[FFmpeg-cvslog] avcodec/ylc: Check count in build_vlc()

[Michael Niedermayer]

ffmpeg | branch: release/3.1 | Michael Niedermayer <michael at niedermayer.cc> | Sun May 28 17:20:42 2017 +0200| [41c6624c885c8ff0a921118b9d8af680d7acee4c] | committer: Michael Niedermayer

avcodec/ylc: Check count in build_vlc()

Fixes: runtime error: signed integer overflow: 211633430 + 2147483647 cannot be represented in type 'int'
Fixes: 1874/clusterfuzz-testcase-minimized-5037763613163520

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 67b30decf7793523f7fdaef6fdf7f1179ef42b18)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=41c6624c885c8ff0a921118b9d8af680d7acee4c
---

 libavcodec/ylc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavcodec/ylc.c b/libavcodec/ylc.c
index 95a5e05baa..1af880f4d4 100644
--- a/libavcodec/ylc.c
+++ b/libavcodec/ylc.c
@@ -108,7 +108,7 @@ static int build_vlc(AVCodecContext *avctx, VLC *vlc, const uint32_t *table)
             int new_node = j;
             int first_node = cur_node;
             int second_node = cur_node;
-            int nd, st;
+            unsigned nd, st;
 
             nodes[cur_node].count = -1;
 
@@ -132,6 +132,10 @@ static int build_vlc(AVCodecContext *avctx, VLC *vlc, const uint32_t *table)
             st = nodes[first_node].count;
             nodes[second_node].count = 0;
             nodes[first_node].count  = 0;
+            if (nd >= UINT32_MAX - st) {
+                av_log(avctx, AV_LOG_ERROR, "count overflow\n");
+                return AVERROR_INVALIDDATA;
+            }
             nodes[cur_node].count = nd + st;
             nodes[cur_node].sym = -1;
             nodes[cur_node].n0 = cur_node;