[FFmpeg-cvslog] avcodec/alsdec: Check for block_length <= 0 in read_var_block_data()

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Fri Jul 26 15:26:08 2019 +0200| [d5cd7fe5af3ee2a3e835f3c020037670dd90620b] | committer: Michael Niedermayer

avcodec/alsdec: Check for block_length <= 0 in read_var_block_data()

Fixes: left shift of negative value -1
Fixes: 15719/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5685731105701888

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 be4fb282f9fb00d9c267dcc477745e2e468e758f)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=d5cd7fe5af3ee2a3e835f3c020037670dd90620b
---

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

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index 6b5774175b..d4451482a4 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -657,7 +657,7 @@ static int read_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
 
     // do not continue in case of a damaged stream since
     // block_length must be evenly divisible by sub_blocks
-    if (bd->block_length & (sub_blocks - 1)) {
+    if (bd->block_length & (sub_blocks - 1) || bd->block_length <= 0) {
         av_log(avctx, AV_LOG_WARNING,
                "Block length is not evenly divisible by the number of subblocks.\n");
         return AVERROR_INVALIDDATA;