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Re: [tor-bugs] #17682 [Tor]: safe_timer_diff is unsafe under wrapping
#17682: safe_timer_diff is unsafe under wrapping
------------------------------+------------------------------------
Reporter: teor | Owner: nickm
Type: defect | Status: needs_revision
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 nickm):
Replying to [comment:12 teor]:
> Code review:
>
> {{{
> + /* There were no computers at signed TIME_MIN, and nothing that
could run
> + * Tor. It's a bug if 'now' is around then. */
> + tor_assert(now > TIME_MIN + LONGEST_TIMER_PERIOD);
> }}}
> 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. But in any case, TIME_MIN on a 32-bit computer
isn't 1970 -- it's 1902. And on a 64-bit time_t, it is 292 billion years
in the past, whereas current cosmological models only put our universe at
13.8 billion years old.
(I continue to maintained that unsigned time_t doesn't actually exist.
Adding a ticket to remove unsigned TIME_T support as #18184 )
> {{{
> + if (next < now - LONGEST_TIMER_PERIOD)
> + return LONGEST_TIMER_PERIOD;
> }}}
> Do you mean `next > now - LONGEST_TIMER_PERIOD`?
>
> Given the assertion, `now - LONGEST_TIMER_PERIOD` never underflows, so
`now - LONGEST_TIMER_PERIOD > TIME_MIN`.
> And if `next > now`, then it's never true that `next < now -
LONGEST_TIMER_PERIOD`.
D'oh. Trying again. I think the fixup in `bug17682` should be right.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17682#comment:13>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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