[tor-bugs] #20502 [Core Tor/Tor]: Setting UseBridges=1 UseEntryGuards=0 means you bypass your bridges

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#20502: Setting UseBridges=1 UseEntryGuards=0 means you bypass your bridges
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     Reporter:  arma          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 If you set UseBridges=1, it's because you wanted to use bridges.

 But if you also happen to set UseEntryGuards to 0, then in
 {{{choose_good_entry_server()}}} we do
 {{{
   if (state && options->UseEntryGuards &&
       (purpose != CIRCUIT_PURPOSE_TESTING || options->BridgeRelay)) {
     /* This request is for an entry server to use for a regular circuit,
      * and we use entry guard nodes.  Just return one of the guard nodes.
 */
     return choose_random_entry(state);
   }
 }}}
 and we end up skipping that section because UseEntryGuards is 0. The
 result is that we make normal 3-hop circuits through normal relays.

 I think the fix is that in config.c when we're validating the config, we
 need to not let the user proceed if UseBridges is 1 yet UseEntryGuards is
 0.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20502>
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