[tor-bugs] #24022 [Core Tor/Tor]: Make clients avoid retrying slow exits when they time out

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#24022: Make clients avoid retrying slow exits when they time out
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 Reporter:  teor                                 |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-performance, tbb-usability,      |  Actual Points:
  performance, tbb-needs                         |
Parent ID:  #21394                               |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by arma):

 Replying to [comment:2 teor]:
 > Maybe we could fix that at the client level by keeping an exit failure
 cache?

 Be very careful of a destination dns server that chooses which requests to
 time out on, with the goal of shifting users away from certain exits
 towards others.

 Some amount of that attack is inevitably possible, since if you can't
 reach the site from one exit then you'll end up reaching it from another.

 But any design where the destination dns server can set cross-circuit
 state on the client makes me itch.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24022#comment:4>
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