From dc3207767d4f06b3179a3238adc44e3043ccd65b Mon Sep 17 00:00:00 2001
From: Greg Hazel <ghazel@gmail.com>
Date: Mon, 30 Jul 2012 16:52:55 -0400
Subject: [PATCH] Avoid segfault on weird timeout during name lookup.

If an evdns_getaddrinfo timeout happens while pending_cb is set, and
a callback is about to run, but we get a call to
evdns_getaddrinfo_gotresolve before it finishes.

Github issue #60. Thanks to Greg Hazel for patch and patience.
---
 evdns.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/evdns.c b/evdns.c
index d648c936cc..e9cea45b52 100644
--- a/evdns.c
+++ b/evdns.c
@@ -4214,6 +4214,8 @@ evdns_getaddrinfo_timeout_cb(evutil_socket_t fd, short what, void *ptr)
 
 	/* Cancel any pending requests, and note which one */
 	if (data->ipv4_request.r) {
+		/* XXXX This does nothing if the request's callback is already
+		 * running (pending_cb is set). */
 		evdns_cancel_request(NULL, data->ipv4_request.r);
 		v4_timedout = 1;
 		EVDNS_LOCK(data->evdns_base);
@@ -4221,6 +4223,8 @@ evdns_getaddrinfo_timeout_cb(evutil_socket_t fd, short what, void *ptr)
 		EVDNS_UNLOCK(data->evdns_base);
 	}
 	if (data->ipv6_request.r) {
+		/* XXXX This does nothing if the request's callback is already
+		 * running (pending_cb is set). */
 		evdns_cancel_request(NULL, data->ipv6_request.r);
 		v6_timedout = 1;
 		EVDNS_LOCK(data->evdns_base);
@@ -4244,6 +4248,10 @@ evdns_getaddrinfo_timeout_cb(evutil_socket_t fd, short what, void *ptr)
 		data->user_cb(e, NULL, data->user_data);
 	}
 
+	data->user_cb = NULL; /* prevent double-call if evdns callbacks are
+			       * in-progress. XXXX It would be better if this
+			       * weren't necessary. */
+
 	if (!v4_timedout && !v6_timedout) {
 		/* should be impossible? XXXX */
 		free_getaddrinfo_request(data);
@@ -4314,6 +4322,13 @@ evdns_getaddrinfo_gotresolve(int result, char type, int count,
 		return;
 	}
 
+	if (data->user_cb == NULL) {
+		/* We already answered.  XXXX This shouldn't be needed; see
+		 * comments in evdns_getaddrinfo_timeout_cb */
+		free_getaddrinfo_request(data);
+		return;
+	}
+
 	if (result == DNS_ERR_NONE) {
 		if (count == 0)
 			err = EVUTIL_EAI_NODATA;