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

["Tomas Härdin" <git@haerdin.se>]

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

/Tomas
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