commit 500f04a74e22686f7659adecea02569b3459c71b
parent 703ab95e9fb94700b6349f539c58705040ede9a8
Author: Nick Mathewson <nickm@torproject.org>
Date: Thu, 30 Nov 2017 11:48:12 -0500
Merge branch 'maint-0.3.0' into maint-0.3.1
Diffstat:
2 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/changes/bug21394 b/changes/bug21394
@@ -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.
diff --git a/src/or/dns.c b/src/or/dns.c
@@ -1426,14 +1426,31 @@ 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
