[FFmpeg-devel] [PATCH 1/5] avcodec/vp56: Consider the alpha start as end of the prior header

[Peter Ross]

On Tue, Aug 06, 2019 at 11:30:02PM +0200, Michael Niedermayer wrote:
> Fixes: Timeout (23sec -> 71ms)
> Fixes: 15661/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP6A_fuzzer-6257865947348992
> 
> 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/vp56.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/vp56.c b/libavcodec/vp56.c
> index 72fea3780e..695f37e972 100644
> --- a/libavcodec/vp56.c
> +++ b/libavcodec/vp56.c
> @@ -572,7 +572,7 @@ int ff_vp56_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
>      VP56Context *s = avctx->priv_data;
>      AVFrame *const p = s->frames[VP56_FRAME_CURRENT];
>      int remaining_buf_size = avpkt->size;
> -    int av_uninit(alpha_offset);
> +    int alpha_offset = remaining_buf_size;
>      int i, res;
>      int ret;
>  
> @@ -585,7 +585,7 @@ int ff_vp56_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
>              return AVERROR_INVALIDDATA;
>      }
>  
> -    res = s->parse_header(s, buf, remaining_buf_size);
> +    res = s->parse_header(s, buf, alpha_offset);
>      if (res < 0)
>          return res;
>  

hi michael, i am strugling to see a problem with the existing logic.

    if (s->has_alpha) {
        if (remaining_buf_size < 3)
            return AVERROR_INVALIDDATA;
        alpha_offset = bytestream_get_be24(&buf);
        remaining_buf_size -= 3;
        if (remaining_buf_size < alpha_offset)
            return AVERROR_INVALIDDATA;
    }

    res = s->parse_header(s, buf, remaining_buf_size);
    if (res < 0)
        return res;


if the sample has alpha, remaining_buf_size is reduced in size.
can you post the sanple that takes 23s to decode?

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
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