[PATCH v4 7/7] misc: Use gmtime instead of localtime

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

We deviate from RFC3164 which states timestamp should be in localtime
because although our __localtime_r does not set tzname, the relay still
might still use localtime (which does) and if the server timezone changes
it might result in wrong timestamp from client.  It still does not help
if a process switches its TZ setting from a timezone that has leap
seconds, to one that doesn't (or vice versa), but this would incur in
other problems.

It also handles the highly unlikely case where gmtime might return NULL,
in this case only the PRI is set to hopefully instruct the relay to
get eh TIMESTAMP (as defined by the RFC).

Finally it also uses internally the 64 bit time_t interfaces (to avoid
y2038 issues on 32 bit legacy architectures).

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 misc/syslog.c | 43 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 35 insertions(+), 8 deletions(-)

diff --git a/misc/syslog.c b/misc/syslog.c
index b184b15eea..62a69cf41a 100644
--- a/misc/syslog.c
+++ b/misc/syslog.c
@@ -156,11 +156,26 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap,
 
   /* "%b %e %H:%M:%S "  */
   char timestamp[sizeof "MMM DD hh:mm:ss "];
-  time_t now = time_now ();
+  __time64_t now = time64_now ();
+
+  /* Deviate from RFC3164 which states timestamp should be in localtime
+     because although  __localtime_r does not set tzname, the relay might
+     still use localtime (which does) and if the server timezone changes
+     it might result in wrong timestamp from client.  It still does not help
+     if a process switches its TZ setting from a timezone that has leap
+     seconds, to one that doesn't (or vice versa), but this would incur in
+     other problems as well.  */
   struct tm now_tm;
-  __localtime_r (&now, &now_tm);
-  __strftime_l (timestamp, sizeof timestamp, "%b %e %T ", &now_tm,
-                _nl_C_locobj_ptr);
+  struct tm *now_tmp = __gmtime64_r (&now, &now_tm);
+  bool has_ts = now_tmp != NULL;
+
+  /* In the unlikely case of gmtime_r failure (tm_year out of int range)
+     skip the hostname so the message is handled as valid PRI but without
+     TIMESTAMP or invalid TIMESTAMP (which should force the relay to add the
+     timestamp itself).  */
+  if (has_ts)
+    __strftime_l (timestamp, sizeof timestamp, "%h %e %T ", now_tmp,
+		  _nl_C_locobj_ptr);
 
 #define SYSLOG_HEADER(__pri, __timestamp, __msgoff, pid) \
   "<%d>%s %n%s%s%.0d%s: ",                               \
@@ -168,8 +183,16 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap,
   LogTag == NULL ? __progname : LogTag,                  \
   "[" + (pid == 0), pid, "]" + (pid == 0)
 
-  int l = __snprintf (bufs, sizeof bufs,
-                      SYSLOG_HEADER (pri, timestamp, &msgoff, pid));
+#define SYSLOG_HEADER_WITHOUT_TS(__pri, __msgoff)        \
+  "<%d>: %n", __pri, __msgoff
+
+  int l;
+  if (has_ts)
+    l = __snprintf (bufs, sizeof bufs,
+		    SYSLOG_HEADER (pri, timestamp, &msgoff, pid));
+  else
+    l = __snprintf (bufs, sizeof bufs,
+		    SYSLOG_HEADER_WITHOUT_TS (pri, &msgoff));
   if (0 <= l && l < sizeof bufs)
     {
       va_list apc;
@@ -197,8 +220,12 @@ __vsyslog_internal(int pri, const char *fmt, va_list ap,
 	  /* Tell the cancellation handler to free this buffer.  */
 	  clarg.buf = buf;
 
-	  __snprintf (buf, sizeof buf,
-		      SYSLOG_HEADER (pri, timestamp, &msgoff, pid));
+	  if (has_ts)
+	    __snprintf (bufs, sizeof bufs,
+			SYSLOG_HEADER (pri, timestamp, &msgoff, pid));
+	  else
+	    __snprintf (bufs, sizeof bufs,
+			SYSLOG_HEADER_WITHOUT_TS (pri, &msgoff));
 	}
       else
         {
-- 
2.32.0