[FFmpeg-devel] [PATCH] avcodec/utvideodec: Fix bytes left check in decode_frame()

[Michael Niedermayer]

On Sat, Feb 03, 2018 at 10:16:07AM +0100, Paul B Mahol wrote:
> On 2/2/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
> > Fixes: out of array read
> > Fixes: poc-2017.avi
> >
> > Found-by: GwanYeong Kim <gy741.kim at gmail.com>
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/utvideodec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/utvideodec.c b/libavcodec/utvideodec.c
> > index 608c8c4998..1bcd14e74c 100644
> > --- a/libavcodec/utvideodec.c
> > +++ b/libavcodec/utvideodec.c
> > @@ -676,7 +676,7 @@ static int decode_frame(AVCodecContext *avctx, void
> > *data, int *got_frame,
> >              for (j = 0; j < c->slices; j++) {
> >                  slice_end   = bytestream2_get_le32u(&gb);
> >                  if (slice_end < 0 || slice_end < slice_start ||
> > -                    bytestream2_get_bytes_left(&gb) < slice_end) {
> > +                    bytestream2_get_bytes_left(&gb) < slice_end + 1024LL) {
> >                      av_log(avctx, AV_LOG_ERROR, "Incorrect slice size\n");
> >                      return AVERROR_INVALIDDATA;
> >                  }
> > --
> > 2.16.1
> >
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> 
> Why this magic number 1024LL ?

Because of the  line later:

bytestream2_skipu(&gb, 1024);

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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