[FFmpeg-devel] [PATCH 2/3] avcodec/smacker: Check remaining bits in SMK_BLK_FULL

[Andreas Rheinhardt]

Michael Niedermayer:
> 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>
> ---
>  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;
>              }
> 
LGTM.
(This is a file in which the type and the full tree consists of only one
entry (so that smk_get_code() never checks for overreads), isn't it? I
have to admit to have overlooked this edge case.)

- Andreas