time_t when, int *tai_offset)
+{
+  static time_t last_ldb_leap_check;
+  static NTP_Leap ldb_leap;
+  static int ldb_tai_offset;
+
+  /* Do this check at most twice a day */
+  when = when / (12 * 3600) * (12 * 3600);
+  if (last_ldb_leap_check == when)
+    goto out;
+
+  last_ldb_leap_check = when;
+  ldb_leap = LEAP_Normal;
+  ldb_tai_offset = 0;
+
+  switch (leap_src) {
+  case SRC_NONE:
+    break;
+  case SRC_TIMEZONE:
+    ldb_leap = get_tz_leap(when, &ldb_tai_offset);
+    break;
+  case SRC_LIST:
+    ldb_leap = get_list_leap(when, &ldb_tai_offset);
+    break;
+  }
+
+out:
+  *tai_offset = ldb_tai_offset;
+  return ldb_leap;
+}
+
+/* ================================================== */
+
+void
+LDB_Finalise(void)
+{
+  /* Nothing to do */
+}
--- a/leapdb.h
+++ b/leapdb.h
@@ -0,0 +1,37 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Patrick Oppenlander 2024
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  This module provides leap second information.
+
+  */
+
+#ifndef GOT_LEAPDB_H
+#define GOT_LEAPDB_H
+
+#include "ntp.h"
+
+extern void LDB_Initialise(void);
+extern NTP_Leap LDB_GetLeap(time_t when, int *tai_offset);
+extern void LDB_Finalise(void);
+
+#endif /* GOT_LEAPDB_H */
--- a/local.c
+++ b/local.c
@@ -97,8 +97,142 @@ static double precision_quantum;

 static double max_clock_error;

+#define NSEC_PER_SEC 1000000000
+
 /* ================================================== */

+/* Ask the system for the resolution of the system clock.  The Linux
+   clock_getres() is not usable, because it reports the internal timer
+   resolution, which is 1 ns when high-resolution timers are enabled,
+   even when using a lower-resolution clocksource. */
+
+static int
+get_clock_resolution(void)
+{
+#if defined(HAVE_CLOCK_GETTIME) && !defined(LINUX)
+  struct timespec res;
+
+  if (clock_getres(CLOCK_REALTIME, &res) < 0)
+    return 0;
+
+  return NSEC_PER_SEC * res.tv_sec + res.tv_nsec;
+#else
+  return 0;
+#endif
+}
+
+/* ================================================== */
+
+#if defined(LINUX) && defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC_RAW)
+
+static int
+compare_ints(const void *a, const void *b)
+{
+  return *(const int *)a - *(const int *)b;
+}
+
+#define READINGS 64
+
+/* On Linux, try to measure the actual resolution of the system
+   clock by performing a varying amount of busy work between clock
+   readings and finding the minimum change in the measured interval.
+   Require a change of at least two nanoseconds to ignore errors
+   caused by conversion to timespec.  Use the raw monotonic clock
+   to avoid the impact of potential frequency changes due to NTP
+   adjustments made by other processes, and the kernel dithering of
+   the 32-bit multiplier. */
+
+static int
+measure_clock_resolution(void)
+{
+  int i, j, b, busy, diffs[READINGS - 1], diff2, min;
+  struct timespec start_ts, ts[READINGS];
+  uint32_t acc;
+
+  if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_ts) < 0)
+    return 0;
+
+  for (acc = 0, busy = 1; busy < 100000; busy = busy * 3 / 2 + 1) {
+    for (i = 0, b = busy * READINGS; i < READINGS; i++, b -= busy) {
+      if (clock_gettime(CLOCK_MONOTONIC_RAW, &ts[i]) < 0)
+        return 0;
+
+      for (j = b; j > 0; j--)
+        acc += (acc & 1) + (uint32_t)ts[i].tv_nsec;
+    }
+
+    /* Give up after 0.1 seconds */
+    if (UTI_DiffTimespecsToDouble(&ts[READINGS - 1], &start_ts) > 0.1) {
+      DEBUG_LOG("Measurement too slow");
+      return 0;
+    }
+
+    for (i = 0; i < READINGS - 1; i++) {
+      diffs[i] = NSEC_PER_SEC * (ts[i + 1].tv_sec - ts[i].tv_sec) +
+                 (ts[i + 1].tv_nsec - ts[i].tv_nsec);
+
+      /* Make sure the differences are sane.  A resolution larger than the
+         reading time will be measured in measure_clock_read_delay(). */
+      if (diffs[i] <= 0 || diffs[i] > NSEC_PER_SEC)
+        return 0;
+    }
+
+    /* Sort the differences and keep values unique within 1 ns from the
+       first half of the array, which are less likely to be impacted by CPU
+       interruptions */
+    qsort(diffs, READINGS - 1, sizeof (diffs[0]), compare_ints);
+    for (i = 1, j = 0; i < READINGS / 2; i++) {
+      if (diffs[j] + 1 < diffs[i])
+        diffs[++j] = diffs[i];
+    }
+    j++;
+
+#if 0
+    for (i = 0; i < j; i++)
+      DEBUG_LOG("busy %d diff %d %d", busy, i, diffs[i]);
+#endif
+
+    /* Require at least three unique differences to be more confident
+       with the result */
+    if (j < 3)
+      continue;
+
+    /* Find the smallest difference between the unique differences */
+    for (i = 1, min = 0; i < j; i++) {
+      diff2 = diffs[i] - diffs[i - 1];
+      if (min == 0 || min > diff2)
+        min = diff2;
+    }
+
+    if (min == 0)
+      continue;
+
+    /* Prevent the compiler from optimising the busy work out */
+    if (acc == 0)
+      min += 1;
+
+    return min;
+  }
+
+  return 0;
+}
+
+#else
+static int
+measure_clock_resolution(void)
+{
+  return 0;
+}
+#endif
+
+/* ================================================== */
+
+/* As a fallback, measure how long it takes to read the clock.  It
+   typically takes longer than the resolution of the clock (and it
+   depends on the CPU speed), i.e. every reading gives a different
+   value, but handle also low-resolution clocks that might give
+   the same reading multiple times. */
+
 /* Define the number of increments of the system clock that we want
   to see to be fairly sure that we've got something approaching
   the minimum increment.  Even on a crummy implementation that can't
@@ -106,10 +240,8 @@ static double max_clock_error;
   under 1s of busy waiting. */
 #define NITERS 100

-#define NSEC_PER_SEC 1000000000
-
-static void
-calculate_sys_precision(void)
+static int
+measure_clock_read_delay(void)
 {
  struct timespec ts, old_ts;
  int iters, diff, best;
@@ -135,18 +267,28 @@ calculate_sys_precision(void)

  assert(best > 0);

-  precision_quantum = 1.0e-9 * best;
+  return best;
+}

-  /* Get rounded log2 value of the measured precision */
-  precision_log = 0;
-  while (best < 707106781) {
-    precision_log--;
-    best *= 2;
-  }
+/* ================================================== */

-  assert(precision_log >= -30);
+static double
+measure_clock_precision(void)
+{
+  int res, delay, prec;

-  DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);
+  res = get_clock_resolution();
+  if (res <= 0)
+    res = measure_clock_resolution();
+
+  delay = measure_clock_read_delay();
+
+  if (res > 0)
+    prec = MIN(res, delay);
+  else
+    prec = delay;
+
+  return prec / 1.0e9;
 }

 /* ================================================== */
@@ -170,7 +312,16 @@ LCL_Initialise(void)
  current_freq_ppm = 0.0;
  temp_comp_ppm = 0.0;

-  calculate_sys_precision();
+  precision_quantum = CNF_GetClockPrecision();
+  if (precision_quantum <= 0.0)
+    precision_quantum = measure_clock_precision();
+
+  precision_quantum = CLAMP(1.0e-9, precision_quantum, 1.0);
+  precision_log = round(log(precision_quantum) / log(2.0));
+  /* NTP code doesn't support smaller log than -30 */
+  assert(precision_log >= -30);
+
+  DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);

  /* This is the maximum allowed frequency offset in ppm, the time must
     never stop or run backwards */
@@ -186,10 +337,8 @@ void
 LCL_Finalise(void)
 {
  /* Make sure all handlers have been removed */
-  if (change_list.next != &change_list)
-    assert(0);
-  if (dispersion_notify_list.next != &dispersion_notify_list)
-    assert(0);
+  BRIEF_ASSERT(change_list.next == &change_list);
+  BRIEF_ASSERT(dispersion_notify_list.next == &dispersion_notify_list);
 }

 /* ================================================== */
@@ -227,9 +376,7 @@ LCL_AddParameterChangeHandler(LCL_ParameterChangeHandler handler, void *anything

  /* Check that the handler is not already registered */
  for (ptr = change_list.next; ptr != &change_list; ptr = ptr->next) {
-    if (!(ptr->handler != handler || ptr->anything != anything)) {
-      assert(0);
-    }
+    BRIEF_ASSERT(ptr->handler != handler || ptr->anything != anything);
  }

  new_entry = MallocNew(ChangeListEntry);
@@ -303,9 +450,7 @@ LCL_AddDispersionNotifyHandler(LCL_DispersionNotifyHandler handler, void *anythi

  /* Check that the handler is not already registered */
  for (ptr = dispersion_notify_list.next; ptr != &dispersion_notify_list; ptr = ptr->next) {
-    if (!(ptr->handler != handler || ptr->anything != anything)) {
-      assert(0);
-    }
+    BRIEF_ASSERT(ptr->handler != handler || ptr->anything != anything);
  }

  new_entry = MallocNew(DispersionNotifyListEntry);
@@ -507,7 +652,7 @@ LCL_AccumulateDeltaFrequency(double dfreq)

 /* ================================================== */

-void
+int
 LCL_AccumulateOffset(double offset, double corr_rate)
 {
  struct timespec raw, cooked;
@@ -519,12 +664,14 @@ LCL_AccumulateOffset(double offset, double corr_rate)
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, offset))
-      return;
+    return 0;

  (*drv_accrue_offset)(offset, corr_rate);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, 0.0, offset, LCL_ChangeAdjust);
+
+  return 1;
 }

 /* ================================================== */
@@ -563,6 +710,8 @@ void
 LCL_NotifyExternalTimeStep(struct timespec *raw, struct timespec *cooked,
    double offset, double dispersion)
 {
+  LCL_CancelOffsetCorrection();
+
  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(raw, cooked, 0.0, offset, LCL_ChangeUnknownStep);

@@ -588,7 +737,7 @@ LCL_NotifyLeap(int leap)

 /* ================================================== */

-void
+int
 LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
 {
  struct timespec raw, cooked;
@@ -600,7 +749,7 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, doffset))
-      return;
+    return 0;

  old_freq_ppm = current_freq_ppm;

@@ -622,6 +771,26 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, dfreq, doffset, LCL_ChangeAdjust);
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+LCL_AccumulateFrequencyAndOffsetNoHandlers(double dfreq, double doffset, double corr_rate)
+{
+  ChangeListEntry *first_handler;
+  int r;
+
+  first_handler = change_list.next;
+  change_list.next = &change_list;
+
+  r = LCL_AccumulateFrequencyAndOffset(dfreq, doffset, corr_rate);
+
+  change_list.next = first_handler;
+
+  return r;
 }

 /* ================================================== */
@@ -679,8 +848,11 @@ LCL_MakeStep(void)

  /* Cancel remaining slew and make the step */
  LCL_AccumulateOffset(correction, 0.0);
-  if (!LCL_ApplyStepOffset(-correction))
+  if (!LCL_ApplyStepOffset(-correction)) {
+    /* Revert the correction */
+    LCL_AccumulateOffset(-correction, 0.0);
    return 0;
+  }

  LOG(LOGS_WARN, "System clock was stepped by %.6f seconds", correction);

@@ -689,6 +861,19 @@ LCL_MakeStep(void)

 /* ================================================== */

+void
+LCL_CancelOffsetCorrection(void)
+{
+  struct timespec raw;
+  double correction;
+
+  LCL_ReadRawTime(&raw);
+  LCL_GetOffsetCorrection(&raw, &correction, NULL);
+  LCL_AccumulateOffset(correction, 0.0);
+}
+
+/* ================================================== */
+
 int
 LCL_CanSystemLeap(void)
 {
--- a/local.h
+++ b/local.h
@@ -149,7 +149,7 @@ extern void LCL_AccumulateDeltaFrequency(double dfreq);
   forwards (i.e. it is currently slow of true time).  Provided is also
   a suggested correction rate (correction time * offset). */

-extern void LCL_AccumulateOffset(double offset, double corr_rate);
+extern int LCL_AccumulateOffset(double offset, double corr_rate);

 /* Routine to apply an immediate offset by doing a sudden step if
   possible. (Intended for use after an initial estimate of offset has
@@ -171,7 +171,12 @@ extern void LCL_NotifyLeap(int leap);

 /* Perform the combination of modifying the frequency and applying
   a slew, in one easy step */
-extern void LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate);
+extern int LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate);
+
+/* Same as the routine above, except it does not call the registered
+   parameter change handlers */
+extern int LCL_AccumulateFrequencyAndOffsetNoHandlers(double dfreq, double doffset,
+                                                      double corr_rate);

 /* Routine to read the system precision as a log to base 2 value. */
 extern int LCL_GetSysPrecisionAsLog(void);
@@ -197,6 +202,9 @@ extern void LCL_Finalise(void);
   to a timezone problem. */
 extern int LCL_MakeStep(void);

+/* Routine to cancel the outstanding system clock correction */
+extern void LCL_CancelOffsetCorrection(void);
+
 /* Check if the system driver supports leap seconds, i.e. LCL_SetSystemLeap
   does something */
 extern int LCL_CanSystemLeap(void);
--- a/logging.c
+++ b/logging.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2014, 2018
+ * Copyright (C) Miroslav Lichvar  2011-2014, 2018-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -39,10 +39,14 @@
 /* This is used by DEBUG_LOG macro */
 LOG_Severity log_min_severity = LOGS_INFO;

+/* Current logging contexts */
+static LOG_Context log_contexts;
+
 /* ================================================== */
 /* Flag indicating we have initialised */
 static int initialised = 0;

+static char *file_log_path = NULL;
 static FILE *file_log = NULL;
 static int system_log = 0;

@@ -72,6 +76,8 @@ void
 LOG_Initialise(void)
 {
  debug_prefix = Strdup("");
+  log_contexts = 0;
+
  initialised = 1;
  LOG_OpenFileLog(NULL);
 }
@@ -85,8 +91,11 @@ LOG_Finalise(void)
  if (system_log)
    closelog();

-  if (file_log)
+  if (file_log && file_log != stderr)
    fclose(file_log);
+  file_log = NULL;
+  Free(file_log_path);
+  file_log_path = NULL;

  LOG_CycleLogFiles();

@@ -140,6 +149,7 @@ void LOG_Message(LOG_Severity severity,
  struct tm *tm;

  assert(initialised);
+  severity = CLAMP(LOGS_DEBUG, severity, LOGS_FATAL);

  if (!system_log && file_log && severity >= log_min_severity) {
    /* Don't clutter up syslog with timestamps and internal debugging info */
@@ -150,8 +160,13 @@ void LOG_Message(LOG_Severity severity,
      fprintf(file_log, "%s ", buf);
    }
 #if DEBUG > 0
-    if (log_min_severity <= LOGS_DEBUG)
-      fprintf(file_log, "%s%s:%d:(%s) ", debug_prefix, filename, line_number, function_name);
+    if (log_min_severity <= LOGS_DEBUG) {
+      /* Log severity to character mapping (debug, info, warn, err, fatal) */
+      const char severity_chars[LOGS_FATAL - LOGS_DEBUG + 1] = {'D', 'I', 'W', 'E', 'F'};
+
+      fprintf(file_log, "%c:%s%s:%d:(%s) ", severity_chars[severity - LOGS_DEBUG],
+              debug_prefix, filename, line_number, function_name);
+    }
 #endif
  }

@@ -174,7 +189,7 @@ void LOG_Message(LOG_Severity severity,
      /* Send the message also to the foreground process if it is
         still running, or stderr if it is still open */
      if (parent_fd > 0) {
-        if (write(parent_fd, buf, strlen(buf) + 1) < 0)
+        if (!LOG_NotifyParent(buf))
          ; /* Not much we can do here */
      } else if (system_log && parent_fd == 0) {
        system_log = 0;
@@ -189,27 +204,42 @@ void LOG_Message(LOG_Severity severity,

 /* ================================================== */

-void
-LOG_OpenFileLog(const char *log_file)
+static FILE *
+open_file_log(const char *log_file, char mode)
 {
  FILE *f;

  if (log_file) {
-    f = UTI_OpenFile(NULL, log_file, NULL, 'A', 0640);
+    f = UTI_OpenFile(NULL, log_file, NULL, mode, 0640);
  } else {
    f = stderr;
  }

  /* Enable line buffering */
-  setvbuf(f, NULL, _IOLBF, BUFSIZ);
+  if (f)
+    setvbuf(f, NULL, _IOLBF, BUFSIZ);
+
+  return f;
+}
+
+/* ================================================== */
+
+void
+LOG_OpenFileLog(const char *log_file)
+{
+  if (file_log_path)
+    Free(file_log_path);
+  if (log_file)
+    file_log_path = Strdup(log_file);
+  else
+    file_log_path = NULL;

  if (file_log && file_log != stderr)
    fclose(file_log);

-  file_log = f;
+  file_log = open_file_log(file_log_path, 'A');
 }

-
 /* ================================================== */

 void
@@ -237,6 +267,30 @@ LOG_GetMinSeverity(void)

 /* ================================================== */

+void
+LOG_SetContext(LOG_Context context)
+{
+  log_contexts |= context;
+}
+
+/* ================================================== */
+
+void
+LOG_UnsetContext(LOG_Context context)
+{
+  log_contexts &= ~context;
+}
+
+/* ================================================== */
+
+LOG_Severity
+LOG_GetContextSeverity(LOG_Context contexts)
+{
+  return log_contexts & contexts ? LOGS_INFO : LOGS_DEBUG;
+}
+
+/* ================================================== */
+
 void
 LOG_SetDebugPrefix(const char *prefix)
 {
@@ -256,6 +310,17 @@ LOG_SetParentFd(int fd)

 /* ================================================== */

+int
+LOG_NotifyParent(const char *message)
+{
+  if (parent_fd <= 0)
+    return 1;
+
+  return write(parent_fd, message, strlen(message) + 1) > 0;
+}
+
+/* ================================================== */
+
 void
 LOG_CloseParentFd()
 {
@@ -339,14 +404,29 @@ LOG_FileWrite(LOG_FileID id, const char *format, ...)
 void
 LOG_CycleLogFiles(void)
 {
+  struct stat st;
  LOG_FileID i;
+  FILE *f;

+  /* The log will be opened later when an entry is logged */
  for (i = 0; i < n_filelogs; i++) {
    if (logfiles[i].file)
      fclose(logfiles[i].file);
    logfiles[i].file = NULL;
    logfiles[i].writes = 0;
  }
+
+  /* Try to open the log specified by the -l option, but only if nothing is
+     present at its path to avoid unnecessary error messages.  Keep the
+     original file if that fails (the process might no longer have the
+     necessary privileges to write in the directory). */
+  if (file_log && file_log != stderr && stat(file_log_path, &st) < 0 && errno == ENOENT) {
+    f = open_file_log(file_log_path, 'a');
+    if (f) {
+      fclose(file_log);
+      file_log = f;
+    }
+  }
 }

 /* ================================================== */
--- a/logging.h
+++ b/logging.h
@@ -100,6 +100,20 @@ extern void LOG_SetMinSeverity(LOG_Severity severity);
 /* Get the minimum severity */
 extern LOG_Severity LOG_GetMinSeverity(void);

+/* Flags for info messages that should be logged only in specific contexts */
+typedef enum {
+  LOGC_Command = 1,
+  LOGC_SourceFile = 2,
+} LOG_Context;
+
+/* Modify current contexts */
+extern void LOG_SetContext(LOG_Context context);
+extern void LOG_UnsetContext(LOG_Context context);
+
+/* Get severity depending on the current active contexts: INFO if they contain
+   at least one of the specified contexts, DEBUG otherwise */
+extern LOG_Severity LOG_GetContextSeverity(LOG_Context contexts);
+
 /* Set a prefix for debug messages */
 extern void LOG_SetDebugPrefix(const char *prefix);

@@ -112,7 +126,10 @@ extern void LOG_OpenSystemLog(void);
 /* Stop using stderr and send fatal message to the foreground process */
 extern void LOG_SetParentFd(int fd);

-/* Close the pipe to the foreground process so it can exit */
+/* Send a message to the foreground process */
+extern int LOG_NotifyParent(const char *message);
+
+/* Close the pipe to the foreground process */
 extern void LOG_CloseParentFd(void);

 /* File logging functions */
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) John G. Hasler  2009
- * Copyright (C) Miroslav Lichvar  2012-2018
+ * Copyright (C) Miroslav Lichvar  2012-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -32,6 +32,7 @@

 #include "main.h"
 #include "sched.h"
+#include "leapdb.h"
 #include "local.h"
 #include "sys.h"
 #include "ntp_io.h"
@@ -76,11 +77,18 @@ static REF_Mode ref_mode = REF_ModeNormal;
 static void
 do_platform_checks(void)
 {
+  struct timespec ts;
+
  /* Require at least 32-bit integers, two's complement representation and
     the usual implementation of conversion of unsigned integers */
  assert(sizeof (int) >= 4);
  assert(-1 == ~0);
  assert((int32_t)4294967295U == (int32_t)-1);
+
+  /* Require time_t and tv_nsec in timespec to be signed */
+  ts.tv_sec = -1;
+  ts.tv_nsec = -1;
+  assert(ts.tv_sec < 0 && ts.tv_nsec < 0);
 }

 /* ================================================== */
@@ -99,11 +107,41 @@ delete_pidfile(void)

 /* ================================================== */

+static void
+notify_system_manager(int start)
+{
+#ifdef LINUX
+  /* The systemd protocol is documented in the sd_notify(3) man page */
+  const char *message, *path = getenv("NOTIFY_SOCKET");
+  int sock_fd;
+
+  if (!path)
+    return;
+
+  if (path[0] != '/')
+    LOG_FATAL("Unsupported notification socket");
+
+  message = start ? "READY=1" : "STOPPING=1";
+
+  sock_fd = SCK_OpenUnixDatagramSocket(path, NULL, 0);
+
+  if (sock_fd < 0 || SCK_Send(sock_fd, message, strlen(message), 0) != strlen(message))
+    LOG_FATAL("Could not send notification to $NOTIFY_SOCKET");
+
+  SCK_CloseSocket(sock_fd);
+#endif
+}
+
+/* ================================================== */
+
 void
 MAI_CleanupAndExit(void)
 {
  if (!initialised) exit(exit_status);
  
+  notify_system_manager(0);
+
+  LCL_CancelOffsetCorrection();
  SRC_DumpSources();

  /* Don't update clock when removing sources */
@@ -126,6 +164,7 @@ MAI_CleanupAndExit(void)
  RCL_Finalise();
  SRC_Finalise();
  REF_Finalise();
+  LDB_Finalise();
  RTC_Finalise();
  SYS_Finalise();

@@ -140,6 +179,8 @@ MAI_CleanupAndExit(void)
  HSH_Finalise();
  LOG_Finalise();

+  UTI_ResetGetRandomFunctions();
+
  exit(exit_status);
 }

@@ -156,6 +197,8 @@ signal_cleanup(int x)
 static void
 quit_timeout(void *arg)
 {
+  LOG(LOGS_INFO, "Timeout reached");
+
  /* Return with non-zero status if the clock is not synchronised */
  exit_status = REF_GetOurStratum() >= NTP_MAX_STRATUM;
  SCH_QuitProgram();
@@ -183,7 +226,7 @@ ntp_source_resolving_end(void)
  NSR_AutoStartSources();

  /* Special modes can end only when sources update their reachability.
-     Give up immediatelly if there are no active sources. */
+     Give up immediately if there are no active sources. */
  if (ref_mode != REF_ModeNormal && !SRC_ActiveSources()) {
    REF_SetUnsynchronised();
  }
@@ -201,7 +244,12 @@ post_init_ntp_hook(void *anything)
    REF_SetMode(ref_mode);
  }

-  /* Close the pipe to the foreground process so it can exit */
+  notify_system_manager(1);
+
+  /* Send an empty message to the foreground process so it can exit.
+     If that fails, indicating the process was killed, exit too. */
+  if (!LOG_NotifyParent(""))
+    SCH_QuitProgram();
  LOG_CloseParentFd();

  CNF_AddSources();
@@ -319,10 +367,16 @@ go_daemon(void)
    char message[1024];
    int r;

-    close(pipefd[1]);
+    /* Don't exit before the 'parent' */
+    waitpid(pid, NULL, 0);
+
    r = read(pipefd[0], message, sizeof (message));
-    if (r) {
-      if (r > 0) {
+
+    close(pipefd[0]);
+    close(pipefd[1]);
+
+    if (r != 1 || message[0] != '\0') {
+      if (r > 1) {
        /* Print the error message from the child */
        message[sizeof (message) - 1] = '\0';
        fprintf(stderr, "%s\n", message);
@@ -331,8 +385,6 @@ go_daemon(void)
    } else
      exit(0);
  } else {
-    close(pipefd[0]);
-
    setsid();

    /* Do 2nd fork, as-per recommended practice for launching daemons. */
@@ -341,7 +393,10 @@ go_daemon(void)
    if (pid < 0) {
      LOG_FATAL("fork() failed : %s", strerror(errno));
    } else if (pid > 0) {
-      exit(0); /* In the 'parent' */
+      /* In the 'parent' */
+      close(pipefd[0]);
+      close(pipefd[1]);
+      exit(0);
    } else {
      /* In the child we want to leave running as the daemon */

@@ -351,9 +406,9 @@ go_daemon(void)
      }

      /* Don't keep stdin/out/err from before. But don't close
-         the parent pipe yet. */
+         the parent pipe yet, or reusable file descriptors. */
      for (fd=0; fd<1024; fd++) {
-        if (fd != pipefd[1])
+        if (fd != pipefd[1] && !SCK_IsReusable(fd))
          close(fd);
      }

@@ -374,8 +429,34 @@ go_daemon(void)
 static void
 print_help(const char *progname)
 {
-      printf("Usage: %s [-4|-6] [-n|-d] [-p|-q|-Q] [-r] [-R] [-s] [-t TIMEOUT] [-f FILE|COMMAND...]\n",
-             progname);
+      printf("Usage: %s [OPTION]... [DIRECTIVE]...\n\n"
+             "Options:\n"
+             "  -4\t\tUse IPv4 addresses only\n"
+             "  -6\t\tUse IPv6 addresses only\n"
+             "  -f FILE\tSpecify configuration file (%s)\n"
+             "  -n\t\tDon't run as daemon\n"
+             "  -d\t\tDon't run as daemon and log to stderr\n"
+#if DEBUG > 0
+             "  -d -d\t\tEnable debug messages\n"
+#endif
+             "  -l FILE\tLog to file\n"
+             "  -L LEVEL\tSet logging threshold (0)\n"
+             "  -p\t\tPrint configuration and exit\n"
+             "  -q\t\tSet clock and exit\n"
+             "  -Q\t\tLog offset and exit\n"
+             "  -r\t\tReload dump files\n"
+             "  -R\t\tAdapt configuration for restart\n"
+             "  -s\t\tSet clock from RTC\n"
+             "  -t SECONDS\tExit after elapsed time\n"
+             "  -u USER\tSpecify user (%s)\n"
+             "  -U\t\tDon't check for root\n"
+             "  -F LEVEL\tSet system call filter level (0)\n"
+             "  -P PRIORITY\tSet process priority (0)\n"
+             "  -m\t\tLock memory\n"
+             "  -x\t\tDon't control clock\n"
+             "  -v, --version\tPrint version and exit\n"
+             "  -h, --help\tPrint usage and exit\n",
+             progname, DEFAULT_CONF_FILE, DEFAULT_USER);
 }

 /* ================================================== */
@@ -411,13 +492,13 @@ int main
  int do_init_rtc = 0, restarted = 0, client_only = 0, timeout = -1;
  int scfilter_level = 0, lock_memory = 0, sched_priority = 0;
  int clock_control = 1, system_log = 1, log_severity = LOGS_INFO;
-  int config_args = 0, print_config = 0;
+  int user_check = 1, config_args = 0, print_config = 0;

  do_platform_checks();

  LOG_Initialise();

-  /* Parse (undocumented) long command-line options */
+  /* Parse long command-line options */
  for (optind = 1; optind < argc; optind++) {
    if (!strcmp("--help", argv[optind])) {
      print_help(progname);
@@ -431,7 +512,7 @@ int main
  optind = 1;

  /* Parse short command-line options */
-  while ((opt = getopt(argc, argv, "46df:F:hl:L:mnpP:qQrRst:u:vx")) != -1) {
+  while ((opt = getopt(argc, argv, "46df:F:hl:L:mnpP:qQrRst:u:Uvx")) != -1) {
    switch (opt) {
      case '4':
      case '6':
@@ -462,9 +543,10 @@ int main
        break;
      case 'p':
        print_config = 1;
-        client_only = 1;
+        user_check = 0;
        nofork = 1;
        system_log = 0;
+        log_severity = LOGS_WARN;
        break;
      case 'P':
        sched_priority = parse_int_arg(optarg);
@@ -479,6 +561,7 @@ int main
        ref_mode = REF_ModePrintOnce;
        nofork = 1;
        client_only = 1;
+        user_check = 0;
        clock_control = 0;
        system_log = 0;
        break;
@@ -497,6 +580,9 @@ int main
      case 'u':
        user = optarg;
        break;
+      case 'U':
+        user_check = 0;
+        break;
      case 'v':
        print_version();
        return 0;
@@ -509,9 +595,12 @@ int main
    }
  }

-  if (getuid() && !client_only)
+  if (user_check && getuid() != 0)
    LOG_FATAL("Not superuser");

+  /* Initialise reusable file descriptors before fork */
+  SCK_PreInitialise();
+
  /* Turn into a daemon */
  if (!nofork) {
    go_daemon();
@@ -594,9 +683,17 @@ int main
  }

  /* Drop root privileges if the specified user has a non-zero UID */
-  if (!geteuid() && (pw->pw_uid || pw->pw_gid))
-    SYS_DropRoot(pw->pw_uid, pw->pw_gid);
+  if (!geteuid() && (pw->pw_uid || pw->pw_gid)) {
+    SYS_DropRoot(pw->pw_uid, pw->pw_gid, SYS_MAIN_PROCESS);

+    /* Warn if missing read access or having write access to keys */
+    CNF_CheckReadOnlyAccess();
+  }
+
+  if (!geteuid())
+    LOG(LOGS_WARN, "Running with root privileges");
+
+  LDB_Initialise();
  REF_Initialise();
  SST_Initialise();
  NSR_Initialise();
--- a/md5.c
+++ b/md5.c
@@ -117,8 +117,7 @@ inline UINT4 ROTATE_LEFT(UINT4 x, int n)
 /* The routine MD5Init initializes the message-digest context
   mdContext. All fields are set to zero.
 */
-void MD5Init (mdContext)
-MD5_CTX *mdContext;
+void MD5Init (MD5_CTX *mdContext)
 {
  mdContext->i[0] = mdContext->i[1] = (UINT4)0;

@@ -134,10 +133,7 @@ MD5_CTX *mdContext;
   account for the presence of each of the characters inBuf[0..inLen-1]
   in the message whose digest is being computed.
 */
-void MD5Update (mdContext, inBuf, inLen)
-MD5_CTX *mdContext;
-unsigned const char *inBuf;
-unsigned int inLen;
+void MD5Update (MD5_CTX *mdContext, unsigned const char *inBuf, unsigned int inLen)
 {
  UINT4 in[16];
  int mdi;
@@ -173,8 +169,7 @@ unsigned int inLen;
   ends with the desired message digest in mdContext->digest[0...15].
 */

-void MD5Final (mdContext)
-MD5_CTX *mdContext;
+void MD5Final (MD5_CTX *mdContext)
 {
  UINT4 in[16];
  int mdi;
@@ -214,9 +209,7 @@ MD5_CTX *mdContext;

 /* Basic MD5 step. Transforms buf based on in.
 */
-static void Transform (buf, in)
-UINT4 *buf;
-UINT4 *in;
+static void Transform (UINT4 *buf, UINT4 *in)
 {
  UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3];

--- a/memory.c
+++ b/memory.c
@@ -47,8 +47,13 @@ Realloc(void *ptr, size_t size)
 {
  void *r;

+  if (size == 0) {
+    Free(ptr);
+    return NULL;
+  }
+
  r = realloc(ptr, size);
-  if (!r && size)
+  if (!r)
    LOG_FATAL("Could not allocate memory");

  return r;
--- a/nameserv.c
+++ b/nameserv.c
@@ -50,12 +50,24 @@ DNS_SetAddressFamily(int family)
 DNS_Status 
 DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
 {
-#ifdef HAVE_GETADDRINFO
  struct addrinfo hints, *res, *ai;
  int i, result;
+  IPAddr ip;

  max_addrs = MIN(max_addrs, DNS_MAX_ADDRESSES);

+  for (i = 0; i < max_addrs; i++)
+    ip_addrs[i].family = IPADDR_UNSPEC;
+
+  /* Avoid calling getaddrinfo() if the name is an IP address */
+  if (UTI_StringToIP(name, &ip)) {
+    if (address_family != IPADDR_UNSPEC && ip.family != address_family)
+      return DNS_Failure;
+    if (max_addrs >= 1)
+      ip_addrs[0] = ip;
+    return DNS_Success;
+  }
+
  memset(&hints, 0, sizeof (hints));

  switch (address_family) {
@@ -107,48 +119,9 @@ DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
    }
  }

-  for (; i < max_addrs; i++)
-        ip_addrs[i].family = IPADDR_UNSPEC;
-
  freeaddrinfo(res);

  return !max_addrs || ip_addrs[0].family != IPADDR_UNSPEC ? DNS_Success : DNS_Failure;
-#else
-  struct hostent *host;
-  int i;
-  
-  if (address_family != IPADDR_UNSPEC && address_family != IPADDR_INET4)
-    return DNS_Failure;
-
-  max_addrs = MIN(max_addrs, DNS_MAX_ADDRESSES);
-
-  host = gethostbyname(name);
-
-  if (host == NULL) {
-    if (h_errno == TRY_AGAIN)
-      return DNS_TryAgain;
-  } else {
-    if (host->h_addrtype != AF_INET || !host->h_addr_list[0])
-      return DNS_Failure;
-
-    for (i = 0; host->h_addr_list[i] && i < max_addrs; i++) {
-      ip_addrs[i].family = IPADDR_INET4;
-      ip_addrs[i].addr.in4 = ntohl(*(uint32_t *)host->h_addr_list[i]);
-    }
-
-    for (; i < max_addrs; i++)
-      ip_addrs[i].family = IPADDR_UNSPEC;
-
-    return DNS_Success;
-  }
-
-#ifdef FORCE_DNSRETRY
-  return DNS_TryAgain;
-#else
-  return DNS_Failure;
-#endif
-
-#endif
 }

 /* ================================================== */
@@ -157,9 +130,11 @@ int
 DNS_IPAddress2Name(IPAddr *ip_addr, char *name, int len)
 {
  char *result = NULL;
-
 #ifdef FEAT_IPV6
-  struct sockaddr_in6 in6;
+  struct sockaddr_in6 saddr;
+#else
+  struct sockaddr_in saddr;
+#endif
  IPSockAddr ip_saddr;
  socklen_t slen;
  char hbuf[NI_MAXHOST];
@@ -167,29 +142,9 @@ DNS_IPAddress2Name(IPAddr *ip_addr, char *name, int len)
  ip_saddr.ip_addr = *ip_addr;
  ip_saddr.port = 0;

-  slen = SCK_IPSockAddrToSockaddr(&ip_saddr, (struct sockaddr *)&in6, sizeof (in6));
-  if (!getnameinfo((struct sockaddr *)&in6, slen, hbuf, sizeof (hbuf), NULL, 0, 0))
+  slen = SCK_IPSockAddrToSockaddr(&ip_saddr, (struct sockaddr *)&saddr, sizeof (saddr));
+  if (!getnameinfo((struct sockaddr *)&saddr, slen, hbuf, sizeof (hbuf), NULL, 0, 0))
    result = hbuf;
-#else
-  struct hostent *host;
-  uint32_t addr;
-
-  switch (ip_addr->family) {
-    case IPADDR_INET4:
-      addr = htonl(ip_addr->addr.in4);
-      host = gethostbyaddr((const char *) &addr, sizeof (ip_addr), AF_INET);
-      break;
-#ifdef FEAT_IPV6
-    case IPADDR_INET6:
-      host = gethostbyaddr((const void *) ip_addr->addr.in6, sizeof (ip_addr->addr.in6), AF_INET6);
-      break;
-#endif
-    default:
-      host = NULL;
-  }
-  if (host)
-    result = host->h_name;
-#endif

  if (result == NULL)
    result = UTI_IPToString(ip_addr);
--- a/ntp.h
+++ b/ntp.h
@@ -113,13 +113,49 @@ typedef struct {
 #define NTP_REFID_LOCAL 0x7F7F0101UL /* 127.127.1.1 */
 #define NTP_REFID_SMOOTH 0x7F7F01FFUL /* 127.127.1.255 */

+/* Non-authentication extension fields and corresponding internal flags */
+
+#define NTP_EF_EXP_MONO_ROOT            0xF323
+#define NTP_EF_EXP_NET_CORRECTION       0xF324
+
+#define NTP_EF_FLAG_EXP_MONO_ROOT       0x1
+#define NTP_EF_FLAG_EXP_NET_CORRECTION  0x2
+
+/* Pre-NTPv5 experimental extension field */
+typedef struct {
+  uint32_t magic;
+  NTP_int32 root_delay;
+  NTP_int32 root_dispersion;
+  NTP_int64 mono_receive_ts;
+  uint32_t mono_epoch;
+} NTP_EFExpMonoRoot;
+
+#define NTP_EF_EXP_MONO_ROOT_MAGIC      0xF5BEDD9AU
+
+/* Experimental extension field to provide PTP corrections */
+typedef struct {
+  uint32_t magic;
+  NTP_int64 correction;
+  uint32_t reserved[3];
+} NTP_EFExpNetCorrection;
+
+#define NTP_EF_EXP_NET_CORRECTION_MAGIC 0x07AC2CEBU
+
+/* Authentication extension fields */
+
+#define NTP_EF_NTS_UNIQUE_IDENTIFIER    0x0104
+#define NTP_EF_NTS_COOKIE               0x0204
+#define NTP_EF_NTS_COOKIE_PLACEHOLDER   0x0304
+#define NTP_EF_NTS_AUTH_AND_EEF         0x0404
+
 /* Enumeration for authentication modes of NTP packets */
 typedef enum {
  NTP_AUTH_NONE = 0,            /* No authentication */
-  NTP_AUTH_SYMMETRIC,           /* MAC using symmetric key (RFC 1305, RFC 5905) */
+  NTP_AUTH_SYMMETRIC,           /* NTP MAC or CMAC using a symmetric key
+                                   (RFC 1305, RFC 5905, RFC 8573) */
  NTP_AUTH_MSSNTP,              /* MS-SNTP authenticator field */
  NTP_AUTH_MSSNTP_EXT,          /* MS-SNTP extended authenticator field */
-  NTP_AUTH_NTS,                 /* Network Time Security (RFC ????) */
+  NTP_AUTH_NTS,                 /* Network Time Security (RFC 8915) */
 } NTP_AuthMode;

 /* Structure describing an NTP packet */
@@ -129,6 +165,7 @@ typedef struct {
  NTP_Mode mode;

  int ext_fields;
+  int ext_field_flags;

  struct {
    NTP_AuthMode mode;
@@ -151,7 +188,13 @@ typedef struct {
  double peer_dispersion;
  double root_delay;
  double root_dispersion;
-  int stratum;
 } NTP_Sample;

+/* Possible sources of timestamps */
+typedef enum {
+  NTP_TS_DAEMON = 0,
+  NTP_TS_KERNEL,
+  NTP_TS_HARDWARE
+} NTP_Timestamp_Source;
+
 #endif /* GOT_NTP_H */
--- a/ntp_auth.c
+++ b/ntp_auth.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2019
+ * Copyright (C) Miroslav Lichvar  2019-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -32,7 +32,6 @@
 #include "logging.h"
 #include "memory.h"
 #include "ntp_auth.h"
-#include "ntp_ext.h"
 #include "ntp_signd.h"
 #include "nts_ntp.h"
 #include "nts_ntp_client.h"
@@ -105,19 +104,6 @@ check_symmetric_auth(NTP_Packet *packet, NTP_PacketInfo *info)

 /* ================================================== */

-static int
-is_zero_data(unsigned char *data, int length)
-{
-  int i;
-
-  for (i = 0; i < length; i++)
-    if (data[i] != 0)
-      return 0;
-  return 1;
-}
-
-/* ================================================== */
-
 static NAU_Instance
 create_instance(NTP_AuthMode mode)
 {
@@ -161,11 +147,12 @@ NAU_CreateSymmetricInstance(uint32_t key_id)
 /* ================================================== */

 NAU_Instance
-NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name, const IPSockAddr *ntp_address)
+NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name, uint32_t cert_set,
+                      uint16_t ntp_port)
 {
  NAU_Instance instance = create_instance(NTP_AUTH_NTS);

-  instance->nts = NNC_CreateInstance(nts_address, name, ntp_address);
+  instance->nts = NNC_CreateInstance(nts_address, name, cert_set, ntp_port);

  return instance;
 }
@@ -175,7 +162,7 @@ NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name, const IPSockAdd
 void
 NAU_DestroyInstance(NAU_Instance instance)
 {
-  if (instance->nts)
+  if (instance->mode == NTP_AUTH_NTS)
    NNC_DestroyInstance(instance->nts);
  Free(instance);
 }
@@ -246,116 +233,6 @@ NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request, NTP_PacketIn

 /* ================================================== */

-int
-NAU_ParsePacket(NTP_Packet *packet, NTP_PacketInfo *info)
-{
-  int parsed, remainder, ef_length, ef_type;
-  unsigned char *data;
-
-  data = (void *)packet;
-  parsed = NTP_HEADER_LENGTH;
-  remainder = info->length - parsed;
-
-  info->ext_fields = 0;
-
-  /* Check if this is a plain NTP packet with no extension fields or MAC */
-  if (remainder <= 0)
-    return 1;
-
-  assert(remainder % 4 == 0);
-
-  /* In NTPv3 and older packets don't have extension fields.  Anything after
-     the header is assumed to be a MAC. */
-  if (info->version <= 3) {
-    info->auth.mode = NTP_AUTH_SYMMETRIC;
-    info->auth.mac.start = parsed;
-    info->auth.mac.length = remainder;
-    info->auth.mac.key_id = ntohl(*(uint32_t *)(data + parsed));
-
-    /* Check if it is an MS-SNTP authenticator field or extended authenticator
-       field with zeroes as digest */
-    if (info->version == 3 && info->auth.mac.key_id != 0) {
-      if (remainder == 20 && is_zero_data(data + parsed + 4, remainder - 4))
-        info->auth.mode = NTP_AUTH_MSSNTP;
-      else if (remainder == 72 && is_zero_data(data + parsed + 8, remainder - 8))
-        info->auth.mode = NTP_AUTH_MSSNTP_EXT;
-    }
-
-    return 1;
-  }
-
-  /* Check for a crypto NAK */
-  if (remainder == 4 && ntohl(*(uint32_t *)(data + parsed)) == 0) {
-    info->auth.mode = NTP_AUTH_SYMMETRIC;
-    info->auth.mac.start = parsed;
-    info->auth.mac.length = remainder;
-    info->auth.mac.key_id = 0;
-    return 1;
-  }
-
-  /* Parse the rest of the NTPv4 packet */
-
-  while (remainder > 0) {
-    /* Check if the remaining data is a MAC */
-    if (remainder >= NTP_MIN_MAC_LENGTH && remainder <= NTP_MAX_V4_MAC_LENGTH)
-      break;
-
-    /* The NTPv4-specific limit for MAC length enables deterministic parsing of
-       packets with extension fields (RFC 7822), but we support longer MACs in
-       packets with no extension fields for compatibility with older chrony
-       clients.  Check if the longer MAC would authenticate the packet before
-       trying to parse the data as an extension field. */
-    if (parsed == NTP_HEADER_LENGTH &&
-        remainder > NTP_MAX_V4_MAC_LENGTH && remainder <= NTP_MAX_MAC_LENGTH &&
-        KEY_CheckAuth(ntohl(*(uint32_t *)(data + parsed)), data, parsed,
-                      data + parsed + 4, remainder - 4, NTP_MAX_MAC_LENGTH - 4))
-      break;
-
-    /* Check if this is a valid NTPv4 extension field and skip it */
-    if (!NEF_ParseField(packet, info->length, parsed, &ef_length, &ef_type, NULL, NULL)) {
-      /* Invalid MAC or format error */
-      DEBUG_LOG("Invalid format or MAC");
-      return 0;
-    }
-
-    assert(ef_length > 0 && ef_length % 4 == 0);
-
-    switch (ef_type) {
-      case NTP_EF_NTS_UNIQUE_IDENTIFIER:
-      case NTP_EF_NTS_COOKIE:
-      case NTP_EF_NTS_COOKIE_PLACEHOLDER:
-      case NTP_EF_NTS_AUTH_AND_EEF:
-        info->auth.mode = NTP_AUTH_NTS;
-        break;
-      default:
-        DEBUG_LOG("Unknown extension field type=%x", (unsigned int)ef_type);
-    }
-
-    info->ext_fields++;
-    parsed += ef_length;
-    remainder = info->length - parsed;
-  }
-
-  if (remainder == 0) {
-    /* No MAC */
-    return 1;
-  } else if (remainder >= NTP_MIN_MAC_LENGTH) {
-    /* This is not 100% reliable as a MAC could fail to authenticate and could
-       pass as an extension field, leaving reminder smaller than the minimum MAC
-       length */
-    info->auth.mode = NTP_AUTH_SYMMETRIC;
-    info->auth.mac.start = parsed;
-    info->auth.mac.length = remainder;
-    info->auth.mac.key_id = ntohl(*(uint32_t *)(data + parsed));
-    return 1;
-  }
-
-  DEBUG_LOG("Invalid format");
-  return 0;
-}
-
-/* ================================================== */
-
 int
 NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod)
 {
--- a/ntp_auth.h
+++ b/ntp_auth.h
@@ -37,7 +37,7 @@ typedef struct NAU_Instance_Record *NAU_Instance;
 extern NAU_Instance NAU_CreateNoneInstance(void);
 extern NAU_Instance NAU_CreateSymmetricInstance(uint32_t key_id);
 extern NAU_Instance NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name,
-                                          const IPSockAddr *ntp_address);
+                                          uint32_t cert_set, uint16_t ntp_port);

 /* Destroy an instance */
 extern void NAU_DestroyInstance(NAU_Instance instance);
@@ -55,9 +55,6 @@ extern int NAU_PrepareRequestAuth(NAU_Instance instance);
 extern int NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request,
                                   NTP_PacketInfo *info);

-/* Parse a request or response to detect the authentication mode */
-extern int NAU_ParsePacket(NTP_Packet *packet, NTP_PacketInfo *info);
-
 /* Verify that a request is authentic.  If it is not authentic and a non-zero
   kod code is returned, a KoD response should be sent back. */
 extern int NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod);
--- a/ntp_core.c
+++ b/ntp_core.c
--- a/ntp_core.h
+++ b/ntp_core.h
@@ -38,16 +38,12 @@ typedef enum {
  NTP_SERVER, NTP_PEER
 } NTP_Source_Type;

-typedef enum {
-  NTP_TS_DAEMON = 0,
-  NTP_TS_KERNEL,
-  NTP_TS_HARDWARE
-} NTP_Timestamp_Source;
-
 typedef struct {
  struct timespec ts;
  double err;
  NTP_Timestamp_Source source;
+  double rx_duration;
+  double net_correction;
 } NTP_Local_Timestamp;

 /* This is a private data type used for storing the instance record for
@@ -117,6 +113,8 @@ extern void NCR_ModifyMaxdelaydevratio(NCR_Instance inst, double new_max_delay_d

 extern void NCR_ModifyMinstratum(NCR_Instance inst, int new_min_stratum);

+extern void NCR_ModifyOffset(NCR_Instance inst, double new_offset);
+
 extern void NCR_ModifyPolltarget(NCR_Instance inst, int new_poll_target);

 extern void NCR_InitiateSampleBurst(NCR_Instance inst, int n_good_samples, int n_total_samples);
--- a/ntp_ext.c
+++ b/ntp_ext.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2019
+ * Copyright (C) Miroslav Lichvar  2019-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
--- a/ntp_io.c
+++ b/ntp_io.c
@@ -4,7 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Timo Teras  2009
- * Copyright (C) Miroslav Lichvar  2009, 2013-2016, 2018
+ * Copyright (C) Miroslav Lichvar  2009, 2013-2016, 2018-2021
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -30,9 +30,11 @@

 #include "sysincl.h"

+#include "memory.h"
 #include "ntp_io.h"
 #include "ntp_core.h"
 #include "ntp_sources.h"
+#include "ptp.h"
 #include "sched.h"
 #include "socket.h"
 #include "local.h"
@@ -70,6 +72,16 @@ static int permanent_server_sockets;
 /* Flag indicating the server IPv4 socket is bound to an address */
 static int bound_server_sock_fd4;

+/* PTP event port, or 0 if disabled */
+static int ptp_port;
+
+/* Shared server/client sockets for NTP-over-PTP */
+static int ptp_sock_fd4;
+static int ptp_sock_fd6;
+
+/* Buffer for transmitted NTP-over-PTP messages */
+static PTP_NtpMessage *ptp_message;
+
 /* Flag indicating that we have been initialised */
 static int initialised=0;

@@ -114,8 +126,14 @@ open_socket(int family, int local_port, int client_only, IPSockAddr *remote_addr
  dscp = CNF_GetNtpDscp();
  if (dscp > 0 && dscp < 64) {
 #ifdef IP_TOS
-    if (!SCK_SetIntOption(sock_fd, IPPROTO_IP, IP_TOS, dscp << 2))
-      ;
+    if (family == IPADDR_INET4)
+      if (!SCK_SetIntOption(sock_fd, IPPROTO_IP, IP_TOS, dscp << 2))
+        ;
+#endif
+#if defined(FEAT_IPV6) && defined(IPV6_TCLASS)
+    if (family == IPADDR_INET6)
+      if (!SCK_SetIntOption(sock_fd, IPPROTO_IPV6, IPV6_TCLASS, dscp << 2))
+        ;
 #endif
  }

@@ -151,9 +169,6 @@ close_socket(int sock_fd)
  if (sock_fd == INVALID_SOCK_FD)
    return;

-#ifdef HAVE_LINUX_TIMESTAMPING
-  NIO_Linux_NotifySocketClosing(sock_fd);
-#endif
  SCH_RemoveFileHandler(sock_fd);
  SCK_CloseSocket(sock_fd);
 }
@@ -221,6 +236,17 @@ NIO_Initialise(void)
       client_sock_fd4 == INVALID_SOCK_FD && client_sock_fd6 == INVALID_SOCK_FD)) {
    LOG_FATAL("Could not open NTP sockets");
  }
+
+  ptp_port = CNF_GetPtpPort();
+  ptp_sock_fd4 = INVALID_SOCK_FD;
+  ptp_sock_fd6 = INVALID_SOCK_FD;
+  ptp_message = NULL;
+
+  if (ptp_port > 0) {
+    ptp_sock_fd4 = open_socket(IPADDR_INET4, ptp_port, 0, NULL);
+    ptp_sock_fd6 = open_socket(IPADDR_INET6, ptp_port, 0, NULL);
+    ptp_message = MallocNew(PTP_NtpMessage);
+  }
 }

 /* ================================================== */
@@ -238,6 +264,11 @@ NIO_Finalise(void)
  close_socket(server_sock_fd6);
  server_sock_fd6 = client_sock_fd6 = INVALID_SOCK_FD;

+  close_socket(ptp_sock_fd4);
+  close_socket(ptp_sock_fd6);
+  ptp_sock_fd4 = ptp_sock_fd6 = INVALID_SOCK_FD;
+  Free(ptp_message);
+
 #ifdef HAVE_LINUX_TIMESTAMPING
  NIO_Linux_Finalise();
 #endif
@@ -247,20 +278,36 @@ NIO_Finalise(void)

 /* ================================================== */

+int
+NIO_IsHwTsEnabled(void)
+{
+#ifdef HAVE_LINUX_TIMESTAMPING
+  return NIO_Linux_IsHwTsEnabled();
+#else
+  return 0;
+#endif
+}
+
+/* ================================================== */
+
 int
 NIO_OpenClientSocket(NTP_Remote_Address *remote_addr)
 {
-  if (separate_client_sockets) {
-    return open_separate_client_socket(remote_addr);
-  } else {
-    switch (remote_addr->ip_addr.family) {
-      case IPADDR_INET4:
-        return client_sock_fd4;
-      case IPADDR_INET6:
-        return client_sock_fd6;
-      default:
-        return INVALID_SOCK_FD;
-    }
+  switch (remote_addr->ip_addr.family) {
+    case IPADDR_INET4:
+      if (ptp_port > 0 && remote_addr->port == ptp_port)
+        return ptp_sock_fd4;
+      if (separate_client_sockets)
+        return open_separate_client_socket(remote_addr);
+      return client_sock_fd4;
+    case IPADDR_INET6:
+      if (ptp_port > 0 && remote_addr->port == ptp_port)
+        return ptp_sock_fd6;
+      if (separate_client_sockets)
+        return open_separate_client_socket(remote_addr);
+      return client_sock_fd6;
+    default:
+      return INVALID_SOCK_FD;
  }
 }

@@ -271,6 +318,8 @@ NIO_OpenServerSocket(NTP_Remote_Address *remote_addr)
 {
  switch (remote_addr->ip_addr.family) {
    case IPADDR_INET4:
+      if (ptp_port > 0 && remote_addr->port == ptp_port)
+        return ptp_sock_fd4;
      if (permanent_server_sockets)
        return server_sock_fd4;
      if (server_sock_fd4 == INVALID_SOCK_FD)
@@ -279,6 +328,8 @@ NIO_OpenServerSocket(NTP_Remote_Address *remote_addr)
        server_sock_ref4++;
      return server_sock_fd4;
    case IPADDR_INET6:
+      if (ptp_port > 0 && remote_addr->port == ptp_port)
+        return ptp_sock_fd6;
      if (permanent_server_sockets)
        return server_sock_fd6;
      if (server_sock_fd6 == INVALID_SOCK_FD)
@@ -293,9 +344,21 @@ NIO_OpenServerSocket(NTP_Remote_Address *remote_addr)

 /* ================================================== */

+static int
+is_ptp_socket(int sock_fd)
+{
+  return ptp_port > 0 && sock_fd != INVALID_SOCK_FD &&
+    (sock_fd == ptp_sock_fd4 || sock_fd == ptp_sock_fd6);
+}
+
+/* ================================================== */
+
 void
 NIO_CloseClientSocket(int sock_fd)
 {
+  if (is_ptp_socket(sock_fd))
+    return;
+
  if (separate_client_sockets)
    close_socket(sock_fd);
 }
@@ -305,7 +368,7 @@ NIO_CloseClientSocket(int sock_fd)
 void
 NIO_CloseServerSocket(int sock_fd)
 {
-  if (permanent_server_sockets || sock_fd == INVALID_SOCK_FD)
+  if (permanent_server_sockets || sock_fd == INVALID_SOCK_FD || is_ptp_socket(sock_fd))
    return;

  if (sock_fd == server_sock_fd4) {
@@ -329,7 +392,7 @@ int
 NIO_IsServerSocket(int sock_fd)
 {
  return sock_fd != INVALID_SOCK_FD &&
-    (sock_fd == server_sock_fd4 || sock_fd == server_sock_fd6);
+    (sock_fd == server_sock_fd4 || sock_fd == server_sock_fd6 || is_ptp_socket(sock_fd));
 }

 /* ================================================== */
@@ -337,7 +400,8 @@ NIO_IsServerSocket(int sock_fd)
 int
 NIO_IsServerSocketOpen(void)
 {
-  return server_sock_fd4 != INVALID_SOCK_FD || server_sock_fd6 != INVALID_SOCK_FD;
+  return server_sock_fd4 != INVALID_SOCK_FD || server_sock_fd6 != INVALID_SOCK_FD ||
+    ptp_sock_fd4 != INVALID_SOCK_FD || ptp_sock_fd6 != INVALID_SOCK_FD;
 }

 /* ================================================== */
@@ -367,6 +431,9 @@ process_message(SCK_Message *message, int sock_fd, int event)

  SCH_GetLastEventTime(&local_ts.ts, &local_ts.err, NULL);
  local_ts.source = NTP_TS_DAEMON;
+  local_ts.rx_duration = 0.0;
+  local_ts.net_correction = 0.0;
+
  sched_ts = local_ts.ts;

  if (message->addr_type != SCK_ADDR_IP) {
@@ -392,6 +459,9 @@ process_message(SCK_Message *message, int sock_fd, int event)
    DEBUG_LOG("Updated RX timestamp delay=%.9f tss=%u",
              UTI_DiffTimespecsToDouble(&sched_ts, &local_ts.ts), local_ts.source);

+  if (!NIO_UnwrapMessage(message, sock_fd, &local_ts.net_correction))
+    return;
+
  /* Just ignore the packet if it's not of a recognized length */
  if (message->length < NTP_HEADER_LENGTH || message->length > sizeof (NTP_Packet)) {
    DEBUG_LOG("Unexpected length");
@@ -409,11 +479,6 @@ read_from_socket(int sock_fd, int event, void *anything)
  SCK_Message *messages;
  int i, received, flags = 0;

-#ifdef HAVE_LINUX_TIMESTAMPING
-  if (NIO_Linux_ProcessEvent(sock_fd, event))
-    return;
-#endif
-
  if (event == SCH_FILE_EXCEPTION) {
 #ifdef HAVE_LINUX_TIMESTAMPING
    flags |= SCK_FLAG_MSG_ERRQUEUE;
@@ -430,6 +495,91 @@ read_from_socket(int sock_fd, int event, void *anything)
    process_message(&messages[i], sock_fd, event);
 }

+/* ================================================== */
+
+int
+NIO_UnwrapMessage(SCK_Message *message, int sock_fd, double *net_correction)
+{
+  double ptp_correction;
+  PTP_NtpMessage *msg;
+
+  if (!is_ptp_socket(sock_fd))
+    return 1;
+
+  if (message->length <= PTP_NTP_PREFIX_LENGTH) {
+    DEBUG_LOG("Unexpected length");
+    return 0;
+  }
+
+  msg = message->data;
+
+  if ((msg->header.type != PTP_TYPE_DELAY_REQ && msg->header.type != PTP_TYPE_SYNC) ||
+      (msg->header.version != PTP_VERSION_2 &&
+       (msg->header.version != PTP_VERSION_2_1 || msg->header.min_sdoid != 0)) ||
+      ntohs(msg->header.length) != message->length ||
+      msg->header.domain != CNF_GetPtpDomain() ||
+      ntohs(msg->header.flags) != PTP_FLAG_UNICAST ||
+      ntohs(msg->tlv_header.type) != PTP_TLV_NTP ||
+      ntohs(msg->tlv_header.length) != message->length - PTP_NTP_PREFIX_LENGTH) {
+    DEBUG_LOG("Unexpected PTP message");
+    return 0;
+  }
+
+  message->data = (char *)message->data + PTP_NTP_PREFIX_LENGTH;
+  message->length -= PTP_NTP_PREFIX_LENGTH;
+
+  ptp_correction = UTI_Integer64NetworkToHost(*(Integer64 *)msg->header.correction) /
+                   ((1 << 16) * 1.0e9);
+
+  /* Use the correction only if the RX duration is known (i.e. HW timestamp) */
+  if (*net_correction > 0.0)
+    *net_correction += ptp_correction;
+
+  DEBUG_LOG("Unwrapped PTP->NTP len=%d corr=%.9f", message->length, ptp_correction);
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+wrap_message(SCK_Message *message, int sock_fd)
+{
+  static uint16_t sequence_id = 0;
+
+  assert(PTP_NTP_PREFIX_LENGTH == 48);
+
+  if (!is_ptp_socket(sock_fd))
+    return 1;
+
+  if (!ptp_message)
+    return 0;
+
+  if (message->length < NTP_HEADER_LENGTH ||
+      message->length + PTP_NTP_PREFIX_LENGTH > sizeof (*ptp_message)) {
+    DEBUG_LOG("Unexpected length");
+    return 0;
+  }
+
+  memset(ptp_message, 0, PTP_NTP_PREFIX_LENGTH);
+  ptp_message->header.type = PTP_TYPE_DELAY_REQ;
+  ptp_message->header.version = PTP_VERSION_2;
+  ptp_message->header.length = htons(PTP_NTP_PREFIX_LENGTH + message->length);
+  ptp_message->header.domain = CNF_GetPtpDomain();
+  ptp_message->header.flags = htons(PTP_FLAG_UNICAST);
+  ptp_message->header.sequence_id = htons(sequence_id++);
+  ptp_message->tlv_header.type = htons(PTP_TLV_NTP);
+  ptp_message->tlv_header.length = htons(message->length);
+  memcpy((char *)ptp_message + PTP_NTP_PREFIX_LENGTH, message->data, message->length);
+
+  message->data = ptp_message;
+  message->length += PTP_NTP_PREFIX_LENGTH;
+
+  DEBUG_LOG("Wrapped NTP->PTP len=%d", message->length - PTP_NTP_PREFIX_LENGTH);
+
+  return 1;
+}
+
 /* ================================================== */
 /* Send a packet to remote address from local address */

@@ -451,6 +601,9 @@ NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
  message.data = packet;
  message.length = length;

+  if (!wrap_message(&message, local_addr->sock_fd))
+    return 0;
+
  /* Specify remote address if the socket is not connected */
  if (NIO_IsServerSocket(local_addr->sock_fd) || !separate_client_sockets) {
    message.remote_addr.ip.ip_addr = remote_addr->ip_addr;
@@ -467,7 +620,7 @@ NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
 #if !defined(HAVE_IN_PKTINFO) && defined(IP_SENDSRCADDR)
  /* On FreeBSD a local IPv4 address cannot be specified on bound socket */
  if (message.local_addr.ip.family == IPADDR_INET4 &&
-      (local_addr->sock_fd != server_sock_fd4 || bound_server_sock_fd4))
+      (bound_server_sock_fd4 || !NIO_IsServerSocket(local_addr->sock_fd)))
    message.local_addr.ip.family = IPADDR_UNSPEC;
 #endif

--- a/ntp_io.h
+++ b/ntp_io.h
@@ -31,6 +31,7 @@

 #include "ntp.h"
 #include "addressing.h"
+#include "socket.h"

 /* Function to initialise the module. */
 extern void NIO_Initialise(void);
@@ -38,6 +39,9 @@ extern void NIO_Initialise(void);
 /* Function to finalise the module */
 extern void NIO_Finalise(void);

+/* Function to check if HW timestamping is enabled on any interface */
+extern int NIO_IsHwTsEnabled(void);
+
 /* Function to obtain a socket for sending client packets */
 extern int NIO_OpenClientSocket(NTP_Remote_Address *remote_addr);

@@ -59,6 +63,9 @@ extern int NIO_IsServerSocketOpen(void);
 /* Function to check if client packets can be sent to a server */
 extern int NIO_IsServerConnectable(NTP_Remote_Address *remote_addr);

+/* Function to unwrap an NTP message from non-native transport (e.g. PTP) */
+extern int NIO_UnwrapMessage(SCK_Message *message, int sock_fd, double *net_correction);
+
 /* Function to transmit a packet */
 extern int NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
                          NTP_Local_Address *local_addr, int length, int process_tx);
--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2019
+ * Copyright (C) Miroslav Lichvar  2016-2019, 2021-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -39,6 +39,7 @@
 #include "hwclock.h"
 #include "local.h"
 #include "logging.h"
+#include "memory.h"
 #include "ntp_core.h"
 #include "ntp_io.h"
 #include "ntp_io_linux.h"
@@ -59,21 +60,22 @@ struct Interface {
  /* Start of UDP data at layer 2 for IPv4 and IPv6 */
  int l2_udp4_ntp_start;
  int l2_udp6_ntp_start;
-  /* Precision of PHC readings */
-  double precision;
  /* Compensation of errors in TX and RX timestamping */
  double tx_comp;
  double rx_comp;
  HCL_Instance clock;
+  int maxpoll;
+  SCH_TimeoutID poll_timeout_id;
 };

 /* Number of PHC readings per HW clock sample */
-#define PHC_READINGS 10
+#define PHC_READINGS 25

-/* Minimum interval between PHC readings */
+/* Minimum and maximum interval between PHC readings */
 #define MIN_PHC_POLL -6
+#define MAX_PHC_POLL 20

-/* Maximum acceptable offset between HW and daemon/kernel timestamp */
+/* Maximum acceptable offset between SW/HW and daemon timestamp */
 #define MAX_TS_DELAY 1.0

 /* Array of Interfaces */
@@ -86,19 +88,6 @@ static int ts_tx_flags;
 /* Flag indicating the socket options can't be changed in control messages */
 static int permanent_ts_options;

-/* When sending client requests to a close and fast server, it is possible that
-   a response will be received before the HW transmit timestamp of the request
-   itself.  To avoid processing of the response without the HW timestamp, we
-   monitor events returned by select() and suspend reading of packets from the
-   receive queue for up to 200 microseconds.  As the requests are normally
-   separated by at least 200 milliseconds, it is sufficient to monitor and
-   suspend one socket at a time. */
-static int monitored_socket;
-static int suspended_socket;
-static SCH_TimeoutID resume_timeout_id;
-
-#define RESUME_TIMEOUT 200.0e-6
-
 /* Unbound socket keeping the kernel RX timestamping permanently enabled
   in order to avoid a race condition between receiving a server response
   and the kernel actually starting to timestamp received packets after
@@ -109,13 +98,17 @@ static int dummy_rxts_socket;

 /* ================================================== */

+static void poll_phc(struct Interface *iface, struct timespec *now);
+
+/* ================================================== */
+
 static int
 add_interface(CNF_HwTsInterface *conf_iface)
 {
+  int sock_fd, if_index, minpoll, phc_fd, req_hwts_flags, rx_filter;
  struct ethtool_ts_info ts_info;
  struct hwtstamp_config ts_config;
  struct ifreq req;
-  int sock_fd, if_index, phc_fd, req_hwts_flags, rx_filter;
  unsigned int i;
  struct Interface *iface;

@@ -189,6 +182,14 @@ add_interface(CNF_HwTsInterface *conf_iface)
      rx_filter = HWTSTAMP_FILTER_NTP_ALL;
      break;
 #endif
+    case CNF_HWTS_RXFILTER_PTP:
+      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_PTP_V2_L4_EVENT))
+        rx_filter = HWTSTAMP_FILTER_PTP_V2_L4_EVENT;
+      else if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_PTP_V2_EVENT))
+        rx_filter = HWTSTAMP_FILTER_PTP_V2_EVENT;
+      else
+        rx_filter = HWTSTAMP_FILTER_NONE;
+      break;
    default:
      rx_filter = HWTSTAMP_FILTER_ALL;
      break;
@@ -200,7 +201,8 @@ add_interface(CNF_HwTsInterface *conf_iface)
  req.ifr_data = (char *)&ts_config;

  if (ioctl(sock_fd, SIOCSHWTSTAMP, &req)) {
-    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCSHWTSTAMP", strerror(errno));
+    LOG(errno == EPERM ? LOGS_ERR : LOGS_DEBUG,
+        "ioctl(%s) failed : %s", "SIOCSHWTSTAMP", strerror(errno));

    /* Check the current timestamping configuration in case this interface
       allows only reading of the configuration and it was already configured
@@ -218,7 +220,7 @@ add_interface(CNF_HwTsInterface *conf_iface)

  SCK_CloseSocket(sock_fd);

-  phc_fd = SYS_Linux_OpenPHC(NULL, ts_info.phc_index);
+  phc_fd = SYS_Linux_OpenPHC(req.ifr_name, O_RDONLY);
  if (phc_fd < 0)
    return 0;

@@ -235,12 +237,18 @@ add_interface(CNF_HwTsInterface *conf_iface)
  iface->l2_udp4_ntp_start = 42;
  iface->l2_udp6_ntp_start = 62;

-  iface->precision = conf_iface->precision;
  iface->tx_comp = conf_iface->tx_comp;
  iface->rx_comp = conf_iface->rx_comp;

+  minpoll = CLAMP(MIN_PHC_POLL, conf_iface->minpoll, MAX_PHC_POLL);
  iface->clock = HCL_CreateInstance(conf_iface->min_samples, conf_iface->max_samples,
-                                    UTI_Log2ToDouble(MAX(conf_iface->minpoll, MIN_PHC_POLL)));
+                                    UTI_Log2ToDouble(minpoll), conf_iface->precision);
+
+  iface->maxpoll = CLAMP(minpoll, conf_iface->maxpoll, MAX_PHC_POLL);
+
+  /* Do not schedule the first poll timeout here!  The argument (interface) can
+     move until all interfaces are added.  Wait for the first HW timestamp. */
+  iface->poll_timeout_id = 0;

  LOG(LOGS_INFO, "Enabled HW timestamping %son %s",
      ts_config.rx_filter == HWTSTAMP_FILTER_NONE ? "(TX only) " : "", iface->name);
@@ -405,8 +413,6 @@ NIO_Linux_Initialise(void)
  /* Kernels before 4.7 ignore timestamping flags set in control messages */
  permanent_ts_options = !SYS_Linux_CheckKernelVersion(4, 7);

-  monitored_socket = INVALID_SOCK_FD;
-  suspended_socket = INVALID_SOCK_FD;
  dummy_rxts_socket = INVALID_SOCK_FD;
 }

@@ -423,6 +429,7 @@ NIO_Linux_Finalise(void)

  for (i = 0; i < ARR_GetSize(interfaces); i++) {
    iface = ARR_GetElement(interfaces, i);
+    SCH_RemoveTimeout(iface->poll_timeout_id);
    HCL_DestroyInstance(iface->clock);
    close(iface->phc_fd);
  }
@@ -432,6 +439,14 @@ NIO_Linux_Finalise(void)

 /* ================================================== */

+int
+NIO_Linux_IsHwTsEnabled(void)
+{
+  return ARR_GetSize(interfaces) > 0;
+}
+
+/* ================================================== */
+
 int
 NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)
 {
@@ -465,73 +480,6 @@ NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)

 /* ================================================== */

-static void
-resume_socket(int sock_fd)
-{
-  if (monitored_socket == sock_fd)
-    monitored_socket = INVALID_SOCK_FD;
-
-  if (sock_fd == INVALID_SOCK_FD || sock_fd != suspended_socket)
-    return;
-
-  suspended_socket = INVALID_SOCK_FD;
-
-  SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_INPUT, 1);
-
-  DEBUG_LOG("Resumed RX processing %s timeout fd=%d",
-            resume_timeout_id ? "before" : "on", sock_fd);
-
-  if (resume_timeout_id) {
-    SCH_RemoveTimeout(resume_timeout_id);
-    resume_timeout_id = 0;
-  }
-}
-
-/* ================================================== */
-
-static void
-resume_timeout(void *arg)
-{
-  resume_timeout_id = 0;
-  resume_socket(suspended_socket);
-}
-
-/* ================================================== */
-
-static void
-suspend_socket(int sock_fd)
-{
-  resume_socket(suspended_socket);
-
-  suspended_socket = sock_fd;
-
-  SCH_SetFileHandlerEvent(suspended_socket, SCH_FILE_INPUT, 0);
-  resume_timeout_id = SCH_AddTimeoutByDelay(RESUME_TIMEOUT, resume_timeout, NULL);
-
-  DEBUG_LOG("Suspended RX processing fd=%d", sock_fd);
-}
-
-/* ================================================== */
-
-int
-NIO_Linux_ProcessEvent(int sock_fd, int event)
-{
-  if (sock_fd != monitored_socket)
-    return 0;
-
-  if (event == SCH_FILE_INPUT) {
-    suspend_socket(monitored_socket);
-    monitored_socket = INVALID_SOCK_FD;
-
-    /* Don't process the message yet */
-    return 1;
-  }
-
-  return 0;
-}
-
-/* ================================================== */
-
 static struct Interface *
 get_interface(int if_index)
 {
@@ -551,26 +499,71 @@ get_interface(int if_index)

 /* ================================================== */

+static void
+poll_timeout(void *arg)
+{
+  struct Interface *iface = arg;
+  struct timespec now;
+
+  iface->poll_timeout_id = 0;
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+  poll_phc(iface, &now);
+}
+
+/* ================================================== */
+
+static void
+poll_phc(struct Interface *iface, struct timespec *now)
+{
+  struct timespec sample_phc_ts, sample_sys_ts, sample_local_ts;
+  struct timespec phc_readings[PHC_READINGS][3];
+  double phc_err, local_err, interval;
+  int n_readings, quality;
+
+  if (!HCL_NeedsNewSample(iface->clock, now))
+    return;
+
+  DEBUG_LOG("Polling PHC on %s%s",
+            iface->name, iface->poll_timeout_id != 0 ? " before timeout" : "");
+
+  n_readings = SYS_Linux_GetPHCReadings(iface->phc_fd, iface->phc_nocrossts,
+                                        &iface->phc_mode, PHC_READINGS, phc_readings);
+
+  /* Add timeout for the next poll in case no HW timestamp will be captured
+     between the minpoll and maxpoll.  Separate reading of different PHCs to
+     avoid long intervals between handling I/O events. */
+  SCH_RemoveTimeout(iface->poll_timeout_id);
+  interval = UTI_Log2ToDouble(iface->maxpoll);
+  iface->poll_timeout_id = SCH_AddTimeoutInClass(interval, interval /
+                                                   ARR_GetSize(interfaces) / 4, 0.1,
+                                                 SCH_PhcPollClass, poll_timeout, iface);
+
+  if (n_readings <= 0)
+    return;
+
+  if (!HCL_ProcessReadings(iface->clock, n_readings, phc_readings,
+                           &sample_phc_ts, &sample_sys_ts, &phc_err, &quality) ||
+      quality <= 0)
+    return;
+
+  LCL_CookTime(&sample_sys_ts, &sample_local_ts, &local_err);
+  HCL_AccumulateSample(iface->clock, &sample_phc_ts, &sample_local_ts, phc_err + local_err);
+
+  update_interface_speed(iface);
+}
+
+/* ================================================== */
+
 static void
 process_hw_timestamp(struct Interface *iface, struct timespec *hw_ts,
                     NTP_Local_Timestamp *local_ts, int rx_ntp_length, int family,
                     int l2_length)
 {
-  struct timespec sample_phc_ts, sample_sys_ts, sample_local_ts, ts;
-  double rx_correction, ts_delay, phc_err, local_err;
+  double rx_correction = 0.0, ts_delay, local_err;
+  struct timespec ts;

-  if (HCL_NeedsNewSample(iface->clock, &local_ts->ts)) {
-    if (!SYS_Linux_GetPHCSample(iface->phc_fd, iface->phc_nocrossts, iface->precision,
-                                &iface->phc_mode, &sample_phc_ts, &sample_sys_ts,
-                                &phc_err))
-      return;
-
-    LCL_CookTime(&sample_sys_ts, &sample_local_ts, &local_err);
-    HCL_AccumulateSample(iface->clock, &sample_phc_ts, &sample_local_ts,
-                         phc_err + local_err);
-
-    update_interface_speed(iface);
-  }
+  poll_phc(iface, &local_ts->ts);

  /* We need to transpose RX timestamps as hardware timestamps are normally
     preamble timestamps and RX timestamps in NTP are supposed to be trailer
@@ -608,6 +601,32 @@ process_hw_timestamp(struct Interface *iface, struct timespec *hw_ts,
  local_ts->ts = ts;
  local_ts->err = local_err;
  local_ts->source = NTP_TS_HARDWARE;
+  local_ts->rx_duration = rx_correction;
+  /* Network correction needs to include the RX duration to avoid
+     asymmetric correction with asymmetric link speeds */
+  local_ts->net_correction = rx_correction;
+}
+
+/* ================================================== */
+
+static void
+process_sw_timestamp(struct timespec *sw_ts, NTP_Local_Timestamp *local_ts)
+{
+  double ts_delay, local_err;
+  struct timespec ts;
+
+  LCL_CookTime(sw_ts, &ts, &local_err);
+
+  ts_delay = UTI_DiffTimespecsToDouble(&local_ts->ts, &ts);
+
+  if (fabs(ts_delay) > MAX_TS_DELAY) {
+    DEBUG_LOG("Unacceptable timestamp delay %.9f", ts_delay);
+    return;
+  }
+
+  local_ts->ts = ts;
+  local_ts->err = local_err;
+  local_ts->source = NTP_TS_KERNEL;
 }

 /* ================================================== */
@@ -709,6 +728,7 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
 {
  struct Interface *iface;
  int is_tx, ts_if_index, l2_length;
+  double c = 0.0;

  is_tx = event == SCH_FILE_EXCEPTION;
  iface = NULL;
@@ -726,17 +746,11 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
    } else {
      DEBUG_LOG("HW clock not found for interface %d", ts_if_index);
    }
-
-    /* If a HW transmit timestamp was received, resume processing
-       of non-error messages on this socket */
-    if (is_tx)
-      resume_socket(local_addr->sock_fd);
  }

  if (local_ts->source == NTP_TS_DAEMON && !UTI_IsZeroTimespec(&message->timestamp.kernel) &&
      (!is_tx || UTI_IsZeroTimespec(&message->timestamp.hw))) {
-    LCL_CookTime(&message->timestamp.kernel, &local_ts->ts, &local_ts->err);
-    local_ts->source = NTP_TS_KERNEL;
+    process_sw_timestamp(&message->timestamp.kernel, local_ts);
  }

  /* If the kernel is slow with enabling RX timestamping, open a dummy
@@ -775,7 +789,10 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
    return 1;
  }

-  if (message->length < NTP_HEADER_LENGTH)
+  if (!NIO_UnwrapMessage(message, local_addr->sock_fd, &c))
+    return 1;
+
+  if (message->length < NTP_HEADER_LENGTH || message->length > sizeof (NTP_Packet))
    return 1;

  NSR_ProcessTx(&message->remote_addr.ip, local_addr, local_ts, message->data, message->length);
@@ -791,23 +808,9 @@ NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd)
  if (!ts_flags)
    return;

-  /* If a HW transmit timestamp is requested on a client socket, monitor
-     events on the socket in order to avoid processing of a fast response
-     without the HW timestamp of the request */
-  if (ts_tx_flags & SOF_TIMESTAMPING_TX_HARDWARE && !NIO_IsServerSocket(sock_fd))
-    monitored_socket = sock_fd;
-
  /* Check if TX timestamping is disabled on this socket */
  if (permanent_ts_options || !NIO_IsServerSocket(sock_fd))
    return;

  message->timestamp.tx_flags = ts_tx_flags;
 }
-
-/* ================================================== */
-
-void
-NIO_Linux_NotifySocketClosing(int sock_fd)
-{
-  resume_socket(sock_fd);
-}
--- a/ntp_io_linux.h
+++ b/ntp_io_linux.h
@@ -33,15 +33,13 @@ extern void NIO_Linux_Initialise(void);

 extern void NIO_Linux_Finalise(void);

-extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);
+extern int NIO_Linux_IsHwTsEnabled(void);

-extern int NIO_Linux_ProcessEvent(int sock_fd, int event);
+extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);

 extern int NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
                                    NTP_Local_Timestamp *local_ts, int event);

 extern void NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd);

-extern void NIO_Linux_NotifySocketClosing(int sock_fd);
-
 #endif
--- a/ntp_signd.c
+++ b/ntp_signd.c
@@ -99,6 +99,9 @@ static int sock_fd;
 /* Flag indicating if the MS-SNTP authentication is enabled */
 static int enabled;

+/* Flag limiting logging of connection error messages */
+static int logged_connection_error;
+
 /* ================================================== */

 static void read_write_socket(int sock_fd, int event, void *anything);
@@ -134,6 +137,14 @@ open_socket(void)
  sock_fd = SCK_OpenUnixStreamSocket(path, NULL, 0);
  if (sock_fd < 0) {
    sock_fd = INVALID_SOCK_FD;
+
+    /* Log an error only once before a successful exchange to avoid
+       flooding the system log */
+    if (!logged_connection_error) {
+      LOG(LOGS_ERR, "Could not connect to signd socket %s : %s", path, strerror(errno));
+      logged_connection_error = 1;
+    }
+
    return 0;
  }

@@ -160,6 +171,8 @@ process_response(SignInstance *inst)
    return;
  }

+  logged_connection_error = 0;
+
  /* Check if the file descriptor is still valid */
  if (!NIO_IsServerSocket(inst->local_addr.sock_fd)) {
    DEBUG_LOG("Invalid NTP socket");
--- a/ntp_sources.c
+++ b/ntp_sources.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2012, 2014, 2016
+ * Copyright (C) Miroslav Lichvar  2011-2012, 2014, 2016, 2020-2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -32,6 +32,7 @@
 #include "sysincl.h"

 #include "array.h"
+#include "conf.h"
 #include "ntp_sources.h"
 #include "ntp_core.h"
 #include "ntp_io.h"
@@ -45,6 +46,9 @@

 /* ================================================== */

+/* Maximum number of sources */
+#define MAX_SOURCES 65536
+
 /* Record type private to this file, used to store information about
   particular sources */
 typedef struct {
@@ -53,13 +57,19 @@ typedef struct {
                                      (an IPADDR_ID address means the address
                                      is not resolved yet) */
  NCR_Instance data;            /* Data for the protocol engine for this source */
-  char *name;                   /* Name of the source, may be NULL */
+  char *name;                   /* Name of the source as it was specified
+                                   (may be an IP address) */
+  IPAddr resolved_addr;         /* Address resolved from the name, which can be
+                                   different from remote_addr (e.g. NTS-KE) */
+  int family;                   /* IP family of acceptable resolved addresses
+                                   (IPADDR_UNSPEC if any) */
  int pool_id;                  /* ID of the pool from which was this source
                                   added or INVALID_POOL */
  int tentative;                /* Flag indicating there was no valid response
                                   received from the source yet */
  uint32_t conf_id;             /* Configuration ID, which can be shared with
                                   different sources in case of a pool */
+  double last_resolving;        /* Time of last name resolving (monotonic) */
 } SourceRecord;

 /* Hash table of SourceRecord, its size is a power of two and it's never
@@ -72,6 +82,9 @@ static int n_sources;
 /* Flag indicating new sources will be started automatically when added */
 static int auto_start_sources = 0;

+/* Flag indicating a record is currently being modified */
+static int record_lock;
+
 /* Last assigned address ID */
 static uint32_t last_address_id = 0;

@@ -87,8 +100,13 @@ struct UnresolvedSource {
  int pool_id;
  /* Name to be resolved */
  char *name;
+  /* Address family to filter resolved addresses */
+  int family;
  /* Flag indicating addresses should be used in a random order */
  int random_order;
+  /* Flag indicating current address should be replaced only if it is
+     no longer returned by the resolver */
+  int refreshment;
  /* Next unresolved source in the list */
  struct UnresolvedSource *next;
 };
@@ -96,10 +114,11 @@ struct UnresolvedSource {
 #define RESOLVE_INTERVAL_UNIT 7
 #define MIN_RESOLVE_INTERVAL 2
 #define MAX_RESOLVE_INTERVAL 9
-#define MIN_REPLACEMENT_INTERVAL 8
+#define MAX_REPLACEMENT_INTERVAL 9

 static struct UnresolvedSource *unresolved_sources = NULL;
 static int resolving_interval = 0;
+static int resolving_restart = 0;
 static SCH_TimeoutID resolving_id;
 static struct UnresolvedSource *resolving_source = NULL;
 static NSR_SourceResolvingEndHandler resolving_end_handler = NULL;
@@ -122,11 +141,21 @@ struct SourcePool {
 /* Array of SourcePool (indexed by their ID) */
 static ARR_Instance pools;

+/* Requested update of a source's address */
+struct AddressUpdate {
+  NTP_Remote_Address old_address;
+  NTP_Remote_Address new_address;
+};
+
+/* Update saved when record_lock is true */
+static struct AddressUpdate saved_address_update;
+
 /* ================================================== */
 /* Forward prototypes */

 static void resolve_sources(void);
 static void rehash_records(void);
+static void handle_saved_address_update(void);
 static void clean_source_record(SourceRecord *record);
 static void remove_pool_sources(int pool_id, int tentative, int unresolved);
 static void remove_unresolved_source(struct UnresolvedSource *us);
@@ -166,6 +195,7 @@ void
 NSR_Initialise(void)
 {
  n_sources = 0;
+  resolving_id = 0;
  initialised = 1;

  records = ARR_CreateInstance(sizeof (SourceRecord));
@@ -181,22 +211,22 @@ NSR_Initialise(void)
 void
 NSR_Finalise(void)
 {
-  SourceRecord *record;
-  unsigned int i;
-
-  for (i = 0; i < ARR_GetSize(records); i++) {
-    record = get_record(i);
-    if (record->remote_addr)
-      clean_source_record(record);
-  }
+  NSR_RemoveAllSources();

  LCL_RemoveParameterChangeHandler(slew_sources, NULL);

  ARR_DestroyInstance(records);
  ARR_DestroyInstance(pools);

-  while (unresolved_sources)
-    remove_unresolved_source(unresolved_sources);
+  SCH_RemoveTimeout(resolving_id);
+
+  /* Leave the unresolved sources allocated if the async resolver is running
+     to avoid reading the name from freed memory.  The handler will not be
+     called as the scheduler should no longer be running at this point. */
+  if (!resolving_source) {
+    while (unresolved_sources)
+      remove_unresolved_source(unresolved_sources);
+  }

  initialised = 0;
 }
@@ -275,6 +305,8 @@ rehash_records(void)
  unsigned int i, old_size, new_size;
  int slot;

+  assert(!record_lock);
+
  old_size = ARR_GetSize(records);

  temp_records = MallocArray(SourceRecord, old_size);
@@ -304,9 +336,34 @@ rehash_records(void)

 /* ================================================== */

+static void
+log_source(SourceRecord *record, int addition, int once_per_pool)
+{
+  int pool, log_addr;
+  char *ip_str;
+
+  if (once_per_pool && record->pool_id != INVALID_POOL) {
+    if (get_pool(record->pool_id)->sources > 1)
+      return;
+    pool = 1;
+    log_addr = 0;
+  } else {
+    ip_str = UTI_IPToString(&record->remote_addr->ip_addr);
+    pool = 0;
+    log_addr = strcmp(record->name, ip_str) != 0;
+  }
+
+  LOG(LOG_GetContextSeverity(LOGC_Command | LOGC_SourceFile), "%s %s %s%s%s%s",
+      addition ? "Added" : "Removed", pool ? "pool" : "source",
+      log_addr ? ip_str : record->name,
+      log_addr ? " (" : "", log_addr ? record->name : "", log_addr ? ")" : "");
+}
+
+/* ================================================== */
+
 /* Procedure to add a new source */
 static NSR_Status
-add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
+add_source(NTP_Remote_Address *remote_addr, char *name, int family, NTP_Source_Type type,
           SourceParameters *params, int pool_id, uint32_t conf_id)
 {
  SourceRecord *record;
@@ -317,6 +374,11 @@ add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
  /* Find empty bin & check that we don't have the address already */
  if (find_slot2(remote_addr, &slot) != 0) {
    return NSR_AlreadyInUse;
+  } else if (!name && !UTI_IsIPReal(&remote_addr->ip_addr)) {
+    /* Name is required for non-real addresses */
+    return NSR_InvalidName;
+  } else if (n_sources >= MAX_SOURCES) {
+    return NSR_TooManySources;
  } else {
    if (remote_addr->ip_addr.family != IPADDR_INET4 &&
        remote_addr->ip_addr.family != IPADDR_INET6 &&
@@ -331,13 +393,21 @@ add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
          assert(0);
      }

+      assert(!record_lock);
+      record_lock = 1;
+
      record = get_record(slot);
-      record->data = NCR_CreateInstance(remote_addr, type, params, name);
+      record->name = Strdup(name ? name : UTI_IPToString(&remote_addr->ip_addr));
+      record->data = NCR_CreateInstance(remote_addr, type, params, record->name);
      record->remote_addr = NCR_GetRemoteAddress(record->data);
-      record->name = name ? Strdup(name) : NULL;
+      record->resolved_addr = remote_addr->ip_addr;
+      record->family = family;
      record->pool_id = pool_id;
      record->tentative = 1;
      record->conf_id = conf_id;
+      record->last_resolving = SCH_GetLastEventMonoTime();
+
+      record_lock = 0;

      if (record->pool_id != INVALID_POOL) {
        get_pool(record->pool_id)->sources++;
@@ -348,6 +418,11 @@ add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
      if (auto_start_sources && UTI_IsIPReal(&remote_addr->ip_addr))
        NCR_StartInstance(record->data);

+      log_source(record, 1, 1);
+
+      /* The new instance is allowed to change its address immediately */
+      handle_saved_address_update();
+
      return NSR_Success;
    }
  }
@@ -365,7 +440,7 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr
  char *name;

  found = find_slot2(old_addr, &slot1);
-  if (found == 0)
+  if (found != 2)
    return NSR_NoSuchSource;

  /* Make sure there is no other source using the new address (with the same
@@ -374,9 +449,17 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr
  if (found == 2 || (found != 0 && slot1 != slot2))
    return NSR_AlreadyInUse;

+  assert(!record_lock);
+  record_lock = 1;
+
  record = get_record(slot1);
  NCR_ChangeRemoteAddress(record->data, new_addr, !replacement);
-  record->remote_addr = NCR_GetRemoteAddress(record->data);
+  if (replacement)
+    record->resolved_addr = new_addr->ip_addr;
+
+  BRIEF_ASSERT(record->remote_addr == NCR_GetRemoteAddress(record->data) &&
+               UTI_CompareIPs(&record->remote_addr->ip_addr, &new_addr->ip_addr, NULL) == 0);
+
  if (!UTI_IsIPReal(&old_addr->ip_addr) && UTI_IsIPReal(&new_addr->ip_addr)) {
    if (auto_start_sources)
      NCR_StartInstance(record->data);
@@ -391,6 +474,8 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr
      get_pool(record->pool_id)->confirmed_sources--;
  }

+  record_lock = 0;
+
  name = record->name;
  severity = UTI_IsIPReal(&old_addr->ip_addr) ? LOGS_INFO : LOGS_DEBUG;

@@ -400,10 +485,10 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr

    LOG(severity, "Source %s %s %s (%s)", UTI_IPToString(&old_addr->ip_addr),
        replacement ? "replaced with" : "changed to",
-        UTI_IPToString(&new_addr->ip_addr), name ? name : "");
+        UTI_IPToString(&new_addr->ip_addr), name);
  } else {
    LOG(severity, "Source %s (%s) changed port to %d",
-        UTI_IPToString(&new_addr->ip_addr), name ? name : "", new_addr->port);
+        UTI_IPToString(&new_addr->ip_addr), name, new_addr->port);
  }

  return NSR_Success;
@@ -411,6 +496,24 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr

 /* ================================================== */

+static void
+handle_saved_address_update(void)
+{
+  if (!UTI_IsIPReal(&saved_address_update.old_address.ip_addr))
+    return;
+
+  if (change_source_address(&saved_address_update.old_address,
+                            &saved_address_update.new_address, 0) != NSR_Success)
+    /* This is expected to happen only if the old address is wrong */
+    LOG(LOGS_ERR, "Could not change %s to %s",
+        UTI_IPSockAddrToString(&saved_address_update.old_address),
+        UTI_IPSockAddrToString(&saved_address_update.new_address));
+
+  saved_address_update.old_address.ip_addr.family = IPADDR_UNSPEC;
+}
+
+/* ================================================== */
+
 static int
 replace_source_connectable(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr)
 {
@@ -422,6 +525,8 @@ replace_source_connectable(NTP_Remote_Address *old_addr, NTP_Remote_Address *new
  if (change_source_address(old_addr, new_addr, 1) == NSR_AlreadyInUse)
    return 0;

+  handle_saved_address_update();
+
  return 1;
 }

@@ -433,7 +538,21 @@ process_resolved_name(struct UnresolvedSource *us, IPAddr *ip_addrs, int n_addrs
  NTP_Remote_Address old_addr, new_addr;
  SourceRecord *record;
  unsigned short first = 0;
-  int i, j;
+  int i, j, slot;
+
+  /* Keep using the current address if it is being refreshed and it is
+     still included in the resolved addresses */
+  if (us->refreshment) {
+    assert(us->pool_id == INVALID_POOL);
+
+    for (i = 0; i < n_addrs; i++) {
+      if (find_slot2(&us->address, &slot) == 2 &&
+          UTI_CompareIPs(&get_record(slot)->resolved_addr, &ip_addrs[i], NULL) == 0) {
+        DEBUG_LOG("%s still fresh", UTI_IPToString(&us->address.ip_addr));
+        return;
+      }
+    }
+  }

  if (us->random_order)
    UTI_GetRandomBytes(&first, sizeof (first));
@@ -443,9 +562,13 @@ process_resolved_name(struct UnresolvedSource *us, IPAddr *ip_addrs, int n_addrs

    DEBUG_LOG("(%d) %s", i + 1, UTI_IPToString(&new_addr.ip_addr));

+    /* Skip addresses not from the requested family */
+    if (us->family != IPADDR_UNSPEC && us->family != new_addr.ip_addr.family)
+      continue;
+
    if (us->pool_id != INVALID_POOL) {
-      /* In the pool resolving mode, try to replace all sources from
-         the pool which don't have a real address yet */
+      /* In the pool resolving mode, try to replace a source from
+         the pool which does not have a real address yet */
      for (j = 0; j < ARR_GetSize(records); j++) {
        record = get_record(j);
        if (!record->remote_addr || record->pool_id != us->pool_id ||
@@ -454,7 +577,8 @@ process_resolved_name(struct UnresolvedSource *us, IPAddr *ip_addrs, int n_addrs
        old_addr = *record->remote_addr;
        new_addr.port = old_addr.port;
        if (replace_source_connectable(&old_addr, &new_addr))
-          break;
+          ;
+        break;
      }
    } else {
      new_addr.port = us->address.port;
@@ -519,10 +643,20 @@ name_resolve_handler(DNS_Status status, int n_addrs, IPAddr *ip_addrs, void *any
  next = us->next;

  /* Don't repeat the resolving if it (permanently) failed, it was a
-     replacement of a real address, or all addresses are already resolved */
-  if (status == DNS_Failure || UTI_IsIPReal(&us->address.ip_addr) || is_resolved(us))
+     replacement of a real address, a refreshment, or all addresses are
+     already resolved */
+  if (status == DNS_Failure || UTI_IsIPReal(&us->address.ip_addr) ||
+      us->refreshment || is_resolved(us))
    remove_unresolved_source(us);

+  /* If a restart was requested and this was the last source in the list,
+     start with the first source again (if there still is one) */
+  if (!next && resolving_restart) {
+    DEBUG_LOG("Restarting");
+    next = unresolved_sources;
+    resolving_restart = 0;
+  }
+
  resolving_source = next;

  if (next) {
@@ -583,11 +717,15 @@ static void
 append_unresolved_source(struct UnresolvedSource *us)
 {
  struct UnresolvedSource **i;
+  int n;

-  for (i = &unresolved_sources; *i; i = &(*i)->next)
+  for (i = &unresolved_sources, n = 0; *i; i = &(*i)->next, n++)
    ;
  *i = us;
  us->next = NULL;
+
+  DEBUG_LOG("Added unresolved source #%d pool_id=%d random=%d refresh=%d",
+            n + 1, us->pool_id, us->random_order, us->refreshment);
 }

 /* ================================================== */
@@ -634,50 +772,70 @@ static int get_unused_pool_id(void)

 /* ================================================== */

-NSR_Status
-NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
-              SourceParameters *params, uint32_t *conf_id)
+static uint32_t
+get_next_conf_id(uint32_t *conf_id)
 {
-  NSR_Status s;
-
-  s = add_source(remote_addr, NULL, type, params, INVALID_POOL, last_conf_id + 1);
-  if (s != NSR_Success)
-    return s;
+  SourceRecord *record;
+  unsigned int i;

+again:
  last_conf_id++;
+
+  /* Make sure the ID is not already used (after 32-bit wraparound) */
+  for (i = 0; i < ARR_GetSize(records); i++) {
+    record = get_record(i);
+    if (record->remote_addr && record->conf_id == last_conf_id)
+      goto again;
+  }
+
  if (conf_id)
    *conf_id = last_conf_id;

-  return s;
+  return last_conf_id;
 }

 /* ================================================== */

 NSR_Status
-NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
+NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
+              SourceParameters *params, uint32_t *conf_id)
+{
+  return add_source(remote_addr, NULL, IPADDR_UNSPEC, type, params, INVALID_POOL,
+                    get_next_conf_id(conf_id));
+}
+
+/* ================================================== */
+
+NSR_Status
+NSR_AddSourceByName(char *name, int family, int port, int pool, NTP_Source_Type type,
                    SourceParameters *params, uint32_t *conf_id)
 {
  struct UnresolvedSource *us;
  struct SourcePool *sp;
  NTP_Remote_Address remote_addr;
  int i, new_sources, pool_id;
+  uint32_t cid;

-  /* If the name is an IP address, don't bother with full resolving now
-     or later when trying to replace the source */
+  /* If the name is an IP address, add the source with the address directly */
  if (UTI_StringToIP(name, &remote_addr.ip_addr)) {
    remote_addr.port = port;
-    return NSR_AddSource(&remote_addr, type, params, conf_id);
+    if (family != IPADDR_UNSPEC && family != remote_addr.ip_addr.family)
+      return NSR_InvalidAF;
+    return add_source(&remote_addr, name, IPADDR_UNSPEC, type, params, INVALID_POOL,
+                      get_next_conf_id(conf_id));
  }

  /* Make sure the name is at least printable and has no spaces */
  for (i = 0; name[i] != '\0'; i++) {
-    if (!isgraph(name[i]))
+    if (!isgraph((unsigned char)name[i]))
      return NSR_InvalidName;
  }

  us = MallocNew(struct UnresolvedSource);
  us->name = Strdup(name);
+  us->family = family;
  us->random_order = 0;
+  us->refreshment = 0;

  remote_addr.ip_addr.family = IPADDR_ID;
  remote_addr.ip_addr.addr.id = ++last_address_id;
@@ -707,14 +865,12 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,

  append_unresolved_source(us);

-  last_conf_id++;
-  if (conf_id)
-    *conf_id = last_conf_id;
+  cid = get_next_conf_id(conf_id);

  for (i = 0; i < new_sources; i++) {
    if (i > 0)
      remote_addr.ip_addr.addr.id = ++last_address_id;
-    if (add_source(&remote_addr, name, type, params, us->pool_id, last_conf_id) != NSR_Success)
+    if (add_source(&remote_addr, name, family, type, params, us->pool_id, cid) != NSR_Success)
      return NSR_TooManySources;
  }

@@ -723,6 +879,31 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,

 /* ================================================== */

+const char *
+NSR_StatusToString(NSR_Status status)
+{
+  switch (status) {
+    case NSR_Success:
+      return "Success";
+    case NSR_NoSuchSource:
+      return "No such source";
+    case NSR_AlreadyInUse:
+      return "Already in use";
+    case NSR_TooManySources:
+      return "Too many sources";
+    case NSR_InvalidAF:
+      return "Invalid address";
+    case NSR_InvalidName:
+      return "Invalid name";
+    case NSR_UnresolvedName:
+      return "Unresolved name";
+    default:
+      return "?";
+  }
+}
+
+/* ================================================== */
+
 void
 NSR_SetSourceResolvingEndHandler(NSR_SourceResolvingEndHandler handler)
 {
@@ -736,7 +917,7 @@ NSR_ResolveSources(void)
 {
  /* Try to resolve unresolved sources now */
  if (unresolved_sources) {
-    /* Make sure no resolving is currently running */
+    /* Allow only one resolving to be running at a time */
    if (!resolving_source) {
      if (resolving_id != 0) {
        SCH_RemoveTimeout(resolving_id);
@@ -744,6 +925,9 @@ NSR_ResolveSources(void)
        resolving_interval--;
      }
      resolve_sources();
+    } else {
+      /* Try again as soon as the current resolving ends */
+      resolving_restart = 1;
    }
  } else {
    /* No unresolved sources, we are done */
@@ -795,8 +979,7 @@ clean_source_record(SourceRecord *record)

  record->remote_addr = NULL;
  NCR_DestroyInstance(record->data);
-  if (record->name)
-    Free(record->name);
+  Free(record->name);

  n_sources--;
 }
@@ -816,6 +999,7 @@ NSR_RemoveSource(IPAddr *address)
  if (find_slot(address, &slot) == 0)
    return NSR_NoSuchSource;

+  log_source(get_record(slot), 0, 0);
  clean_source_record(get_record(slot));

  /* Rehash the table to make sure there are no broken probe sequences.
@@ -838,6 +1022,7 @@ NSR_RemoveSourcesById(uint32_t conf_id)
    record = get_record(i);
    if (!record->remote_addr || record->conf_id != conf_id)
      continue;
+    log_source(record, 0, 1);
    clean_source_record(record);
  }

@@ -865,24 +1050,32 @@ NSR_RemoveAllSources(void)
 /* ================================================== */

 static void
-resolve_source_replacement(SourceRecord *record)
+resolve_source_replacement(SourceRecord *record, int refreshment)
 {
  struct UnresolvedSource *us;

-  DEBUG_LOG("trying to replace %s", UTI_IPToString(&record->remote_addr->ip_addr));
+  DEBUG_LOG("%s %s (%s)", refreshment ? "refreshing" : "trying to replace",
+            UTI_IPToString(&record->remote_addr->ip_addr), record->name);
+
+  record->last_resolving = SCH_GetLastEventMonoTime();

  us = MallocNew(struct UnresolvedSource);
  us->name = Strdup(record->name);
-  /* If there never was a valid reply from this source (e.g. it was a bad
-     replacement), ignore the order of addresses from the resolver to not get
-     stuck to a pair of addresses if the order doesn't change, or a group of
-     IPv4/IPv6 addresses if the resolver prefers inaccessible IP family */
-  us->random_order = record->tentative;
+  us->family = record->family;
+  /* Ignore the order of addresses from the resolver to not get
+     stuck with a pair of unreachable or otherwise unusable servers
+     (e.g. falsetickers) in case the order doesn't change, or a group
+     of servers if they are ordered by IP family */
+  us->random_order = 1;
+  us->refreshment = refreshment;
  us->pool_id = INVALID_POOL;
  us->address = *record->remote_addr;

  append_unresolved_source(us);
-  NSR_ResolveSources();
+
+  /* Don't restart resolving round if already running */
+  if (!resolving_source)
+    NSR_ResolveSources();
 }

 /* ================================================== */
@@ -890,10 +1083,11 @@ resolve_source_replacement(SourceRecord *record)
 void
 NSR_HandleBadSource(IPAddr *address)
 {
-  static struct timespec last_replacement;
-  struct timespec now;
+  static double next_replacement = 0.0;
  SourceRecord *record;
-  double diff;
+  IPAddr ip_addr;
+  uint32_t rnd;
+  double now;
  int slot;

  if (!find_slot(address, &slot))
@@ -901,20 +1095,63 @@ NSR_HandleBadSource(IPAddr *address)

  record = get_record(slot);

-  /* Only sources with a name can be replaced */
-  if (!record->name)
+  /* Don't try to replace a source specified by an IP address unless the
+     address changed since the source was added (e.g. by NTS-KE) */
+  if (UTI_StringToIP(record->name, &ip_addr) &&
+      UTI_CompareIPs(&record->remote_addr->ip_addr, &ip_addr, NULL) == 0)
    return;

  /* Don't resolve names too frequently */
-  SCH_GetLastEventTime(NULL, NULL, &now);
-  diff = UTI_DiffTimespecsToDouble(&now, &last_replacement);
-  if (fabs(diff) < RESOLVE_INTERVAL_UNIT * (1 << MIN_REPLACEMENT_INTERVAL)) {
+  now = SCH_GetLastEventMonoTime();
+  if (now < next_replacement) {
    DEBUG_LOG("replacement postponed");
    return;
  }
-  last_replacement = now;

-  resolve_source_replacement(record);
+  UTI_GetRandomBytes(&rnd, sizeof (rnd));
+  next_replacement = now + ((double)rnd / (uint32_t)-1) *
+                     (RESOLVE_INTERVAL_UNIT * (1 << MAX_REPLACEMENT_INTERVAL));
+
+  resolve_source_replacement(record, 0);
+}
+
+/* ================================================== */
+
+static void
+maybe_refresh_source(void)
+{
+  static double last_refreshment = 0.0;
+  SourceRecord *record, *oldest_record;
+  int i, min_interval;
+  double now;
+
+  min_interval = CNF_GetRefresh();
+
+  now = SCH_GetLastEventMonoTime();
+  if (min_interval <= 0 || now < last_refreshment + min_interval)
+    return;
+
+  last_refreshment = now;
+
+  for (i = 0, oldest_record = NULL; i < ARR_GetSize(records); i++) {
+    record = get_record(i);
+    if (!record->remote_addr || UTI_IsStringIP(record->name))
+      continue;
+
+    if (!oldest_record || oldest_record->last_resolving > record->last_resolving)
+      oldest_record = record;
+  }
+
+  if (!oldest_record)
+    return;
+
+  /* Check if the name wasn't already resolved in the last interval */
+  if (now < oldest_record->last_resolving + min_interval) {
+    last_refreshment = oldest_record->last_resolving;
+    return;
+  }
+
+  resolve_source_replacement(oldest_record, 1);
 }

 /* ================================================== */
@@ -927,10 +1164,10 @@ NSR_RefreshAddresses(void)

  for (i = 0; i < ARR_GetSize(records); i++) {
    record = get_record(i);
-    if (!record->remote_addr || !record->name)
+    if (!record->remote_addr)
      continue;

-    resolve_source_replacement(record);
+    resolve_source_replacement(record, 1);
  }
 }

@@ -939,10 +1176,28 @@ NSR_RefreshAddresses(void)
 NSR_Status
 NSR_UpdateSourceNtpAddress(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr)
 {
-  if (new_addr->ip_addr.family == IPADDR_UNSPEC)
+  int slot;
+
+  if (!UTI_IsIPReal(&old_addr->ip_addr) || !UTI_IsIPReal(&new_addr->ip_addr))
    return NSR_InvalidAF;

-  return change_source_address(old_addr, new_addr, 0);
+  if (UTI_CompareIPs(&old_addr->ip_addr, &new_addr->ip_addr, NULL) != 0 &&
+      find_slot(&new_addr->ip_addr, &slot))
+    return NSR_AlreadyInUse;
+
+  /* If a record is being modified (e.g. by change_source_address(), or the
+     source is just being created), postpone the change to avoid corruption */
+
+  if (!record_lock)
+    return change_source_address(old_addr, new_addr, 0);
+
+  if (UTI_IsIPReal(&saved_address_update.old_address.ip_addr))
+    return NSR_TooManySources;
+
+  saved_address_update.old_address = *old_addr;
+  saved_address_update.new_address = *new_addr;
+
+  return NSR_Success;
 }

 /* ================================================== */
@@ -991,17 +1246,12 @@ NSR_GetLocalRefid(IPAddr *address)
 char *
 NSR_GetName(IPAddr *address)
 {
-  SourceRecord *record;
  int slot;

  if (!find_slot(address, &slot))
-    return 0;
+    return NULL;

-  record = get_record(slot);
-  if (record->name)
-    return record->name;
-
-  return UTI_IPToString(&record->remote_addr->ip_addr); 
+  return get_record(slot)->name;
 }

 /* ================================================== */
@@ -1018,8 +1268,10 @@ NSR_ProcessRx(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,

  assert(initialised);

-  /* Must match IP address AND port number */
-  if (find_slot2(remote_addr, &slot) == 2) {
+  /* Avoid unnecessary lookup if the packet cannot be a response from our
+     source.  Otherwise, it must match both IP address and port number. */
+  if (NTP_LVM_TO_MODE(message->lvm) != MODE_CLIENT &&
+      find_slot2(remote_addr, &slot) == 2) {
    record = get_record(slot);

    if (!NCR_ProcessRxKnown(record->data, local_addr, rx_ts, message, length))
@@ -1041,6 +1293,8 @@ NSR_ProcessRx(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
          remove_pool_sources(record->pool_id, 1, 0);
      }
    }
+
+    maybe_refresh_source();
  } else {
    NCR_ProcessRxUnknown(remote_addr, local_addr, rx_ts, message, length);
  }
@@ -1055,8 +1309,10 @@ NSR_ProcessTx(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
  SourceRecord *record;
  int slot;

-  /* Must match IP address AND port number */
-  if (find_slot2(remote_addr, &slot) == 2) {
+  /* Avoid unnecessary lookup if the packet cannot be a request to our
+     source.  Otherwise, it must match both IP address and port number. */
+  if (NTP_LVM_TO_MODE(message->lvm) != MODE_SERVER &&
+      find_slot2(remote_addr, &slot) == 2) {
    record = get_record(slot);
    NCR_ProcessTxKnown(record->data, local_addr, tx_ts, message, length);
  } else {
@@ -1214,6 +1470,20 @@ NSR_ModifyMinstratum(IPAddr *address, int new_min_stratum)

 /* ================================================== */

+int
+NSR_ModifyOffset(IPAddr *address, double new_offset)
+{
+  int slot;
+
+  if (!find_slot(address, &slot))
+    return 0;
+
+  NCR_ModifyOffset(get_record(slot)->data, new_offset);
+  return 1;
+}
+
+/* ================================================== */
+
 int
 NSR_ModifyPolltarget(IPAddr *address, int new_poll_target)
 {
--- a/ntp_sources.h
+++ b/ntp_sources.h
@@ -55,11 +55,16 @@ extern NSR_Status NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type

 /* Procedure to add a new server, peer source, or pool of servers specified by
   name instead of address.  The name is resolved in exponentially increasing
-   intervals until it succeeds or fails with a non-temporary error.  If the
-   name is an address, it is equivalent to NSR_AddSource(). */
-extern NSR_Status NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
+   intervals until it succeeds or fails with a non-temporary error.  The
+   specified family filters resolved addresses.  If the name is an address
+   and its family does not conflict with the specified family, it is equivalent
+   to NSR_AddSource(). */
+extern NSR_Status NSR_AddSourceByName(char *name, int family, int port, int pool,
+                                      NTP_Source_Type type,
                                      SourceParameters *params, uint32_t *conf_id);

+extern const char *NSR_StatusToString(NSR_Status status);
+
 /* Function type for handlers to be called back when an attempt
 * (possibly unsuccessful) to resolve unresolved sources ends */
 typedef void (*NSR_SourceResolvingEndHandler)(void);
@@ -91,15 +96,16 @@ extern void NSR_HandleBadSource(IPAddr *address);
 /* Procedure to resolve all names again */
 extern void NSR_RefreshAddresses(void);

-/* Procedure to update the address of a source */
+/* Procedure to update the address of a source.  The update may be
+   postponed. */
 extern NSR_Status NSR_UpdateSourceNtpAddress(NTP_Remote_Address *old_addr,
                                             NTP_Remote_Address *new_addr);

 /* Procedure to get local reference ID corresponding to a source */
 extern uint32_t NSR_GetLocalRefid(IPAddr *address);

-/* Procedure to get the name of a source.  If the source doesn't have a name,
-   it returns a temporary string containing formatted address. */
+/* Procedure to get the name of a source as it was specified (it may be
+   an IP address) */
 extern char *NSR_GetName(IPAddr *address);

 /* This routine is called by ntp_io when a new packet arrives off the network */
@@ -134,6 +140,8 @@ extern int NSR_ModifyMaxdelaydevratio(IPAddr *address, double new_max_delay_rati

 extern int NSR_ModifyMinstratum(IPAddr *address, int new_min_stratum);

+extern int NSR_ModifyOffset(IPAddr *address, double new_offset);
+
 extern int NSR_ModifyPolltarget(IPAddr *address, int new_poll_target);

 extern int NSR_InitiateSampleBurst(int n_good_samples, int n_total_samples, IPAddr *mask, IPAddr *address);
--- a/nts_ke.h
+++ b/nts_ke.h
@@ -40,6 +40,7 @@
 #define NKE_RECORD_COOKIE               5
 #define NKE_RECORD_NTPV4_SERVER_NEGOTIATION 6
 #define NKE_RECORD_NTPV4_PORT_NEGOTIATION 7
+#define NKE_RECORD_COMPLIANT_128GCM_EXPORT 1024

 #define NKE_NEXT_PROTOCOL_NTPV4         0

@@ -49,8 +50,6 @@

 #define NKE_ALPN_NAME                   "ntske/1"
 #define NKE_EXPORTER_LABEL              "EXPORTER-network-time-security"
-#define NKE_EXPORTER_CONTEXT_C2S        "\x0\x0\x0\xf\x0"
-#define NKE_EXPORTER_CONTEXT_S2C        "\x0\x0\x0\xf\x1"

 #define NKE_MAX_MESSAGE_LENGTH          16384
 #define NKE_MAX_RECORD_BODY_LENGTH      256
--- a/nts_ke_client.c
+++ b/nts_ke_client.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020-2021, 2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -44,22 +44,25 @@
 struct NKC_Instance_Record {
  char *name;
  IPSockAddr address;
+  NKSN_Credentials credentials;
  NKSN_Instance session;
  int destroying;
  int got_response;
  int resolving_name;

+  int compliant_128gcm;
  NKE_Context context;
+  NKE_Context alt_context;
  NKE_Cookie cookies[NKE_MAX_COOKIES];
  int num_cookies;
-  char server_name[NKE_MAX_RECORD_BODY_LENGTH + 1];
+  char server_name[NKE_MAX_RECORD_BODY_LENGTH + 2];
  IPSockAddr ntp_address;
 };

 /* ================================================== */

-static void *client_credentials = NULL;
-static int client_credentials_refs = 0;
+static NKSN_Credentials default_credentials = NULL;
+static int default_credentials_refs = 0;

 /* ================================================== */

@@ -97,22 +100,39 @@ name_resolve_handler(DNS_Status status, int n_addrs, IPAddr *ip_addrs, void *arg

 /* ================================================== */

+#define MAX_AEAD_ALGORITHMS 4
+
 static int
 prepare_request(NKC_Instance inst)
 {
  NKSN_Instance session = inst->session;
-  uint16_t datum;
+  uint16_t data[MAX_AEAD_ALGORITHMS];
+  int i, aead_algorithm, length;

  NKSN_BeginMessage(session);

-  datum = htons(NKE_NEXT_PROTOCOL_NTPV4);
-  if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
+  data[0] = htons(NKE_NEXT_PROTOCOL_NTPV4);
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, data, sizeof (data[0])))
    return 0;

-  datum = htons(AEAD_AES_SIV_CMAC_256);
-  if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
+  for (i = length = 0; i < ARR_GetSize(CNF_GetNtsAeads()) && length < MAX_AEAD_ALGORITHMS;
+       i++) {
+    aead_algorithm = *(int *)ARR_GetElement(CNF_GetNtsAeads(), i);
+    if (SIV_GetKeyLength(aead_algorithm) > 0)
+      data[length++] = htons(aead_algorithm);
+  }
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, data,
+                      length * sizeof (data[0])))
    return 0;

+  for (i = 0; i < length; i++) {
+    if (data[i] == htons(AEAD_AES_128_GCM_SIV)) {
+      if (!NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0))
+        return 0;
+      break;
+    }
+  }
+
  if (!NKSN_EndMessage(session))
    return 0;

@@ -126,11 +146,14 @@ process_response(NKC_Instance inst)
 {
  int next_protocol = -1, aead_algorithm = -1, error = 0;
  int i, critical, type, length;
-  uint16_t data[NKE_MAX_COOKIE_LENGTH / sizeof (uint16_t)];
+  uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];

-  assert(NKE_MAX_COOKIE_LENGTH % sizeof (uint16_t) == 0);
+  assert(NKE_MAX_COOKIE_LENGTH <= NKE_MAX_RECORD_BODY_LENGTH);
+  assert(sizeof (data) % sizeof (uint16_t) == 0);
  assert(sizeof (uint16_t) == 2);

+  inst->compliant_128gcm = 0;
+  inst->alt_context.algorithm = AEAD_SIV_INVALID;
  inst->num_cookies = 0;
  inst->ntp_address.ip_addr.family = IPADDR_UNSPEC;
  inst->ntp_address.port = 0;
@@ -140,6 +163,13 @@ process_response(NKC_Instance inst)
    if (!NKSN_GetRecord(inst->session, &critical, &type, &length, &data, sizeof (data)))
      break;

+    if (length > sizeof (data)) {
+      DEBUG_LOG("Record too long type=%d length=%d critical=%d", type, length, critical);
+      if (critical)
+        error = 1;
+      continue;
+    }
+
    switch (type) {
      case NKE_RECORD_NEXT_PROTOCOL:
        if (!critical || length != 2 || ntohs(data[0]) != NKE_NEXT_PROTOCOL_NTPV4) {
@@ -150,13 +180,31 @@ process_response(NKC_Instance inst)
        next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
        break;
      case NKE_RECORD_AEAD_ALGORITHM:
-        if (length != 2 || ntohs(data[0]) != AEAD_AES_SIV_CMAC_256) {
-          DEBUG_LOG("Unexpected NTS-KE AEAD algorithm");
+        if (length != 2) {
+          DEBUG_LOG("Unexpected AEAD algorithm");
          error = 1;
          break;
        }
-        aead_algorithm = AEAD_AES_SIV_CMAC_256;
-        inst->context.algorithm = aead_algorithm;
+        for (i = 0; i < ARR_GetSize(CNF_GetNtsAeads()); i++) {
+          if (ntohs(data[0]) == *(int *)ARR_GetElement(CNF_GetNtsAeads(), i) &&
+              SIV_GetKeyLength(ntohs(data[0])) > 0) {
+            aead_algorithm = ntohs(data[0]);
+            inst->context.algorithm = aead_algorithm;
+          }
+        }
+        if (aead_algorithm < 0) {
+          DEBUG_LOG("Unexpected AEAD algorithm");
+          error = 1;
+        }
+        break;
+      case NKE_RECORD_COMPLIANT_128GCM_EXPORT:
+        if (length != 0) {
+          DEBUG_LOG("Non-empty compliant-128gcm record");
+          error = 1;
+          break;
+        }
+        DEBUG_LOG("Compliant AES-128-GCM-SIV export");
+        inst->compliant_128gcm = 1;
        break;
      case NKE_RECORD_ERROR:
        if (length == 2)
@@ -196,7 +244,7 @@ process_response(NKC_Instance inst)
        inst->server_name[length] = '\0';

        /* Make sure the name is printable and has no spaces */
-        for (i = 0; i < length && isgraph(inst->server_name[i]); i++)
+        for (i = 0; i < length && isgraph((unsigned char)inst->server_name[i]); i++)
          ;
        if (i != length) {
          DEBUG_LOG("Invalid server name");
@@ -227,7 +275,7 @@ process_response(NKC_Instance inst)

  if (error || inst->num_cookies == 0 ||
      next_protocol != NKE_NEXT_PROTOCOL_NTPV4 ||
-      aead_algorithm != AEAD_AES_SIV_CMAC_256)
+      aead_algorithm < 0)
    return 0;

  return 1;
@@ -238,6 +286,7 @@ process_response(NKC_Instance inst)
 static int
 handle_message(void *arg)
 {
+  SIV_Algorithm exporter_algorithm;
  NKC_Instance inst = arg;

  if (!process_response(inst)) {
@@ -245,14 +294,42 @@ handle_message(void *arg)
    return 0;
  }

-  if (!NKSN_GetKeys(inst->session, inst->context.algorithm,
-                    &inst->context.c2s, &inst->context.s2c))
+  exporter_algorithm = inst->context.algorithm;
+
+  /* With AES-128-GCM-SIV, set the algorithm ID in the RFC5705 key exporter
+     context incorrectly for compatibility with older chrony servers unless
+     the server confirmed support for the compliant context.  Generate both
+     sets of keys in case the server uses the compliant context, but does not
+     support the negotiation record, assuming it will respond with an NTS NAK
+     to a request authenticated with the noncompliant key. */
+  if (exporter_algorithm == AEAD_AES_128_GCM_SIV && !inst->compliant_128gcm) {
+    inst->alt_context.algorithm = inst->context.algorithm;
+    if (!NKSN_GetKeys(inst->session, inst->alt_context.algorithm, exporter_algorithm,
+                      NKE_NEXT_PROTOCOL_NTPV4, &inst->alt_context.c2s, &inst->alt_context.s2c))
+      return 0;
+
+    exporter_algorithm = AEAD_AES_SIV_CMAC_256;
+  }
+
+  if (!NKSN_GetKeys(inst->session, inst->context.algorithm, exporter_algorithm,
+                    NKE_NEXT_PROTOCOL_NTPV4, &inst->context.c2s, &inst->context.s2c))
    return 0;

  if (inst->server_name[0] != '\0') {
    if (inst->resolving_name)
      return 0;
    if (!UTI_StringToIP(inst->server_name, &inst->ntp_address.ip_addr)) {
+      int length = strlen(inst->server_name);
+
+      /* Add a trailing dot if not present to force the name to be
+         resolved as a fully qualified domain name */
+      if (length < 1 || length + 1 >= sizeof (inst->server_name))
+        return 0;
+      if (inst->server_name[length - 1] != '.') {
+        inst->server_name[length] = '.';
+        inst->server_name[length + 1] = '\0';
+      }
+
      DNS_Name2IPAddressAsync(inst->server_name, name_resolve_handler, inst);
      inst->resolving_name = 1;
    }
@@ -266,9 +343,12 @@ handle_message(void *arg)
 /* ================================================== */

 NKC_Instance
-NKC_CreateInstance(IPSockAddr *address, const char *name)
+NKC_CreateInstance(IPSockAddr *address, const char *name, uint32_t cert_set)
 {
+  const char **trusted_certs;
+  uint32_t *certs_ids;
  NKC_Instance inst;
+  int n_certs;

  inst = MallocNew(struct NKC_Instance_Record);

@@ -279,10 +359,21 @@ NKC_CreateInstance(IPSockAddr *address, const char *name)
  inst->destroying = 0;
  inst->got_response = 0;

-  /* Share the credentials with other client instances */
-  if (!client_credentials)
-    client_credentials = NKSN_CreateCertCredentials(NULL, NULL, CNF_GetNtsTrustedCertFile());
-  client_credentials_refs++;
+  n_certs = CNF_GetNtsTrustedCertsPaths(&trusted_certs, &certs_ids);
+
+  /* Share the credentials among clients using the default set of trusted
+     certificates, which likely contains most certificates */
+  if (cert_set == 0) {
+    if (!default_credentials)
+      default_credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
+                                                             n_certs, cert_set);
+    inst->credentials = default_credentials;
+    if (default_credentials)
+      default_credentials_refs++;
+  } else {
+    inst->credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
+                                                         n_certs, cert_set);
+  }

  return inst;
 }
@@ -296,10 +387,16 @@ NKC_DestroyInstance(NKC_Instance inst)

  Free(inst->name);

-  client_credentials_refs--;
-  if (client_credentials_refs <= 0 && client_credentials) {
-    NKSN_DestroyCertCredentials(client_credentials);
-    client_credentials = NULL;
+  if (inst->credentials) {
+    if (inst->credentials == default_credentials) {
+      default_credentials_refs--;
+      if (default_credentials_refs <= 0) {
+        NKSN_DestroyCertCredentials(default_credentials);
+        default_credentials = NULL;
+      }
+    } else {
+      NKSN_DestroyCertCredentials(inst->credentials);
+    }
  }

  /* If the asynchronous resolver is running, let the handler free
@@ -325,27 +422,36 @@ NKC_Start(NKC_Instance inst)

  inst->got_response = 0;

-  if (!client_credentials) {
+  if (!inst->credentials) {
    DEBUG_LOG("Missing client credentials");
    return 0;
  }

+  /* Don't try to connect if missing the algorithm which all servers
+     are required to support */
+  if (SIV_GetKeyLength(AEAD_AES_SIV_CMAC_256) <= 0) {
+    LOG(LOGS_ERR, "Missing AES-SIV-CMAC-256");
+    return 0;
+  }
+
  /* Follow the bindacqaddress and bindacqdevice settings */
  CNF_GetBindAcquisitionAddress(inst->address.ip_addr.family, &local_addr.ip_addr);
  local_addr.port = 0;
  iface = CNF_GetBindAcquisitionInterface();

-  sock_fd = SCK_OpenTcpSocket(&inst->address, &local_addr, iface, 0);
-  if (sock_fd < 0)
-    return 0;
-
  /* Make a label containing both the address and name of the server */
  if (snprintf(label, sizeof (label), "%s (%s)",
               UTI_IPSockAddrToString(&inst->address), inst->name) >= sizeof (label))
    ;

+  sock_fd = SCK_OpenTcpSocket(&inst->address, &local_addr, iface, 0);
+  if (sock_fd < 0) {
+    LOG(LOGS_ERR, "Could not connect to %s", label);
+    return 0;
+  }
+
  /* Start an NTS-KE session */
-  if (!NKSN_StartSession(inst->session, sock_fd, label, client_credentials, CLIENT_TIMEOUT)) {
+  if (!NKSN_StartSession(inst->session, sock_fd, label, inst->credentials, CLIENT_TIMEOUT)) {
    SCK_CloseSocket(sock_fd);
    return 0;
  }
@@ -371,7 +477,7 @@ NKC_IsActive(NKC_Instance inst)
 /* ================================================== */

 int
-NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
+NKC_GetNtsData(NKC_Instance inst, NKE_Context *context, NKE_Context *alt_context,
               NKE_Cookie *cookies, int *num_cookies, int max_cookies,
               IPSockAddr *ntp_address)
 {
@@ -381,6 +487,7 @@ NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
    return 0;

  *context = inst->context;
+  *alt_context = inst->alt_context;

  for (i = 0; i < inst->num_cookies && i < max_cookies; i++)
    cookies[i] = inst->cookies[i];
--- a/nts_ke_client.h
+++ b/nts_ke_client.h
@@ -33,7 +33,7 @@
 typedef struct NKC_Instance_Record *NKC_Instance;

 /* Create a client NTS-KE instance */
-extern NKC_Instance NKC_CreateInstance(IPSockAddr *address, const char *name);
+extern NKC_Instance NKC_CreateInstance(IPSockAddr *address, const char *name, uint32_t cert_set);

 /* Destroy an instance */
 extern void NKC_DestroyInstance(NKC_Instance inst);
@@ -46,7 +46,7 @@ extern int NKC_Start(NKC_Instance inst);
 extern int NKC_IsActive(NKC_Instance inst);

 /* Get the NTS data if the session was successful */
-extern int NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
+extern int NKC_GetNtsData(NKC_Instance inst, NKE_Context *context, NKE_Context *alt_context,
                          NKE_Cookie *cookies, int *num_cookies, int max_cookies,
                          IPSockAddr *ntp_address);

--- a/nts_ke_server.c
+++ b/nts_ke_server.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020, 2022, 2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -47,31 +47,33 @@

 #define SERVER_TIMEOUT 2.0

-#define SERVER_COOKIE_SIV AEAD_AES_SIV_CMAC_256
-#define SERVER_COOKIE_NONCE_LENGTH 16
+#define MAX_COOKIE_NONCE_LENGTH 16

 #define KEY_ID_INDEX_BITS 2
 #define MAX_SERVER_KEYS (1U << KEY_ID_INDEX_BITS)
 #define FUTURE_KEYS 1

 #define DUMP_FILENAME "ntskeys"
-#define DUMP_IDENTIFIER "NKS0\n"
+#define DUMP_IDENTIFIER "NKS1\n"
+#define OLD_DUMP_IDENTIFIER "NKS0\n"

 #define INVALID_SOCK_FD (-7)

 typedef struct {
  uint32_t key_id;
-  unsigned char nonce[SERVER_COOKIE_NONCE_LENGTH];
 } ServerCookieHeader;

 typedef struct {
  uint32_t id;
  unsigned char key[SIV_MAX_KEY_LENGTH];
+  SIV_Algorithm siv_algorithm;
  SIV_Instance siv;
+  int nonce_length;
 } ServerKey;

 typedef struct {
  uint32_t key_id;
+  uint32_t siv_algorithm;
  unsigned char key[SIV_MAX_KEY_LENGTH];
  IPAddr client_addr;
  uint16_t client_port;
@@ -95,7 +97,7 @@ static int initialised = 0;

 /* Array of NKSN instances */
 static ARR_Instance sessions;
-static void *server_credentials;
+static NKSN_Credentials server_credentials;

 /* ================================================== */

@@ -148,12 +150,30 @@ handle_client(int sock_fd, IPSockAddr *addr)

 /* ================================================== */

+static void
+update_key_siv(ServerKey *key, SIV_Algorithm algorithm)
+{
+  if (!key->siv || key->siv_algorithm != algorithm) {
+    if (key->siv)
+      SIV_DestroyInstance(key->siv);
+    key->siv_algorithm = algorithm;
+    key->siv = SIV_CreateInstance(algorithm);
+    key->nonce_length = MIN(SIV_GetMaxNonceLength(key->siv), MAX_COOKIE_NONCE_LENGTH);
+  }
+
+  if (!key->siv || !SIV_SetKey(key->siv, key->key, SIV_GetKeyLength(key->siv_algorithm)))
+    LOG_FATAL("Could not set SIV key");
+}
+
+/* ================================================== */
+
 static void
 handle_helper_request(int fd, int event, void *arg)
 {
  SCK_Message *message;
  HelperRequest *req;
  IPSockAddr client_addr;
+  ServerKey *key;
  int sock_fd;

  /* Receive the helper request with the NTS-KE session socket.
@@ -181,16 +201,14 @@ handle_helper_request(int fd, int event, void *arg)
  req = message->data;

  /* Extract the current server key and client address from the request */
-  server_keys[current_server_key].id = ntohl(req->key_id);
-  assert(sizeof (server_keys[current_server_key].key) == sizeof (req->key));
-  memcpy(server_keys[current_server_key].key, req->key,
-         sizeof (server_keys[current_server_key].key));
+  key = &server_keys[current_server_key];
+  key->id = ntohl(req->key_id);
+  assert(sizeof (key->key) == sizeof (req->key));
+  memcpy(key->key, req->key, sizeof (key->key));
  UTI_IPNetworkToHost(&req->client_addr, &client_addr.ip_addr);
  client_addr.port = ntohs(req->client_port);

-  if (!SIV_SetKey(server_keys[current_server_key].siv, server_keys[current_server_key].key,
-                  SIV_GetKeyLength(SERVER_COOKIE_SIV)))
-    LOG_FATAL("Could not set SIV key");
+  update_key_siv(key, ntohl(req->siv_algorithm));

  if (!handle_client(sock_fd, &client_addr)) {
    SCK_CloseSocket(sock_fd);
@@ -224,7 +242,7 @@ accept_connection(int listening_fd, int event, void *arg)
  SCH_GetLastEventTime(&now, NULL, NULL);

  log_index = CLG_LogServiceAccess(CLG_NTSKE, &addr.ip_addr, &now);
-  if (log_index >= 0 && CLG_LimitServiceRate(CLG_NTSKE, log_index)) {
+  if (log_index >= 0 && CLG_LimitServiceRate(CLG_NTSKE, log_index) != CLG_PASS) {
    DEBUG_LOG("Rejected connection from %s (%s)",
              UTI_IPSockAddrToString(&addr), "rate limit");
    SCK_CloseSocket(sock_fd);
@@ -240,6 +258,7 @@ accept_connection(int listening_fd, int event, void *arg)

    /* Include the current server key and client address in the request */
    req.key_id = htonl(server_keys[current_server_key].id);
+    req.siv_algorithm = htonl(server_keys[current_server_key].siv_algorithm);
    assert(sizeof (req.key) == sizeof (server_keys[current_server_key].key));
    memcpy(req.key, server_keys[current_server_key].key, sizeof (req.key));
    UTI_IPHostToNetwork(&addr.ip_addr, &req.client_addr);
@@ -318,8 +337,10 @@ helper_signal(int x)
 /* ================================================== */

 static int
-prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm)
+prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm,
+                 int compliant_128gcm)
 {
+  SIV_Algorithm exporter_algorithm;
  NKE_Context context;
  NKE_Cookie cookie;
  char *ntp_server;
@@ -352,6 +373,11 @@ prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_a
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
      return 0;

+    if (aead_algorithm == AEAD_AES_128_GCM_SIV && compliant_128gcm) {
+      if (!NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0))
+        return 0;
+    }
+
    if (CNF_GetNTPPort() != NTP_PORT) {
      datum = htons(CNF_GetNTPPort());
      if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_PORT_NEGOTIATION, &datum, sizeof (datum)))
@@ -366,8 +392,16 @@ prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_a
    }

    context.algorithm = aead_algorithm;
+    exporter_algorithm = aead_algorithm;

-    if (!NKSN_GetKeys(session, aead_algorithm, &context.c2s, &context.s2c))
+    /* With AES-128-GCM-SIV, set the algorithm ID in the RFC5705 key exporter
+       context incorrectly for compatibility with older chrony clients unless
+       the client requested the compliant context */
+    if (exporter_algorithm == AEAD_AES_128_GCM_SIV && !compliant_128gcm)
+      exporter_algorithm = AEAD_AES_SIV_CMAC_256;
+
+    if (!NKSN_GetKeys(session, aead_algorithm, exporter_algorithm,
+                      NKE_NEXT_PROTOCOL_NTPV4, &context.c2s, &context.s2c))
      return 0;

    for (i = 0; i < NKE_MAX_COOKIES; i++) {
@@ -392,7 +426,8 @@ process_request(NKSN_Instance session)
  int next_protocol_records = 0, aead_algorithm_records = 0;
  int next_protocol_values = 0, aead_algorithm_values = 0;
  int next_protocol = -1, aead_algorithm = -1, error = -1;
-  int i, critical, type, length;
+  int i, j, critical, type, length;
+  int compliant_128gcm = 0;
  uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];

  assert(NKE_MAX_RECORD_BODY_LENGTH % sizeof (uint16_t) == 0);
@@ -427,10 +462,21 @@ process_request(NKSN_Instance session)

        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
          aead_algorithm_values++;
-          if (ntohs(data[i]) == AEAD_AES_SIV_CMAC_256)
-            aead_algorithm = AEAD_AES_SIV_CMAC_256;
+          /* Use the first enabled and supported algorithm */
+          for (j = 0; j < ARR_GetSize(CNF_GetNtsAeads()); j++) {
+            if (ntohs(data[i]) == *(int *)ARR_GetElement(CNF_GetNtsAeads(), j) &&
+                aead_algorithm < 0 && SIV_GetKeyLength(ntohs(data[i])) > 0)
+              aead_algorithm = ntohs(data[i]);
+          }
        }
        break;
+      case NKE_RECORD_COMPLIANT_128GCM_EXPORT:
+        if (length != 0) {
+          error = NKE_ERROR_BAD_REQUEST;
+          break;
+        }
+        compliant_128gcm = 1;
+        break;
      case NKE_RECORD_ERROR:
      case NKE_RECORD_WARNING:
      case NKE_RECORD_COOKIE:
@@ -449,7 +495,7 @@ process_request(NKSN_Instance session)
      error = NKE_ERROR_BAD_REQUEST;
  }

-  if (!prepare_response(session, error, next_protocol, aead_algorithm))
+  if (!prepare_response(session, error, next_protocol, aead_algorithm, compliant_128gcm))
    return 0;

  return 1;
@@ -470,28 +516,37 @@ handle_message(void *arg)
 static void
 generate_key(int index)
 {
+  SIV_Algorithm algorithm;
+  ServerKey *key;
  int key_length;

-  if (index < 0 || index >= MAX_SERVER_KEYS)
-    assert(0);
+  BRIEF_ASSERT(index >= 0 && index < MAX_SERVER_KEYS);

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
-  if (key_length > sizeof (server_keys[index].key))
-    assert(0);
+  /* Prefer AES-128-GCM-SIV if available.  Note that if older keys loaded
+     from ntsdumpdir use a different algorithm, responding to NTP requests
+     with cookies encrypted with those keys will not work if the new algorithm
+     produces longer cookies (i.e. response would be longer than request).
+     Switching from AES-SIV-CMAC-256 to AES-128-GCM-SIV is ok. */
+  algorithm = SIV_GetKeyLength(AEAD_AES_128_GCM_SIV) > 0 ?
+              AEAD_AES_128_GCM_SIV : AEAD_AES_SIV_CMAC_256;

-  UTI_GetRandomBytesUrandom(server_keys[index].key, key_length);
+  key = &server_keys[index];

-  if (!server_keys[index].siv ||
-      !SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
-    LOG_FATAL("Could not set SIV key");
+  key_length = SIV_GetKeyLength(algorithm);
+  BRIEF_ASSERT(key_length <= sizeof (key->key));

-  UTI_GetRandomBytes(&server_keys[index].id, sizeof (server_keys[index].id));
+  UTI_GetRandomBytesUrandom(key->key, key_length);
+  if (key_length < sizeof (key->key))
+    memset(key->key + key_length, 0, sizeof (key->key) - key_length);
+  UTI_GetRandomBytes(&key->id, sizeof (key->id));

  /* Encode the index in the lowest bits of the ID */
-  server_keys[index].id &= -1U << KEY_ID_INDEX_BITS;
-  server_keys[index].id |= index;
+  key->id &= -1U << KEY_ID_INDEX_BITS;
+  key->id |= index;

-  DEBUG_LOG("Generated server key %"PRIX32, server_keys[index].id);
+  update_key_siv(key, algorithm);
+
+  DEBUG_LOG("Generated key %08"PRIX32" (%d)", key->id, (int)key->siv_algorithm);

  last_server_key_ts = SCH_GetLastEventMonoTime();
 }
@@ -519,18 +574,19 @@ save_keys(void)
  if (!f)
    return;

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
  last_key_age = SCH_GetLastEventMonoTime() - last_server_key_ts;

-  if (fprintf(f, "%s%d %.1f\n", DUMP_IDENTIFIER, SERVER_COOKIE_SIV, last_key_age) < 0)
+  if (fprintf(f, "%s%.1f\n", DUMP_IDENTIFIER, last_key_age) < 0)
    goto error;

  for (i = 0; i < MAX_SERVER_KEYS; i++) {
    index = (current_server_key + i + 1 + FUTURE_KEYS) % MAX_SERVER_KEYS;
+    key_length = SIV_GetKeyLength(server_keys[index].siv_algorithm);

    if (key_length > sizeof (server_keys[index].key) ||
        !UTI_BytesToHex(server_keys[index].key, key_length, buf, sizeof (buf)) ||
-        fprintf(f, "%08"PRIX32" %s\n", server_keys[index].id, buf) < 0)
+        fprintf(f, "%08"PRIX32" %s %d\n", server_keys[index].id, buf,
+                (int)server_keys[index].siv_algorithm) < 0)
      goto error;
  }

@@ -545,7 +601,7 @@ save_keys(void)
  return;

 error:
-  DEBUG_LOG("Could not %s server keys", "save");
+  LOG(LOGS_ERR, "Could not %s %s", "save", "server NTS keys");
  fclose(f);

  if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, NULL))
@@ -554,64 +610,80 @@ error:

 /* ================================================== */

-#define MAX_WORDS 2
+#define MAX_WORDS 3

-static void
+static int
 load_keys(void)
 {
+  int i, index, key_length, algorithm = 0, old_ver;
  char *dump_dir, line[1024], *words[MAX_WORDS];
-  unsigned char key[SIV_MAX_KEY_LENGTH];
-  int i, index, key_length, algorithm;
+  ServerKey new_keys[MAX_SERVER_KEYS];
  double key_age;
  FILE *f;
-  uint32_t id;

  dump_dir = CNF_GetNtsDumpDir();
  if (!dump_dir)
-    return;
+    return 0;

  f = UTI_OpenFile(dump_dir, DUMP_FILENAME, NULL, 'r', 0);
  if (!f)
-    return;
+    return 0;

-  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
-      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
-        sscanf(words[0], "%d", &algorithm) != 1 || algorithm != SERVER_COOKIE_SIV ||
-        sscanf(words[1], "%lf", &key_age) != 1)
+  if (!fgets(line, sizeof (line), f) ||
+      (strcmp(line, DUMP_IDENTIFIER) != 0 && strcmp(line, OLD_DUMP_IDENTIFIER) != 0))
    goto error;

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
-  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);
+  old_ver = strcmp(line, DUMP_IDENTIFIER) != 0;
+
+  if (!fgets(line, sizeof (line), f) ||
+      UTI_SplitString(line, words, MAX_WORDS) != (old_ver ? 2 : 1) ||
+      (old_ver && sscanf(words[0], "%d", &algorithm) != 1) ||
+      sscanf(words[old_ver ? 1 : 0], "%lf", &key_age) != 1)
+    goto error;

  for (i = 0; i < MAX_SERVER_KEYS && fgets(line, sizeof (line), f); i++) {
-    if (UTI_SplitString(line, words, MAX_WORDS) != 2 ||
-        sscanf(words[0], "%"PRIX32, &id) != 1)
+    if (UTI_SplitString(line, words, MAX_WORDS) != (old_ver ? 2 : 3) ||
+        sscanf(words[0], "%"PRIX32, &new_keys[i].id) != 1 ||
+        (!old_ver && sscanf(words[2], "%d", &algorithm) != 1))
      goto error;

-    if (UTI_HexToBytes(words[1], key, sizeof (key)) != key_length)
+    new_keys[i].siv_algorithm = algorithm;
+    key_length = SIV_GetKeyLength(algorithm);
+
+    if ((i > 0 && (new_keys[i].id - new_keys[i - 1].id) % MAX_SERVER_KEYS != 1) ||
+        key_length <= 0 ||
+        UTI_HexToBytes(words[1], new_keys[i].key, sizeof (new_keys[i].key)) != key_length)
      goto error;
-
-    index = id % MAX_SERVER_KEYS;
-
-    server_keys[index].id = id;
-    assert(sizeof (server_keys[index].key) == sizeof (key));
-    memcpy(server_keys[index].key, key, key_length);
-
-    if (!SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
-      LOG_FATAL("Could not set SIV key");
-
-    DEBUG_LOG("Loaded key %"PRIX32, id);
-
-    current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
+    memset(new_keys[i].key + key_length, 0, sizeof (new_keys[i].key) - key_length);
  }

+  if (i < MAX_SERVER_KEYS)
+    goto error;
+
+  for (i = 0; i < MAX_SERVER_KEYS; i++) {
+    index = new_keys[i].id % MAX_SERVER_KEYS;
+    server_keys[index].id = new_keys[i].id;
+    memcpy(server_keys[index].key, new_keys[i].key, sizeof (server_keys[index].key));
+
+    update_key_siv(&server_keys[index], new_keys[i].siv_algorithm);
+
+    DEBUG_LOG("Loaded key %08"PRIX32" (%d)",
+              server_keys[index].id, (int)server_keys[index].siv_algorithm);
+  }
+
+  current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
+  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);
+
  fclose(f);

-  return;
+  LOG(LOGS_INFO, "Loaded %s", "server NTS keys");
+  return 1;

 error:
-  DEBUG_LOG("Could not %s server keys", "load");
+  LOG(LOGS_ERR, "Could not %s %s", "load", "server NTS keys");
  fclose(f);
+
+  return 0;
 }

 /* ================================================== */
@@ -629,7 +701,7 @@ key_timeout(void *arg)
 /* ================================================== */

 static void
-run_helper(uid_t uid, gid_t gid, int scfilter_level)
+run_helper(uid_t uid, gid_t gid, int scfilter_level, int sock_fd)
 {
  LOG_Severity log_severity;

@@ -638,6 +710,8 @@ run_helper(uid_t uid, gid_t gid, int scfilter_level)

  DEBUG_LOG("Helper started");

+  SCK_CloseReusableSockets();
+
  /* Suppress a log message about disabled clock control */
  log_severity = LOG_GetMinSeverity();
  LOG_SetMinSeverity(LOGS_ERR);
@@ -646,7 +720,7 @@ run_helper(uid_t uid, gid_t gid, int scfilter_level)
  LOG_SetMinSeverity(log_severity);

  if (!geteuid() && (uid || gid))
-    SYS_DropRoot(uid, gid);
+    SYS_DropRoot(uid, gid, SYS_NTSKE_HELPER);

  NKS_Initialise();

@@ -654,10 +728,15 @@ run_helper(uid_t uid, gid_t gid, int scfilter_level)
  if (scfilter_level != 0)
    SYS_EnableSystemCallFilter(scfilter_level, SYS_NTSKE_HELPER);

+  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, handle_helper_request, NULL);
+
  SCH_MainLoop();

  DEBUG_LOG("Helper exiting");

+  SCH_RemoveFileHandler(sock_fd);
+  close(sock_fd);
+
  NKS_Finalise();
  SCK_Finalise();
  SYS_Finalise();
@@ -667,6 +746,8 @@ run_helper(uid_t uid, gid_t gid, int scfilter_level)
  CNF_Finalise();
  LOG_Finalise();

+  UTI_ResetGetRandomFunctions();
+
  exit(0);
 }

@@ -676,13 +757,14 @@ void
 NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)
 {
  int i, processes, sock_fd1, sock_fd2;
+  const char **certs, **keys;
  char prefix[16];
  pid_t pid;

  helper_sock_fd = INVALID_SOCK_FD;
  is_helper = 0;

-  if (!CNF_GetNtsServerCertFile() || !CNF_GetNtsServerKeyFile())
+  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0)
    return;

  processes = CNF_GetNtsServerProcesses();
@@ -707,14 +789,15 @@ NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)

    is_helper = 1;

+    UTI_ResetGetRandomFunctions();
+
    snprintf(prefix, sizeof (prefix), "nks#%d:", i + 1);
    LOG_SetDebugPrefix(prefix);
    LOG_CloseParentFd();

    SCK_CloseSocket(sock_fd1);
-    SCH_AddFileHandler(sock_fd2, SCH_FILE_INPUT, handle_helper_request, NULL);

-    run_helper(uid, gid, scfilter_level);
+    run_helper(uid, gid, scfilter_level, sock_fd2);
  }

  SCK_CloseSocket(sock_fd2);
@@ -726,21 +809,19 @@ NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)
 void
 NKS_Initialise(void)
 {
-  char *cert, *key;
+  const char **certs, **keys;
+  int i, n_certs_keys;
  double key_delay;
-  int i;

  server_sock_fd4 = INVALID_SOCK_FD;
  server_sock_fd6 = INVALID_SOCK_FD;

-  cert = CNF_GetNtsServerCertFile();
-  key = CNF_GetNtsServerKeyFile();
-
-  if (!cert || !key)
+  n_certs_keys = CNF_GetNtsServerCertAndKeyFiles(&certs, &keys);
+  if (n_certs_keys <= 0)
    return;

  if (helper_sock_fd == INVALID_SOCK_FD) {
-    server_credentials = NKSN_CreateCertCredentials(cert, key, NULL);
+    server_credentials = NKSN_CreateServerCertCredentials(certs, keys, n_certs_keys);
    if (!server_credentials)
      return;
  } else {
@@ -754,7 +835,7 @@ NKS_Initialise(void)
  /* Generate random keys, even if they will be replaced by reloaded keys,
     or unused (in the helper) */
  for (i = 0; i < MAX_SERVER_KEYS; i++) {
-    server_keys[i].siv = SIV_CreateInstance(SERVER_COOKIE_SIV);
+    server_keys[i].siv = NULL;
    generate_key(i);
  }

@@ -764,14 +845,21 @@ NKS_Initialise(void)
    server_sock_fd4 = open_socket(IPADDR_INET4);
    server_sock_fd6 = open_socket(IPADDR_INET6);

-    load_keys();
-
    key_rotation_interval = MAX(CNF_GetNtsRotate(), 0);

+    /* Reload saved keys, or save the new keys */
+    if (!load_keys())
+      save_keys();
+
    if (key_rotation_interval > 0) {
      key_delay = key_rotation_interval - (SCH_GetLastEventMonoTime() - last_server_key_ts);
      SCH_AddTimeoutByDelay(MAX(key_delay, 0.0), key_timeout, NULL);
    }
+
+    /* Warn if keys are not saved, which can cause a flood of requests
+       after server restart */
+    if (!CNF_GetNtsDumpDir())
+      LOG(LOGS_WARN, "No ntsdumpdir to save server keys");
  }

  initialised = 1;
@@ -845,7 +933,7 @@ NKS_ReloadKeys(void)
 int
 NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
 {
-  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  unsigned char *nonce, plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;
@@ -855,14 +943,12 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
    return 0;
  }

-  /* The algorithm is hardcoded for now */
-  if (context->algorithm != AEAD_AES_SIV_CMAC_256) {
-    DEBUG_LOG("Unexpected SIV algorithm");
-    return 0;
-  }
+  /* The AEAD ID is not encoded in the cookie.  It is implied from the key
+     length (as long as only algorithms with different key lengths are
+     supported). */

  if (context->c2s.length < 0 || context->c2s.length > NKE_MAX_KEY_LENGTH ||
-      context->s2c.length < 0 || context->s2c.length > NKE_MAX_KEY_LENGTH) {
+      context->s2c.length != context->c2s.length) {
    DEBUG_LOG("Invalid key length");
    return 0;
  }
@@ -872,7 +958,10 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
  header = (ServerCookieHeader *)cookie->cookie;

  header->key_id = htonl(key->id);
-  UTI_GetRandomBytes(header->nonce, sizeof (header->nonce));
+
+  nonce = cookie->cookie + sizeof (*header);
+  BRIEF_ASSERT(key->nonce_length <= sizeof (cookie->cookie) - sizeof (*header));
+  UTI_GetRandomBytes(nonce, key->nonce_length);

  plaintext_length = context->c2s.length + context->s2c.length;
  assert(plaintext_length <= sizeof (plaintext));
@@ -880,11 +969,11 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
  memcpy(plaintext + context->c2s.length, context->s2c.key, context->s2c.length);

  tag_length = SIV_GetTagLength(key->siv);
-  cookie->length = sizeof (*header) + plaintext_length + tag_length;
+  cookie->length = sizeof (*header) + key->nonce_length + plaintext_length + tag_length;
  assert(cookie->length <= sizeof (cookie->cookie));
-  ciphertext = cookie->cookie + sizeof (*header);
+  ciphertext = cookie->cookie + sizeof (*header) + key->nonce_length;

-  if (!SIV_Encrypt(key->siv, header->nonce, sizeof (header->nonce),
+  if (!SIV_Encrypt(key->siv, nonce, key->nonce_length,
                   "", 0,
                   plaintext, plaintext_length,
                   ciphertext, plaintext_length + tag_length)) {
@@ -900,7 +989,7 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
 int
 NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
 {
-  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  unsigned char *nonce, plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int ciphertext_length, plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;
@@ -917,8 +1006,6 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
  }

  header = (ServerCookieHeader *)cookie->cookie;
-  ciphertext = cookie->cookie + sizeof (*header);
-  ciphertext_length = cookie->length - sizeof (*header);

  key_id = ntohl(header->key_id);
  key = &server_keys[key_id % MAX_SERVER_KEYS];
@@ -928,18 +1015,23 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
  }

  tag_length = SIV_GetTagLength(key->siv);
-  if (tag_length >= ciphertext_length) {
+
+  if (cookie->length <= (int)sizeof (*header) + key->nonce_length + tag_length) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

+  nonce = cookie->cookie + sizeof (*header);
+  ciphertext = cookie->cookie + sizeof (*header) + key->nonce_length;
+  ciphertext_length = cookie->length - sizeof (*header) - key->nonce_length;
  plaintext_length = ciphertext_length - tag_length;
+
  if (plaintext_length > sizeof (plaintext) || plaintext_length % 2 != 0) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

-  if (!SIV_Decrypt(key->siv, header->nonce, sizeof (header->nonce),
+  if (!SIV_Decrypt(key->siv, nonce, key->nonce_length,
                   "", 0,
                   ciphertext, ciphertext_length,
                   plaintext, plaintext_length)) {
@@ -947,7 +1039,19 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
    return 0;
  }

-  context->algorithm = AEAD_AES_SIV_CMAC_256;
+  /* Select a supported algorithm corresponding to the key length, avoiding
+     potentially slow SIV_GetKeyLength() */
+  switch (plaintext_length / 2) {
+    case 16:
+      context->algorithm = AEAD_AES_128_GCM_SIV;
+      break;
+    case 32:
+      context->algorithm = AEAD_AES_SIV_CMAC_256;
+      break;
+    default:
+      DEBUG_LOG("Unknown key length");
+      return 0;
+  }

  context->c2s.length = plaintext_length / 2;
  context->s2c.length = plaintext_length / 2;
--- a/nts_ke_session.c
+++ b/nts_ke_session.c
@@ -2,7 +2,8 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020-2021
+ * Copyright (C) Anthony Brandon  2025
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -37,11 +38,9 @@
 #include "siv.h"
 #include "socket.h"
 #include "sched.h"
+#include "tls.h"
 #include "util.h"

-#include <gnutls/gnutls.h>
-#include <gnutls/x509.h>
-
 #define INVALID_SOCK_FD (-8)

 struct RecordHeader {
@@ -75,7 +74,7 @@ struct NKSN_Instance_Record {
  KeState state;
  int sock_fd;
  char *label;
-  gnutls_session_t tls_session;
+  TLS_Instance tls_session;
  SCH_TimeoutID timeout_id;
  int retry_factor;

@@ -85,8 +84,6 @@ struct NKSN_Instance_Record {

 /* ================================================== */

-static gnutls_priority_t priority_cache;
-
 static int credentials_counter = 0;

 static int clock_updates = 0;
@@ -206,67 +203,6 @@ check_message_format(struct Message *message, int eof)

 /* ================================================== */

-static gnutls_session_t
-create_tls_session(int server_mode, int sock_fd, const char *server_name,
-                   gnutls_certificate_credentials_t credentials,
-                   gnutls_priority_t priority)
-{
-  unsigned char alpn_name[sizeof (NKE_ALPN_NAME)];
-  gnutls_session_t session;
-  gnutls_datum_t alpn;
-  unsigned int flags;
-  int r;
-
-  r = gnutls_init(&session, GNUTLS_NONBLOCK | GNUTLS_NO_TICKETS |
-                  (server_mode ? GNUTLS_SERVER : GNUTLS_CLIENT));
-  if (r < 0) {
-    LOG(LOGS_ERR, "Could not %s TLS session : %s", "create", gnutls_strerror(r));
-    return NULL;
-  }
-
-  if (!server_mode) {
-    r = gnutls_server_name_set(session, GNUTLS_NAME_DNS, server_name, strlen(server_name));
-    if (r < 0)
-      goto error;
-
-    flags = 0;
-
-    if (clock_updates < CNF_GetNoCertTimeCheck()) {
-      flags |= GNUTLS_VERIFY_DISABLE_TIME_CHECKS | GNUTLS_VERIFY_DISABLE_TRUSTED_TIME_CHECKS;
-      DEBUG_LOG("Disabled time checks");
-    }
-
-    gnutls_session_set_verify_cert(session, server_name, flags);
-  }
-
-  r = gnutls_priority_set(session, priority);
-  if (r < 0)
-    goto error;
-
-  r = gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, credentials);
-  if (r < 0)
-    goto error;
-
-  memcpy(alpn_name, NKE_ALPN_NAME, sizeof (alpn_name));
-  alpn.data = alpn_name;
-  alpn.size = sizeof (alpn_name) - 1;
-
-  r = gnutls_alpn_set_protocols(session, &alpn, 1, 0);
-  if (r < 0)
-    goto error;
-
-  gnutls_transport_set_int(session, sock_fd);
-
-  return session;
-
-error:
-  LOG(LOGS_ERR, "Could not %s TLS session : %s", "set", gnutls_strerror(r));
-  gnutls_deinit(session);
-  return NULL;
-}
-
-/* ================================================== */
-
 static void
 stop_session(NKSN_Instance inst)
 {
@@ -282,7 +218,7 @@ stop_session(NKSN_Instance inst)
  Free(inst->label);
  inst->label = NULL;

-  gnutls_deinit(inst->tls_session);
+  TLS_DestroyInstance(inst->tls_session);
  inst->tls_session = NULL;

  SCH_RemoveTimeout(inst->timeout_id);
@@ -304,21 +240,6 @@ session_timeout(void *arg)

 /* ================================================== */

-static int
-check_alpn(NKSN_Instance inst)
-{
-  gnutls_datum_t alpn;
-
-  if (gnutls_alpn_get_selected_protocol(inst->tls_session, &alpn) < 0 ||
-      alpn.size != sizeof (NKE_ALPN_NAME) - 1 ||
-      memcmp(alpn.data, NKE_ALPN_NAME, sizeof (NKE_ALPN_NAME) - 1) != 0)
-    return 0;
-
-  return 1;
-}
-
-/* ================================================== */
-
 static void
 set_input_output(NKSN_Instance inst, int output)
 {
@@ -360,6 +281,7 @@ static int
 handle_event(NKSN_Instance inst, int event)
 {
  struct Message *message = &inst->message;
+  TLS_Status s;
  int r;

  DEBUG_LOG("Session event %d fd=%d state=%d", event, inst->sock_fd, (int)inst->state);
@@ -386,56 +308,28 @@ handle_event(NKSN_Instance inst, int event)
      return 0;

    case KE_HANDSHAKE:
-      r = gnutls_handshake(inst->tls_session);
-
-      if (r < 0) {
-        if (gnutls_error_is_fatal(r)) {
-          gnutls_datum_t cert_error;
-
-          /* Get a description of verification errors */
-          if (r != GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR ||
-              gnutls_certificate_verification_status_print(
-                          gnutls_session_get_verify_cert_status(inst->tls_session),
-                          gnutls_certificate_type_get(inst->tls_session), &cert_error, 0) < 0)
-            cert_error.data = NULL;
-
-          LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
-              "TLS handshake with %s failed : %s%s%s", inst->label, gnutls_strerror(r),
-              cert_error.data ? " " : "", cert_error.data ? (const char *)cert_error.data : "");
-
-          if (cert_error.data)
-            gnutls_free(cert_error.data);
+      s = TLS_DoHandshake(inst->tls_session);

+      switch (s) {
+        case TLS_SUCCESS:
+          break;
+        case TLS_AGAIN_OUTPUT:
+        case TLS_AGAIN_INPUT:
+          set_input_output(inst, s == TLS_AGAIN_OUTPUT);
+          return 0;
+        default:
          stop_session(inst);

          /* Increase the retry interval if the handshake did not fail due
             to the other end closing the connection */
-          if (r != GNUTLS_E_PULL_ERROR && r != GNUTLS_E_PREMATURE_TERMINATION)
+          if (s != TLS_CLOSED)
            inst->retry_factor = NKE_RETRY_FACTOR2_TLS;

          return 0;
-        }
-
-        /* Disable output when the handshake is trying to receive data */
-        set_input_output(inst, gnutls_record_get_direction(inst->tls_session));
-        return 0;
      }

      inst->retry_factor = NKE_RETRY_FACTOR2_TLS;

-      if (DEBUG) {
-        char *description = gnutls_session_get_desc(inst->tls_session);
-        DEBUG_LOG("Handshake with %s completed %s",
-                  inst->label, description ? description : "");
-        gnutls_free(description);
-      }
-
-      if (!check_alpn(inst)) {
-        LOG(inst->server ? LOGS_DEBUG : LOGS_ERR, "NTS-KE not supported by %s", inst->label);
-        stop_session(inst);
-        return 0;
-      }
-
      /* Client will send a request to the server */
      change_state(inst, inst->server ? KE_RECEIVE : KE_SEND);
      return 0;
@@ -444,16 +338,17 @@ handle_event(NKSN_Instance inst, int event)
      assert(inst->new_message && message->complete);
      assert(message->length <= sizeof (message->data) && message->length > message->sent);

-      r = gnutls_record_send(inst->tls_session, &message->data[message->sent],
-                             message->length - message->sent);
+      s = TLS_Send(inst->tls_session, &message->data[message->sent],
+                   message->length - message->sent, &r);

-      if (r < 0) {
-        if (gnutls_error_is_fatal(r)) {
-          LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
-              "Could not send NTS-KE message to %s : %s", inst->label, gnutls_strerror(r));
+      switch (s) {
+        case TLS_SUCCESS:
+          break;
+        case TLS_AGAIN_OUTPUT:
+          return 0;
+        default:
          stop_session(inst);
-        }
-        return 0;
+          return 0;
      }

      DEBUG_LOG("Sent %d bytes to %s", r, inst->label);
@@ -476,26 +371,24 @@ handle_event(NKSN_Instance inst, int event)
          return 0;
        }

-        r = gnutls_record_recv(inst->tls_session, &message->data[message->length],
-                               sizeof (message->data) - message->length);
+        s = TLS_Receive(inst->tls_session, &message->data[message->length],
+                        sizeof (message->data) - message->length, &r);

-        if (r < 0) {
-          /* Handle a renegotiation request on both client and server as
-             a protocol error */
-          if (gnutls_error_is_fatal(r) || r == GNUTLS_E_REHANDSHAKE) {
-            LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
-                "Could not receive NTS-KE message from %s : %s",
-                inst->label, gnutls_strerror(r));
+        switch (s) {
+          case TLS_SUCCESS:
+            break;
+          case TLS_AGAIN_INPUT:
+            return 0;
+          default:
            stop_session(inst);
-          }
-          return 0;
+            return 0;
        }

        DEBUG_LOG("Received %d bytes from %s", r, inst->label);

        message->length += r;

-      } while (gnutls_record_check_pending(inst->tls_session) > 0);
+      } while (TLS_CheckPending(inst->tls_session));

      if (!check_message_format(message, r == 0)) {
        LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
@@ -515,18 +408,18 @@ handle_event(NKSN_Instance inst, int event)
      return 1;

    case KE_SHUTDOWN:
-      r = gnutls_bye(inst->tls_session, GNUTLS_SHUT_RDWR);
+      s = TLS_Shutdown(inst->tls_session);

-      if (r < 0) {
-        if (gnutls_error_is_fatal(r)) {
-          DEBUG_LOG("Shutdown with %s failed : %s", inst->label, gnutls_strerror(r));
+      switch (s) {
+        case TLS_SUCCESS:
+          break;
+        case TLS_AGAIN_OUTPUT:
+        case TLS_AGAIN_INPUT:
+          set_input_output(inst, s == TLS_AGAIN_OUTPUT);
+          return 0;
+        default:
          stop_session(inst);
          return 0;
-        }
-
-        /* Disable output when the TLS shutdown is trying to receive data */
-        set_input_output(inst, gnutls_record_get_direction(inst->tls_session));
-        return 0;
      }

      SCK_ShutdownConnection(inst->sock_fd);
@@ -588,107 +481,89 @@ handle_step(struct timespec *raw, struct timespec *cooked, double dfreq,

 /* ================================================== */

-static int gnutls_initialised = 0;
+static int tls_initialised = 0;

-static void
-init_gnutls(void)
+static int
+init_tls(void)
 {
-  int r;
+  if (tls_initialised)
+    return 1;

-  if (gnutls_initialised)
-    return;
+  if (!TLS_Initialise(&get_time))
+    return 0;

-  r = gnutls_global_init();
-  if (r < 0)
-    LOG_FATAL("Could not initialise %s : %s", "gnutls", gnutls_strerror(r));
-
-  /* Prepare a priority cache for server and client NTS-KE sessions
-     (the NTS specification requires TLS1.3 or later) */
-  r = gnutls_priority_init2(&priority_cache,
-                            "-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1:-VERS-TLS1.2:-VERS-DTLS-ALL",
-                            NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND);
-  if (r < 0)
-    LOG_FATAL("Could not initialise %s : %s", "priority cache", gnutls_strerror(r));
-
-  /* Use our clock instead of the system clock in certificate verification */
-  gnutls_global_set_time_function(get_time);
-
-  gnutls_initialised = 1;
+  tls_initialised = 1;
  DEBUG_LOG("Initialised");

  LCL_AddParameterChangeHandler(handle_step, NULL);
+
+  return 1;
 }

 /* ================================================== */

 static void
-deinit_gnutls(void)
+deinit_tls(void)
 {
-  if (!gnutls_initialised || credentials_counter > 0)
+  if (!tls_initialised || credentials_counter > 0)
    return;

  LCL_RemoveParameterChangeHandler(handle_step, NULL);

-  gnutls_priority_deinit(priority_cache);
-  gnutls_global_deinit();
-  gnutls_initialised = 0;
+  TLS_Finalise();
+  tls_initialised = 0;
  DEBUG_LOG("Deinitialised");
 }

 /* ================================================== */

-void *
-NKSN_CreateCertCredentials(char *cert, char *key, char *trusted_certs)
+static NKSN_Credentials
+create_credentials(const char **certs, const char **keys, int n_certs_keys,
+                   const char **trusted_certs, uint32_t *trusted_certs_ids,
+                   int n_trusted_certs, uint32_t trusted_cert_set)
 {
-  gnutls_certificate_credentials_t credentials = NULL;
-  int r;
+  TLS_Credentials credentials;

-  init_gnutls();
+  if (!init_tls())
+    return NULL;

-  r = gnutls_certificate_allocate_credentials(&credentials);
-  if (r < 0)
-    goto error;
-
-  if (cert && key) {
-    r = gnutls_certificate_set_x509_key_file(credentials, cert, key,
-                                             GNUTLS_X509_FMT_PEM);
-    if (r < 0)
-      goto error;
-  } else {
-    if (!CNF_GetNoSystemCert()) {
-      r = gnutls_certificate_set_x509_system_trust(credentials);
-      if (r < 0)
-        goto error;
-    }
-
-    if (trusted_certs) {
-      r = gnutls_certificate_set_x509_trust_file(credentials, trusted_certs,
-                                                 GNUTLS_X509_FMT_PEM);
-      if (r < 0)
-        goto error;
-    }
+  credentials = TLS_CreateCredentials(certs, keys, n_certs_keys, trusted_certs,
+                                      trusted_certs_ids, n_trusted_certs, trusted_cert_set);
+  if (!credentials) {
+    deinit_tls();
+    return NULL;
  }

  credentials_counter++;

  return credentials;
+}

-error:
-  LOG(LOGS_ERR, "Could not set credentials : %s", gnutls_strerror(r));
-  if (credentials)
-    gnutls_certificate_free_credentials(credentials);
-  deinit_gnutls();
-  return NULL;
+/* ================================================== */
+
+NKSN_Credentials
+NKSN_CreateServerCertCredentials(const char **certs, const char **keys, int n_certs_keys)
+{
+  return create_credentials(certs, keys, n_certs_keys, NULL, NULL, 0, 0);
+}
+
+/* ================================================== */
+
+NKSN_Credentials
+NKSN_CreateClientCertCredentials(const char **certs, uint32_t *ids,
+                                 int n_certs_ids, uint32_t trusted_cert_set)
+{
+  return create_credentials(NULL, NULL, 0, certs, ids, n_certs_ids, trusted_cert_set);
 }

 /* ================================================== */

 void
-NKSN_DestroyCertCredentials(void *credentials)
+NKSN_DestroyCertCredentials(NKSN_Credentials credentials)
 {
-  gnutls_certificate_free_credentials(credentials);
+  TLS_DestroyCredentials(credentials);
  credentials_counter--;
-  deinit_gnutls();
+  deinit_tls();
 }

 /* ================================================== */
@@ -734,12 +609,13 @@ NKSN_DestroyInstance(NKSN_Instance inst)

 int
 NKSN_StartSession(NKSN_Instance inst, int sock_fd, const char *label,
-                  void *credentials, double timeout)
+                  NKSN_Credentials credentials, double timeout)
 {
  assert(inst->state == KE_STOPPED);

-  inst->tls_session = create_tls_session(inst->server, sock_fd, inst->server_name,
-                                         credentials, priority_cache);
+  inst->tls_session = TLS_CreateInstance(inst->server, sock_fd, inst->server_name,
+                                         label, NKE_ALPN_NAME, credentials,
+                                         clock_updates < CNF_GetNoCertTimeCheck());
  if (!inst->tls_session)
    return 0;

@@ -823,23 +699,45 @@ NKSN_GetRecord(NKSN_Instance inst, int *critical, int *type, int *body_length,
 /* ================================================== */

 int
-NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm siv, NKE_Key *c2s, NKE_Key *s2c)
+NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm algorithm, SIV_Algorithm exporter_algorithm,
+             int next_protocol, NKE_Key *c2s, NKE_Key *s2c)
 {
-  c2s->length = SIV_GetKeyLength(siv);
-  s2c->length = SIV_GetKeyLength(siv);
-  assert(c2s->length <= sizeof (c2s->key));
-  assert(s2c->length <= sizeof (s2c->key));
+  int length = SIV_GetKeyLength(algorithm);
+  struct {
+    uint16_t next_protocol;
+    uint16_t algorithm;
+    uint8_t is_s2c;
+    uint8_t _pad;
+  } context;

-  if (gnutls_prf_rfc5705(inst->tls_session,
-                         sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
-                         sizeof (NKE_EXPORTER_CONTEXT_C2S) - 1, NKE_EXPORTER_CONTEXT_C2S,
-                         c2s->length, (char *)c2s->key) < 0)
+  if (!inst->tls_session)
    return 0;
-  if (gnutls_prf_rfc5705(inst->tls_session,
-                         sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
-                         sizeof (NKE_EXPORTER_CONTEXT_S2C) - 1, NKE_EXPORTER_CONTEXT_S2C,
-                         s2c->length, (char *)s2c->key) < 0)
+
+  if (length <= 0 || length > sizeof (c2s->key) || length > sizeof (s2c->key)) {
+    DEBUG_LOG("Invalid algorithm");
    return 0;
+  }
+
+  assert(sizeof (context) == 6);
+  context.next_protocol = htons(next_protocol);
+  context.algorithm = htons(exporter_algorithm);
+
+  context.is_s2c = 0;
+  if (!TLS_ExportKey(inst->tls_session, sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
+                     sizeof (context) - 1, &context, length, c2s->key)) {
+    DEBUG_LOG("Could not export key");
+    return 0;
+  }
+
+  context.is_s2c = 1;
+  if (!TLS_ExportKey(inst->tls_session, sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
+                     sizeof (context) - 1, &context, length, s2c->key)) {
+    DEBUG_LOG("Could not export key");
+    return 0;
+  }
+
+  c2s->length = length;
+  s2c->length = length;

  return 1;
 }
--- a/nts_ke_session.h
+++ b/nts_ke_session.h
@@ -30,19 +30,25 @@
 #include "nts_ke.h"
 #include "siv.h"

+typedef struct NKSN_Credentials_Record *NKSN_Credentials;
+
 typedef struct NKSN_Instance_Record *NKSN_Instance;

 /* Handler for received NTS-KE messages.  A zero return code stops
   the session. */
 typedef int (*NKSN_MessageHandler)(void *arg);

-/* Get client or server credentials using certificates of trusted CAs,
-   or a server certificate and key.  The credentials may be shared between
+/* Get server or client credentials using a server certificate and key,
+   or certificates of trusted CAs.  The credentials may be shared between
   different clients or servers. */
-extern void *NKSN_CreateCertCredentials(char *cert, char *key, char *trusted_certs);
+extern NKSN_Credentials NKSN_CreateServerCertCredentials(const char **certs, const char **keys,
+                                                         int n_certs_keys);
+extern NKSN_Credentials NKSN_CreateClientCertCredentials(const char **certs, uint32_t *ids,
+                                                         int n_certs_ids,
+                                                         uint32_t trusted_cert_set);

 /* Destroy the credentials */
-extern void NKSN_DestroyCertCredentials(void *credentials);
+extern void NKSN_DestroyCertCredentials(NKSN_Credentials credentials);

 /* Create an instance */
 extern NKSN_Instance NKSN_CreateInstance(int server_mode, const char *server_name,
@@ -53,7 +59,7 @@ extern void NKSN_DestroyInstance(NKSN_Instance inst);

 /* Start a new NTS-KE session */
 extern int NKSN_StartSession(NKSN_Instance inst, int sock_fd, const char *label,
-                             void *credentials, double timeout);
+                             NKSN_Credentials credentials, double timeout);

 /* Begin an NTS-KE message.  A request should be made right after starting
   the session and response should be made in the message handler. */
@@ -71,8 +77,11 @@ extern int NKSN_EndMessage(NKSN_Instance inst);
 extern int NKSN_GetRecord(NKSN_Instance inst, int *critical, int *type, int *body_length,
                          void *body, int buffer_length);

-/* Export NTS keys for a specified algorithm */
-extern int NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm siv, NKE_Key *c2s, NKE_Key *s2c);
+/* Export NTS keys for a specified algorithm (for compatibility reasons the
+   RFC5705 exporter context is allowed to have a different algorithm) */
+extern int NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm algorithm,
+                        SIV_Algorithm exporter_algorithm,
+                        int next_protocol, NKE_Key *c2s, NKE_Key *s2c);

 /* Check if the session has stopped */
 extern int NKSN_IsStopped(NKSN_Instance inst);
--- a/nts_ntp.h
+++ b/nts_ntp.h
@@ -27,11 +27,6 @@
 #ifndef GOT_NTS_NTP_H
 #define GOT_NTS_NTP_H

-#define NTP_EF_NTS_UNIQUE_IDENTIFIER    0x0104
-#define NTP_EF_NTS_COOKIE               0x0204
-#define NTP_EF_NTS_COOKIE_PLACEHOLDER   0x0304
-#define NTP_EF_NTS_AUTH_AND_EEF         0x0404
-
 #define NTP_KOD_NTS_NAK                 0x4e54534e

 #define NTS_MIN_UNIQ_ID_LENGTH          32
--- a/nts_ntp_auth.c
+++ b/nts_ntp_auth.c
@@ -61,23 +61,25 @@ get_padded_length(int length)

 int
 NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
-                   const unsigned char *nonce, int nonce_length,
+                   const unsigned char *nonce, int max_nonce_length,
                   const unsigned char *plaintext, int plaintext_length,
                   int min_ef_length)
 {
-  int auth_length, ciphertext_length, assoc_length;
+  int auth_length, ciphertext_length, assoc_length, nonce_length, max_siv_nonce_length;
  int nonce_padding, ciphertext_padding, additional_padding;
  unsigned char *ciphertext, *body;
  struct AuthHeader *header;

  assert(sizeof (*header) == 4);

-  if (nonce_length <= 0 || plaintext_length < 0) {
+  if (max_nonce_length <= 0 || plaintext_length < 0) {
    DEBUG_LOG("Invalid nonce/plaintext length");
    return 0;
  }

  assoc_length = info->length;
+  max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
+  nonce_length = MIN(max_nonce_length, max_siv_nonce_length);
  ciphertext_length = SIV_GetTagLength(siv) + plaintext_length;
  nonce_padding = get_padding_length(nonce_length);
  ciphertext_padding = get_padding_length(ciphertext_length);
@@ -86,8 +88,8 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
  auth_length = sizeof (*header) + nonce_length + nonce_padding +
                ciphertext_length + ciphertext_padding;
  additional_padding = MAX(min_ef_length - auth_length - 4, 0);
-  additional_padding = MAX(NTS_MIN_UNPADDED_NONCE_LENGTH - nonce_length - nonce_padding,
-                           additional_padding);
+  additional_padding = MAX(MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) -
+                           nonce_length - nonce_padding, additional_padding);
  auth_length += additional_padding;

  if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_AUTH_AND_EEF, auth_length,
@@ -102,9 +104,8 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
  body = (unsigned char *)(header + 1);
  ciphertext = body + nonce_length + nonce_padding;

-  if ((unsigned char *)header + auth_length !=
-      ciphertext + ciphertext_length + ciphertext_padding + additional_padding)
-    assert(0);
+  BRIEF_ASSERT((unsigned char *)header + auth_length ==
+               ciphertext + ciphertext_length + ciphertext_padding + additional_padding);

  memcpy(body, nonce, nonce_length);
  memset(body + nonce_length, 0, nonce_padding);
@@ -112,6 +113,8 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
  if (!SIV_Encrypt(siv, nonce, nonce_length, packet, assoc_length,
                   plaintext, plaintext_length, ciphertext, ciphertext_length)) {
    DEBUG_LOG("SIV encrypt failed");
+    info->length = assoc_length;
+    info->ext_fields--;
    return 0;
  }

@@ -126,7 +129,7 @@ int
 NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, int ef_start,
                  unsigned char *plaintext, int buffer_length, int *plaintext_length)
 {
-  unsigned int siv_tag_length, nonce_length, ciphertext_length;
+  int siv_tag_length, max_siv_nonce_length, nonce_length, ciphertext_length;
  unsigned char *nonce, *ciphertext;
  int ef_type, ef_body_length;
  void *ef_body;
@@ -154,6 +157,7 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
  nonce = (unsigned char *)(header + 1);
  ciphertext = nonce + get_padded_length(nonce_length);

+  max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
  siv_tag_length = SIV_GetTagLength(siv);

  if (nonce_length < 1 ||
@@ -163,8 +167,8 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
    return 0;
  }

-  if (ef_body_length < sizeof (*header) +
-        NTS_MIN_UNPADDED_NONCE_LENGTH + get_padded_length(ciphertext_length)) {
+  if (sizeof (*header) + MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) +
+      get_padded_length(ciphertext_length) > ef_body_length) {
    DEBUG_LOG("Missing padding");
    return 0;
  }
--- a/nts_ntp_auth.h
+++ b/nts_ntp_auth.h
@@ -32,7 +32,7 @@
 #include "siv.h"

 extern int NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
-                              const unsigned char *nonce, int nonce_length,
+                              const unsigned char *nonce, int max_nonce_length,
                              const unsigned char *plaintext, int plaintext_length,
                              int min_ef_length);

--- a/nts_ntp_client.c
+++ b/nts_ntp_client.c
@@ -46,26 +46,38 @@
 /* Maximum length of all cookies to avoid IP fragmentation */
 #define MAX_TOTAL_COOKIE_LENGTH (8 * 108)

+/* Retry interval for NTS-KE start (which doesn't generate network traffic) */
+#define RETRY_INTERVAL_KE_START 2.0
+
 /* Magic string of files containing keys and cookies */
 #define DUMP_IDENTIFIER "NNC0\n"

 struct NNC_Instance_Record {
-  const IPSockAddr *ntp_address;
+  /* Address of NTS-KE server */
  IPSockAddr nts_address;
+  /* Hostname or IP address for certificate verification */
  char *name;
+  /* ID of trusted certificates */
+  uint32_t cert_set;
+  /* Configured NTP port */
+  uint16_t default_ntp_port;
+  /* Address of NTP server (can be negotiated in NTS-KE) */
+  IPSockAddr ntp_address;
+
  NKC_Instance nke;
  SIV_Instance siv;

-  int load_attempt;
  int nke_attempts;
  double next_nke_attempt;
  double last_nke_success;

  NKE_Context context;
+  NKE_Context alt_context;
  unsigned int context_id;
  NKE_Cookie cookies[NTS_MAX_COOKIES];
  int num_cookies;
  int cookie_index;
+  int auth_ready;
  int nak_response;
  int ok_response;
  unsigned char nonce[NTS_MIN_UNPADDED_NONCE_LENGTH];
@@ -82,16 +94,24 @@ static void load_cookies(NNC_Instance inst);
 static void
 reset_instance(NNC_Instance inst)
 {
-  inst->load_attempt = 0;
+  if (inst->nke)
+    NKC_DestroyInstance(inst->nke);
+  inst->nke = NULL;
+  if (inst->siv)
+    SIV_DestroyInstance(inst->siv);
+  inst->siv = NULL;
+
  inst->nke_attempts = 0;
  inst->next_nke_attempt = 0.0;
  inst->last_nke_success = 0.0;

  memset(&inst->context, 0, sizeof (inst->context));
+  memset(&inst->alt_context, 0, sizeof (inst->alt_context));
  inst->context_id = 0;
  memset(inst->cookies, 0, sizeof (inst->cookies));
  inst->num_cookies = 0;
  inst->cookie_index = 0;
+  inst->auth_ready = 0;
  inst->nak_response = 0;
  inst->ok_response = 1;
  memset(inst->nonce, 0, sizeof (inst->nonce));
@@ -101,20 +121,26 @@ reset_instance(NNC_Instance inst)
 /* ================================================== */

 NNC_Instance
-NNC_CreateInstance(IPSockAddr *nts_address, const char *name, const IPSockAddr *ntp_address)
+NNC_CreateInstance(IPSockAddr *nts_address, const char *name, uint32_t cert_set, uint16_t ntp_port)
 {
  NNC_Instance inst;

  inst = MallocNew(struct NNC_Instance_Record);

-  inst->ntp_address = ntp_address;
  inst->nts_address = *nts_address;
-  inst->name = name ? Strdup(name) : NULL;
+  inst->name = Strdup(name);
+  inst->cert_set = cert_set;
+  inst->default_ntp_port = ntp_port;
+  inst->ntp_address.ip_addr = nts_address->ip_addr;
+  inst->ntp_address.port = ntp_port;
  inst->siv = NULL;
  inst->nke = NULL;

  reset_instance(inst);

+  /* Try to reload saved keys and cookies */
+  load_cookies(inst);
+
  return inst;
 }

@@ -125,10 +151,7 @@ NNC_DestroyInstance(NNC_Instance inst)
 {
  save_cookies(inst);

-  if (inst->nke)
-    NKC_DestroyInstance(inst->nke);
-  if (inst->siv)
-    SIV_DestroyInstance(inst->siv);
+  reset_instance(inst);

  Free(inst->name);
  Free(inst);
@@ -144,6 +167,21 @@ check_cookies(NNC_Instance inst)
  if (inst->num_cookies > 0 &&
      ((inst->nak_response && !inst->ok_response) ||
       SCH_GetLastEventMonoTime() - inst->last_nke_success > CNF_GetNtsRefresh())) {
+
+    /* Before dropping the cookies, check whether there is an alternate set of
+       keys available (exported with the compliant context for AES-128-GCM-SIV)
+       and the NAK was the only valid response after the last NTS-KE session,
+       indicating we use incorrect keys and switching to the other set of keys
+       for the following NTP requests might work */
+    if (inst->alt_context.algorithm != AEAD_SIV_INVALID &&
+        inst->alt_context.algorithm == inst->context.algorithm &&
+        inst->nke_attempts > 0 && inst->nak_response && !inst->ok_response) {
+      inst->context = inst->alt_context;
+      inst->alt_context.algorithm = AEAD_SIV_INVALID;
+      DEBUG_LOG("Switched to compliant keys");
+      return 1;
+    }
+
    inst->num_cookies = 0;
    DEBUG_LOG("Dropped cookies");
  }
@@ -158,13 +196,13 @@ set_ntp_address(NNC_Instance inst, NTP_Remote_Address *negotiated_address)
 {
  NTP_Remote_Address old_address, new_address;

-  old_address = *inst->ntp_address;
+  old_address = inst->ntp_address;
  new_address = *negotiated_address;

  if (new_address.ip_addr.family == IPADDR_UNSPEC)
-    new_address.ip_addr = old_address.ip_addr;
+    new_address.ip_addr = inst->nts_address.ip_addr;
  if (new_address.port == 0)
-    new_address.port = old_address.port;
+    new_address.port = inst->default_ntp_port;

  if (UTI_CompareIPs(&old_address.ip_addr, &new_address.ip_addr, NULL) == 0 &&
      old_address.port == new_address.port)
@@ -177,16 +215,23 @@ set_ntp_address(NNC_Instance inst, NTP_Remote_Address *negotiated_address)
    return 0;
  }

+  inst->ntp_address = new_address;
+
  return 1;
 }

 /* ================================================== */

 static void
-update_next_nke_attempt(NNC_Instance inst, double now)
+update_next_nke_attempt(NNC_Instance inst, int failed_start, double now)
 {
  int factor, interval;

+  if (failed_start) {
+    inst->next_nke_attempt = now + RETRY_INTERVAL_KE_START;
+    return;
+  }
+
  if (!inst->nke)
    return;

@@ -201,8 +246,8 @@ static int
 get_cookies(NNC_Instance inst)
 {
  NTP_Remote_Address ntp_address;
+  int got_data, failed_start = 0;
  double now;
-  int got_data;

  assert(inst->num_cookies == 0);

@@ -216,22 +261,15 @@ get_cookies(NNC_Instance inst)
      return 0;
    }

-    if (!inst->name) {
-      LOG(LOGS_ERR, "Missing name of %s for NTS-KE",
-          UTI_IPToString(&inst->nts_address.ip_addr));
-      return 0;
-    }
-
-    inst->nke = NKC_CreateInstance(&inst->nts_address, inst->name);
+    inst->nke = NKC_CreateInstance(&inst->nts_address, inst->name, inst->cert_set);

    inst->nke_attempts++;
-    update_next_nke_attempt(inst, now);

    if (!NKC_Start(inst->nke))
-      return 0;
+      failed_start = 1;
  }

-  update_next_nke_attempt(inst, now);
+  update_next_nke_attempt(inst, failed_start, now);

  /* Wait until the session stops */
  if (NKC_IsActive(inst->nke))
@@ -240,7 +278,7 @@ get_cookies(NNC_Instance inst)
  assert(sizeof (inst->cookies) / sizeof (inst->cookies[0]) == NTS_MAX_COOKIES);

  /* Get the new keys, cookies and NTP address if the session was successful */
-  got_data = NKC_GetNtsData(inst->nke, &inst->context,
+  got_data = NKC_GetNtsData(inst->nke, &inst->context, &inst->alt_context,
                            inst->cookies, &inst->num_cookies, NTS_MAX_COOKIES,
                            &ntp_address);

@@ -266,8 +304,6 @@ get_cookies(NNC_Instance inst)
  inst->last_nke_success = now;
  inst->cookie_index = 0;

-  inst->nak_response = 0;
-
  return 1;
 }

@@ -276,11 +312,12 @@ get_cookies(NNC_Instance inst)
 int
 NNC_PrepareForAuth(NNC_Instance inst)
 {
-  /* Try to reload saved keys and cookies (once for the NTS-KE address) */
-  if (!inst->load_attempt) {
-    load_cookies(inst);
-    inst->load_attempt = 1;
-  }
+  inst->auth_ready = 0;
+
+  /* Prepare data for the next request and invalidate any responses to the
+     previous request */
+  UTI_GetRandomBytes(inst->uniq_id, sizeof (inst->uniq_id));
+  UTI_GetRandomBytes(inst->nonce, sizeof (inst->nonce));

  /* Get new cookies if there are not any, or they are no longer usable */
  if (!check_cookies(inst)) {
@@ -288,6 +325,8 @@ NNC_PrepareForAuth(NNC_Instance inst)
      return 0;
  }

+  inst->nak_response = 0;
+
  if (!inst->siv)
    inst->siv = SIV_CreateInstance(inst->context.algorithm);

@@ -297,9 +336,7 @@ NNC_PrepareForAuth(NNC_Instance inst)
    return 0;
  }

-  /* Prepare data for NNC_GenerateRequestAuth() */
-  UTI_GetRandomBytes(inst->uniq_id, sizeof (inst->uniq_id));
-  UTI_GetRandomBytes(inst->nonce, sizeof (inst->nonce));
+  inst->auth_ready = 1;

  return 1;
 }
@@ -314,14 +351,22 @@ NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
  int i, req_cookies;
  void *ef_body;

-  if (inst->num_cookies == 0 || !inst->siv)
+  if (!inst->auth_ready)
+    return 0;
+
+  inst->auth_ready = 0;
+
+  if (inst->num_cookies <= 0 || !inst->siv)
    return 0;

  if (info->mode != MODE_CLIENT)
    return 0;

  cookie = &inst->cookies[inst->cookie_index];
-  req_cookies = MIN(NTS_MAX_COOKIES - inst->num_cookies + 1,
+  inst->num_cookies--;
+  inst->cookie_index = (inst->cookie_index + 1) % NTS_MAX_COOKIES;
+
+  req_cookies = MIN(NTS_MAX_COOKIES - inst->num_cookies,
                    MAX_TOTAL_COOKIE_LENGTH / (cookie->length + 4));

  if (!NEF_AddField(packet, info, NTP_EF_NTS_UNIQUE_IDENTIFIER,
@@ -343,9 +388,6 @@ NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
                          (const unsigned char *)"", 0, NTP_MAX_V4_MAC_LENGTH + 4))
    return 0;

-  inst->num_cookies--;
-  inst->cookie_index = (inst->cookie_index + 1) % NTS_MAX_COOKIES;
-  inst->nak_response = 0;
  inst->ok_response = 0;

  return 1;
@@ -427,7 +469,7 @@ NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
    return 0;

  /* Accept at most one response per request */
-  if (inst->ok_response)
+  if (inst->ok_response || inst->auth_ready)
    return 0;

  if (!inst->siv ||
@@ -439,7 +481,7 @@ NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
  for (parsed = NTP_HEADER_LENGTH; parsed < info->length; parsed += ef_length) {
    if (!NEF_ParseField(packet, info->length, parsed,
                        &ef_length, &ef_type, &ef_body, &ef_body_length))
-      /* This is not expected as the packet already passed NAU_ParsePacket() */
+      /* This is not expected as the packet already passed parsing */
      return 0;

    switch (ef_type) {
@@ -495,6 +537,7 @@ NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
     new NTS-KE session to be started as soon as the cookies run out. */
  inst->nke_attempts = 0;
  inst->next_nke_attempt = 0.0;
+  inst->alt_context.algorithm = AEAD_SIV_INVALID;

  return 1;
 }
@@ -506,16 +549,14 @@ NNC_ChangeAddress(NNC_Instance inst, IPAddr *address)
 {
  save_cookies(inst);

-  if (inst->nke)
-    NKC_DestroyInstance(inst->nke);
-
-  inst->nke = NULL;
-  inst->num_cookies = 0;
  inst->nts_address.ip_addr = *address;
+  inst->ntp_address.ip_addr = *address;

  reset_instance(inst);

  DEBUG_LOG("NTS reset");
+
+  load_cookies(inst);
 }

 /* ================================================== */
@@ -546,9 +587,10 @@ save_cookies(NNC_Instance inst)
  context_time = inst->last_nke_success - SCH_GetLastEventMonoTime();
  context_time += UTI_TimespecToDouble(&now);

-  if (fprintf(f, "%s%.1f\n%s %d\n%u %d ",
-              DUMP_IDENTIFIER, context_time, UTI_IPToString(&inst->ntp_address->ip_addr),
-              inst->ntp_address->port, inst->context_id, (int)inst->context.algorithm) < 0 ||
+  if (fprintf(f, "%s%s\n%.1f\n%s %d\n%u %d ",
+              DUMP_IDENTIFIER, inst->name, context_time,
+              UTI_IPToString(&inst->ntp_address.ip_addr), inst->ntp_address.port,
+              inst->context_id, (int)inst->context.algorithm) < 0 ||
      !UTI_BytesToHex(inst->context.s2c.key, inst->context.s2c.length, buf, sizeof (buf)) ||
      fprintf(f, "%s ", buf) < 0 ||
      !UTI_BytesToHex(inst->context.c2s.key, inst->context.c2s.length, buf, sizeof (buf)) ||
@@ -609,6 +651,8 @@ load_cookies(NNC_Instance inst)
  inst->siv = NULL;

  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 1 ||
+        strcmp(words[0], inst->name) != 0 ||
      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 1 ||
        sscanf(words[0], "%lf", &context_time) != 1 ||
      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
@@ -617,6 +661,7 @@ load_cookies(NNC_Instance inst)
        sscanf(words[0], "%u", &context_id) != 1 || sscanf(words[1], "%d", &algorithm) != 1)
    goto error;

+  inst->alt_context.algorithm = AEAD_SIV_INVALID;
  inst->context.algorithm = algorithm;
  inst->context.s2c.length = UTI_HexToBytes(words[2], inst->context.s2c.key,
                                            sizeof (inst->context.s2c.key));
@@ -624,6 +669,7 @@ load_cookies(NNC_Instance inst)
                                            sizeof (inst->context.c2s.key));

  if (inst->context.s2c.length != SIV_GetKeyLength(algorithm) ||
+      inst->context.s2c.length <= 0 ||
      inst->context.c2s.length != inst->context.s2c.length)
    goto error;

@@ -650,6 +696,8 @@ load_cookies(NNC_Instance inst)
  inst->last_nke_success = context_time + SCH_GetLastEventMonoTime();
  inst->context_id = context_id;

+  fclose(f);
+
  DEBUG_LOG("Loaded %d cookies for %s", i, filename);
  return;

@@ -658,6 +706,7 @@ error:
  fclose(f);

  memset(&inst->context, 0, sizeof (inst->context));
+  memset(&inst->alt_context, 0, sizeof (inst->alt_context));
  inst->num_cookies = 0;
 }

--- a/nts_ntp_client.h
+++ b/nts_ntp_client.h
@@ -34,7 +34,7 @@
 typedef struct NNC_Instance_Record *NNC_Instance;

 extern NNC_Instance NNC_CreateInstance(IPSockAddr *nts_address, const char *name,
-                                                   const IPSockAddr *ntp_address);
+                                       uint32_t cert_set, uint16_t ntp_port);
 extern void NNC_DestroyInstance(NNC_Instance inst);
 extern int NNC_PrepareForAuth(NNC_Instance inst);
 extern int NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
--- a/nts_ntp_server.c
+++ b/nts_ntp_server.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -41,13 +41,15 @@
 #include "siv.h"
 #include "util.h"

-#define SERVER_SIV AEAD_AES_SIV_CMAC_256
+#define MAX_SERVER_SIVS 2

 struct NtsServer {
-  SIV_Instance siv;
+  SIV_Instance sivs[MAX_SERVER_SIVS];
+  SIV_Algorithm siv_algorithms[MAX_SERVER_SIVS];
  unsigned char nonce[NTS_MIN_UNPADDED_NONCE_LENGTH];
  NKE_Cookie cookies[NTS_MAX_COOKIES];
  int num_cookies;
+  int siv_index;
  NTP_int64 req_tx;
 };

@@ -59,16 +61,27 @@ struct NtsServer *server;
 void
 NNS_Initialise(void)
 {
+  const char **certs, **keys;
+  int i;
+
  /* Create an NTS-NTP server instance only if NTS-KE server is enabled */
-  if (!CNF_GetNtsServerCertFile() || !CNF_GetNtsServerKeyFile()) {
+  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0) {
    server = NULL;
    return;
  }

  server = Malloc(sizeof (struct NtsServer));
-  server->siv = SIV_CreateInstance(SERVER_SIV);
-  if (!server->siv)
-    LOG_FATAL("Could not initialise SIV cipher");
+
+  server->siv_algorithms[0] = AEAD_AES_SIV_CMAC_256;
+  server->siv_algorithms[1] = AEAD_AES_128_GCM_SIV;
+  assert(MAX_SERVER_SIVS == 2);
+
+  for (i = 0; i < 2; i++)
+    server->sivs[i] = SIV_CreateInstance(server->siv_algorithms[i]);
+
+  /* AES-SIV-CMAC-256 is required on servers */
+  if (!server->sivs[0])
+    LOG_FATAL("Missing AES-SIV-CMAC-256");
 }

 /* ================================================== */
@@ -76,10 +89,15 @@ NNS_Initialise(void)
 void
 NNS_Finalise(void)
 {
+  int i;
+
  if (!server)
    return;

-  SIV_DestroyInstance(server->siv);
+  for (i = 0; i < MAX_SERVER_SIVS; i++) {
+    if (server->sivs[i])
+      SIV_DestroyInstance(server->sivs[i]);
+  }
  Free(server);
  server = NULL;
 }
@@ -94,14 +112,16 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
  unsigned char plaintext[NTP_MAX_EXTENSIONS_LENGTH];
  NKE_Context context;
  NKE_Cookie cookie;
+  SIV_Instance siv;
  void *ef_body;

+  *kod = 0;
+
  if (!server)
    return 0;

-  *kod = 0;
-
  server->num_cookies = 0;
+  server->siv_index = -1;
  server->req_tx = packet->transmit_ts;

  if (info->ext_fields == 0 || info->mode != MODE_CLIENT)
@@ -161,17 +181,22 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
    return 0;
  }

-  if (context.algorithm != SERVER_SIV) {
+  /* Find the SIV instance needed for authentication */
+  for (i = 0; i < MAX_SERVER_SIVS && context.algorithm != server->siv_algorithms[i]; i++)
+    ;
+  if (i == MAX_SERVER_SIVS || !server->sivs[i]) {
    DEBUG_LOG("Unexpected SIV");
    return 0;
  }
+  server->siv_index = i;
+  siv = server->sivs[i];

-  if (!SIV_SetKey(server->siv, context.c2s.key, context.c2s.length)) {
+  if (!SIV_SetKey(siv, context.c2s.key, context.c2s.length)) {
    DEBUG_LOG("Could not set C2S key");
    return 0;
  }

-  if (!NNA_DecryptAuthEF(packet, info, server->siv, auth_start,
+  if (!NNA_DecryptAuthEF(packet, info, siv, auth_start,
                         plaintext, sizeof (plaintext), &plaintext_length)) {
    *kod = NTP_KOD_NTS_NAK;
    return 0;
@@ -197,7 +222,7 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
    }
  }

-  if (!SIV_SetKey(server->siv, context.s2c.key, context.s2c.length)) {
+  if (!SIV_SetKey(siv, context.s2c.key, context.s2c.length)) {
    DEBUG_LOG("Could not set S2C key");
    return 0;
  }
@@ -234,13 +259,12 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,

  /* Make sure this is a response to the request from the last call
     of NNS_CheckRequestAuth() */
-  if (UTI_CompareNtp64(&server->req_tx, &request->transmit_ts) != 0)
-    assert(0);
+  BRIEF_ASSERT(UTI_CompareNtp64(&server->req_tx, &request->transmit_ts) == 0);

  for (parsed = NTP_HEADER_LENGTH; parsed < req_info->length; parsed += ef_length) {
    if (!NEF_ParseField(request, req_info->length, parsed,
                        &ef_length, &ef_type, &ef_body, &ef_body_length))
-      /* This is not expected as the packet already passed NAU_ParsePacket() */
+      /* This is not expected as the packet already passed parsing */
      return 0;

    switch (ef_type) {
@@ -254,7 +278,7 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
  }

  /* NTS NAK response does not have any other fields */
-  if (kod)
+  if (kod == NTP_KOD_NTS_NAK)
    return 1;

  for (i = 0, plaintext_length = 0; i < server->num_cookies; i++) {
@@ -269,9 +293,12 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,

  server->num_cookies = 0;

+  if (server->siv_index < 0)
+    return 0;
+
  /* Generate an authenticator field which will make the length
     of the response equal to the length of the request */
-  if (!NNA_GenerateAuthEF(response, res_info, server->siv,
+  if (!NNA_GenerateAuthEF(response, res_info, server->sivs[server->siv_index],
                          server->nonce, sizeof (server->nonce),
                          plaintext, plaintext_length,
                          req_info->length - res_info->length))
--- a/pktlength.c
+++ b/pktlength.c
@@ -55,7 +55,7 @@ struct request_length {
 };

 static const struct request_length request_lengths[] = {
-  REQ_LENGTH_ENTRY(null, null),                 /* NULL */
+  { 0, 0 },                                     /* NULL - not supported */
  REQ_LENGTH_ENTRY(online, null),               /* ONLINE */
  REQ_LENGTH_ENTRY(offline, null),              /* OFFLINE */
  REQ_LENGTH_ENTRY(burst, null),                /* BURST */
@@ -65,7 +65,7 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(modify_maxdelay, null),      /* MODIFY_MAXDELAY */
  REQ_LENGTH_ENTRY(modify_maxdelayratio, null), /* MODIFY_MAXDELAYRATIO */
  REQ_LENGTH_ENTRY(modify_maxupdateskew, null), /* MODIFY_MAXUPDATESKEW */
-  REQ_LENGTH_ENTRY(logon, null),                /* LOGON */
+  { 0, 0 },                                     /* LOGON - not supported */
  REQ_LENGTH_ENTRY(settime, manual_timestamp),  /* SETTIME */
  { 0, 0 },                                     /* LOCAL */
  REQ_LENGTH_ENTRY(manual, null),               /* MANUAL */
@@ -87,7 +87,7 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(del_source, null),           /* DEL_SOURCE */
  REQ_LENGTH_ENTRY(null, null),                 /* WRITERTC */
  REQ_LENGTH_ENTRY(dfreq, null),                /* DFREQ */
-  REQ_LENGTH_ENTRY(doffset, null),              /* DOFFSET */
+  { 0, 0 },                                     /* DOFFSET - not supported */
  REQ_LENGTH_ENTRY(null, tracking),             /* TRACKING */
  REQ_LENGTH_ENTRY(sourcestats, sourcestats),   /* SOURCESTATS */
  REQ_LENGTH_ENTRY(null, rtc),                  /* RTCREPORT */
@@ -111,7 +111,7 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(null, null),                 /* REFRESH */
  REQ_LENGTH_ENTRY(null, server_stats),         /* SERVER_STATS */
  { 0, 0 },                                     /* CLIENT_ACCESSES_BY_INDEX2 - not supported */
-  REQ_LENGTH_ENTRY(local, null),                /* LOCAL2 */
+  { 0, 0 },                                     /* LOCAL2 - not supported */
  REQ_LENGTH_ENTRY(ntp_data, ntp_data),         /* NTP_DATA */
  { 0, 0 },                                     /* ADD_SERVER2 */
  { 0, 0 },                                     /* ADD_PEER2 */
@@ -128,6 +128,10 @@ static const struct request_length request_lengths[] = {
                   client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX3 */
  REQ_LENGTH_ENTRY(select_data, select_data),   /* SELECT_DATA */
  REQ_LENGTH_ENTRY(null, null),                 /* RELOAD_SOURCES */
+  REQ_LENGTH_ENTRY(doffset, null),              /* DOFFSET2 */
+  REQ_LENGTH_ENTRY(modify_select_opts, null),   /* MODIFY_SELECTOPTS */
+  REQ_LENGTH_ENTRY(modify_offset, null),        /* MODIFY_OFFSET */
+  REQ_LENGTH_ENTRY(local, null),                /* LOCAL3 */
 };

 static const uint16_t reply_lengths[] = {
@@ -147,14 +151,17 @@ static const uint16_t reply_lengths[] = {
  RPY_LENGTH_ENTRY(smoothing),                  /* SMOOTHING */
  0,                                            /* SERVER_STATS - not supported */
  0,                                            /* CLIENT_ACCESSES_BY_INDEX2 - not supported */
-  RPY_LENGTH_ENTRY(ntp_data),                   /* NTP_DATA */
+  0,                                            /* NTP_DATA - not supported */
  RPY_LENGTH_ENTRY(manual_timestamp),           /* MANUAL_TIMESTAMP2 */
  RPY_LENGTH_ENTRY(manual_list),                /* MANUAL_LIST2 */
  RPY_LENGTH_ENTRY(ntp_source_name),            /* NTP_SOURCE_NAME */
  RPY_LENGTH_ENTRY(auth_data),                  /* AUTH_DATA */
  RPY_LENGTH_ENTRY(client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX3 */
-  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS2 */
+  0,                                            /* SERVER_STATS2 - not supported */
  RPY_LENGTH_ENTRY(select_data),                /* SELECT_DATA */
+  0,                                            /* SERVER_STATS3 - not supported */
+  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS4 */
+  RPY_LENGTH_ENTRY(ntp_data),                   /* NTP_DATA2 */
 };

 /* ================================================== */
--- a/privops.c
+++ b/privops.c
@@ -141,6 +141,7 @@ have_helper(void)
 /* ======================================================================= */

 /* HELPER - prepare fatal error for daemon */
+FORMAT_ATTRIBUTE_PRINTF(2, 3)
 static void
 res_fatal(PrvResponse *res, const char *fmt, ...)
 {
@@ -255,7 +256,7 @@ do_bind_socket(ReqBindSocket *req, PrvResponse *res)

  SCK_SockaddrToIPSockAddr(sa, sa_len, &ip_saddr);
  if (ip_saddr.port != 0 && ip_saddr.port != CNF_GetNTPPort() &&
-      ip_saddr.port != CNF_GetAcquisitionPort()) {
+      ip_saddr.port != CNF_GetAcquisitionPort() && ip_saddr.port != CNF_GetPtpPort()) {
    SCK_CloseSocket(sock_fd);
    res_fatal(res, "Invalid port %d", ip_saddr.port);
    return;
@@ -546,9 +547,9 @@ PRV_BindSocket(int sock, struct sockaddr *address, socklen_t address_len)
  PrvResponse res;

  SCK_SockaddrToIPSockAddr(address, address_len, &ip_saddr);
-  if (ip_saddr.port != 0 && ip_saddr.port != CNF_GetNTPPort() &&
-      ip_saddr.port != CNF_GetAcquisitionPort())
-    assert(0);
+  BRIEF_ASSERT(ip_saddr.port == 0 || ip_saddr.port == CNF_GetNTPPort() ||
+               ip_saddr.port == CNF_GetAcquisitionPort() ||
+               ip_saddr.port == CNF_GetPtpPort());

  if (!have_helper())
    return bind(sock, address, address_len);
@@ -662,6 +663,8 @@ PRV_StartHelper(void)
        close(fd);
    }

+    UTI_ResetGetRandomFunctions();
+
    /* ignore signals, the process will exit on OP_QUIT request */
    UTI_SetQuitSignalsHandler(SIG_IGN, 1);

--- a/ptp.h
+++ b/ptp.h
@@ -0,0 +1,70 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2021
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  This is the header file for the Precision Time Protocol (PTP).
+
+  */
+#ifndef GOT_PTP_H
+#define GOT_PTP_H
+
+#include "sysincl.h"
+
+#include "ntp.h"
+
+#define PTP_VERSION_2 2
+#define PTP_VERSION_2_1 (2 | 1 << 4)
+#define PTP_TYPE_SYNC 0
+#define PTP_TYPE_DELAY_REQ 1
+#define PTP_FLAG_UNICAST (1 << (2 + 8))
+#define PTP_TLV_NTP 0x2023
+
+typedef struct {
+  uint8_t type;
+  uint8_t version;
+  uint16_t length;
+  uint8_t domain;
+  uint8_t min_sdoid;
+  uint16_t flags;
+  uint8_t correction[8];
+  uint8_t msg_specific[4];
+  uint8_t port_id[10];
+  uint16_t sequence_id;
+  uint8_t control;
+  int8_t interval;
+} PTP_Header;
+
+typedef struct {
+  uint16_t type;
+  uint16_t length;
+} PTP_TlvHeader;
+
+typedef struct {
+  PTP_Header header;
+  uint8_t origin_ts[10];
+  PTP_TlvHeader tlv_header;
+  NTP_Packet ntp_msg;
+} PTP_NtpMessage;
+
+#define PTP_NTP_PREFIX_LENGTH (int)offsetof(PTP_NtpMessage, ntp_msg)
+
+#endif
--- a/quantiles.c
+++ b/quantiles.c
@@ -0,0 +1,232 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2022
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Estimation of quantiles using the Frugal-2U streaming algorithm
+  (https://arxiv.org/pdf/1407.1121v1.pdf)
+  */
+
+#include "config.h"
+
+#include "logging.h"
+#include "memory.h"
+#include "quantiles.h"
+#include "regress.h"
+#include "util.h"
+
+/* Maximum number of repeated estimates for stabilisation */
+#define MAX_REPEAT 64
+
+struct Quantile {
+  double est;
+  double step;
+  int sign;
+};
+
+struct QNT_Instance_Record {
+  struct Quantile *quants;
+  int n_quants;
+  int repeat;
+  int q;
+  int min_k;
+  double min_step;
+  double neg_step_limit;
+  int n_set;
+};
+
+/* ================================================== */
+
+QNT_Instance
+QNT_CreateInstance(int min_k, int max_k, int q, int repeat,
+                   int large_step_delay, double min_step)
+{
+  QNT_Instance inst;
+  long seed;
+
+  BRIEF_ASSERT(q >= 2 && min_k <= max_k && min_k >= 1 && max_k < q && repeat >= 1 &&
+               repeat <= MAX_REPEAT && min_step > 0.0 && large_step_delay >= 0);
+
+  inst = MallocNew(struct QNT_Instance_Record);
+  inst->n_quants = (max_k - min_k + 1) * repeat;
+  inst->quants = MallocArray(struct Quantile, inst->n_quants);
+  inst->repeat = repeat;
+  inst->q = q;
+  inst->min_k = min_k;
+  inst->min_step = min_step;
+  inst->neg_step_limit = -large_step_delay * min_step;
+
+  QNT_Reset(inst);
+
+  /* Seed the random number generator, which will not be isolated from
+     other instances and other random() users */
+  UTI_GetRandomBytes(&seed, sizeof (seed));
+  srandom(seed);
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+QNT_DestroyInstance(QNT_Instance inst)
+{
+  Free(inst->quants);
+  Free(inst);
+}
+
+/* ================================================== */
+
+void
+QNT_Reset(QNT_Instance inst)
+{
+  int i;
+
+  inst->n_set = 0;
+
+  for (i = 0; i < inst->n_quants; i++) {
+    inst->quants[i].est = 0.0;
+    inst->quants[i].step = inst->min_step;
+    inst->quants[i].sign = 1;
+  }
+}
+
+/* ================================================== */
+
+static void
+insert_initial_value(QNT_Instance inst, double value)
+{
+  int i, j, r = inst->repeat;
+
+  BRIEF_ASSERT(inst->n_set * r < inst->n_quants);
+
+  /* Keep the initial estimates repeated and ordered */
+  for (i = inst->n_set; i > 0 && inst->quants[(i - 1) * r].est > value; i--) {
+    for (j = 0; j < r; j++)
+      inst->quants[i * r + j].est = inst->quants[(i - 1) * r].est;
+  }
+
+  for (j = 0; j < r; j++)
+    inst->quants[i * r + j].est = value;
+  inst->n_set++;
+
+  /* Duplicate the largest value in unset quantiles */
+  for (i = inst->n_set * r; i < inst->n_quants; i++)
+    inst->quants[i].est = inst->quants[i - 1].est;
+}
+
+/* ================================================== */
+
+static void
+update_estimate(struct Quantile *quantile, double value, double p, double rand,
+                double min_step, double neg_step_limit)
+{
+  if (value >= quantile->est) {
+    if (rand < (1.0 - p))
+        return;
+    quantile->step += quantile->sign > 0 ? min_step : -min_step;
+    quantile->est += quantile->step > min_step ? quantile->step : min_step;
+    if (quantile->est > value) {
+      quantile->step += value - quantile->est;
+      quantile->est = value + min_step / 4.0;
+    }
+    if (quantile->sign < 0 && quantile->step > min_step)
+      quantile->step = min_step;
+    quantile->sign = 1;
+  } else {
+    if (rand < p)
+      return;
+    quantile->step += quantile->sign < 0 ? min_step : -min_step;
+    quantile->est -= quantile->step > min_step ? quantile->step : min_step;
+    if (quantile->est < value) {
+      quantile->step += quantile->est - value;
+      quantile->est = value - min_step / 4.0;
+    }
+    if (quantile->sign > 0 && quantile->step > min_step)
+      quantile->step = min_step;
+    quantile->sign = -1;
+  }
+
+  if (quantile->step < neg_step_limit)
+    quantile->step = neg_step_limit;
+}
+
+/* ================================================== */
+
+void
+QNT_Accumulate(QNT_Instance inst, double value)
+{
+  double p, rand;
+  int i;
+
+  /* Initialise the estimates with first received values */
+  if (inst->n_set * inst->repeat < inst->n_quants) {
+    insert_initial_value(inst, value);
+    return;
+  }
+
+  for (i = 0; i < inst->n_quants; i++) {
+    p = (double)(i / inst->repeat + inst->min_k) / inst->q;
+    rand = (double)random() / ((1U << 31) - 1);
+
+    update_estimate(&inst->quants[i], value, p, rand, inst->min_step, inst->neg_step_limit);
+  }
+}
+
+/* ================================================== */
+
+int
+QNT_GetMinK(QNT_Instance inst)
+{
+  return inst->min_k;
+}
+
+/* ================================================== */
+
+int
+QNT_GetMaxK(QNT_Instance inst)
+{
+  return inst->min_k + (inst->n_quants / inst->repeat) - 1;
+}
+
+/* ================================================== */
+
+double
+QNT_GetMinStep(QNT_Instance inst)
+{
+  return inst->min_step;
+}
+
+/* ================================================== */
+
+double
+QNT_GetQuantile(QNT_Instance inst, int k)
+{
+  double estimates[MAX_REPEAT];
+  int i;
+
+  BRIEF_ASSERT(k >= inst->min_k && (k - inst->min_k) * inst->repeat < inst->n_quants);
+
+  for (i = 0; i < inst->repeat; i++)
+    estimates[i] = inst->quants[(k - inst->min_k) * inst->repeat + i].est;
+
+  return RGR_FindMedian(estimates, inst->repeat);
+}
--- a/quantiles.h
+++ b/quantiles.h
@@ -0,0 +1,44 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2022
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for estimation of quantiles.
+
+  */
+
+#ifndef GOT_QUANTILES_H
+#define GOT_QUANTILES_H
+
+typedef struct QNT_Instance_Record *QNT_Instance;
+
+extern QNT_Instance QNT_CreateInstance(int min_k, int max_k, int q, int repeat,
+                                       int large_step_delay, double min_step);
+extern void QNT_DestroyInstance(QNT_Instance inst);
+
+extern void QNT_Reset(QNT_Instance inst);
+extern void QNT_Accumulate(QNT_Instance inst, double value);
+extern int QNT_GetMinK(QNT_Instance inst);
+extern int QNT_GetMaxK(QNT_Instance inst);
+extern double QNT_GetMinStep(QNT_Instance inst);
+extern double QNT_GetQuantile(QNT_Instance inst, int k);
+
+#endif
--- a/refclock.c
+++ b/refclock.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2019
+ * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2019, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -40,11 +40,15 @@
 #include "samplefilt.h"
 #include "sched.h"

+/* Maximum offset of locked reference as a fraction of the PPS interval */
+#define PPS_LOCK_LIMIT 0.4
+
 /* list of refclock drivers */
 extern RefclockDriver RCL_SHM_driver;
 extern RefclockDriver RCL_SOCK_driver;
 extern RefclockDriver RCL_PPS_driver;
 extern RefclockDriver RCL_PHC_driver;
+extern RefclockDriver RCL_RTC_driver;

 struct FilterSample {
  double offset;
@@ -52,21 +56,6 @@ struct FilterSample {
  struct timespec sample_time;
 };

-struct MedianFilter {
-  int length;
-  int index;
-  int used;
-  int last;
-  int avg_var_n;
-  double avg_var;
-  double max_var;
-  struct FilterSample *samples;
-  int *selected;
-  double *x_data;
-  double *y_data;
-  double *w_data;
-};
-
 struct RCL_Instance_Record {
  RefclockDriver *driver;
  void *data;
@@ -75,7 +64,9 @@ struct RCL_Instance_Record {
  int driver_poll;
  int driver_polled;
  int poll;
+  int reached;
  int leap_status;
+  int local;
  int pps_forced;
  int pps_rate;
  int pps_active;
@@ -170,6 +161,8 @@ RCL_AddRefclock(RefclockParameters *params)
    inst->driver = &RCL_PPS_driver;
  } else if (strcmp(params->driver_name, "PHC") == 0) {
    inst->driver = &RCL_PHC_driver;
+  } else if (strcmp(params->driver_name, "RTC") == 0) {
+    inst->driver = &RCL_RTC_driver;
  } else {
    LOG_FATAL("unknown refclock driver %s", params->driver_name);
  }
@@ -177,16 +170,18 @@ RCL_AddRefclock(RefclockParameters *params)
  if (!inst->driver->init && !inst->driver->poll)
    LOG_FATAL("refclock driver %s is not compiled in", params->driver_name);

-  if (params->tai && !CNF_GetLeapSecTimezone())
-    LOG_FATAL("refclock tai option requires leapsectz");
+  if (params->tai && !CNF_GetLeapSecList() && !CNF_GetLeapSecTimezone())
+    LOG_FATAL("refclock tai option requires leapseclist or leapsectz");

  inst->data = NULL;
-  inst->driver_parameter = params->driver_parameter;
+  inst->driver_parameter = Strdup(params->driver_parameter);
  inst->driver_parameter_length = 0;
  inst->driver_poll = params->driver_poll;
  inst->poll = params->poll;
  inst->driver_polled = 0;
+  inst->reached = 0;
  inst->leap_status = LEAP_Normal;
+  inst->local = params->local;
  inst->pps_forced = params->pps_forced;
  inst->pps_rate = params->pps_rate;
  inst->pps_active = 0;
@@ -228,48 +223,40 @@ RCL_AddRefclock(RefclockParameters *params)
    inst->ref_id = (uint32_t)ref[0] << 24 | ref[1] << 16 | ref[2] << 8 | ref[3];
  }

-  if (inst->driver->poll) {
-    int max_samples;
+  if (inst->local) {
+    inst->pps_forced = 1;
+    inst->lock_ref = inst->ref_id;
+    inst->leap_status = LEAP_Unsynchronised;
+    inst->max_lock_age = MAX(inst->max_lock_age, 3);
+  }

+  if (inst->driver->poll) {
    if (inst->driver_poll > inst->poll)
      inst->driver_poll = inst->poll;
-
-    max_samples = 1 << (inst->poll - inst->driver_poll);
-    if (max_samples < params->filter_length) {
-      if (max_samples < 4) {
-        LOG(LOGS_WARN, "Setting filter length for %s to %d",
-            UTI_RefidToString(inst->ref_id), max_samples);
-      }
-      params->filter_length = max_samples;
-    }
  }

  if (inst->driver->init && !inst->driver->init(inst))
    LOG_FATAL("refclock %s initialisation failed", params->driver_name);

-  /* Require the filter to have at least 4 samples to produce a filtered
-     sample, or be full for shorter lengths, and combine 60% of samples
-     closest to the median */
-  inst->filter = SPF_CreateInstance(MIN(params->filter_length, 4), params->filter_length,
-                                    params->max_dispersion, 0.6);
+  /* Don't require more than one sample per poll and combine 60% of the
+     samples closest to the median offset */
+  inst->filter = SPF_CreateInstance(1, params->filter_length, params->max_dispersion, 0.6);

  inst->source = SRC_CreateNewInstance(inst->ref_id, SRC_REFCLOCK, 0, params->sel_options,
                                       NULL, params->min_samples, params->max_samples,
-                                       0.0, 0.0);
+                                       0.0, 0.0, params->max_unreach);

  DEBUG_LOG("refclock %s refid=%s poll=%d dpoll=%d filter=%d",
      params->driver_name, UTI_RefidToString(inst->ref_id),
      inst->poll, inst->driver_poll, params->filter_length);

-  Free(params->driver_name);
-
  return 1;
 }

 void
 RCL_StartRefclocks(void)
 {
-  unsigned int i, j, n;
+  unsigned int i, j, n, lock_index;

  n = ARR_GetSize(refclocks);

@@ -279,13 +266,31 @@ RCL_StartRefclocks(void)
    SRC_SetActive(inst->source);
    inst->timeout_id = SCH_AddTimeoutByDelay(0.0, poll_timeout, (void *)inst);

-    if (inst->lock_ref) {
-      /* Replace lock refid with index to refclocks */
-      for (j = 0; j < n && get_refclock(j)->ref_id != inst->lock_ref; j++)
-        ;
-      inst->lock_ref = j < n ? j : -1;
-    } else
-      inst->lock_ref = -1;
+    /* Replace lock refid with the refclock's index, or -1 if not valid */
+
+    lock_index = -1;
+
+    if (inst->lock_ref != 0) {
+      for (j = 0; j < n; j++) {
+        RCL_Instance inst2 = get_refclock(j);
+
+        if (inst->lock_ref != inst2->ref_id)
+          continue;
+
+        if (inst->driver->poll && inst2->driver->poll &&
+            (double)inst->max_lock_age / inst->pps_rate < UTI_Log2ToDouble(inst2->driver_poll))
+          LOG(LOGS_WARN, "%s maxlockage too small for %s",
+              UTI_RefidToString(inst->ref_id), UTI_RefidToString(inst2->ref_id));
+
+        lock_index = j;
+        break;
+      }
+
+      if (lock_index == -1 || (lock_index == i && !inst->local))
+        LOG(LOGS_WARN, "Invalid lock refid %s", UTI_RefidToString(inst->lock_ref));
+    }
+
+    inst->lock_ref = lock_index;
  }
 }

@@ -308,6 +313,22 @@ RCL_ReportSource(RPT_SourceReport *report, struct timespec *now)
  }
 }

+int
+RCL_ModifyOffset(uint32_t ref_id, double offset)
+{
+  unsigned int i;
+
+  for (i = 0; i < ARR_GetSize(refclocks); i++) {
+    RCL_Instance inst = get_refclock(i);
+    if (inst->ref_id == ref_id) {
+      inst->offset = offset;
+      LOG(LOGS_INFO, "Source %s new offset %f", UTI_RefidToString(ref_id), offset);
+      return 1;
+    }
+  }
+  return 0;
+}
+
 void
 RCL_SetDriverData(RCL_Instance instance, void *data)
 {
@@ -406,10 +427,21 @@ convert_tai_offset(struct timespec *sample_time, double *offset)
 }

 static int
-accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double offset, double dispersion)
+accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double offset, double dispersion,
+                  int quality)
 {
  NTP_Sample sample;

+  instance->reached++;
+
+  /* Don't accumulate the sample if the driver is suggesting it should be
+     dropped due to low quality.  The only reason it went so far was to update
+     the reachability. */
+  if (quality < 1) {
+    DEBUG_LOG("refclock sample ignored quality=%d", quality);
+    return 0;
+  }
+
  sample.time = *sample_time;
  sample.offset = offset;
  sample.peer_delay = instance->delay;
@@ -417,30 +449,28 @@ accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double of
  sample.peer_dispersion = dispersion;
  sample.root_dispersion = dispersion;

-  /* Handle special case when PPS is used with the local reference */
-  if (instance->pps_active && instance->lock_ref == -1)
-    sample.stratum = pps_stratum(instance, &sample.time);
-  else
-    sample.stratum = instance->stratum;
-
  return SPF_AccumulateSample(instance->filter, &sample);
 }

 int
-RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap)
+RCL_AddSample(RCL_Instance instance, struct timespec *sample_time,
+              struct timespec *ref_time, int leap, int quality)
 {
-  double correction, dispersion;
+  double correction, dispersion, raw_offset, offset;
  struct timespec cooked_time;

  if (instance->pps_forced)
-    return RCL_AddPulse(instance, sample_time, -offset);
+    return RCL_AddPulse(instance, sample_time,
+                        1.0e-9 * (sample_time->tv_nsec - ref_time->tv_nsec), quality);
+
+  raw_offset = UTI_DiffTimespecsToDouble(ref_time, sample_time);

  LCL_GetOffsetCorrection(sample_time, &correction, &dispersion);
  UTI_AddDoubleToTimespec(sample_time, correction, &cooked_time);
  dispersion += instance->precision;

  /* Make sure the timestamp and offset provided by the driver are sane */
-  if (!UTI_IsTimeOffsetSane(sample_time, offset) ||
+  if (!UTI_IsTimeOffsetSane(sample_time, raw_offset) ||
      !valid_sample_time(instance, &cooked_time))
    return 0;

@@ -455,18 +485,24 @@ RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset
      return 0;
  }

+  /* Calculate offset = raw_offset - correction + instance->offset
+     in parts to avoid loss of precision if there are large differences */
+  offset = ref_time->tv_sec - sample_time->tv_sec -
+           (time_t)correction + (time_t)instance->offset;
+  offset += 1.0e-9 * (ref_time->tv_nsec - sample_time->tv_nsec) -
+            (correction - (time_t)correction) + (instance->offset - (time_t)instance->offset);
+
  if (instance->tai && !convert_tai_offset(sample_time, &offset)) {
    DEBUG_LOG("refclock sample ignored unknown TAI offset");
    return 0;
  }

-  if (!accumulate_sample(instance, &cooked_time,
-                         offset - correction + instance->offset, dispersion))
+  if (!accumulate_sample(instance, &cooked_time, offset, dispersion, quality))
    return 0;

  instance->pps_active = 0;

-  log_sample(instance, &cooked_time, 0, 0, offset, offset - correction + instance->offset, dispersion);
+  log_sample(instance, &cooked_time, 0, 0, raw_offset, offset, dispersion);

  /* for logging purposes */
  if (!instance->driver->poll)
@@ -476,7 +512,7 @@ RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset
 }

 int
-RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second)
+RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second, int quality)
 {
  double correction, dispersion;
  struct timespec cooked_time;
@@ -488,7 +524,7 @@ RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second)
  if (!UTI_IsTimeOffsetSane(pulse_time, 0.0))
    return 0;

-  return RCL_AddCookedPulse(instance, &cooked_time, second, dispersion, correction);
+  return RCL_AddCookedPulse(instance, &cooked_time, second, dispersion, correction, quality);
 }

 static int
@@ -514,7 +550,7 @@ check_pulse_edge(RCL_Instance instance, double offset, double distance)

 int
 RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
-                   double second, double dispersion, double raw_correction)
+                   double second, double dispersion, double raw_correction, int quality)
 {
  double offset;
  int rate;
@@ -545,29 +581,40 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
    lock_refclock = get_refclock(instance->lock_ref);

    if (!SPF_GetLastSample(lock_refclock->filter, &ref_sample)) {
-      DEBUG_LOG("refclock pulse ignored no ref sample");
-      return 0;
+      if (instance->local) {
+        /* Make the first sample in order to lock to itself */
+        ref_sample.time = *cooked_time;
+        ref_sample.offset = offset;
+        ref_sample.peer_delay = ref_sample.peer_dispersion = 0;
+        ref_sample.root_delay = ref_sample.root_dispersion = 0;
+      } else {
+        DEBUG_LOG("refclock pulse ignored no ref sample");
+        return 0;
+      }
    }

    ref_sample.root_dispersion += SPF_GetAvgSampleDispersion(lock_refclock->filter);

    sample_diff = UTI_DiffTimespecsToDouble(cooked_time, &ref_sample.time);
    if (fabs(sample_diff) >= (double)instance->max_lock_age / rate) {
-      DEBUG_LOG("refclock pulse ignored samplediff=%.9f",
-          sample_diff);
+      DEBUG_LOG("refclock pulse ignored samplediff=%.9f", sample_diff);
+
+      /* Restart the local mode */
+      if (instance->local) {
+        LOG(LOGS_WARN, "Local refclock lost lock");
+        SPF_DropSamples(instance->filter);
+        SRC_ResetInstance(instance->source);
+      }
      return 0;
    }

    /* Align the offset to the reference sample */
-    if ((ref_sample.offset - offset) >= 0.0)
-      shift = (long)((ref_sample.offset - offset) * rate + 0.5) / (double)rate;
-    else
-      shift = (long)((ref_sample.offset - offset) * rate - 0.5) / (double)rate;
+    shift = round((ref_sample.offset - offset) * rate) / rate;

    offset += shift;

    if (fabs(ref_sample.offset - offset) +
-        ref_sample.root_dispersion + dispersion >= 0.2 / rate) {
+        ref_sample.root_dispersion + dispersion > PPS_LOCK_LIMIT / rate) {
      DEBUG_LOG("refclock pulse ignored offdiff=%.9f refdisp=%.9f disp=%.9f",
                ref_sample.offset - offset, ref_sample.root_dispersion, dispersion);
      return 0;
@@ -605,7 +652,7 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
      return 0;
  }

-  if (!accumulate_sample(instance, cooked_time, offset, dispersion))
+  if (!accumulate_sample(instance, cooked_time, offset, dispersion, quality))
    return 0;

  instance->leap_status = leap;
@@ -683,11 +730,57 @@ pps_stratum(RCL_Instance instance, struct timespec *ts)
  return 0;
 }

+static void
+get_local_stats(RCL_Instance inst, struct timespec *ref, double *freq, double *offset)
+{
+  double offset_sd, freq_sd, skew, root_delay, root_disp;
+  SST_Stats stats = SRC_GetSourcestats(inst->source);
+
+  if (SST_Samples(stats) < SST_GetMinSamples(stats)) {
+    UTI_ZeroTimespec(ref);
+    return;
+  }
+
+  SST_GetTrackingData(stats, ref, offset, &offset_sd, freq, &freq_sd,
+                      &skew, &root_delay, &root_disp);
+}
+
+static void
+follow_local(RCL_Instance inst, struct timespec *prev_ref_time, double prev_freq,
+             double prev_offset)
+{
+  SST_Stats stats = SRC_GetSourcestats(inst->source);
+  double freq, dfreq, offset, doffset, elapsed;
+  struct timespec now, ref_time;
+
+  get_local_stats(inst, &ref_time, &freq, &offset);
+
+  if (UTI_IsZeroTimespec(prev_ref_time) || UTI_IsZeroTimespec(&ref_time))
+    return;
+
+  dfreq = (freq - prev_freq) / (1.0 - prev_freq);
+  elapsed = UTI_DiffTimespecsToDouble(&ref_time, prev_ref_time);
+  doffset = offset - elapsed * prev_freq - prev_offset;
+
+  if (!REF_AdjustReference(doffset, dfreq))
+    return;
+
+  LCL_ReadCookedTime(&now, NULL);
+  SST_SlewSamples(stats, &now, dfreq, doffset);
+  SPF_SlewSamples(inst->filter, &now, dfreq, doffset);
+
+  /* Keep the offset close to zero to not lose precision */
+  if (fabs(offset) >= 1.0) {
+    SST_CorrectOffset(stats, -round(offset));
+    SPF_CorrectOffset(inst->filter, -round(offset));
+  }
+}
+
 static void
 poll_timeout(void *arg)
 {
  NTP_Sample sample;
-  int poll;
+  int poll, stratum;

  RCL_Instance inst = (RCL_Instance)arg;

@@ -702,15 +795,32 @@ poll_timeout(void *arg)
  if (!(inst->driver->poll && inst->driver_polled < (1 << (inst->poll - inst->driver_poll)))) {
    inst->driver_polled = 0;

+    SRC_UpdateReachability(inst->source, inst->reached > 0);
+    inst->reached = 0;
+
    if (SPF_GetFilteredSample(inst->filter, &sample)) {
-      SRC_UpdateReachability(inst->source, 1);
-      SRC_SetLeapStatus(inst->source, inst->leap_status);
+      double local_freq, local_offset;
+      struct timespec local_ref_time;
+
+      /* Handle special case when PPS is used with the local reference */
+      if (inst->pps_active && inst->lock_ref == -1)
+        stratum = pps_stratum(inst, &sample.time);
+      else
+        stratum = inst->stratum;
+
+      if (inst->local) {
+        get_local_stats(inst, &local_ref_time, &local_freq, &local_offset);
+        inst->leap_status = LEAP_Unsynchronised;
+      }
+
+      SRC_UpdateStatus(inst->source, stratum, inst->leap_status);
      SRC_AccumulateSample(inst->source, &sample);
      SRC_SelectSource(inst->source);

+      if (inst->local)
+        follow_local(inst, &local_ref_time, local_freq, local_offset);
+
      log_sample(inst, &sample.time, 1, 0, 0.0, sample.offset, sample.peer_dispersion);
-    } else {
-      SRC_UpdateReachability(inst->source, 0);
    }
  }

--- a/refclock.h
+++ b/refclock.h
@@ -37,10 +37,12 @@ typedef struct {
  int driver_poll;
  int poll;
  int filter_length;
+  int local;
  int pps_forced;
  int pps_rate;
  int min_samples;
  int max_samples;
+  int max_unreach;
  int sel_options;
  int max_lock_age;
  int stratum;
@@ -67,6 +69,7 @@ extern void RCL_Finalise(void);
 extern int RCL_AddRefclock(RefclockParameters *params);
 extern void RCL_StartRefclocks(void);
 extern void RCL_ReportSource(RPT_SourceReport *report, struct timespec *now);
+extern int RCL_ModifyOffset(uint32_t ref_id, double offset);

 /* functions used by drivers */
 extern void RCL_SetDriverData(RCL_Instance instance, void *data);
@@ -74,10 +77,13 @@ extern void *RCL_GetDriverData(RCL_Instance instance);
 extern char *RCL_GetDriverParameter(RCL_Instance instance);
 extern void RCL_CheckDriverOptions(RCL_Instance instance, const char **options);
 extern char *RCL_GetDriverOption(RCL_Instance instance, char *name);
-extern int RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap);
-extern int RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second);
+extern int RCL_AddSample(RCL_Instance instance, struct timespec *sample_time,
+                         struct timespec *ref_time, int leap, int quality);
+extern int RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second,
+                        int quality);
 extern int RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
-                              double second, double dispersion, double raw_correction);
+                              double second, double dispersion, double raw_correction,
+                              int quality);
 extern double RCL_GetPrecision(RCL_Instance instance);
 extern int RCL_GetDriverPoll(RCL_Instance instance);

--- a/refclock_phc.c
+++ b/refclock_phc.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2013, 2017
+ * Copyright (C) Miroslav Lichvar  2013, 2017, 2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +33,9 @@

 #include "sysincl.h"

+#include <sys/sysmacros.h>
+
+#include "array.h"
 #include "refclock.h"
 #include "hwclock.h"
 #include "local.h"
@@ -44,38 +47,49 @@

 struct phc_instance {
  int fd;
+  int dev_index;
  int mode;
  int nocrossts;
  int extpps;
  int pin;
  int channel;
+  struct timespec last_extts;
  HCL_Instance clock;
 };

+/* Array of RCL_Instance with enabled extpps */
+static ARR_Instance extts_phcs = NULL;
+
 static void read_ext_pulse(int sockfd, int event, void *anything);

 static int phc_initialise(RCL_Instance instance)
 {
  const char *options[] = {"nocrossts", "extpps", "pin", "channel", "clear", NULL};
  struct phc_instance *phc;
-  int phc_fd, rising_edge;
+  int rising_edge;
+  struct stat st;
  char *path, *s;

  RCL_CheckDriverOptions(instance, options);

  path = RCL_GetDriverParameter(instance);
 
-  phc_fd = SYS_Linux_OpenPHC(path, 0);
-  if (phc_fd < 0) {
-    LOG_FATAL("Could not open PHC");
-    return 0;
-  }
-
  phc = MallocNew(struct phc_instance);
-  phc->fd = phc_fd;
  phc->mode = 0;
  phc->nocrossts = RCL_GetDriverOption(instance, "nocrossts") ? 1 : 0;
  phc->extpps = RCL_GetDriverOption(instance, "extpps") ? 1 : 0;
+  UTI_ZeroTimespec(&phc->last_extts);
+
+  phc->fd = SYS_Linux_OpenPHC(path, phc->extpps ? O_RDWR : O_RDONLY);
+  if (phc->fd < 0)
+    LOG_FATAL("Could not open PHC");
+
+  if (fstat(phc->fd, &st) < 0 || !S_ISCHR(st.st_mode))
+    LOG_FATAL("Could not get PHC index");
+  phc->dev_index = minor(st.st_rdev);
+
+  phc->clock = HCL_CreateInstance(0, 16, UTI_Log2ToDouble(RCL_GetDriverPoll(instance)),
+                                  RCL_GetPrecision(instance));

  if (phc->extpps) {
    s = RCL_GetDriverOption(instance, "pin");
@@ -83,16 +97,18 @@ static int phc_initialise(RCL_Instance instance)
    s = RCL_GetDriverOption(instance, "channel");
    phc->channel = s ? atoi(s) : 0;
    rising_edge = RCL_GetDriverOption(instance, "clear") ? 0 : 1;
-    phc->clock = HCL_CreateInstance(0, 16, UTI_Log2ToDouble(RCL_GetDriverPoll(instance)));

    if (!SYS_Linux_SetPHCExtTimestamping(phc->fd, phc->pin, phc->channel,
                                         rising_edge, !rising_edge, 1))
      LOG_FATAL("Could not enable external PHC timestamping");

    SCH_AddFileHandler(phc->fd, SCH_FILE_INPUT, read_ext_pulse, instance);
+
+    if (!extts_phcs)
+      extts_phcs = ARR_CreateInstance(sizeof (RCL_Instance));
+    ARR_AppendElement(extts_phcs, &instance);
  } else {
    phc->pin = phc->channel = 0;
-    phc->clock = NULL;
  }

  RCL_SetDriverData(instance, phc);
@@ -102,68 +118,108 @@ static int phc_initialise(RCL_Instance instance)
 static void phc_finalise(RCL_Instance instance)
 {
  struct phc_instance *phc;
+  unsigned int i;

  phc = (struct phc_instance *)RCL_GetDriverData(instance);

  if (phc->extpps) {
    SCH_RemoveFileHandler(phc->fd);
    SYS_Linux_SetPHCExtTimestamping(phc->fd, phc->pin, phc->channel, 0, 0, 0);
-    HCL_DestroyInstance(phc->clock);
+
+    for (i = 0; i < ARR_GetSize(extts_phcs); i++) {
+      if ((*(RCL_Instance *)ARR_GetElement(extts_phcs, i)) == instance)
+        ARR_RemoveElement(extts_phcs, i--);
+    }
+    if (ARR_GetSize(extts_phcs) == 0) {
+      ARR_DestroyInstance(extts_phcs);
+      extts_phcs = NULL;
+    }
  }

+  HCL_DestroyInstance(phc->clock);
  close(phc->fd);
  Free(phc);
 }

+static void process_ext_pulse(RCL_Instance instance, struct timespec *phc_ts)
+{
+  struct phc_instance *phc;
+  struct timespec local_ts;
+  double local_err;
+
+  phc = RCL_GetDriverData(instance);
+
+  if (UTI_CompareTimespecs(&phc->last_extts, phc_ts) == 0) {
+    DEBUG_LOG("Ignoring duplicated PHC timestamp");
+    return;
+  }
+  phc->last_extts = *phc_ts;
+
+  if (!HCL_CookTime(phc->clock, phc_ts, &local_ts, &local_err))
+    return;
+
+  RCL_AddCookedPulse(instance, &local_ts, 1.0e-9 * local_ts.tv_nsec, local_err,
+                     UTI_DiffTimespecsToDouble(phc_ts, &local_ts), 1);
+}
+
 static void read_ext_pulse(int fd, int event, void *anything)
 {
  RCL_Instance instance;
-  struct phc_instance *phc;
-  struct timespec phc_ts, local_ts;
-  double local_err;
+  struct phc_instance *phc1, *phc2;
+  struct timespec phc_ts;
+  unsigned int i;
  int channel;

+  if (!SYS_Linux_ReadPHCExtTimestamp(fd, &phc_ts, &channel))
+    return;
+
  instance = anything;
-  phc = RCL_GetDriverData(instance);
+  phc1 = RCL_GetDriverData(instance);

-  if (!SYS_Linux_ReadPHCExtTimestamp(phc->fd, &phc_ts, &channel))
-    return;
+  /* Linux versions before 6.7 had one shared queue of timestamps for all
+     descriptors of the same PHC.  Search for all refclocks that expect
+     the timestamp. */

-  if (channel != phc->channel) {
-    DEBUG_LOG("Unexpected extts channel %d\n", channel);
-    return;
+  for (i = 0; i < ARR_GetSize(extts_phcs); i++) {
+    instance = *(RCL_Instance *)ARR_GetElement(extts_phcs, i);
+    phc2 = RCL_GetDriverData(instance);
+    if (!phc2->extpps || phc2->dev_index != phc1->dev_index || phc2->channel != channel)
+      continue;
+    process_ext_pulse(instance, &phc_ts);
  }
-
-  if (!HCL_CookTime(phc->clock, &phc_ts, &local_ts, &local_err))
-    return;
-
-  RCL_AddCookedPulse(instance, &local_ts, 1.0e-9 * local_ts.tv_nsec, local_err,
-                     UTI_DiffTimespecsToDouble(&phc_ts, &local_ts));
 }

+#define PHC_READINGS 25
+
 static int phc_poll(RCL_Instance instance)
 {
+  struct timespec phc_ts, sys_ts, local_ts, readings[PHC_READINGS][3];
  struct phc_instance *phc;
-  struct timespec phc_ts, sys_ts, local_ts;
-  double offset, phc_err, local_err;
+  double phc_err, local_err;
+  int n_readings, quality;

  phc = (struct phc_instance *)RCL_GetDriverData(instance);

-  if (!SYS_Linux_GetPHCSample(phc->fd, phc->nocrossts, RCL_GetPrecision(instance),
-                              &phc->mode, &phc_ts, &sys_ts, &phc_err))
+  n_readings = SYS_Linux_GetPHCReadings(phc->fd, phc->nocrossts, &phc->mode,
+                                        PHC_READINGS, readings);
+  if (n_readings < 1)
    return 0;

-  if (phc->extpps) {
-    LCL_CookTime(&sys_ts, &local_ts, &local_err);
+  if (!HCL_ProcessReadings(phc->clock, n_readings, readings,
+                           &phc_ts, &sys_ts, &phc_err, &quality))
+    return 0;
+
+  LCL_CookTime(&sys_ts, &local_ts, &local_err);
+  if (quality > 0)
    HCL_AccumulateSample(phc->clock, &phc_ts, &local_ts, phc_err + local_err);
+
+  if (phc->extpps)
    return 0;
-  }

-  offset = UTI_DiffTimespecsToDouble(&phc_ts, &sys_ts);
+  DEBUG_LOG("PHC offset: %+.9f err: %.9f",
+            UTI_DiffTimespecsToDouble(&phc_ts, &sys_ts), phc_err);

-  DEBUG_LOG("PHC offset: %+.9f err: %.9f", offset, phc_err);
-
-  return RCL_AddSample(instance, &sys_ts, offset, LEAP_Normal);
+  return RCL_AddSample(instance, &sys_ts, &phc_ts, LEAP_Normal, quality);
 }

 RefclockDriver RCL_PHC_driver = {
--- a/refclock_pps.c
+++ b/refclock_pps.c
@@ -61,49 +61,36 @@ static int pps_initialise(RCL_Instance instance) {
  edge_clear = RCL_GetDriverOption(instance, "clear") ? 1 : 0;

  fd = open(path, O_RDWR);
-  if (fd < 0) {
+  if (fd < 0)
    LOG_FATAL("Could not open %s : %s", path, strerror(errno));
-    return 0;
-  }

  UTI_FdSetCloexec(fd);

-  if (time_pps_create(fd, &handle) < 0) {
+  if (time_pps_create(fd, &handle) < 0)
    LOG_FATAL("time_pps_create() failed on %s : %s", path, strerror(errno));
-    return 0;
-  }

-  if (time_pps_getcap(handle, &mode) < 0) {
+  if (time_pps_getcap(handle, &mode) < 0)
    LOG_FATAL("time_pps_getcap() failed on %s : %s", path, strerror(errno));
-    return 0;
-  }

-  if (time_pps_getparams(handle, &params) < 0) {
+  if (time_pps_getparams(handle, &params) < 0)
    LOG_FATAL("time_pps_getparams() failed on %s : %s", path, strerror(errno));
-    return 0;
-  }

  if (!edge_clear) {
-    if (!(mode & PPS_CAPTUREASSERT)) {
+    if (!(mode & PPS_CAPTUREASSERT))
      LOG_FATAL("CAPTUREASSERT not supported on %s", path);
-      return 0;
-    }
+
    params.mode |= PPS_CAPTUREASSERT;
    params.mode &= ~PPS_CAPTURECLEAR;
  } else {
-    if (!(mode & PPS_CAPTURECLEAR)) {
+    if (!(mode & PPS_CAPTURECLEAR))
      LOG_FATAL("CAPTURECLEAR not supported on %s", path);
-      return 0;
-    }
+
    params.mode |= PPS_CAPTURECLEAR;
    params.mode &= ~PPS_CAPTUREASSERT;
  }

-  if (time_pps_setparams(handle, &params) < 0) {
+  if (time_pps_setparams(handle, &params) < 0)
    LOG_FATAL("time_pps_setparams() failed on %s : %s", path, strerror(errno));
-    return 0;
-  }
-

  pps = MallocNew(struct pps_instance);
  pps->handle = handle;
@@ -156,7 +143,7 @@ static int pps_poll(RCL_Instance instance)

  pps->last_seq = seq;

-  return RCL_AddPulse(instance, &ts, 1.0e-9 * ts.tv_nsec);
+  return RCL_AddPulse(instance, &ts, 1.0e-9 * ts.tv_nsec, 1);
 }

 RefclockDriver RCL_PPS_driver = {
--- a/refclock_rtc.c
+++ b/refclock_rtc.c
@@ -0,0 +1,180 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Uwe Kleine-König, Pengutronix  2021
+ * Copyright (C) Ahmad Fatoum, Pengutronix  2024
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  RTC refclock driver.
+
+  */
+
+#include "config.h"
+
+#include "refclock.h"
+
+#ifdef FEAT_RTC
+
+#include <linux/rtc.h>
+
+#include "conf.h"
+#include "local.h"
+
+#include "logging.h"
+#include "memory.h"
+#include "sched.h"
+#include "util.h"
+#include "rtc_linux.h"
+
+struct refrtc_instance {
+  int fd;
+  int polling;
+  int utc;
+};
+
+static int refrtc_add_sample(RCL_Instance instance, struct timespec *now,
+                             time_t rtc_sec, long rtc_nsec)
+{
+  struct timespec rtc_ts;
+  int status;
+
+  rtc_ts.tv_sec = rtc_sec;
+  rtc_ts.tv_nsec = rtc_nsec;
+
+  status = RCL_AddSample(instance, now, &rtc_ts, LEAP_Normal, 1);
+
+  return status;
+}
+
+static void refrtc_read_after_uie(int rtcfd, int event, void *data)
+{
+  RCL_Instance instance = (RCL_Instance)data;
+  struct refrtc_instance *rtc = RCL_GetDriverData(instance);
+  struct timespec now;
+  time_t rtc_sec;
+  int status;
+
+  status = RTC_Linux_CheckInterrupt(rtcfd);
+  if (status < 0) {
+    SCH_RemoveFileHandler(rtcfd);
+    RTC_Linux_SwitchInterrupt(rtcfd, 0); /* Likely to raise error too, but just to be sure... */
+    close(rtcfd);
+    rtc->fd = -1;
+    return;
+  } else if (status == 0) {
+    /* Wait for the next interrupt, this one may be bogus */
+    return;
+  }
+
+  rtc_sec = RTC_Linux_ReadTimeAfterInterrupt(rtcfd, rtc->utc, NULL, &now);
+  if (rtc_sec == (time_t)-1)
+    return;
+
+  refrtc_add_sample(instance, &now, rtc_sec, 0);
+}
+
+static int refrtc_initialise(RCL_Instance instance)
+{
+  const char *options[] = {"utc", NULL};
+  struct refrtc_instance *rtc;
+  int rtcfd, status;
+  const char *path;
+
+  RCL_CheckDriverOptions(instance, options);
+
+  if (CNF_GetRtcSync() || CNF_GetRtcFile())
+    LOG_FATAL("RTC refclock cannot be used together with rtcsync or rtcfile");
+
+  path = RCL_GetDriverParameter(instance);
+
+  rtcfd = open(path, O_RDONLY);
+  if (rtcfd < 0)
+    LOG_FATAL("Could not open RTC device %s : %s", path, strerror(errno));
+
+  /* Close on exec */
+  UTI_FdSetCloexec(rtcfd);
+
+  rtc = MallocNew(struct refrtc_instance);
+  rtc->fd = rtcfd;
+  rtc->utc = RCL_GetDriverOption(instance, "utc") ? 1 : 0;
+
+  RCL_SetDriverData(instance, rtc);
+
+  /* Try to enable update interrupts */
+  status = RTC_Linux_SwitchInterrupt(rtcfd, 1);
+  if (status) {
+    SCH_AddFileHandler(rtcfd, SCH_FILE_INPUT, refrtc_read_after_uie, instance);
+    rtc->polling = 0;
+  } else {
+    LOG(LOGS_INFO, "Falling back to polling for %s", path);
+    rtc->polling = 1;
+  }
+
+  return 1;
+}
+
+static void refrtc_finalise(RCL_Instance instance)
+{
+  struct refrtc_instance *rtc;
+
+  rtc = RCL_GetDriverData(instance);
+
+  if (rtc->fd >= 0) {
+    if (!rtc->polling) {
+      SCH_RemoveFileHandler(rtc->fd);
+      RTC_Linux_SwitchInterrupt(rtc->fd, 0);
+    }
+
+    close(rtc->fd);
+  }
+
+  Free(rtc);
+}
+
+static int refrtc_poll(RCL_Instance instance)
+{
+  struct refrtc_instance *rtc;
+  struct timespec now;
+  time_t rtc_sec;
+
+  rtc = RCL_GetDriverData(instance);
+
+  if (!rtc->polling)
+    return 0;
+
+  rtc_sec = RTC_Linux_ReadTimeNow(rtc->fd, rtc->utc, NULL, &now);
+  if (rtc_sec == (time_t)-1)
+    return 0;
+
+  /* As the rtc has a resolution of 1s, only add half a second */
+  return refrtc_add_sample(instance, &now, rtc_sec, 500000000);
+}
+
+RefclockDriver RCL_RTC_driver = {
+  refrtc_initialise,
+  refrtc_finalise,
+  refrtc_poll
+};
+
+#else
+
+RefclockDriver RCL_RTC_driver = { NULL, NULL, NULL };
+
+#endif
--- a/refclock_shm.c
+++ b/refclock_shm.c
@@ -95,7 +95,6 @@ static int shm_poll(RCL_Instance instance)
 {
  struct timespec receive_ts, clock_ts;
  struct shmTime t, *shm;
-  double offset;

  shm = (struct shmTime *)RCL_GetDriverData(instance);

@@ -124,9 +123,8 @@ static int shm_poll(RCL_Instance instance)

  UTI_NormaliseTimespec(&clock_ts);
  UTI_NormaliseTimespec(&receive_ts);
-  offset = UTI_DiffTimespecsToDouble(&clock_ts, &receive_ts);

-  return RCL_AddSample(instance, &receive_ts, offset, t.leap);
+  return RCL_AddSample(instance, &receive_ts, &clock_ts, t.leap, 1);
 }

 RefclockDriver RCL_SHM_driver = {
--- a/refclock_sock.c
+++ b/refclock_sock.c
@@ -58,23 +58,63 @@ struct sock_sample {
  int magic;
 };

+/* On 32-bit glibc-based systems enable conversion between timevals using
+   32-bit and 64-bit time_t to support SOCK clients compiled with different
+   time_t size than chrony */
+#ifdef __GLIBC_PREREQ
+#if __GLIBC_PREREQ(2, 34) && __TIMESIZE == 32
+#define CONVERT_TIMEVAL 1
+#if defined(_TIME_BITS) && _TIME_BITS == 64
+typedef int32_t alt_time_t;
+typedef int32_t alt_suseconds_t;
+#else
+typedef int64_t alt_time_t;
+typedef int64_t alt_suseconds_t;
+#endif
+struct alt_timeval {
+  alt_time_t tv_sec;
+  alt_suseconds_t tv_usec;
+};
+#endif
+#endif
+
 static void read_sample(int sockfd, int event, void *anything)
 {
+  char buf[sizeof (struct sock_sample) + 16];
+  struct timespec sys_ts, ref_ts;
  struct sock_sample sample;
-  struct timespec ts;
  RCL_Instance instance;
  int s;

  instance = (RCL_Instance)anything;

-  s = recv(sockfd, &sample, sizeof (sample), 0);
+  s = recv(sockfd, buf, sizeof (buf), 0);

  if (s < 0) {
    DEBUG_LOG("Could not read SOCK sample : %s", strerror(errno));
    return;
  }

-  if (s != sizeof (sample)) {
+  if (s == sizeof (sample)) {
+    memcpy(&sample, buf, sizeof (sample));
+#ifdef CONVERT_TIMEVAL
+  } else if (s == sizeof (sample) - sizeof (struct timeval) + sizeof (struct alt_timeval)) {
+    struct alt_timeval atv;
+    memcpy(&atv, buf, sizeof (atv));
+#ifndef HAVE_LONG_TIME_T
+    if (atv.tv_sec > INT32_MAX || atv.tv_sec < INT32_MIN ||
+        atv.tv_usec > INT32_MAX || atv.tv_usec < INT32_MIN) {
+      DEBUG_LOG("Could not convert 64-bit timeval");
+      return;
+    }
+#endif
+    sample.tv.tv_sec = atv.tv_sec;
+    sample.tv.tv_usec = atv.tv_usec;
+    DEBUG_LOG("Converted %d-bit timeval", 8 * (int)sizeof (alt_time_t));
+    memcpy((char *)&sample + sizeof (struct timeval), buf + sizeof (struct alt_timeval),
+           sizeof (sample) - sizeof (struct timeval));
+#endif
+  } else {
    DEBUG_LOG("Unexpected length of SOCK sample : %d != %ld",
              s, (long)sizeof (sample));
    return;
@@ -86,13 +126,18 @@ static void read_sample(int sockfd, int event, void *anything)
    return;
  }

-  UTI_TimevalToTimespec(&sample.tv, &ts);
-  UTI_NormaliseTimespec(&ts);
+  UTI_TimevalToTimespec(&sample.tv, &sys_ts);
+  UTI_NormaliseTimespec(&sys_ts);
+
+  if (!UTI_IsTimeOffsetSane(&sys_ts, sample.offset))
+    return;
+
+  UTI_AddDoubleToTimespec(&sys_ts, sample.offset, &ref_ts);

  if (sample.pulse) {
-    RCL_AddPulse(instance, &ts, sample.offset);
+    RCL_AddPulse(instance, &sys_ts, sample.offset, 1);
  } else {
-    RCL_AddSample(instance, &ts, sample.offset, sample.leap);
+    RCL_AddSample(instance, &sys_ts, &ref_ts, sample.leap, 1);
  }
 }

--- a/reference.c
+++ b/reference.c
@@ -3,7 +3,8 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009-2018
+ * Copyright (C) Miroslav Lichvar  2009-2018, 2020, 2022
+ * Copyright (C) Andy Fiddaman  2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +34,7 @@
 #include "reference.h"
 #include "util.h"
 #include "conf.h"
+#include "leapdb.h"
 #include "logging.h"
 #include "local.h"
 #include "sched.h"
@@ -45,14 +47,15 @@
 /* The update interval of the reference in the local reference mode */
 #define LOCAL_REF_UPDATE_INTERVAL 64.0

-/* Interval between updates of the drift file */
-#define MAX_DRIFTFILE_AGE 3600.0
-
 static int are_we_synchronised;
 static int enable_local_stratum;
 static int local_stratum;
 static int local_orphan;
 static double local_distance;
+static int local_activate_ok;
+static double local_activate;
+static double local_wait_synced;
+static double local_wait_unsynced;
 static struct timespec local_ref_time;
 static NTP_Leap our_leap_status;
 static int our_leap_sec;
@@ -61,6 +64,7 @@ static int our_stratum;
 static uint32_t our_ref_id;
 static IPAddr our_ref_ip;
 static struct timespec our_ref_time;
+static double unsynchronised_since;
 static double our_skew;
 static double our_residual_freq;
 static double our_root_delay;
@@ -106,6 +110,7 @@ static REF_ModeEndHandler mode_end_handler = NULL;
 /* Filename of the drift file. */
 static char *drift_file=NULL;
 static double drift_file_age;
+static int drift_file_interval;

 static void update_drift_file(double, double);

@@ -122,9 +127,6 @@ static int leap_in_progress;
 /* Timer for the leap second handler */
 static SCH_TimeoutID leap_timeout_id;

-/* Name of a system timezone containing leap seconds occuring at midnight */
-static char *leap_tzname;
-
 /* ================================================== */

 static LOG_FileID logfileid;
@@ -150,9 +152,11 @@ static SCH_TimeoutID fb_drift_timeout_id;
 static double last_ref_update;
 static double last_ref_update_interval;

+static double last_ref_adjustment;
+static int ref_adjustments;
+
 /* ================================================== */

-static NTP_Leap get_tz_leap(time_t when, int *tai_offset);
 static void update_leap_status(NTP_Leap leap, time_t now, int reset);

 /* ================================================== */
@@ -192,7 +196,6 @@ REF_Initialise(void)
  FILE *in;
  double file_freq_ppm, file_skew_ppm;
  double our_frequency_ppm;
-  int tai_offset;

  mode = REF_ModeNormal;
  are_we_synchronised = 0;
@@ -208,9 +211,10 @@ REF_Initialise(void)
  our_frequency_sd = 0.0;
  our_offset_sd = 0.0;
  drift_file_age = 0.0;
+  local_activate_ok = 0;

  /* Now see if we can get the drift file opened */
-  drift_file = CNF_GetDriftFile();
+  drift_file = CNF_GetDriftFile(&drift_file_interval);
  if (drift_file) {
    in = UTI_OpenFile(NULL, drift_file, NULL, 'r', 0);
    if (in) {
@@ -246,8 +250,12 @@ REF_Initialise(void)

  correction_time_ratio = CNF_GetCorrectionTimeRatio();

-  enable_local_stratum = CNF_AllowLocalReference(&local_stratum, &local_orphan, &local_distance);
+  enable_local_stratum = CNF_AllowLocalReference(&local_stratum, &local_orphan,
+                                                 &local_distance, &local_activate,
+                                                 &local_wait_synced,
+                                                 &local_wait_unsynced);
  UTI_ZeroTimespec(&local_ref_time);
+  unsynchronised_since = SCH_GetLastEventMonoTime();

  leap_when = 0;
  leap_timeout_id = 0;
@@ -257,18 +265,6 @@ REF_Initialise(void)
  if (leap_mode == REF_LeapModeSystem && !LCL_CanSystemLeap())
    leap_mode = REF_LeapModeStep;

-  leap_tzname = CNF_GetLeapSecTimezone();
-  if (leap_tzname) {
-    /* Check that the timezone has good data for Jun 30 2012 and Dec 31 2012 */
-    if (get_tz_leap(1341014400, &tai_offset) == LEAP_InsertSecond && tai_offset == 34 &&
-        get_tz_leap(1356912000, &tai_offset) == LEAP_Normal && tai_offset == 35) {
-      LOG(LOGS_INFO, "Using %s timezone to obtain leap second data", leap_tzname);
-    } else {
-      LOG(LOGS_WARN, "Timezone %s failed leap second check, ignoring", leap_tzname);
-      leap_tzname = NULL;
-    }
-  }
-
  CNF_GetMakeStep(&make_step_limit, &make_step_threshold);
  CNF_GetMaxChange(&max_offset_delay, &max_offset_ignore, &max_offset);
  CNF_GetMailOnChange(&do_mail_change, &mail_change_threshold, &mail_change_user);
@@ -286,6 +282,8 @@ REF_Initialise(void)
  UTI_ZeroTimespec(&our_ref_time);
  last_ref_update = 0.0;
  last_ref_update_interval = 0.0;
+  last_ref_adjustment = 0.0;
+  ref_adjustments = 0;

  LCL_AddParameterChangeHandler(handle_slew, NULL);

@@ -588,77 +586,6 @@ is_leap_second_day(time_t when)

 /* ================================================== */

-static NTP_Leap
-get_tz_leap(time_t when, int *tai_offset)
-{
-  static time_t last_tz_leap_check;
-  static NTP_Leap tz_leap;
-  static int tz_tai_offset;
-
-  struct tm stm, *tm;
-  time_t t;
-  char *tz_env, tz_orig[128];
-
-  *tai_offset = tz_tai_offset;
-
-  /* Do this check at most twice a day */
-  when = when / (12 * 3600) * (12 * 3600);
-  if (last_tz_leap_check == when)
-      return tz_leap;
-
-  last_tz_leap_check = when;
-  tz_leap = LEAP_Normal;
-  tz_tai_offset = 0;
-
-  tm = gmtime(&when);
-  if (!tm)
-    return tz_leap;
-
-  stm = *tm;
-
-  /* Temporarily switch to the timezone containing leap seconds */
-  tz_env = getenv("TZ");
-  if (tz_env) {
-    if (strlen(tz_env) >= sizeof (tz_orig))
-      return tz_leap;
-    strcpy(tz_orig, tz_env);
-  }
-  setenv("TZ", leap_tzname, 1);
-  tzset();
-
-  /* Get the TAI-UTC offset, which started at the epoch at 10 seconds */
-  t = mktime(&stm);
-  if (t != -1)
-    tz_tai_offset = t - when + 10;
-
-  /* Set the time to 23:59:60 and see how it overflows in mktime() */
-  stm.tm_sec = 60;
-  stm.tm_min = 59;
-  stm.tm_hour = 23;
-
-  t = mktime(&stm);
-
-  if (tz_env)
-    setenv("TZ", tz_orig, 1);
-  else
-    unsetenv("TZ");
-  tzset();
-
-  if (t == -1)
-    return tz_leap;
-
-  if (stm.tm_sec == 60)
-    tz_leap = LEAP_InsertSecond;
-  else if (stm.tm_sec == 1)
-    tz_leap = LEAP_DeleteSecond;
-
-  *tai_offset = tz_tai_offset;
-
-  return tz_leap;
-}
-
-/* ================================================== */
-
 static void
 leap_end_timeout(void *arg)
 {
@@ -746,16 +673,16 @@ set_leap_timeout(time_t now)
 static void
 update_leap_status(NTP_Leap leap, time_t now, int reset)
 {
-  NTP_Leap tz_leap;
+  NTP_Leap ldb_leap;
  int leap_sec, tai_offset;

  leap_sec = 0;
  tai_offset = 0;

-  if (leap_tzname && now) {
-    tz_leap = get_tz_leap(now, &tai_offset);
+  if (now) {
+    ldb_leap = LDB_GetLeap(now, &tai_offset);
    if (leap == LEAP_Normal)
-      leap = tz_leap;
+      leap = ldb_leap;
  }

  if (leap == LEAP_InsertSecond || leap == LEAP_DeleteSecond) {
@@ -960,6 +887,27 @@ fuzz_ref_time(struct timespec *ts)

 /* ================================================== */

+static double
+get_correction_rate(double offset_sd, double update_interval)
+{
+  /* We want to correct the offset quickly, but we also want to keep the
+     frequency error caused by the correction itself low.
+
+     Define correction rate as the area of the region bounded by the graph of
+     offset corrected in time.  Set the rate so that the time needed to correct
+     an offset equal to the current sourcestats stddev will be equal to the
+     update interval multiplied by the correction time ratio (assuming linear
+     adjustment).  The offset and the time needed to make the correction are
+     inversely proportional.
+
+     This is only a suggestion and it's up to the system driver how the
+     adjustment will be executed. */
+
+  return correction_time_ratio * 0.5 * offset_sd * update_interval;
+}
+
+/* ================================================== */
+
 void
 REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
                 uint32_t ref_id, IPAddr *ref_ip, struct timespec *ref_time,
@@ -969,7 +917,7 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
 {
  double uncorrected_offset, accumulate_offset, step_offset;
  double residual_frequency, local_abs_frequency;
-  double elapsed, mono_now, update_interval, correction_rate, orig_root_distance;
+  double elapsed, mono_now, update_interval, orig_root_distance;
  struct timespec now, raw_now;
  int manual;

@@ -1024,21 +972,6 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  last_ref_update_interval = update_interval;
  last_offset = offset;

-  /* We want to correct the offset quickly, but we also want to keep the
-     frequency error caused by the correction itself low.
-
-     Define correction rate as the area of the region bounded by the graph of
-     offset corrected in time. Set the rate so that the time needed to correct
-     an offset equal to the current sourcestats stddev will be equal to the
-     update interval multiplied by the correction time ratio (assuming linear
-     adjustment). The offset and the time needed to make the correction are
-     inversely proportional.
-
-     This is only a suggestion and it's up to the system driver how the
-     adjustment will be executed. */
-
-  correction_rate = correction_time_ratio * 0.5 * offset_sd * update_interval;
-
  /* Check if the clock should be stepped */
  if (is_step_limit_reached(offset, uncorrected_offset)) {
    /* Cancel the uncorrected offset and correct the total offset by step */
@@ -1050,13 +983,16 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  }

  /* Adjust the clock */
-  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset, correction_rate);
+  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset,
+                                   get_correction_rate(offset_sd, update_interval));
    
  maybe_log_offset(offset, raw_now.tv_sec);

  if (step_offset != 0.0) {
    if (LCL_ApplyStepOffset(step_offset))
      LOG(LOGS_WARN, "System clock was stepped by %.6f seconds", -step_offset);
+    else
+      LCL_AccumulateOffset(step_offset, 0.0);
  }

  update_leap_status(leap, raw_now.tv_sec, 0);
@@ -1075,7 +1011,7 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  if (drift_file) {
    /* Update drift file at most once per hour */
    drift_file_age += update_interval;
-    if (drift_file_age >= MAX_DRIFTFILE_AGE) {
+    if (drift_file_age >= drift_file_interval) {
      update_drift_file(local_abs_frequency, our_skew);
      drift_file_age = 0.0;
    }
@@ -1095,6 +1031,27 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
      avg2_moving = 1;
    avg2_offset = SQUARE(offset);
  }
+
+  ref_adjustments = 0;
+}
+
+/* ================================================== */
+
+int
+REF_AdjustReference(double offset, double frequency)
+{
+  double adj_corr_rate, ref_corr_rate, mono_now;
+
+  mono_now = SCH_GetLastEventMonoTime();
+  ref_adjustments++;
+
+  adj_corr_rate = get_correction_rate(fabs(offset), mono_now - last_ref_adjustment);
+  ref_corr_rate = get_correction_rate(our_offset_sd, last_ref_update_interval) /
+                  ref_adjustments;
+  last_ref_adjustment = mono_now;
+
+  return LCL_AccumulateFrequencyAndOffsetNoHandlers(frequency, offset,
+                                                    MAX(adj_corr_rate, ref_corr_rate));
 }

 /* ================================================== */
@@ -1144,6 +1101,9 @@ REF_SetUnsynchronised(void)
  our_ref_ip.family = IPADDR_INET4;
  our_ref_ip.addr.in4 = 0;
  our_stratum = 0;
+
+  if (are_we_synchronised)
+    unsynchronised_since = SCH_GetLastEventMonoTime();
  are_we_synchronised = 0;

  LCL_SetSyncStatus(0, 0.0, 0.0);
@@ -1186,21 +1146,30 @@ REF_GetReferenceParams
 double *root_dispersion
 )
 {
-  double dispersion, delta;
+  double dispersion, delta, distance;
+  int wait_local_ok;

  assert(initialised);

  if (are_we_synchronised) {
    dispersion = get_root_dispersion(local_time);
+    wait_local_ok = UTI_DiffTimespecsToDouble(local_time, &our_ref_time) >= local_wait_synced;
  } else {
    dispersion = 0.0;
+    wait_local_ok = SCH_GetLastEventMonoTime() - unsynchronised_since >= local_wait_unsynced;
  }

+  distance = our_root_delay / 2 + dispersion;
+
+  if (local_activate == 0.0 || (are_we_synchronised && distance < local_activate))
+    local_activate_ok = 1;
+
  /* Local reference is active when enabled and the clock is not synchronised
     or the root distance exceeds the threshold */

  if (are_we_synchronised &&
-      !(enable_local_stratum && our_root_delay / 2 + dispersion > local_distance)) {
+      !(enable_local_stratum && local_activate_ok && wait_local_ok &&
+        distance > local_distance)) {

    *is_synchronised = 1;

@@ -1212,7 +1181,7 @@ REF_GetReferenceParams
    *root_delay = our_root_delay;
    *root_dispersion = dispersion;

-  } else if (enable_local_stratum) {
+  } else if (enable_local_stratum && local_activate_ok && wait_local_ok) {

    *is_synchronised = 0;

@@ -1296,6 +1265,7 @@ void
 REF_ModifyMaxupdateskew(double new_max_update_skew)
 {
  max_update_skew = new_max_update_skew * 1.0e-6;
+  LOG(LOGS_INFO, "New maxupdateskew %f ppm", new_max_update_skew);
 }

 /* ================================================== */
@@ -1305,17 +1275,23 @@ REF_ModifyMakestep(int limit, double threshold)
 {
  make_step_limit = limit;
  make_step_threshold = threshold;
+  LOG(LOGS_INFO, "New makestep %f %d", threshold, limit);
 }

 /* ================================================== */

 void
-REF_EnableLocal(int stratum, double distance, int orphan)
+REF_EnableLocal(int stratum, double distance, int orphan, double activate,
+                double wait_synced, double wait_unsynced)
 {
  enable_local_stratum = 1;
  local_stratum = CLAMP(1, stratum, NTP_MAX_STRATUM - 1);
  local_distance = distance;
  local_orphan = !!orphan;
+  local_activate = activate;
+  local_wait_synced = wait_synced;
+  local_wait_unsynced = wait_unsynced;
+  LOG(LOGS_INFO, "%s local reference mode", "Enabled");
 }

 /* ================================================== */
@@ -1324,6 +1300,7 @@ void
 REF_DisableLocal(void)
 {
  enable_local_stratum = 0;
+  LOG(LOGS_INFO, "%s local reference mode", "Disabled");
 }

 /* ================================================== */
@@ -1331,9 +1308,10 @@ REF_DisableLocal(void)
 #define LEAP_SECOND_CLOSE 5

 static int
-is_leap_close(time_t t)
+is_leap_close(double t)
 {
-  return t >= leap_when - LEAP_SECOND_CLOSE && t < leap_when + LEAP_SECOND_CLOSE;
+  return leap_when != 0 &&
+         t >= leap_when - LEAP_SECOND_CLOSE && t < leap_when + LEAP_SECOND_CLOSE;
 }

 /* ================================================== */
@@ -1360,7 +1338,7 @@ REF_GetTaiOffset(struct timespec *ts)
 {
  int tai_offset;

-  get_tz_leap(ts->tv_sec, &tai_offset);
+  LDB_GetLeap(ts->tv_sec, &tai_offset);

  return tai_offset;
 }
--- a/reference.h
+++ b/reference.h
@@ -162,6 +162,10 @@ extern void REF_SetManualReference
 extern void
 REF_SetUnsynchronised(void);

+/* Make a small correction of the clock without updating the reference
+   parameters and calling the clock change handlers */
+extern int REF_AdjustReference(double offset, double frequency);
+
 /* Announce a leap second before the full reference update */
 extern void REF_UpdateLeapStatus(NTP_Leap leap);

@@ -181,7 +185,8 @@ extern void REF_ModifyMaxupdateskew(double new_max_update_skew);
 /* Modify makestep settings */
 extern void REF_ModifyMakestep(int limit, double threshold);

-extern void REF_EnableLocal(int stratum, double distance, int orphan);
+extern void REF_EnableLocal(int stratum, double distance, int orphan, double activate,
+                            double wait_synced, double wait_unsynced);
 extern void REF_DisableLocal(void);

 /* Check if either of the current raw and cooked time, and optionally a
--- a/regress.c
+++ b/regress.c
@@ -377,7 +377,7 @@ find_ordered_entry_with_flags(double *x, int n, int index, char *flags)
      r = v;
      do {
        while (l < v && x[l] < piv) l++;
-        while (x[r] > piv) r--;
+        while (r > 0 && x[r] > piv) r--;
        if (r <= l) break;
        EXCH(x[l], x[r]);
        l++;
--- a/reports.h
+++ b/reports.h
@@ -36,7 +36,14 @@ typedef struct {
  int stratum;
  int poll;
  enum {RPT_NTP_CLIENT, RPT_NTP_PEER, RPT_LOCAL_REFERENCE} mode;
-  enum {RPT_SYNC, RPT_UNREACH, RPT_FALSETICKER, RPT_JITTERY, RPT_CANDIDATE, RPT_OUTLIER} state;
+  enum {
+    RPT_NONSELECTABLE,
+    RPT_FALSETICKER,
+    RPT_JITTERY,
+    RPT_SELECTABLE,
+    RPT_UNSELECTED,
+    RPT_SELECTED,
+  } state;

  int reachability;
  unsigned long latest_meas_ago; /* seconds */
@@ -102,14 +109,23 @@ typedef struct {
 } RPT_ClientAccessByIndex_Report;

 typedef struct {
-  uint32_t ntp_hits;
-  uint32_t nke_hits;
-  uint32_t cmd_hits;
-  uint32_t ntp_drops;
-  uint32_t nke_drops;
-  uint32_t cmd_drops;
-  uint32_t log_drops;
-  uint32_t ntp_auth_hits;
+  uint64_t ntp_hits;
+  uint64_t nke_hits;
+  uint64_t cmd_hits;
+  uint64_t ntp_drops;
+  uint64_t nke_drops;
+  uint64_t cmd_drops;
+  uint64_t log_drops;
+  uint64_t ntp_auth_hits;
+  uint64_t ntp_interleaved_hits;
+  uint64_t ntp_timestamps;
+  uint64_t ntp_span_seconds;
+  uint64_t ntp_daemon_rx_timestamps;
+  uint64_t ntp_daemon_tx_timestamps;
+  uint64_t ntp_kernel_rx_timestamps;
+  uint64_t ntp_kernel_tx_timestamps;
+  uint64_t ntp_hw_rx_timestamps;
+  uint64_t ntp_hw_tx_timestamps;
 } RPT_ServerStatsReport;

 typedef struct {
@@ -164,6 +180,11 @@ typedef struct {
  uint32_t total_tx_count;
  uint32_t total_rx_count;
  uint32_t total_valid_count;
+  uint32_t total_good_count;
+  uint32_t total_kernel_tx_ts;
+  uint32_t total_kernel_rx_ts;
+  uint32_t total_hw_tx_ts;
+  uint32_t total_hw_rx_ts;
 } RPT_NTPReport;

 typedef struct {
@@ -183,6 +204,7 @@ typedef struct {
  IPAddr ip_addr;
  char state_char;
  int authentication;
+  NTP_Leap leap;
  int conf_options;
  int eff_options;
  uint32_t last_sample_ago;
--- a/rtc.c
+++ b/rtc.c
@@ -81,8 +81,9 @@ get_driftfile_time(void)
 {
  struct stat buf;
  char *drift_file;
+  int interval;

-  drift_file = CNF_GetDriftFile();
+  drift_file = CNF_GetDriftFile(&interval);
  if (!drift_file)
    return 0;

@@ -148,6 +149,8 @@ RTC_Initialise(int initial_set)
    if (driver.init) {
      if ((driver.init)()) {
        driver_initialised = 1;
+      } else {
+        LOG(LOGS_ERR, "RTC driver could not be initialised");
      }
    } else {
      LOG(LOGS_ERR, "RTC not supported on this operating system");
--- a/rtc_linux.c
+++ b/rtc_linux.c
@@ -4,6 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Miroslav Lichvar  2012-2014
+ * Copyright (C) Ahmad Fatoum, Pengutronix  2024
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -64,7 +65,7 @@ static OperatingMode operating_mode = OM_NORMAL;

 /* ================================================== */

-static int fd = -1;
+static int fd;

 #define LOWEST_MEASUREMENT_PERIOD 15
 #define HIGHEST_MEASUREMENT_PERIOD 480
@@ -82,16 +83,12 @@ static int skip_interrupts;
 #define MAX_SAMPLES 64

 /* Real time clock samples.  We store the seconds count as originally
-   measured, together with a 'trim' that compensates these values for
-   any steps made to the RTC to bring it back into line
-   occasionally.  The trim is in seconds. */
+   measured. */
 static time_t *rtc_sec = NULL;
-static double *rtc_trim = NULL;

 /* Reference time, against which delta times on the RTC scale are measured */
 static time_t rtc_ref;

-
 /* System clock samples associated with the above samples. */
 static struct timespec *system_times = NULL;

@@ -145,7 +142,7 @@ static double file_ref_offset, file_rate_ppm;
 /* ================================================== */

 /* Flag to remember whether to assume the RTC is running on UTC */
-static int rtc_on_utc = 1;
+static int rtc_on_utc;

 /* ================================================== */

@@ -168,7 +165,6 @@ discard_samples(int new_first)
  n_to_save = n_samples - new_first;

  memmove(rtc_sec, rtc_sec + new_first, n_to_save * sizeof(time_t));
-  memmove(rtc_trim, rtc_trim + new_first, n_to_save * sizeof(double));
  memmove(system_times, system_times + new_first, n_to_save * sizeof(struct timespec));

  n_samples = n_to_save;
@@ -188,21 +184,16 @@ accumulate_sample(time_t rtc, struct timespec *sys)
  }

  /* Discard all samples if the RTC was stepped back (not our trim) */
-  if (n_samples > 0 && rtc_sec[n_samples - 1] - rtc >= rtc_trim[n_samples - 1]) {
+  if (n_samples > 0 && rtc_sec[n_samples - 1] >= rtc) {
    DEBUG_LOG("RTC samples discarded");
    n_samples = 0;
  }

  /* Always use most recent sample as reference */
-  /* use sample only if n_sample is not negative*/
-  if(n_samples >=0)
-  {
  rtc_ref = rtc;
  rtc_sec[n_samples] = rtc;
-  rtc_trim[n_samples] = 0.0;
  system_times[n_samples] = *sys;
  ++n_samples_since_regression;
-  }
  ++n_samples;
 }

@@ -227,7 +218,7 @@ run_regression(int new_sample,
  if (n_samples > 0) {

    for (i=0; i<n_samples; i++) {
-      rtc_rel[i] = rtc_trim[i] + (double)(rtc_sec[i] - rtc_ref);
+      rtc_rel[i] = (double)(rtc_sec[i] - rtc_ref);
      offsets[i] = ((double) (rtc_ref - system_times[i].tv_sec) -
                    (1.0e-9 * system_times[i].tv_nsec) +
                    rtc_rel[i]);
@@ -306,14 +297,25 @@ slew_samples
   corresponding real time clock 'DMY HMS' form, taking account of
   whether the user runs his RTC on the local time zone or UTC */

-static struct tm *
-rtc_from_t(const time_t *t)
+static void
+rtc_from_t(const time_t *t, struct rtc_time *rtc_raw, int utc)
 {
-  if (rtc_on_utc) {
-    return gmtime(t);
+  struct tm *rtc_tm;
+  if (utc) {
+    rtc_tm = gmtime(t);
  } else {
-    return localtime(t);
+    rtc_tm = localtime(t);
  }
+
+  rtc_raw->tm_sec = rtc_tm->tm_sec;
+  rtc_raw->tm_min = rtc_tm->tm_min;
+  rtc_raw->tm_hour = rtc_tm->tm_hour;
+  rtc_raw->tm_mday = rtc_tm->tm_mday;
+  rtc_raw->tm_mon = rtc_tm->tm_mon;
+  rtc_raw->tm_year = rtc_tm->tm_year;
+  rtc_raw->tm_wday = rtc_tm->tm_wday;
+  rtc_raw->tm_yday = rtc_tm->tm_yday;
+  rtc_raw->tm_isdst = rtc_tm->tm_isdst;
 }

 /* ================================================== */
@@ -351,17 +353,27 @@ rtc_from_t(const time_t *t)
 */

 static time_t
-t_from_rtc(struct tm *stm) {
-  struct tm temp1, temp2, *tm;
+t_from_rtc(struct rtc_time *rtc_raw, int utc)
+{
+  struct tm rtc_tm, temp1, temp2, *tm;
  long diff;
  time_t t1, t2;

-  temp1 = *stm;
+  /* Convert to seconds since 1970 */
+  memset(&rtc_tm, 0, sizeof (rtc_tm));
+  rtc_tm.tm_sec = rtc_raw->tm_sec;
+  rtc_tm.tm_min = rtc_raw->tm_min;
+  rtc_tm.tm_hour = rtc_raw->tm_hour;
+  rtc_tm.tm_mday = rtc_raw->tm_mday;
+  rtc_tm.tm_mon = rtc_raw->tm_mon;
+  rtc_tm.tm_year = rtc_raw->tm_year;
+
+  temp1 = rtc_tm;
  temp1.tm_isdst = 0;

  t1 = mktime(&temp1);

-  tm = rtc_on_utc ? gmtime(&t1) : localtime(&t1);
+  tm = utc ? gmtime(&t1) : localtime(&t1);
  if (!tm) {
    DEBUG_LOG("gmtime()/localtime() failed");
    return -1;
@@ -434,6 +446,7 @@ setup_config(void)
 static void
 read_coefs_from_file(void)
 {
+  double ref_time;
  FILE *in;

  if (!tried_to_load_coefs) {
@@ -444,11 +457,12 @@ read_coefs_from_file(void)

    if (coefs_file_name &&
        (in = UTI_OpenFile(NULL, coefs_file_name, NULL, 'r', 0))) {
-      if (fscanf(in, "%d%ld%lf%lf",
+      if (fscanf(in, "%d%lf%lf%lf",
                 &valid_coefs_from_file,
-                 &file_ref_time,
+                 &ref_time,
                 &file_ref_offset,
                 &file_rate_ppm) == 4) {
+        file_ref_time = ref_time;
      } else {
        LOG(LOGS_WARN, "Could not read coefficients from %s", coefs_file_name);
      }
@@ -472,7 +486,7 @@ write_coefs_to_file(int valid,time_t ref_time,double offset,double rate)
    return RTC_ST_BADFILE;

  /* Gain rate is written out in ppm */
-  fprintf(out, "%1d %ld %.6f %.3f\n", valid, ref_time, offset, 1.0e6 * rate);
+  fprintf(out, "%1d %.0f %.6f %.3f\n", valid, (double)ref_time, offset, 1.0e6 * rate);
  fclose(out);

  /* Rename the temporary file to the correct location */
@@ -484,8 +498,8 @@ write_coefs_to_file(int valid,time_t ref_time,double offset,double rate)

 /* ================================================== */

-static int
-switch_interrupts(int on_off)
+int
+RTC_Linux_SwitchInterrupt(int fd, int on_off)
 {
  if (ioctl(fd, on_off ? RTC_UIE_ON : RTC_UIE_OFF, 0) < 0) {
    LOG(LOGS_ERR, "Could not %s RTC interrupt : %s",
@@ -516,7 +530,7 @@ RTC_Linux_Initialise(void)
  }

  /* Make sure the RTC supports interrupts */
-  if (!switch_interrupts(1) || !switch_interrupts(0)) {
+  if (!RTC_Linux_SwitchInterrupt(fd, 1) || !RTC_Linux_SwitchInterrupt(fd, 0)) {
    close(fd);
    return 0;
  }
@@ -525,7 +539,6 @@ RTC_Linux_Initialise(void)
  UTI_FdSetCloexec(fd);

  rtc_sec = MallocArray(time_t, MAX_SAMPLES);
-  rtc_trim = MallocArray(double, MAX_SAMPLES);
  system_times = MallocArray(struct timespec, MAX_SAMPLES);

  /* Setup details depending on configuration options */
@@ -566,7 +579,7 @@ RTC_Linux_Finalise(void)
  /* Remove input file handler */
  if (fd >= 0) {
    SCH_RemoveFileHandler(fd);
-    switch_interrupts(0);
+    RTC_Linux_SwitchInterrupt(fd, 0);
    close(fd);

    /* Save the RTC data */
@@ -578,7 +591,6 @@ RTC_Linux_Finalise(void)
    LCL_RemoveParameterChangeHandler(slew_samples, NULL);

  Free(rtc_sec);
-  Free(rtc_trim);
  Free(system_times);
 }

@@ -588,7 +600,7 @@ static void
 measurement_timeout(void *any)
 {
  timeout_id = 0;
-  switch_interrupts(1);
+  RTC_Linux_SwitchInterrupt(fd, 1);
 }

 /* ================================================== */
@@ -596,21 +608,10 @@ measurement_timeout(void *any)
 static void
 set_rtc(time_t new_rtc_time)
 {
-  struct tm rtc_tm;
  struct rtc_time rtc_raw;
  int status;

-  rtc_tm = *rtc_from_t(&new_rtc_time);
-
-  rtc_raw.tm_sec = rtc_tm.tm_sec;
-  rtc_raw.tm_min = rtc_tm.tm_min;
-  rtc_raw.tm_hour = rtc_tm.tm_hour;
-  rtc_raw.tm_mday = rtc_tm.tm_mday;
-  rtc_raw.tm_mon = rtc_tm.tm_mon;
-  rtc_raw.tm_year = rtc_tm.tm_year;
-  rtc_raw.tm_wday = rtc_tm.tm_wday;
-  rtc_raw.tm_yday = rtc_tm.tm_yday;
-  rtc_raw.tm_isdst = rtc_tm.tm_isdst;
+  rtc_from_t(&new_rtc_time, &rtc_raw, rtc_on_utc);

  status = ioctl(fd, RTC_SET_TIME, &rtc_raw);
  if (status < 0) {
@@ -639,11 +640,7 @@ handle_initial_trim(void)
  run_regression(1, &coefs_valid, &coef_ref_time, &coef_seconds_fast, &coef_gain_rate);

  n_samples_since_regression = 0;
-
-  /* Set sample number to -1 so the next sample is not used, as it will not yet be corrected for System Trim*/
-
-  n_samples = -1;
-
+  n_samples = 0;

  read_coefs_from_file();

@@ -764,16 +761,11 @@ process_reading(time_t rtc_time, struct timespec *system_time)

 /* ================================================== */

-static void
-read_from_device(int fd_, int event, void *any)
+int
+RTC_Linux_CheckInterrupt(int fd)
 {
  int status;
  unsigned long data;
-  struct timespec sys_time;
-  struct rtc_time rtc_raw;
-  struct tm rtc_tm;
-  time_t rtc_t;
-  int error = 0;

  status = read(fd, &data, sizeof(data));

@@ -781,63 +773,79 @@ read_from_device(int fd_, int event, void *any)
    /* This looks like a bad error : the file descriptor was indicating it was
     * ready to read but we couldn't read anything.  Give up. */
    LOG(LOGS_ERR, "Could not read flags %s : %s", CNF_GetRtcDevice(), strerror(errno));
-    SCH_RemoveFileHandler(fd);
-    switch_interrupts(0); /* Likely to raise error too, but just to be sure... */
-    close(fd);
-    fd = -1;
-    return;
+    return -1;
  }

  if (skip_interrupts > 0) {
    /* Wait for the next interrupt, this one may be bogus */
    skip_interrupts--;
+    return 0;
+  }
+
+  /* Update interrupt detected? */
+  return (data & RTC_UF) == RTC_UF;
+}
+
+time_t
+RTC_Linux_ReadTimeAfterInterrupt(int fd, int utc,
+                                 struct timespec *sys_time_cooked,
+                                 struct timespec *sys_time_raw)
+{
+  int status;
+  struct rtc_time rtc_raw;
+
+  /* Read RTC time, sandwiched between two polls of the system clock
+     so we can bound any error */
+
+  SCH_GetLastEventTime(sys_time_cooked, NULL, sys_time_raw);
+
+  status = ioctl(fd, RTC_RD_TIME, &rtc_raw);
+  if (status < 0) {
+    LOG(LOGS_ERR, "Could not read time from %s : %s", CNF_GetRtcDevice(), strerror(errno));
+    return -1;
+  }
+
+  /* Convert RTC time into a struct timespec */
+  return t_from_rtc(&rtc_raw, utc);
+}
+
+static void
+read_from_device(int fd_, int event, void *any)
+{
+  struct timespec sys_time;
+  int status, error = 0;
+  time_t rtc_t;
+
+  status = RTC_Linux_CheckInterrupt(fd);
+  if (status < 0) {
+    SCH_RemoveFileHandler(fd);
+    RTC_Linux_SwitchInterrupt(fd, 0); /* Likely to raise error too, but just to be sure... */
+    close(fd);
+    fd = -1;
+    return;
+  } else if (status == 0) {
+    /* Wait for the next interrupt, this one may be bogus */
    return;
  }

-  if ((data & RTC_UF) == RTC_UF) {
-    /* Update interrupt detected */
+  rtc_t = RTC_Linux_ReadTimeAfterInterrupt(fd, rtc_on_utc, &sys_time, NULL);
+  if (rtc_t == (time_t)-1) {
+    error = 1;
+    goto turn_off_interrupt;
+  }

-    /* Read RTC time, sandwiched between two polls of the system clock
-       so we can bound any error. */
-
-    SCH_GetLastEventTime(&sys_time, NULL, NULL);
-
-    status = ioctl(fd, RTC_RD_TIME, &rtc_raw);
-    if (status < 0) {
-      LOG(LOGS_ERR, "Could not read time from %s : %s", CNF_GetRtcDevice(), strerror(errno));
-      error = 1;
-      goto turn_off_interrupt;
-    }
-
-    /* Convert RTC time into a struct timespec */
-    rtc_tm.tm_sec = rtc_raw.tm_sec;
-    rtc_tm.tm_min = rtc_raw.tm_min;
-    rtc_tm.tm_hour = rtc_raw.tm_hour;
-    rtc_tm.tm_mday = rtc_raw.tm_mday;
-    rtc_tm.tm_mon = rtc_raw.tm_mon;
-    rtc_tm.tm_year = rtc_raw.tm_year;
-
-    rtc_t = t_from_rtc(&rtc_tm);
-
-    if (rtc_t == (time_t)(-1)) {
-      error = 1;
-      goto turn_off_interrupt;
-    }      
-
-    process_reading(rtc_t, &sys_time);
-
-    if (n_samples < 4) {
-      measurement_period = LOWEST_MEASUREMENT_PERIOD;
-    } else if (n_samples < 6) {
-      measurement_period = LOWEST_MEASUREMENT_PERIOD << 1;
-    } else if (n_samples < 10) {
-      measurement_period = LOWEST_MEASUREMENT_PERIOD << 2;
-    } else if (n_samples < 14) {
-      measurement_period = LOWEST_MEASUREMENT_PERIOD << 3;
-    } else {
-      measurement_period = LOWEST_MEASUREMENT_PERIOD << 4;
-    }
+  process_reading(rtc_t, &sys_time);

+  if (n_samples < 4) {
+    measurement_period = LOWEST_MEASUREMENT_PERIOD;
+  } else if (n_samples < 6) {
+    measurement_period = LOWEST_MEASUREMENT_PERIOD << 1;
+  } else if (n_samples < 10) {
+    measurement_period = LOWEST_MEASUREMENT_PERIOD << 2;
+  } else if (n_samples < 14) {
+    measurement_period = LOWEST_MEASUREMENT_PERIOD << 3;
+  } else {
+    measurement_period = LOWEST_MEASUREMENT_PERIOD << 4;
  }

 turn_off_interrupt:
@@ -849,7 +857,7 @@ turn_off_interrupt:
        operating_mode = OM_NORMAL;
        (after_init_hook)(after_init_hook_arg);

-        switch_interrupts(0);
+        RTC_Linux_SwitchInterrupt(fd, 0);
    
        timeout_id = SCH_AddTimeoutByDelay((double) measurement_period, measurement_timeout, NULL);
      }
@@ -861,7 +869,7 @@ turn_off_interrupt:
        DEBUG_LOG("Could not complete after trim relock due to errors");
        operating_mode = OM_NORMAL;

-        switch_interrupts(0);
+        RTC_Linux_SwitchInterrupt(fd, 0);
    
        timeout_id = SCH_AddTimeoutByDelay((double) measurement_period, measurement_timeout, NULL);
      }
@@ -869,7 +877,7 @@ turn_off_interrupt:
      break;

    case OM_NORMAL:
-      switch_interrupts(0);
+      RTC_Linux_SwitchInterrupt(fd, 0);
    
      timeout_id = SCH_AddTimeoutByDelay((double) measurement_period, measurement_timeout, NULL);

@@ -891,7 +899,7 @@ RTC_Linux_TimeInit(void (*after_hook)(void *), void *anything)

  operating_mode = OM_INITIAL;
  timeout_id = 0;
-  switch_interrupts(1);
+  RTC_Linux_SwitchInterrupt(fd, 1);
 }

 /* ================================================== */
@@ -924,6 +932,33 @@ RTC_Linux_WriteParameters(void)
  return(retval);
 }

+time_t
+RTC_Linux_ReadTimeNow(int fd, int utc,
+                      struct timespec *old_sys_cooked,
+                      struct timespec *old_sys_raw)
+{
+  struct rtc_time rtc_raw, rtc_raw_retry;
+  int status;
+
+  /* Retry reading the RTC until both read attempts give the same sec value.
+     This way the race condition is prevented that the RTC has updated itself
+     during the first read operation. */
+  do {
+    status = ioctl(fd, RTC_RD_TIME, &rtc_raw);
+    if (status >= 0) {
+      status = ioctl(fd, RTC_RD_TIME, &rtc_raw_retry);
+    }
+  } while (status >= 0 && rtc_raw.tm_sec != rtc_raw_retry.tm_sec);
+
+  /* Read system clock */
+  if (old_sys_raw)
+    LCL_ReadRawTime(old_sys_raw);
+  if (old_sys_cooked)
+    LCL_ReadCookedTime(old_sys_cooked, NULL);
+
+  return status >= 0 ? t_from_rtc(&rtc_raw, utc) : -1;
+}
+
 /* ================================================== */
 /* Try to set the system clock from the RTC, in the same manner as
   /sbin/hwclock -s would do.  We're not as picky about OS version
@@ -933,12 +968,10 @@ RTC_Linux_WriteParameters(void)
 int
 RTC_Linux_TimePreInit(time_t driftfile_time)
 {
-  int fd, status;
-  struct rtc_time rtc_raw, rtc_raw_retry;
-  struct tm rtc_tm;
  time_t rtc_t;
  double accumulated_error, sys_offset;
  struct timespec new_sys_time, old_sys_time;
+  int fd;

  coefs_file_name = CNF_GetRtcFile();

@@ -951,66 +984,41 @@ RTC_Linux_TimePreInit(time_t driftfile_time)
    return 0; /* Can't open it, and won't be able to later */
  }

-  /* Retry reading the rtc until both read attempts give the same sec value.
-     This way the race condition is prevented that the RTC has updated itself
-     during the first read operation. */
-  do {
-    status = ioctl(fd, RTC_RD_TIME, &rtc_raw);
-    if (status >= 0) {
-      status = ioctl(fd, RTC_RD_TIME, &rtc_raw_retry);
-    }
-  } while (status >= 0 && rtc_raw.tm_sec != rtc_raw_retry.tm_sec);
-
-  /* Read system clock */
-  LCL_ReadCookedTime(&old_sys_time, NULL);
+  rtc_t = RTC_Linux_ReadTimeNow(fd, rtc_on_utc, &old_sys_time, NULL);

  close(fd);

-  if (status >= 0) {
-    /* Convert to seconds since 1970 */
-    rtc_tm.tm_sec = rtc_raw.tm_sec;
-    rtc_tm.tm_min = rtc_raw.tm_min;
-    rtc_tm.tm_hour = rtc_raw.tm_hour;
-    rtc_tm.tm_mday = rtc_raw.tm_mday;
-    rtc_tm.tm_mon = rtc_raw.tm_mon;
-    rtc_tm.tm_year = rtc_raw.tm_year;
+  if (rtc_t != (time_t)(-1)) {

-    rtc_t = t_from_rtc(&rtc_tm);
-
-    if (rtc_t != (time_t)(-1)) {
-
-      /* Work out approximatation to correct time (to about the
-         nearest second) */
-      if (valid_coefs_from_file) {
-        accumulated_error = file_ref_offset +
-          (rtc_t - file_ref_time) * 1.0e-6 * file_rate_ppm;
-      } else {
-        accumulated_error = 0.0;
-      }
-
-      /* Correct time */
-
-      new_sys_time.tv_sec = rtc_t;
-      /* Average error in the RTC reading */
-      new_sys_time.tv_nsec = 500000000;
-
-      UTI_AddDoubleToTimespec(&new_sys_time, -accumulated_error, &new_sys_time);
-
-      if (new_sys_time.tv_sec < driftfile_time) {
-        LOG(LOGS_WARN, "RTC time before last driftfile modification (ignored)");
-        return 0;
-      }
-
-      sys_offset = UTI_DiffTimespecsToDouble(&old_sys_time, &new_sys_time);
-
-      /* Set system time only if the step is larger than 1 second */
-      if (fabs(sys_offset) >= 1.0) {
-        if (LCL_ApplyStepOffset(sys_offset))
-          LOG(LOGS_INFO, "System time set from RTC");
-      }
+    /* Work out approximation to correct time (to about the
+       nearest second) */
+    if (valid_coefs_from_file) {
+      accumulated_error = file_ref_offset +
+        (rtc_t - file_ref_time) * 1.0e-6 * file_rate_ppm;
    } else {
+      accumulated_error = 0.0;
+    }
+
+    /* Correct time */
+
+    new_sys_time.tv_sec = rtc_t;
+    /* Average error in the RTC reading */
+    new_sys_time.tv_nsec = 500000000;
+
+    UTI_AddDoubleToTimespec(&new_sys_time, -accumulated_error, &new_sys_time);
+
+    if (new_sys_time.tv_sec < driftfile_time) {
+      LOG(LOGS_WARN, "RTC time before last driftfile modification (ignored)");
      return 0;
    }
+
+    sys_offset = UTI_DiffTimespecsToDouble(&old_sys_time, &new_sys_time);
+
+    /* Set system time only if the step is larger than 1 second */
+    if (fabs(sys_offset) >= 1.0) {
+      if (LCL_ApplyStepOffset(sys_offset))
+        LOG(LOGS_INFO, "System time set from RTC");
+    }
  } else {
    return 0;
  }
@@ -1028,8 +1036,7 @@ RTC_Linux_GetReport(RPT_RTC_Report *report)
  report->n_samples = n_samples;
  report->n_runs = n_runs;
  if (n_samples > 1) {
-    report->span_seconds = ((rtc_sec[n_samples-1] - rtc_sec[0]) +
-                            (long)(rtc_trim[n_samples-1] - rtc_trim[0]));
+    report->span_seconds = rtc_sec[n_samples - 1] - rtc_sec[0];
  } else {
    report->span_seconds = 0;
  }
@@ -1079,7 +1086,7 @@ RTC_Linux_Trim(void)
    /* And start rapid sampling, interrupts on now */
    SCH_RemoveTimeout(timeout_id);
    timeout_id = 0;
-    switch_interrupts(1);
+    RTC_Linux_SwitchInterrupt(fd, 1);
  }

  return 1;
--- a/rtc_linux.h
+++ b/rtc_linux.h
@@ -42,4 +42,13 @@ extern int RTC_Linux_Trim(void);

 extern void RTC_Linux_CycleLogFile(void);

+extern int RTC_Linux_SwitchInterrupt(int fd, int on_off);
+extern int RTC_Linux_CheckInterrupt(int fd);
+extern time_t RTC_Linux_ReadTimeAfterInterrupt(int fd, int utc,
+                                               struct timespec *sys_time_cooked,
+                                               struct timespec *sys_time_raw);
+extern time_t RTC_Linux_ReadTimeNow(int fd, int utc,
+                                    struct timespec *sys_time_cooked,
+                                    struct timespec *sys_time_raw);
+
 #endif /* _GOT_RTC_LINUX_H */
--- a/samplefilt.c
+++ b/samplefilt.c
@@ -162,6 +162,14 @@ SPF_GetNumberOfSamples(SPF_Instance filter)

 /* ================================================== */

+int
+SPF_GetMaxSamples(SPF_Instance filter)
+{
+  return filter->max_samples;
+}
+
+/* ================================================== */
+
 double
 SPF_GetAvgSampleDispersion(SPF_Instance filter)
 {
@@ -170,11 +178,21 @@ SPF_GetAvgSampleDispersion(SPF_Instance filter)

 /* ================================================== */

-void
-SPF_DropSamples(SPF_Instance filter)
+static void
+drop_samples(SPF_Instance filter, int keep_last)
 {
  filter->index = -1;
  filter->used = 0;
+  if (!keep_last)
+    filter->last = -1;
+}
+
+/* ================================================== */
+
+void
+SPF_DropSamples(SPF_Instance filter)
+{
+  drop_samples(filter, 0);
 }

 /* ================================================== */
@@ -386,7 +404,6 @@ combine_selected_samples(SPF_Instance filter, int n, NTP_Sample *result)
  result->root_dispersion = MAX(disp, mean_root_dispersion);
  result->peer_delay = mean_peer_delay;
  result->root_delay = mean_root_delay;
-  result->stratum = last_sample->stratum;

  return 1;
 }
@@ -400,17 +417,40 @@ SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample)

  n = select_samples(filter);

+  DEBUG_LOG("selected %d from %d samples", n, filter->used);
+
  if (n < 1)
    return 0;

  if (!combine_selected_samples(filter, n, sample))
    return 0;

-  SPF_DropSamples(filter);
+  drop_samples(filter, 1);

  return 1;
 }

+/* ================================================== */
+
+static int
+get_first_last(SPF_Instance filter, int *first, int *last)
+{
+  if (filter->last < 0)
+    return 0;
+
+  /* Always slew the last sample as it may be returned even if no new
+     samples were accumulated */
+  if (filter->used > 0) {
+    *first = 0;
+    *last = filter->used - 1;
+  } else {
+    *first = *last = filter->last;
+  }
+
+  return 1;
+}
+
+
 /* ================================================== */

 void
@@ -419,18 +459,9 @@ SPF_SlewSamples(SPF_Instance filter, struct timespec *when, double dfreq, double
  int i, first, last;
  double delta_time;

-  if (filter->last < 0)
+  if (!get_first_last(filter, &first, &last))
    return;

-  /* Always slew the last sample as it may be returned even if no new
-     samples were accumulated */
-  if (filter->used > 0) {
-    first = 0;
-    last = filter->used - 1;
-  } else {
-    first = last = filter->last;
-  }
-
  for (i = first; i <= last; i++) {
    UTI_AdjustTimespec(&filter->samples[i].time, when, &filter->samples[i].time,
                       &delta_time, dfreq, doffset);
@@ -440,6 +471,20 @@ SPF_SlewSamples(SPF_Instance filter, struct timespec *when, double dfreq, double

 /* ================================================== */

+void
+SPF_CorrectOffset(SPF_Instance filter, double doffset)
+{
+  int i, first, last;
+
+  if (!get_first_last(filter, &first, &last))
+    return;
+
+  for (i = first; i <= last; i++)
+    filter->samples[i].offset -= doffset;
+}
+
+/* ================================================== */
+
 void
 SPF_AddDispersion(SPF_Instance filter, double dispersion)
 {
--- a/Show More
+++ b/Show More