[FFmpeg-cvslog] avcodec/smacker: Check remaining bits in SMK_BLK_FULL

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Fri Oct  2 10:54:31 2020 +0200| [42ded4d1e6fb0086a235dc584118414ae2bf30c9] | committer: Michael Niedermayer

avcodec/smacker: Check remaining bits in SMK_BLK_FULL

Fixes: out of array access
Fixes: 26047/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SMACKER_fuzzer-5083031667474432

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

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=42ded4d1e6fb0086a235dc584118414ae2bf30c9
---

 libavcodec/smacker.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
index 813eb862c0..6b1faec09e 100644
--- a/libavcodec/smacker.c
+++ b/libavcodec/smacker.c
@@ -448,6 +448,8 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
         case SMK_BLK_FULL:
             mode = 0;
             if(avctx->codec_tag == MKTAG('S', 'M', 'K', '4')) { // In case of Smacker v4 we have three modes
+                if (get_bits_left(&gb) < 1)
+                    return AVERROR_INVALIDDATA;
                 if(get_bits1(&gb)) mode = 1;
                 else if(get_bits1(&gb)) mode = 2;
             }