blob: 33b81108e890c23c716d0ff8d59bbc18228ca9c8 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
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 905ff6b..e9dbc35 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 */
--
2.1.4
|