[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 01:19:28AM +0100, Andreas Rheinhardt wrote:
> 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
> > 
> 
> That explains it. Thanks. Patch is fine by me, 

will apply

thx


> but I haven't looked at
> it in detail. But neither dv nor avi set the AVFMTCTX_NOHEADER flag, so
> adding streams later is an API violation.
> 
> > 
> >> 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
> > 
> > 
> 
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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