[FFmpeg-cvslog] avcodec/snowdec: Check intra block dc differences.

[Michael Niedermayer]

ffmpeg | branch: release/2.8 | Michael Niedermayer <michael at niedermayer.cc> | Wed Nov 15 21:17:15 2017 +0100| [7d6319e5e65825402bf666217288b49d5e25e40f] | committer: Michael Niedermayer

avcodec/snowdec: Check intra block dc differences.

Fixes: Timeout
Fixes: 3142/clusterfuzz-testcase-5007853163118592

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 c3b9bbcc6edf2d83fe4857484cfa0839872188c6)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7d6319e5e65825402bf666217288b49d5e25e40f
---

 libavcodec/snowdec.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/libavcodec/snowdec.c b/libavcodec/snowdec.c
index 88cee3e872..f95f538f6c 100644
--- a/libavcodec/snowdec.c
+++ b/libavcodec/snowdec.c
@@ -180,13 +180,22 @@ static int decode_q_branch(SnowContext *s, int level, int x, int y){
         int my_context= av_log2(2*FFABS(left->my - top->my)) + 0*av_log2(2*FFABS(tr->my - top->my));
 
         type= get_rac(&s->c, &s->block_state[1 + left->type + top->type]) ? BLOCK_INTRA : 0;
-
         if(type){
+            int ld, cbd, crd;
             pred_mv(s, &mx, &my, 0, left, top, tr);
-            l += get_symbol(&s->c, &s->block_state[32], 1);
+            ld = get_symbol(&s->c, &s->block_state[32], 1);
+            if (ld < -255 || ld > 255) {
+                return AVERROR_INVALIDDATA;
+            }
+            l += ld;
             if (s->nb_planes > 2) {
-                cb+= get_symbol(&s->c, &s->block_state[64], 1);
-                cr+= get_symbol(&s->c, &s->block_state[96], 1);
+                cbd = get_symbol(&s->c, &s->block_state[64], 1);
+                crd = get_symbol(&s->c, &s->block_state[96], 1);
+                if (cbd < -255 || cbd > 255 || crd < -255 || crd > 255) {
+                    return AVERROR_INVALIDDATA;
+                }
+                cb += cbd;
+                cr += crd;
             }
         }else{
             if(s->ref_frames > 1)