[FFmpeg-devel] [PATCH 1/5] avcodec/pngdec: Check last AVFrame before deref

[Michael Niedermayer]

On Sat, Apr 27, 2024 at 11:36:30AM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: NULL pointer dereference
> > Fixes: 68184/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APNG_fuzzer-4926478069334016
> > 
> > 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/pngdec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> > index f7751223b81..b24bfa248dc 100644
> > --- a/libavcodec/pngdec.c
> > +++ b/libavcodec/pngdec.c
> > @@ -1218,7 +1218,7 @@ static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
> >          return AVERROR_INVALIDDATA;
> >      }
> >  
> > -    if ((sequence_number == 0 || !s->last_picture.f->data[0]) &&
> > +    if ((sequence_number == 0 || !s->last_picture.f || !s->last_picture.f->data[0]) &&
> >          dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
> >          // No previous frame to revert to for the first frame
> >          // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND
> 
> Just checking for !s->last_picture.f is enough -- s->last_picture.f is
> set if and only if s->last_picture.f->data[0] is set.

ok will apply with that simplified

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is a danger to trust the dream we wish for rather than
the science we have, -- Dr. Kenneth Brown
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20240427/0dfc98e2/attachment.sig>