[FFmpeg-cvslog] avcodec/mpeg4videodec: Check mb_num also against 0

[Michael Niedermayer]

ffmpeg | branch: release/3.0 | Michael Niedermayer <michael at niedermayer.cc> | Sun Jan 28 02:29:00 2018 +0100| [78b1d57a4bc4337816dd5e88b6c2fab20cefdefb] | committer: Michael Niedermayer

avcodec/mpeg4videodec: Check mb_num also against 0

The spec implies that 0 is invalid in addition to the existing checks

Found-by: <kierank>
Reviewed-by: Kieran Kunhya <kieran618 at googlemail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 05f4703a168a336363750e32bcfdd6f303fbdbc3)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=78b1d57a4bc4337816dd5e88b6c2fab20cefdefb
---

 libavcodec/mpeg4videodec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
index eff809aafc..19ab1ef288 100644
--- a/libavcodec/mpeg4videodec.c
+++ b/libavcodec/mpeg4videodec.c
@@ -459,7 +459,7 @@ int ff_mpeg4_decode_video_packet_header(Mpeg4DecContext *ctx)
     }
 
     mb_num = get_bits(&s->gb, mb_num_bits);
-    if (mb_num >= s->mb_num) {
+    if (mb_num >= s->mb_num || !mb_num) {
         av_log(s->avctx, AV_LOG_ERROR,
                "illegal mb_num in video packet (%d %d) \n", mb_num, s->mb_num);
         return -1;