[FFmpeg-devel] [PATCH] lavc/cbs_h2645: Fix incorrect max size of nalu unit

[Andriy Gelman]

On Fri, 06. Dec 17:47, Andreas Rheinhardt wrote:
> Andriy Gelman:
> > From: Andriy Gelman <andriy.gelman at gmail.com>
> > 
> > In the worst case the startcode prefix has 4 bytes.
> > 
> > This fixes a trigerred assertion:
> > Assertion dp <= max_size failed at libavcodec/cbs_h2645.c:1451
> > 
> > Found-by:libFuzzer
> > Signed-off-by: Andriy Gelman <andriy.gelman at gmail.com>
> > ---
> >  libavcodec/cbs_h2645.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
> > index 88fa0029cd6..5f71d805848 100644
> > --- a/libavcodec/cbs_h2645.c
> > +++ b/libavcodec/cbs_h2645.c
> > @@ -1395,7 +1395,7 @@ static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
> >      max_size = 0;
> >      for (i = 0; i < frag->nb_units; i++) {
> >          // Start code + content with worst-case emulation prevention.
> > -        max_size += 3 + frag->units[i].data_size * 3 / 2;
> > +        max_size += 4 + frag->units[i].data_size * 3 / 2;
> >      }
> >  
> >      data = av_realloc(NULL, max_size + AV_INPUT_BUFFER_PADDING_SIZE);
> > 

> LGTM. I presume you used a NAL unit of size 1?

Yes, nal unit size 1 caused the problem.

> 
> (I found this out, too, when I tried (and postponed) to add mp4
> writing support for H.264.)

Thanks,
-- 
Andriy