[tor-bugs] #16625 [Tor Browser]: Verify network predictor doesn't introduce linkability

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#16625: Verify network predictor doesn't introduce linkability
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     Reporter:           |      Owner:  mikeperry
  mikeperry              |     Status:  assigned
         Type:  defect   |  Milestone:
     Priority:  normal   |    Version:
    Component:  Tor      |   Keywords:  tbb-linkability, tbb-5.0a4,
  Browser                |  ff38-esr, TorBrowserTeam201507, MikePerry201507
   Resolution:           |  Parent ID:
Actual Points:           |
       Points:           |
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Comment (by mikeperry):

 I looked at the source, and nsIOService::SpeculativeConnect() in
 combination with IOServiceProxyCallback::OnProxyAvailable() seems to
 prevent predictions from happening because we have a proxy set. However,
 the code still seems to create cache entries in about:cache somehow, and
 disabling the pref prevents that.

 It is simple enough to hack the code to actually enable prediction for
 proxied connections, which I think might be a good idea for us, except
 that Arthur's OCSP patch doesn't properly carry through the isolation
 parameters involved in predicted requests, so they would violate our
 connection isolation. The isolation parameters were similarly not applied
 in the cached prediction entries, which is also worrisome.

 I am going to commit a pref flip to disable prediction entirely, and file
 a new ticket for fixing prediction and actually enabling it post-5.0. My
 guess is that in addition to potential isolation issues, it probably will
 turn up a few fun connection usage edge cases, since it seems that Mozilla
 likely has never even tested it with proxy support enabled.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16625#comment:4>
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