File libevent-CVE-2016-10197.patch of Package libevent.6437

From ec65c42052d95d2c23d1d837136d1cf1d9ecef9e Mon Sep 17 00:00:00 2001
From: Azat Khuzhin <a3at.mail@gmail.com>
Date: Fri, 25 Mar 2016 00:33:47 +0300
Subject: [PATCH] evdns: fix searching empty hostnames

From #332:
  Here follows a bug report by **Guido Vranken** via the _Tor bug bounty program_. Please credit Guido accordingly.

  ## Bug report

  The DNS code of Libevent contains this rather obvious OOB read:

  ```c
  static char *
  search_make_new(const struct search_state *const state, int n, const char *const base_name) {
      const size_t base_len = strlen(base_name);
      const char need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
  ```

  If the length of ```base_name``` is 0, then line 3125 reads 1 byte before the buffer. This will trigger a crash on ASAN-protected builds.

  To reproduce:

  Build libevent with ASAN:
  ```
  $ CFLAGS='-fomit-frame-pointer -fsanitize=address' ./configure && make -j4
  ```
  Put the attached ```resolv.conf``` and ```poc.c``` in the source directory and then do:

  ```
  $ gcc -fsanitize=address -fomit-frame-pointer poc.c .libs/libevent.a
  $ ./a.out
  =================================================================
  ==22201== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60060000efdf at pc 0x4429da bp 0x7ffe1ed47300 sp 0x7ffe1ed472f8
  READ of size 1 at 0x60060000efdf thread T0
  ```

P.S. we can add a check earlier, but since this is very uncommon, I didn't add it.

Fixes: #332
---
 evdns.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/evdns.c b/evdns.c
index 905ff6b51..e9dbc35c6 100644
--- a/evdns.c
+++ b/evdns.c
@@ -3175,9 +3175,12 @@ search_set_from_hostname(struct evdns_base *base) {
 static char *
 search_make_new(const struct search_state *const state, int n, const char *const base_name) {
 	const size_t base_len = strlen(base_name);
-	const char need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
+	char need_to_append_dot;
 	struct search_domain *dom;
 
+	if (!base_len) return NULL;
+	need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
+
 	for (dom = state->head; dom; dom = dom->next) {
 		if (!n--) {
 			/* this is the postfix we want */