[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 Tor/Tor                         |        Version:  Tor:
                                                 |  0.3.4.1-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  035-backport, 040-backport,          |  Actual Points:  0.5
  041-backport                                   |
Parent ID:                                       |         Points:  1
 Reviewer:  nickm                                |        Sponsor:
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Changes (by teor):

 * reviewer:   => nickm


Comment:

 Here's a draft fix for initial review:
 * master: https://github.com/torproject/tor/pull/1249

 Here's my TODO list:
 * changes file
 * tests for simplify_fraction32()
 * tests for monotime_coarse_stamp_units_to_approx_msec() and
 monotime_msec_to_approx_coarse_stamp_units(), underflow and overflow

 I have some questions:
 * do I need to do any extra tests for monotime_init_internal()
 * does anyone run our unit tests on iOS?
 * how serious is this bug in rate_per_sec_to_rate_per_sec()? Do we
 actually use token bucket rates close to 2^30^? Is my math on that limit
 correct?
 * are there any other callers of
 monotime_coarse_stamp_units_to_approx_msec() or
 monotime_msec_to_approx_coarse_stamp_units() that might trigger this bug?
 * Have I missed anything?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31482#comment:1>
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