[FFmpeg-devel] [PATCH] avcodec/jpeg2000dec: Move reslevelno check before use in case JPEG2000_PGOD_RPCL

[Gautam Ramakrishnan]

On Mon, Jul 27, 2020 at 1:46 PM Michael Niedermayer
<michael at niedermayer.cc> wrote:
>
> On Mon, Jul 27, 2020 at 09:55:31AM +0530, Gautam Ramakrishnan wrote:
> > On Mon, Jul 27, 2020 at 9:48 AM Gautam Ramakrishnan
> > <gautamramk at gmail.com> wrote:
> > >
> > > On Mon, Jul 27, 2020 at 3:16 AM Michael Niedermayer
> > > <michael at niedermayer.cc> wrote:
> > > >
> > > > Fixes: division by zero
> > > > Fixes: 24201/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5665813827420160
> > > > Fixes: 24245/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-6285831682392064
> > > >
> > > > 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/jpeg2000dec.c | 6 +++---
> > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
> > > > index a470cf47da..b168e52db6 100644
> > > > --- a/libavcodec/jpeg2000dec.c
> > > > +++ b/libavcodec/jpeg2000dec.c
> > > > @@ -1401,12 +1401,12 @@ static int jpeg2000_decode_packets_po_iteration(Jpeg2000DecoderContext *s, Jpeg2
> > > >                          if (!s->cdx[compno] || !s->cdy[compno])
> > > >                              return AVERROR_INVALIDDATA;
> > > >
> > > > -                        trx0 = ff_jpeg2000_ceildiv(tile->coord[0][0], s->cdx[compno] << reducedresno);
> > > > -                        try0 = ff_jpeg2000_ceildiv(tile->coord[1][0], s->cdy[compno] << reducedresno);
> > > > -
> > > >                          if (reslevelno >= codsty->nreslevels)
> > > >                              continue;
> > > >
> > > > +                        trx0 = ff_jpeg2000_ceildiv(tile->coord[0][0], s->cdx[compno] << reducedresno);
> > > > +                        try0 = ff_jpeg2000_ceildiv(tile->coord[1][0], s->cdy[compno] << reducedresno);
> > > > +
> > > >                          if (!(y % ((uint64_t)s->cdy[compno] << (rlevel->log2_prec_height + reducedresno)) == 0 ||
> > > >                               (y == tile->coord[1][0] && (try0 << reducedresno) % (1U << (reducedresno + rlevel->log2_prec_height)))))
> > > >                              continue;
> > > > --
> > > > 2.17.1
> > > >
> > > > _______________________________________________
> > > > ffmpeg-devel mailing list
> > > > ffmpeg-devel at ffmpeg.org
> > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > > >
> > > > To unsubscribe, visit link above, or email
> > > > ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
> > >
> > > Looks good to me.
> > > I guess the division by zero happens because shifting by reducedresno
> > > overflows?
>
> yes
>
> > >
> > > --
> > > -------------
> > > Gautam |
> > Just realized, this might happen in one more place, shall send a
> > patch for the same.
>
> yes
Went through the code again, looks like this would not occur in other cases.
The other loops take into account whether reslvlno < codsty->nreslevels

I think this might be the only patch necessary
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Dictatorship naturally arises out of democracy, and the most aggravated
> form of tyranny and slavery out of the most extreme liberty. -- Plato
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".



-- 
-------------
Gautam |