nihilist/tor
1
0
Fork 0
mirror of https://gitlab.torproject.org/tpo/core/tor.git synced 2024-11-24 04:13:28 +01:00
Code Issues Packages Projects Releases Wiki Activity

Fix DNS resolution on busy exit relays

Browse Source 
Thanks to Dhalgren who analyzed this issue two years ago and found a
solution!
This commit is contained in:
Sebastian Hahn 2017-11-03 03:06:12 +01:00 committed by Nick Mathewson
parent 04d4786cc4
commit 9827574308
2 changed files with 29 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
changes/bug21394 Normal file
View File

@ -0,0 +1,9 @@
o Major bugfixes (Exit nodes):
- Fix an issue causing high-bandwidth exit nodes to fail a majority
or all of their DNS requests, making them basically unsuitable for
regular usage in Tor circuits. The problem is related to
libevent's DNS handling, but we can work around it in Tor. Fixes
bugs 21394 and 18580; bugfix on 0.1.2.2-alpha which introduced
eventdns. Credit goes to Dhalgren for identifying and finding a
workaround to this bug and to gamambel, arthuredelstein and
arma in helping to track it down and analyze it.

23
src/or/dns.c
View File

@ -1425,14 +1425,31 @@ configure_nameservers(int force)
#define SET(k,v) evdns_base_set_option(the_evdns_base, (k), (v))
// If we only have one nameserver, it does not make sense to back off
// from it for a timeout. Unfortunately, the value for max-timeouts is
// currently clamped by libevent to 255, but it does not hurt to set
// it higher in case libevent gets a patch for this.
// Reducing attempts in the case of just one name server too, because
// it is very likely to be a local one where a network connectivity
// issue should not cause an attempt to fail.
if (evdns_base_count_nameservers(the_evdns_base) == 1) {
SET("max-timeouts:", "16");
SET("timeout:", "10");
SET("max-timeouts:", "1000000");
SET("attempts:", "1");
} else {
SET("max-timeouts:", "3");
SET("timeout:", "5");
}
// Elongate the queue of maximum inflight dns requests, so if a bunch
// time out at the resolver (happens commonly with unbound) we won't
// stall every other DNS request. This potentially means some wasted
// CPU as there's a walk over a linear queue involved, but this is a
// much better tradeoff compared to just failing DNS requests because
// of a full queue.
SET("max-inflight:", "8192");
// Time out after 5 seconds if no reply.
SET("timeout:", "5");
if (options->ServerDNSRandomizeCase)
SET("randomize-case:", "1");
else