[tor-commits] [tor/maint-0.2.5] Avoid attempts to double-remove edge connections from the DNS resolver.

[nickm at torproject.org]

commit 905287415b834db1a92205e8436f66a3b2d6846c
Author: Nick Mathewson <nickm at torproject.org>
Date:   Thu Jan 8 11:00:21 2015 -0500

    Avoid attempts to double-remove edge connections from the DNS resolver.
    
    Also, avoid crashing when we attempt to double-remove an edge
    connection from the DNS resolver: just log a bug warning instead.
    
    Fixes bug 14129.  Bugfix on 0d20fee2fbd48978, which was in 0.0.7rc1.
    
    jowr found the bug.  cypherpunks wrote the fix.  I added the log
    message and removed the assert.
---
 changes/bug14129 |    7 +++++++
 src/or/dns.c     |    6 +++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/changes/bug14129 b/changes/bug14129
new file mode 100644
index 0000000..6153cd8
--- /dev/null
+++ b/changes/bug14129
@@ -0,0 +1,7 @@
+  o Major bugfixes (exit node stability):
+
+    - Fix an assertion failure that could occur under high DNS load.  Fixes
+      bug 14129; bugfix on Tor 0.0.7rc1. Found by "jowr"; diagnosed and fixed
+      by "cypherpunks".
+
+
diff --git a/src/or/dns.c b/src/or/dns.c
index fb1b10d..8b6e3b0 100644
--- a/src/or/dns.c
+++ b/src/or/dns.c
@@ -557,6 +557,8 @@ purge_expired_resolves(time_t now)
         /* Connections should only be pending if they have no socket. */
         tor_assert(!SOCKET_OK(pend->conn->base_.s));
         pendconn = pend->conn;
+        /* Prevent double-remove */
+        pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED;
         if (!pendconn->base_.marked_for_close) {
           connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT);
           circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
@@ -1132,7 +1134,9 @@ connection_dns_remove(edge_connection_t *conn)
         return; /* more are pending */
       }
     }
-    tor_assert(0); /* not reachable unless onlyconn not in pending list */
+    log_warn(LD_BUG, "Connection (fd "TOR_SOCKET_T_FORMAT") was not waiting "
+             "for a resolve of %s, but we tried to remove it.",
+             conn->base_.s, escaped_safe_str(conn->base_.address));
   }
 }