From: Juergen Perlinger <perlinger@ntp.org>
Date: Fri, 20 Sep 2013 11:40:43 +0000 (+0200)
Subject: [Bug 2473] revisited: Avoid possible unsigned underrun for startup condition when... 
X-Git-Tag: NTP_4_2_7P389~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7a534829e26cf8abe3f5e0da2dc6be8cb72cef03;p=thirdparty%2Fntp.git

[Bug 2473] revisited: Avoid possible unsigned underrun for startup condition when testing for clock backstep.

bk: 523c343blTFb9GnJ9C43jv3f5ABwXA
---

diff --git a/ChangeLog b/ChangeLog
index 10684a878..fb3640088 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,6 @@
+* [Bug 2473] revisited: NTPD exits after clock is stepped backwards
+  Avoid possible unsigned underrun for startup condition when testing
+  for clock backstep.
 (4.2.7p388) 2013/09/19 Released by Harlan Stenn <stenn@ntp.org>
 * [Bug 2473] NTPD exits after clock is stepped backwards externally
 (4.2.7p387) 2013/09/16 Released by Harlan Stenn <stenn@ntp.org>
diff --git a/libntp/systime.c b/libntp/systime.c
index e8583c543..f5eabcd1c 100644
--- a/libntp/systime.c
+++ b/libntp/systime.c
@@ -76,6 +76,11 @@ int	trunc_os_clock;		/* sys_tick > measured_tick */
 time_stepped_callback	step_callback;
 
 #ifndef SIM
+/* perlinger@ntp.org: As 'get_sysime()' does it's own check for clock
+ * backstepping, this could probably become a local variable in
+ * 'get_systime()' and the cruft associated with communicating via a
+ * static value could be removed after the v4.2.8 release.
+ */
 static int lamport_violated;	/* clock was stepped back */
 #endif	/* !SIM */
 
@@ -179,9 +184,12 @@ get_systime(
         /* First check if here was a Lamport violation, that is, two
          * successive calls to 'get_ostime()' resulted in negative
          * time difference. Use a few milliseconds of permissible
-         * tolerance -- being too sharp can hurt here.
+         * tolerance -- being too sharp can hurt here. (This is intented
+         * for the Win32 target, where the HPC interpolation might
+         * introduce small steps backward. It should not be an issue on
+         * systems where get_ostime() results in a true syscall.)
          */
-        if (cmp_tspec(ts, sub_tspec_ns(ts_last, 50000000)) < 0)
+        if (cmp_tspec(add_tspec_ns(ts, 50000000), ts_last) < 0)
                 lamport_violated = 1;
         ts_last = ts;