[tor-bugs] #6480 [Tor Relay]: double connection_free() in dns_resolve()

["Tor Bug Tracker & Wiki" <torproject-admin@xxxxxxxxxxxxxx>]

#6480: double connection_free() in dns_resolve()
-----------------------+----------------------------------------------------
 Reporter:  arma       |          Owner:                    
     Type:  defect     |         Status:  new               
 Priority:  normal     |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor Relay  |        Version:                    
 Keywords:             |         Parent:                    
   Points:             |   Actualpoints:                    
-----------------------+----------------------------------------------------
 If dns_resolve()'s call to dns_resolve_impl() returns -1, it ends up
 running
 {{{
       dns_cancel_pending_resolve(exitconn->_base.address);

       if (!exitconn->_base.marked_for_close) {
         connection_free(TO_CONN(exitconn));
 }}}

 But dns_cancel_pending_resolve() runs
 {{{
   while (resolve->pending_connections) {
 ...
     if (!pendconn->_base.marked_for_close)
       connection_free(TO_CONN(pendconn));
 }}}

 So we would end up calling connection_free() on it twice. But we don't in
 practice, since the first connection_free() scribbles 0xCC on it, which
 sets marked_for_close to true, so we don't free it the second time! Cue
 Nick's circus music.

 Our friendly irc person says "fix not so easy btw, connection_free() still
 need to call if no it was attached to pending resolve list."

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/6480>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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