Re: [FFmpeg-devel] [PATCH 1/3] avcodec/jpeg2000htdec: Check magp before using it in a shift

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sat, Mar 30, 2024 at 09:56:58AM +0100, Tomas Härdin wrote:
> fre 2024-03-29 klockan 20:32 +0100 skrev Michael Niedermayer:
> > Fixes: shift exponent -1 is negative
> > Fixes: 65378/clusterfuzz-testcase-minimized-
> > ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5457678193197056
> > 
> > Found-by: continuous fuzzing process
> > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/jpeg2000dec.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
> > index 1afc6b1e2dd..fe2afb05057 100644
> > --- a/libavcodec/jpeg2000dec.c
> > +++ b/libavcodec/jpeg2000dec.c
> > @@ -1910,6 +1910,8 @@ static inline void tile_codeblocks(const
> > Jpeg2000DecoderContext *s, Jpeg2000Tile
> >                  int nb_precincts, precno;
> >                  Jpeg2000Band *band = rlevel->band + bandno;
> >                  int cblkno = 0, bandpos;
> > +                /* See Rec. ITU-T T.800, Equation E-2 */
> > +                int magp = quantsty->expn[subbandno] + quantsty-
> > >nguardbits - 1;
> >  
> >                  bandpos = bandno + (reslevelno > 0);
> >  
> > @@ -1917,6 +1919,9 @@ static inline void tile_codeblocks(const
> > Jpeg2000DecoderContext *s, Jpeg2000Tile
> >                      band->coord[1][0] == band->coord[1][1])
> >                      continue;
> >  
> > +                if ((codsty->cblk_style & JPEG2000_CTSY_HTJ2K_F) &&
> > magp >= 31)
> > +                    return;
> 
> Please also print an error message and return AVERROR_PATCHWELCOME

will apply with these changes

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato

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