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

[Gautam Ramakrishnan]

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
>
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Looks good to me.
I guess the division by zero happens because shifting by reducedresno
overflows?

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