kc3-lang/libevent

2016-03-25T00:33:47

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