[FFmpeg-devel] [PATCH 1/5] avcodec/vp56: Consider the alpha start as end of the prior header

[Peter Ross]

On Sun, Aug 11, 2019 at 05:02:47PM +0200, Michael Niedermayer wrote:
> On Sun, Aug 11, 2019 at 09:29:14AM +1000, Peter Ross wrote:
> > On Tue, Aug 06, 2019 at 11:30:02PM +0200, Michael Niedermayer wrote:
> > > Fixes: Timeout (23sec -> 71ms)
> > > Fixes: 15661/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP6A_fuzzer-6257865947348992
> > > 
> > > 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/vp56.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/libavcodec/vp56.c b/libavcodec/vp56.c
> > > index 72fea3780e..695f37e972 100644
> > > --- a/libavcodec/vp56.c
> > > +++ b/libavcodec/vp56.c
> > > @@ -572,7 +572,7 @@ int ff_vp56_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
> > >      VP56Context *s = avctx->priv_data;
> > >      AVFrame *const p = s->frames[VP56_FRAME_CURRENT];
> > >      int remaining_buf_size = avpkt->size;
> > > -    int av_uninit(alpha_offset);
> > > +    int alpha_offset = remaining_buf_size;
> > >      int i, res;
> > >      int ret;
> > >  
> > > @@ -585,7 +585,7 @@ int ff_vp56_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
> > >              return AVERROR_INVALIDDATA;
> > >      }
> > >  
> > > -    res = s->parse_header(s, buf, remaining_buf_size);
> > > +    res = s->parse_header(s, buf, alpha_offset);
> > >      if (res < 0)
> > >          return res;
> > >  
> > 
> > hi michael, i am strugling to see a problem with the existing logic.
> > 
> >     if (s->has_alpha) {
> >         if (remaining_buf_size < 3)
> >             return AVERROR_INVALIDDATA;
> >         alpha_offset = bytestream_get_be24(&buf);
> >         remaining_buf_size -= 3;
> >         if (remaining_buf_size < alpha_offset)
> >             return AVERROR_INVALIDDATA;
> >     }
> > 
> >     res = s->parse_header(s, buf, remaining_buf_size);
> >     if (res < 0)
> >         return res;
> > 
> > 
> > if the sample has alpha, remaining_buf_size is reduced in size.
> 
> > can you post the sanple that takes 23s to decode?
> 
> ill send the sample to you privatly

thanks, was able to reproduce. disregard my comment above regarding remaining_buf_size.

approve.

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20190812/125d2d55/attachment.sig>