[tor-bugs] #17682 [Tor]: safe_timer_diff is unsafe under wrapping

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#17682: safe_timer_diff is unsafe under wrapping
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 Reporter:  teor              |          Owner:  nickm
     Type:  defect            |         Status:  needs_review
 Priority:  High              |      Milestone:  Tor: 0.2.8.x-final
Component:  Tor               |        Version:  Tor: unspecified
 Severity:  Normal            |     Resolution:
 Keywords:  regression, easy  |  Actual Points:
Parent ID:  #17983            |         Points:  small
  Sponsor:                    |
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Comment (by robgjansen):

 Replying to [comment:13 nickm]:
 > Replying to [comment:12 teor]:
 > > Doesn't shadow rely on starting Tor at the epoch?
 > > (I think I heard that once, I'm not sure how accurate it is.)
 >
 > I believe it once did.

 Shadow internally starts at time 0, and maintains a simulation clock that
 ticks with nanosecond granularity. Because applications like Tor rely on
 time() and gettimeofday() to properly function, the time that Shadow
 emulates to Tor indeed starts at the epoch. (I.e., at the first tick,
 Shadow would return 0 if Tor called time() or gettimeofday()).

 The logic for what time gets returned from Shadow to Tor starts here:
 https://github.com/shadow/shadow/blob/master/src/host/shd-process.c#L3404

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17682#comment:15>
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