[FFmpeg-cvslog] avcodec/ituh263dec: Make the condition for the studio slice start code match between ff_h263_resync() and ff_mpeg4_decode_studio_slice_header()

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Sat Sep 14 18:31:40 2019 +0200| [8335ba8ae99941422bef0e16ea8cf1ebe2e9a7b3] | committer: Michael Niedermayer

avcodec/ituh263dec: Make the condition for the studio slice start code match between ff_h263_resync() and ff_mpeg4_decode_studio_slice_header()

If they mismatch an infinite loop can occur
Fixes: Timeout (infinite loop)
Fixes: 17043/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5695051748868096

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=8335ba8ae99941422bef0e16ea8cf1ebe2e9a7b3
---

 libavcodec/ituh263dec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/ituh263dec.c b/libavcodec/ituh263dec.c
index afc786bd8b..c37f872b3c 100644
--- a/libavcodec/ituh263dec.c
+++ b/libavcodec/ituh263dec.c
@@ -222,7 +222,7 @@ int ff_h263_resync(MpegEncContext *s){
             get_bits(&s->gb, 8);
         }
 
-        if (show_bits_long(&s->gb, 32) == SLICE_START_CODE)
+        if (get_bits_left(&s->gb) >= 32 && show_bits_long(&s->gb, 32) == SLICE_START_CODE)
             return get_bits_count(&s->gb);
         else
             return -1;