sys_linux: fix building with older compilers and some archs

The recent replacement of <termios.h> with <linux/termios.h> to get
TCGETS2 seems to work only with compilers (or C standards) that allow
the same structure to be defined multiple times. There is a conflict
between <sys/ioctl.h> and <linux/termios.h>.

Another problem is that TCGETS2 is not used on some archs like ppc64.

Switch back to <termios.h> and move TCGETS2 to a list in a separate
file where it can be compiled without <sys/ioctl.h>.

Fixes: 03875f1ea5 ("sys_linux: allow ioctl(TCGETS2) in seccomp filter")

configure

@@ -808,6 +808,7 @@ then
   # 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

sys_linux.c

@@ -48,7 +48,7 @@
 #ifdef FEAT_SCFILTER
 #include <sys/prctl.h>
 #include <seccomp.h>
-#include <linux/termios.h>
+#include <termios.h>
 #ifdef FEAT_PPS
 #include <linux/pps.h>
 #endif
@@ -63,6 +63,7 @@
 #endif
 
 #include "sys_linux.h"
+#include "sys_linux_scmp.h"
 #include "sys_timex.h"
 #include "conf.h"
 #include "local.h"
@@ -615,7 +616,7 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
   const static int fcntls[] = { F_GETFD, F_SETFD, F_GETFL, F_SETFL };
 
   const static unsigned long ioctls[] = {
-    FIONREAD, TCGETS, TCGETS2, TIOCGWINSZ,
+    FIONREAD, TCGETS, TIOCGWINSZ,
 #if defined(FEAT_PHC) || defined(HAVE_LINUX_TIMESTAMPING)
     PTP_EXTTS_REQUEST, PTP_SYS_OFFSET,
 #ifdef PTP_PIN_SETFUNC
@@ -728,6 +729,14 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
                            SCMP_A1(SCMP_CMP_EQ, ioctls[i])) < 0)
         goto add_failed;
     }
+
+    /* Allow selected ioctls that need to be specified in a separate
+       file to avoid conflicting headers (e.g. TCGETS2) */
+    for (i = 0; SYS_Linux_GetExtraScmpIoctl(i) != 0; i++) {
+      if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1,
+                           SCMP_A1(SCMP_CMP_EQ, SYS_Linux_GetExtraScmpIoctl(i))) < 0)
+        goto add_failed;
+    }
   }
 
   if (seccomp_load(ctx) < 0)

sys_linux_scmp.c

@@ -0,0 +1,44 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  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
+ * 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.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Lists of values that are needed in seccomp filters but need to
+  be compiled separately from sys_linux.c due to conflicting headers.
+  */
+
+#include <linux/termios.h>
+
+#include "sys_linux_scmp.h"
+
+unsigned long
+SYS_Linux_GetExtraScmpIoctl(int index)
+{
+  const unsigned long ioctls[] = {
+#ifdef TCGETS2
+    /* Conflict between <linux/termios.h> and <sys/ioctl.h> */
+    TCGETS2,
+#endif
+    0
+  };
+
+  return ioctls[index];
+}

sys_linux_scmp.h

@@ -0,0 +1,28 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  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
+ * 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 lists that are needed in seccomp filters but need to
+  be compiled separately from sys_linux.c due to conflicting headers.
+  */
+
+extern unsigned long SYS_Linux_GetExtraScmpIoctl(int index);