[FFmpeg-devel] [PATCH 5/5] avcodec/dstdec: Use get_ur_golomb_jpegls()

[Michael Niedermayer]

On Tue, Oct 08, 2019 at 05:44:55PM +0200, Paul B Mahol wrote:
> How are you sure this is still correctly decoding samples?

get_ur_golomb() implements a optimized ur golomb reader for short limits with
escape codes.
get_ur_golomb_jpegls() supports longer codes but is slower, it differs in how
it handles escape codes

DST uses no limit and no escape coding it thus cannot use get_ur_golomb()
the apparent schoolbook form of ur codes used in DST should produce the
same value with both functions where they support it.

Do you still think there is a problem ? if so please explain, i do
not see one but iam human i can certainly miss issues.

Thanks

> 
> On 10/1/19, Michael Niedermayer <michael at niedermayer.cc> wrote:
> > Fixes: shift exponent -4 is negative
> > Fixes:
> > 17793/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DST_fuzzer-5766088435957760
> >
> > 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/dstdec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/dstdec.c b/libavcodec/dstdec.c
> > index 8a1bc6a738..b2dea4a177 100644
> > --- a/libavcodec/dstdec.c
> > +++ b/libavcodec/dstdec.c
> > @@ -120,7 +120,7 @@ static int read_map(GetBitContext *gb, Table *t,
> > unsigned int map[DST_MAX_CHANNE
> >
> >  static av_always_inline int get_sr_golomb_dst(GetBitContext *gb, unsigned
> > int k)
> >  {
> > -    int v = get_ur_golomb(gb, k, get_bits_left(gb), 0);
> > +    int v = get_ur_golomb_jpegls(gb, k, get_bits_left(gb), 0);
> >      if (v && get_bits1(gb))
> >          v = -v;
> >      return v;
> > --
> > 2.23.0
> >
> > _______________________________________________
> > 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".
> _______________________________________________
> 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".

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20191109/58c09f73/attachment.sig>