[FFmpeg-devel] [PATCH 1/4] avformat/avidec: Check for dv streams before using priv_data in parse ##dc/##wb

[Michael Niedermayer]

On Fri, Mar 19, 2021 at 12:20:23AM +0100, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: null pointer dereference
> > Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavformat/avidec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> > index fa0599501a..48370fe5ce 100644
> > --- a/libavformat/avidec.c
> > +++ b/libavformat/avidec.c
> > @@ -1288,7 +1288,7 @@ start_sync:
> >                  AVStream *st1   = s->streams[1];
> >                  AVIStream *ast1 = st1->priv_data;
> >                  // workaround for broken small-file-bug402.avi
> > -                if (   d[2] == 'w' && d[3] == 'b'
> > +                if (ast1 && d[2] == 'w' && d[3] == 'b'
> >                     && n == 0
> >                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
> >                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
> > 
> How is this possible? After all, dv streams also have an AVIStream as

The DV demuxer creates streams in dv_extract_audio_info() without a AVIStream


> priv_data; and only the very first stream can ever be a dv stream due to
> the check in line 605.

I assume they are created after that check



[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
-------------- 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/20210319/db1ece57/attachment.sig>