[tor-bugs] #31482 [Core Tor/Tor]: Avoid possible overflow when converting between coarse stamp to approx ms

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#31482: Avoid possible overflow when converting between coarse stamp to approx ms
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     Reporter:  teor     |      Owner:  teor
         Type:  defect   |     Status:  assigned
     Priority:  Medium   |  Milestone:  Tor: 0.4.2.x-final
    Component:  Core     |    Version:  Tor: 0.3.4.1-alpha
  Tor/Tor                |   Keywords:  035-backport, 040-backport,
     Severity:  Normal   |  041-backport
Actual Points:  0.5      |  Parent ID:
       Points:  1        |   Reviewer:
      Sponsor:           |
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 Our coarse monotonic time conversion code can overflow on some platforms.

 In particular, passing a large rate to a token bucket will overflow on
 iOS, and any other platform where monotime.numerator^2^ /
 monotime.denominator > 512.

 I have a fix that makes sure that token bucket's
 rate_per_sec_to_rate_per_sec() can't cause an overflow. I can do tests and
 a changes file after nickm answers some of my remaining questions.

 Gaba, this is a fix on a refactor for #25766, which was originally for
 sponsor 8. Are refactor bug fixes covered by sponsor 31 now?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31482>
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