[Openvpn-devel,v2] Fix update_time() and openvpn_gettimeofday() coexistance

Message ID 20200922122134.12634-1-themiron@yandex-team.ru
State Superseded
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  • [Openvpn-devel,v2] Fix update_time() and openvpn_gettimeofday() coexistance
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Commit Message

Vladislav Grishenko Sept. 22, 2020, 12:21 p.m.
With TIME_BACKTRACK_PROTECTION defined, openvpn_gettimeofday() uses and
updates global variable "now_usec" along with "now" only if current time
is ahead of the previsouly stored, taking nanoseconds into account.
But, update_time() function updates only "now" leaving "now_usec" as
is with any previously value stored.
This breaks both update_time() and openvpn_gettimeofday() results and
leads to time jumps in the future within one second, can affect shaper
and user timers.

100.900 openvpn_gettimeofday():
    now set to 100s, now_usec set to 900ns, stored time is 100.900
101.300 update_time():
    now set to 101s, but now_usec is not updated and still 900ns, stored
    time jumps to the future 101.900
101.600 openvpn_gettimeofday():
    current time 101.600 is in the past relatively stored time 101.900,
    now & now_usec variables are not updated, returned time 101.900 is
    still and again incorrect
102.100 openvpn_gettimeofday():
    current time 102.100 is no longer in the past relatively stored time
    101.900, so now & now_usec get updated with wrong time delta from
    previous openvpn_gettimeofday() call or now/now_usec math

Since update_time() and openvpn_gettimeofday() calls are mixed in runtime,
there're two ways to fix their coexistance:
* either fix update_time() to always update "now_usec" for example by
  moving update_time() to gettimeofday(). Unfortunately, it may bring
  performance penalty depending on Arch/OS and vuruallized/hw environmant
  according the tests on various Linux, FreeBSD and MacOS versions.
* or, for now, allow update_time() to break "now_usec" value, since it's
  used directly only in time ajusting and always invalidate it in
  openvpn_gettimeofday() w/o checking the previous and possibly obsolete
  value with no performance changes against the current implementation.
This patch implements the second way.

Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>
 src/openvpn/otime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/src/openvpn/otime.c b/src/openvpn/otime.c
index 640168a9..d27d1f9d 100644
--- a/src/openvpn/otime.c
+++ b/src/openvpn/otime.c
@@ -73,7 +73,7 @@  update_now_usec(struct timeval *tv)
     const time_t last = now;
-    if (now > last || (now == last && tv->tv_usec > now_usec))
+    if (now >= last)
         now_usec = tv->tv_usec;