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h264: prevent theoretical infinite loop in SEI parsing

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Properly address CVE-2011-3946 and parse bitstream as described in the spec.

CC: libav-stable@libav.org
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
This commit is contained in:
Vittorio Giovara
2014-07-30 19:33:36 +01:00
parent 01f9540320
commit 5123541913
1 changed files with 14 additions and 9 deletions
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23
libavcodec/h264_sei.c
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@@ -165,17 +165,22 @@ int ff_h264_decode_sei(H264Context *h){
MpegEncContext * const s = &h->s;
while (get_bits_left(&s->gb) > 16) {
int size, type;
int type = 0;
int size = 0;
int last = 0;
type=0;
do{
type+= show_bits(&s->gb, 8);
}while(get_bits(&s->gb, 8) == 255);
while (get_bits_left(&s->gb) >= 8 &&
(last = get_bits(&s->gb, 8)) == 255) {
type += 255;
}
type += last;
size=0;
do{
size+= show_bits(&s->gb, 8);
}while(get_bits(&s->gb, 8) == 255);
last = 0;
while (get_bits_left(&s->gb) >= 8 &&
(last = get_bits(&s->gb, 8)) == 255) {
size += 255;
}
size += last;
if (size > get_bits_left(&s->gb) / 8) {
av_log(s->avctx, AV_LOG_ERROR, "SEI type %d truncated at %d\n",