[tor-bugs] #7691 [Tor]: Path bias code should probe unusable circuits

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#7691: Path bias code should probe unusable circuits
-----------------------------+----------------------------------------------
 Reporter:  mikeperry        |          Owner:  mikeperry         
     Type:  enhancement      |         Status:  needs_revision    
 Priority:  major            |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor              |        Version:                    
 Keywords:  MikePerry201212  |         Parent:                    
   Points:                   |   Actualpoints:  4                 
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Changes (by nickm):

  * status:  needs_review => needs_revision


Comment:

 Reading the second one now.

 --
 {{{
  /// XXX: Generate a random 0.a.b.c address
 }}}
 This is trivial to do.  It could be approximately:
 {{{
   char *probe_nonce;
   uint32_t addr;
   crypto_rand(&addr, sizeof(addr));
   addr &= 0x00ffffff;
   probe_nonce = tor_dup_ip(addr);
 }}}
 (unchecked).  The port should probably be random too, right?

 -- The documentation is sparser than I would prefer.  Like, "Sends a probe
 down a circuit that wasn't usable."  Not usable how?  A probe of what
 type?  For what purpose?  (I know the answers, but a reader later on is
 going to have to figure out what's going on here.)

 -- Forcing the response length to be 9 seems wrong.  As a rule, we allow
 more bytes than expected and ignore them.

 -- No raw memcmp calls; either tor_memeq() or fast_memeq() will be
 correct.

 -- The cell_t* argument to pathbias_check_probe_response should probably
 be const.

 Other than that, it seems plausible so far.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7691#comment:7>
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