[FFmpeg-devel] [PATCH 1/2] avcodec/cbs_av1_syntax_template: Set seen_frame_header only after successfull uncompressed_header()

[James Almer]

On 12/14/2019 2:43 PM, Michael Niedermayer wrote:
> Fixes: assertion failure
> Fixes: 19301/clusterfuzz-testcase-minimized-ffmpeg_BSF_AV1_FRAME_MERGE_fuzzer-5743212006473728
> 
> 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/cbs_av1_syntax_template.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/cbs_av1_syntax_template.c b/libavcodec/cbs_av1_syntax_template.c
> index 523f9359e4..01c180e4af 100644
> --- a/libavcodec/cbs_av1_syntax_template.c
> +++ b/libavcodec/cbs_av1_syntax_template.c
> @@ -1601,8 +1601,6 @@ static int FUNC(frame_header_obu)(CodedBitstreamContext *ctx, RWContext *rw,
>          else
>              HEADER("Frame Header");
>  
> -        priv->seen_frame_header = 1;
> -
>  #ifdef READ
>          start_pos = get_bits_count(rw);
>  #else
> @@ -1611,6 +1609,8 @@ static int FUNC(frame_header_obu)(CodedBitstreamContext *ctx, RWContext *rw,
>  
>          CHECK(FUNC(uncompressed_header)(ctx, rw, current));
>  
> +        priv->seen_frame_header = 1;
> +
>          if (current->show_existing_frame) {
>              priv->seen_frame_header = 0;
>          } else {

What's the assertion that fails? av_assert0(priv->frame_header_ref &&
priv->frame_header)? If so, then if priv->frame_header_ref fails to be
allocated and the error is ignored, the same assertion could trigger as
seen_frame_header will be 1 even after this patch.

I think you can just remove the above line instead of moving it. Right
below the call to uncompressed_header() it's going to be set to either 0
or 1 anyway.
Another option could be replacing the assertion for a simple check for
priv->frame_header_ref that returns invalid data if it's not set.