[tor-bugs] #23406 [Core Tor/Tor]: Sampled guards are not re-weighted when a new consensus arrives

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#23406: Sampled guards are not re-weighted when a new consensus arrives
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     Reporter:  teor          |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.0.1-alpha
     Severity:  Normal        |   Keywords:  path-selection, tor-guard
Actual Points:                |  Parent ID:  #23318
       Points:  1             |   Reviewer:
      Sponsor:                |
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 Replying to
 [https://trac.torproject.org/projects/tor/ticket/23318#comment:5]:
 > It's not only case when code bypassing limits, as noticed by pastly in
 IRC. Guard nodes weights only if new guard added by
 `entry_guards_expand_sample`. Sample guard or subsets never being re-
 weighted: once sampled non-Exit Guard will be used as Exit+Guard (if
 operator change it policy) by client.

 This is probably the behaviour we want: re-weighting based on the latest
 consensus allows Guard operators to detect exactly when a client downloads
 the next consensus (because it would stop using that Guard).

 That said, keeping old weights might allow attacks based on knowing the
 weightings in a really old consensus.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23406>
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