[tor-bugs] #24895 [Core Tor/Tor]: MAX_REND_FAILURES is 1, but we will try three times

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#24895: MAX_REND_FAILURES is 1, but we will try three times
------------------------------+--------------------------------
     Reporter:  arma          |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  032-backport
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 Off-by-2 error counting to MAX_REND_FAILURES for onion services:

 In can_relaunch_service_rendezvous_point(), we check
 {{{
   if (circ->build_state->failure_count > MAX_REND_FAILURES ||
       circ->build_state->expiry_time <= time(NULL)) {
 }}}
 to decide whether to abort the relaunch.

 But the incrementing of failure_count happens in the relaunch, i.e. after
 this code. Also, it says ">" rather than ">=".

 Yet the definition of MAX_REND_FAILURES is
 {{{
 /** How many times will a hidden service operator attempt to connect to a
  * requested rendezvous point before giving up? */
 #define MAX_REND_FAILURES 1
 }}}

 So when the first attempt fails, failure_count is 0, which is not > 1, so
 we try again. When the second attempt fails, failure_count is 0, which is
 also not > 1. It's only after the third attempt fails that we decide that
 MAX_REND_FAILURES has been reached.

 This bug affects legacy onion services, and it will also affect nextgen
 onion services once #24894 is fixed.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24895>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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