[FFmpeg-devel] [PATCH] avcodec/wavpack: check for overflow

[Michael Niedermayer]

On Wed, Jul 03, 2013 at 12:13:45AM +0000, Paul B Mahol wrote:
> On 7/3/13, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Jul 02, 2013 at 11:05:09PM +0000, Paul B Mahol wrote:
> >> On 7/2/13, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Mon, Jun 17, 2013 at 05:49:47PM +0200, Michael Niedermayer wrote:
> >> >> On Mon, Jun 17, 2013 at 10:54:28AM +0000, Paul B Mahol wrote:
> >> >> > On 6/15/13, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> >> > > Fix integer overflow in fate
> >> >> > >
> >> >> > > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> >> >> > > ---
> >> >> > >  libavcodec/wavpack.c |   10 ++++++++--
> >> >> > >  1 file changed, 8 insertions(+), 2 deletions(-)
> >> >> > >
> >> >> > > diff --git a/libavcodec/wavpack.c b/libavcodec/wavpack.c
> >> >> > > index 47f598a..dd273f7 100644
> >> >> > > --- a/libavcodec/wavpack.c
> >> >> > > +++ b/libavcodec/wavpack.c
> >> >> > > @@ -581,8 +581,14 @@ static inline int
> >> >> > > wv_unpack_stereo(WavpackFrameContext
> >> >> > > *s, GetBitContext *gb,
> >> >> > >                      L2 = L + ((s->decorr[i].weightA * (int64_t)A
> >> >> > > +
> >> >> > > 512) >>
> >> >> > > 10);
> >> >> > >                      R2 = R + ((s->decorr[i].weightB * (int64_t)B
> >> >> > > +
> >> >> > > 512) >>
> >> >> > > 10);
> >> >> > >                  } else {
> >> >> > > -                    L2 = L + ((s->decorr[i].weightA * A + 512) >>
> >> >> > > 10);
> >> >> > > -                    R2 = R + ((s->decorr[i].weightB * B + 512) >>
> >> >> > > 10);
> >> >> > > +                    int64_t Lt = s->decorr[i].weightA * (int64_t)A
> >> >> > > +
> >> >> > > 512;
> >> >> > > +                    int64_t Rt = s->decorr[i].weightB * (int64_t)B
> >> >> > > +
> >> >> > > 512;
> >> >> > > +                    if ((int32_t)Lt != Lt || (int32_t)Rt != Rt) {
> >> >> > > +                        av_log(s->avctx, AV_LOG_ERROR, "sample
> >> >> > > overflow %d
> >> >> >
> >> >> > This looks extremly ugly.
> >> >>
> >> >> Iam quite aware of that, which is part of the reason why i posted this
> >> >> (aka do you know a less ugly solution?)
> >> >
> >> > ping
> >> > anyone has a better solution ?
> >> > do any objections to the original patch remain ?
> >>
> >> Yes, i see no point to apply this patch as is.
> >
> > what alternative solution do you suggest?
> 
> There is no alternative solution yet, as you did not provided any real
> solution to this problem.

If i had a real solution i wouldnt ask for one.
Repeating my question with different wording isnt going to solve this
i suspect but then again yeah trying cant hurt. sadly no i still
have only that ugly solution an alternativ or real or whatever you
call it solution is still highly welcome


> 
> Why only this overflow in decoder need checking?


> 
> Why check is needed at all?

It crashes with the right compiler flags, Its undefined behavior


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

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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