[FFmpeg-devel] [PATCH 1/4] avformat/avidec: Check for dv streams before using priv_data in parse ##dc/##wb

[Andreas Rheinhardt]

Michael Niedermayer:
> Fixes: null pointer dereference
> Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavformat/avidec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> index fa0599501a..48370fe5ce 100644
> --- a/libavformat/avidec.c
> +++ b/libavformat/avidec.c
> @@ -1288,7 +1288,7 @@ start_sync:
>                  AVStream *st1   = s->streams[1];
>                  AVIStream *ast1 = st1->priv_data;
>                  // workaround for broken small-file-bug402.avi
> -                if (   d[2] == 'w' && d[3] == 'b'
> +                if (ast1 && d[2] == 'w' && d[3] == 'b'
>                     && n == 0
>                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
>                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
> 
How is this possible? After all, dv streams also have an AVIStream as
priv_data; and only the very first stream can ever be a dv stream due to
the check in line 605.

- Andreas