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ntp: add copy option

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When separate client and server instances of chronyd are running on one
computer (e.g. for security or performance reasons) and are synchronized
to each other, the server instance provides a reference ID based on the
local address used for synchronization of its NTP clock, which breaks
detection of synchronization loops for its own clients.

Add a "copy" option to specify that the server and client are closely
related, no loop can form between them, and the client should assume the
reference ID and stratum of the server to fix detection of loops between
the server and clients of the client.
This commit is contained in:
Miroslav Lichvar
2021-04-14 15:58:51 +02:00
parent 635a9d3f5a
commit 84d2811800
8 changed files with 49 additions and 3 deletions
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15
ntp_core.c
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@@ -107,6 +107,8 @@ struct NCR_Instance_Record {
int min_stratum; /* Increase stratum in received packets to the
minimum */
int copy; /* Boolean suppressing own refid and stratum */
int poll_target; /* Target number of sourcestats samples */
int version; /* Version set in packets for server/peer */
@@ -560,6 +562,7 @@ NCR_CreateInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
result->auto_iburst = params->iburst;
result->auto_burst = params->burst;
result->auto_offline = params->auto_offline;
result->copy = params->copy && result->mode == MODE_CLIENT;
result->poll_target = params->poll_target;
if (params->nts) {
@@ -1766,8 +1769,16 @@ process_response(NCR_Instance inst, NTP_Local_Address *local_addr,
inst->tx_count = 0;
SRC_UpdateReachability(inst->source, synced_packet);
if (synced_packet)
SRC_UpdateStatus(inst->source, MAX(message->stratum, inst->min_stratum), pkt_leap);
if (synced_packet) {
if (inst->copy && inst->remote_stratum > 0) {
/* Assume the reference ID and stratum of the server */
inst->remote_stratum--;
SRC_SetRefid(inst->source, ntohl(message->reference_id), &inst->remote_addr.ip_addr);
}
SRC_UpdateStatus(inst->source, MAX(inst->remote_stratum, inst->min_stratum), pkt_leap);
}
if (good_packet) {
/* Adjust the polling interval, accumulate the sample, etc. */