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Bulletproof the safe_timer_diff function

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Originally it can overflow in some weird cases.  Now it should no longer
be able to do so.

Additionally, limit main's timers to 30 days rather than to 38 years;
we don't actually want any 38-year timers.

Closes bug 17682.
This commit is contained in:
Nick Mathewson 2016-01-28 22:04:24 -05:00
parent a5bed4dab2
commit 601b41084a
1 changed files with 13 additions and 1 deletions
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14
src/or/main.c
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@ -1414,11 +1414,23 @@ reschedule_directory_downloads(void)
periodic_event_reschedule(launch_descriptor_fetches_event);
}
#define LONGEST_TIMER_PERIOD (30 * 86400)
/** Helper: Return the number of seconds between <b>now</b> and <b>next</b>,
* clipped to the range [1 second, LONGEST_TIMER_PERIOD]. */
static inline int
safe_timer_diff(time_t now, time_t next)
{
if (next > now) {
tor_assert(next - now <= INT_MAX);
/* There were no computers at signed TIME_MIN (1902 on 32-bit systems),
* and nothing that could run Tor. It's a bug if 'next' is around then.
* On 64-bit systems with signed TIME_MIN, TIME_MIN is before the Big
* Bang. We cannot extrapolate past a singularity, but there was probably
* nothing that could run Tor then, either.
**/
tor_assert(next > TIME_MIN + LONGEST_TIMER_PERIOD);
if (next - LONGEST_TIMER_PERIOD > now)
return LONGEST_TIMER_PERIOD;
return (int)(next - now);
} else {
return 1;