Re: [FFmpeg-devel] [PATCH] lavc/vvc: Check fc->ref contains valid reference

[Lynne <dev@lynne.ee>]

Feb 8, 2024, 22:16 by post@frankplowman.com:

> From: Frank Plowman <post@frankplowman.com>
>
> Depending on where exactly decode_nal_unit failed, it is possible that
> fc->ref holds a VVCFrame which has had ff_vvc_unref_frame called on it
> and not yet had ref_frame called on it.  In this case, fc->ref most of
> the fields of fc->ref are NULL and attempting to call
> ff_vvc_report_frame_finished on it will result in a null dereference.
>
> Patch fixes the error described above by checking fc->ref has not only
> been allocated, but also references a valid AVFrame before attempting to
> call ff_vvc_report_frame_finished on it.
>
> Signed-off-by: Frank Plowman <post@frankplowman.com>
> ---
>  libavcodec/vvc/vvcdec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/vvc/vvcdec.c b/libavcodec/vvc/vvcdec.c
> index 8163b5ecb6..246ee79299 100644
> --- a/libavcodec/vvc/vvcdec.c
> +++ b/libavcodec/vvc/vvcdec.c
> @@ -820,7 +820,7 @@ static int decode_nal_units(VVCContext *s, VVCFrameContext *fc, AVPacket *avpkt)
>  return 0;
>  
>  fail:
> -    if (fc->ref)
> +    if (fc->ref && fc->ref->frame->buf[0])
>  ff_vvc_report_frame_finished(fc->ref);
>  return ret;
>  }
>

In general, for other codecs, if a reference does not exist,
we simply allocate it and pretend it existed and was correctly decoded.
This has better resilience against corrupt bitstreams or just bad muxing,
and yields an (maybe corrupt) output, which is better than nothing.

Is this not possible for VVC?
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