[FFmpeg-devel] [PATCH] avcodec/mpegpicture: guard "stride changed" failures against unknown uvlinesize

Michael Niedermayer michael at niedermayer.cc
Wed Apr 11 01:44:37 EEST 2018


On Tue, Apr 10, 2018 at 03:25:33PM -0700, Aman Gupta wrote:
> On Tue, Apr 10, 2018 at 3:15 PM, Michael Niedermayer <michael at niedermayer.cc
> > wrote:
> 
> > On Tue, Apr 10, 2018 at 10:20:07AM -0700, Aman Gupta wrote:
> > > From: Aman Gupta <aman at tmm1.net>
> > >
> > > Before adding uvlinesize check, I was seeing failures decoding
> > > some samples (shown with extra logging added):
> > >
> > > [mpeg2video @ 0x7fa193818c00] get_buffer() failed (stride changed:
> > linesize=1280/1280 uvlinesize=0/640)
> > > [mpeg2video @ 0x7fa193818c00] get_buffer() failed (stride changed:
> > linesize=1280/1280 uvlinesize=0/640)
> > > ---
> > >  libavcodec/mpegpicture.c | 9 ++++++---
> > >  1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/libavcodec/mpegpicture.c b/libavcodec/mpegpicture.c
> > > index 2be670cdbc..80898c161c 100644
> > > --- a/libavcodec/mpegpicture.c
> > > +++ b/libavcodec/mpegpicture.c
> > > @@ -148,10 +148,13 @@ static int alloc_frame_buffer(AVCodecContext
> > *avctx,  Picture *pic,
> > >          }
> > >      }
> > >
> > > -    if (linesize && (linesize   != pic->f->linesize[0] ||
> > > -                     uvlinesize != pic->f->linesize[1])) {
> > > +    if (linesize && uvlinesize &&
> > > +        (linesize   != pic->f->linesize[0] ||
> > > +         uvlinesize != pic->f->linesize[1])) {
> >
> > without checking if this can be reached with grayscale.
> > If it can then uvlinesize may be 0 in which case this change would be
> > wrong
> >
> 
> I forgot to mention that I was only seeing this bug with gray mode
> (--enable-gray + AV_CODEC_FLAG_GRAY), and that after this patch it works as
> expected.

The patch looks like it skips the linesize check in grayscale then.
This seems not correct

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

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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