[tor-bugs] #27678 [Core Tor/Tor]: Emit CIRC_BW event early for dropped cells

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#27678: Emit CIRC_BW event early for dropped cells
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     Reporter:  mikeperry     |      Owner:  (none)
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.5.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 While reviewing the dropmark paper
 (https://petsymposium.org/2018/files/papers/issue2/popets-2018-0011.pdf)
 and asking the authors to test it against vanguards's dropped cell
 detection, I realized that since we only normally emit CIRC_BW events once
 per second, the attack may still have enough time succeed against
 vanguards.

 The fix is to emit the CIRC_BW event as soon as we get a relay cell that
 does not cause us to update our delivered or overhead byte counts. It's
 pretty simply to do this. Patch incoming.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27678>
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