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Cygwin: timerfd: fix read(2) running wild

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- On systems with inexact realtime clock, the current timestamp may
  be fractionally smaller than the desired timestamp.  This breaks the
  computation for incrementing overrun_count so overrun_count may end
  up as 0.  Expiring the timer with an overrun_count of 0 is a no-go.
  Make sure we always increment overrun_count by at least one after
  timer expiry.

- Do not expire the timer when another process deletes its timer_tracker.
  This, too, may result in a 0 overrun_count.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2019-01-20 22:18:17 +01:00
parent e32d1510da
commit 597285ca58
1 changed files with 3 additions and 1 deletions
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4
winsup/cygwin/timerfd.cc
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@ -69,6 +69,9 @@ timerfd_tracker::thread_func ()
LONG64 now = get_clock_now (); LONG64 now = get_clock_now ();
LONG64 ts = get_exp_ts (); LONG64 ts = get_exp_ts ();
/* Make concessions for unexact realtime clock */
if (ts > now)
ts = now - 1;
increment_overrun_count ((now - ts + get_interval () - 1) increment_overrun_count ((now - ts + get_interval () - 1)
/ get_interval ()); / get_interval ());
/* Set exp_ts to current timestamp. Make sure exp_ts ends up /* Set exp_ts to current timestamp. Make sure exp_ts ends up
@ -251,7 +254,6 @@ timerfd_shared::dtor ()
{ {
return false; return false;
} }
timer_expired ();
disarm_timer (); disarm_timer ();
NtClose (_timer); NtClose (_timer);
NtClose (_arm_evt); NtClose (_arm_evt);