[FFmpeg-devel] [PATCH 2/2] avcodec/wavpack: Prevent frame format from being wrong

[Anton Khirnov]

Quoting Michael Niedermayer (2020-03-24 01:41:24)
> On Mon, Mar 23, 2020 at 05:49:06PM +0100, Anton Khirnov wrote:
> > Quoting Michael Niedermayer (2020-03-20 21:50:18)
> > > On Fri, Mar 20, 2020 at 10:18:49AM +0100, Anton Khirnov wrote:
> > > > Quoting Michael Niedermayer (2020-03-20 01:03:36)
> > > > > Fixes: out of array access
> > > > > Fixes: 21193/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WAVPACK_fuzzer-5125168956702720
> > > > > 
> > > > > 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/wavpack.c | 1 +
> > > > >  1 file changed, 1 insertion(+)
> > > > > 
> > > > > diff --git a/libavcodec/wavpack.c b/libavcodec/wavpack.c
> > > > > index b27262b94e..e9c870e41e 100644
> > > > > --- a/libavcodec/wavpack.c
> > > > > +++ b/libavcodec/wavpack.c
> > > > > @@ -1488,6 +1488,7 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
> > > > >  
> > > > >          /* get output buffer */
> > > > >          wc->curr_frame.f->nb_samples = s->samples;
> > > > > +        wc->curr_frame.f->format     = avctx->sample_fmt;
> > > > 
> > > > How does this have any effect? curr_frame.f should now be clean and get
> > > > initialized from avctx->sample_fmt.
> > > 
> > > IIRC
> > > The format changes between frames, so the struct is still set to the one
> > > from the previous frame and that overrides the use of the avctx value
> > > 
> > > setting it to NONE (here or somewhere else) should work too.
> > 
> > ff_thread_release_buffer() is called on that frame immediately before,
> > which should reset it to defaults (setting format to FMT_NONE).
> 
> ff_thread_release_buffer() does not reset it in all cases

Then I would say that is the bug that should be fixed.
ff_thread_release_buffer() should have the same semantics as
av_frame_unref() and always reset the frame to a clean state.

-- 
Anton Khirnov