[FFmpeg-devel] [PATCH 2/2] avcodec/qdm2: Check frame size

[Michael Niedermayer]

On Fri, Sep 06, 2019 at 11:08:06PM +0200, Paul B Mahol wrote:
> Are you sure this is not band aid but actually real fix?

Sorry, I did not see your reply yesterday before applying the change.

Without a real (non fuzzer) sample and no reference specification or 
reference implementation that is open source. Asking for a sample 
seems the obvious solution to me. Having a sample for this case would
be quite usefull ...

I do not know if this corner case ever occurs in a real sample,
but if it does occur then yes this is not a real fix for it, 
it just avoids the anomaly found by the fuzzer.
If this never occurs in any encoder output then it would be a
real fix. (minus asking for a sample)

Thanks

> 
> On 8/29/19, Michael Niedermayer <michael at niedermayer.cc> wrote:
> > Fixes: index 2304 out of bounds for type 'float [2304]'
> > Fixes:
> > 16332/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_QDM2_fuzzer-5679142481166336
> >
> > 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/qdm2.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/libavcodec/qdm2.c b/libavcodec/qdm2.c
> > index eaffb36dcc..ac8ae8cbbb 100644
> > --- a/libavcodec/qdm2.c
> > +++ b/libavcodec/qdm2.c
> > @@ -1727,6 +1727,11 @@ static av_cold int qdm2_decode_init(AVCodecContext
> > *avctx)
> >      s->sub_sampling = s->fft_order - 7;
> >      s->frequency_range = 255 / (1 << (2 - s->sub_sampling));
> >
> > +    if (s->frame_size * 4 >> s->sub_sampling > MPA_FRAME_SIZE) {
> > +        avpriv_request_sample(avctx, "large frames");
> > +        return AVERROR_PATCHWELCOME;
> > +    }
> > +
> >      switch ((s->sub_sampling * 2 + s->channels - 1)) {
> >          case 0: tmp = 40; break;
> >          case 1: tmp = 48; break;
> > --
> > 2.23.0
> >
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
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