[tor-bugs] #5654 [ttdnsd]: ttdnsd has concurrency issues

[Tor Bug Tracker & Wiki]

#5654: ttdnsd has concurrency issues
--------------------+-------------------------------------------------------
 Reporter:  anonym  |          Owner:  ioerror         
     Type:  defect  |         Status:  new             
 Priority:  normal  |      Milestone:                  
Component:  ttdnsd  |        Version:  Tor: unspecified
 Keywords:          |         Parent:                  
   Points:          |   Actualpoints:                  
--------------------+-------------------------------------------------------
 This is with `ttdnsd` `0.7-1~squeeze` (`i386`) from `deb.torproject.org`,
 invoked with:

 {{{
 ttdnsd -P /var/lib/ttdnsd/pid -f /etc/ttdnsd.conf -b 127.0.0.2 -p 53
 }}}
 Short story:

  * Concurrent DNS requests with a non-working DNS server causes `ttdnsd`
 to crash.
  * Concurrent DNS requests with a working DNS server causes no crash, but
 all requests fail.

 Long story:

 `ttdnsd` crashes reliably when it gets two (or more) concurrent (and
 distinct) DNS request, e.g:

 {{{
     host torproject.org 127.0.0.2 &
     host boum.org 127.0.0.2 &
 }}}
 Running ttdnsd with the `-c` (no chroot) option seems to prevent the
 crash, but no circuits are built and nothing is resolved, so `ttdnsd` is
 still useless.

 It seems this crash only occurs when `ttdnsd` is configured to use a DNS
 server that blocks the Tor network (it seems like Google's DNS (`8.8.8.8`)
 does this currently). Switching to e.g. OpenDNS (`208.67.222.222`)
 prevents the crash, but...

 When using OpenDNS, running the above two commands fails with timeout
 errors for both requests even though a circuit is built. It seems `ttdnsd`
 can only handle one request at a time; if a request is made while it
 handles another, '''both''' fails.

 All this can be reproduced in Tails 0.10.2, but if you wanna try that,
 first see [https://tails.boum.org/bugs/ttdnsd_broken/ our ticket] about
 this issue.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/5654>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online