[FFmpeg-cvslog] avcodec/h264_cavlc: Check mb_skip_run

[Michael Niedermayer]

ffmpeg | branch: release/3.2 | Michael Niedermayer <michael at niedermayer.cc> | Thu Oct  4 03:13:41 2018 +0200| [72268fbdc37ea692f01e0afbddae3939a9c02eb7] | committer: Michael Niedermayer

avcodec/h264_cavlc: Check mb_skip_run

Fixes: 10300/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-6292205497483264
Fixes: signed integer overflow: -2147483648 - 1 cannot be represented in type 'int'

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit f72b9904fefa79d799d0f6ecc8bd97ce52658725)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=72268fbdc37ea692f01e0afbddae3939a9c02eb7
---

 libavcodec/h264_cavlc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libavcodec/h264_cavlc.c b/libavcodec/h264_cavlc.c
index ffed204441..c88140650a 100644
--- a/libavcodec/h264_cavlc.c
+++ b/libavcodec/h264_cavlc.c
@@ -714,8 +714,14 @@ int ff_h264_decode_mb_cavlc(const H264Context *h, H264SliceContext *sl)
     cbp = 0; /* avoid warning. FIXME: find a solution without slowing
                 down the code */
     if (sl->slice_type_nos != AV_PICTURE_TYPE_I) {
-        if (sl->mb_skip_run == -1)
-            sl->mb_skip_run = get_ue_golomb_long(&sl->gb);
+        if (sl->mb_skip_run == -1) {
+            unsigned mb_skip_run = get_ue_golomb_long(&sl->gb);
+            if (mb_skip_run > h->mb_num) {
+                av_log(h->avctx, AV_LOG_ERROR, "mb_skip_run %d is invalid\n", mb_skip_run);
+                return AVERROR_INVALIDDATA;
+            }
+            sl->mb_skip_run = mb_skip_run;
+        }
 
         if (sl->mb_skip_run--) {
             if (FRAME_MBAFF(h) && (sl->mb_y & 1) == 0) {