[FFmpeg-cvslog] avcodec/snowdec: Fix integer overflow with motion vector residual

[Michael Niedermayer]

ffmpeg | branch: release/3.3 | Michael Niedermayer <michael at niedermayer.cc> | Mon Aug 20 20:15:19 2018 +0200| [dc8ec1a5bc8539339f866c77f1f1b917b6a4e125] | committer: Michael Niedermayer

avcodec/snowdec: Fix integer overflow with motion vector residual

Fixes: signed integer overflow: -19818 + -2147483648 cannot be represented in type 'int'
Fixes: 9545/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SNOW_fuzzer-4928769537081344

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 acba153a148782c08f9fd17f0c05b93468f3cbd0)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=dc8ec1a5bc8539339f866c77f1f1b917b6a4e125
---

 libavcodec/snowdec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/snowdec.c b/libavcodec/snowdec.c
index 00fa064102..a9fe91d251 100644
--- a/libavcodec/snowdec.c
+++ b/libavcodec/snowdec.c
@@ -208,8 +208,8 @@ static int decode_q_branch(SnowContext *s, int level, int x, int y){
                 return AVERROR_INVALIDDATA;
             }
             pred_mv(s, &mx, &my, ref, left, top, tr);
-            mx+= get_symbol(&s->c, &s->block_state[128 + 32*(mx_context + 16*!!ref)], 1);
-            my+= get_symbol(&s->c, &s->block_state[128 + 32*(my_context + 16*!!ref)], 1);
+            mx+= (unsigned)get_symbol(&s->c, &s->block_state[128 + 32*(mx_context + 16*!!ref)], 1);
+            my+= (unsigned)get_symbol(&s->c, &s->block_state[128 + 32*(my_context + 16*!!ref)], 1);
         }
         set_blocks(s, level, x, y, l, cb, cr, mx, my, ref, type);
     }else{