[FFmpeg-devel] [PATCH v3 1/3] libavcodec/jpeg2000dec: Fix codeblock decode check

[Gautam Ramakrishnan]

On Thu, Jul 23, 2020 at 7:56 PM Michael Niedermayer
<michael at niedermayer.cc> wrote:
>
> On Tue, Jul 21, 2020 at 11:37:13PM +0530, gautamramk at gmail.com wrote:
> > From: Gautam Ramakrishnan <gautamramk at gmail.com>
> >
> > The codeblock decoder checks whether the mqc decoder
> > has decoded the right number of bytes. However, this
> > check does not account for the fact that the mqc encoder's
> > flush routine adds 2 bytes of data which does not have to be
> > read by the decoder. The check is modified to account for
> > this. This patch solves issue #4827
> > ---
> >  libavcodec/jpeg2000dec.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
> > index f5ad8402fb..5e9e97eb6a 100644
> > --- a/libavcodec/jpeg2000dec.c
> > +++ b/libavcodec/jpeg2000dec.c
> > @@ -1753,9 +1753,9 @@ static int decode_cblk(Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *codsty,
> >          pass_cnt ++;
> >      }
> >
> > -    if (cblk->data + cblk->length - 2*(term_cnt < cblk->nb_terminations) != t1->mqc.bp) {
> > +    if (cblk->data + cblk->length - 2 > t1->mqc.bp) {
> >          av_log(s->avctx, AV_LOG_WARNING, "End mismatch %"PTRDIFF_SPECIFIER"\n",
>
> This changes a equals check to a larger than check, so it removes checking
> in one direction. The commit message doesnt explain this sufficiently i think
>
I think a good solution would be to add a check in the other direction
and warn when the added
0xFF bytes are read.
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Concerning the gods, I have no means of knowing whether they exist or not
> or of what sort they may be, because of the obscurity of the subject, and
> the brevity of human life -- Protagoras
> _______________________________________________
> 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".



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