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

[Nuo Mi <nuomi2021@gmail.com>]

On Fri, Feb 9, 2024 at 6:46 AM Frank Plowman <post@frankplowman.com> wrote:

>
>
> On 08/02/2024 21:50, Lynne wrote:
> > 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?
>
> I think the naming is confusing here.  fc->ref is a pointer to the
> VVCFrame currently being decoded.
>
HI Lynee,
the name is from hevc. I do not like it either, but so many functions
copied from hevc will use it. ...

Hi Frank,
Please try https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=10775
thank you

>
> --
> Frank
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