[FFmpeg-devel] [PATCH] avcodec/vp9block: fix runtime error: signed integer overflow: 196675 * 20670 cannot be represented in type 'int'

[Michael Niedermayer]

On Sun, May 21, 2017 at 12:51:56PM +0200, Michael Niedermayer wrote:
> On Sat, May 20, 2017 at 10:35:34PM -0400, Ronald S. Bultje wrote:
> > Hi,
> > 
> > On Sat, May 20, 2017 at 8:12 PM, Michael Niedermayer <michael at niedermayer.cc
> > > wrote:
> > 
> > > Fixes: 1710/clusterfuzz-testcase-minimized-4837032931098624
> > >
> > > 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/vp9block.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libavcodec/vp9block.c b/libavcodec/vp9block.c
> > > index ae2f0e4c6f..a16ccdccdb 100644
> > > --- a/libavcodec/vp9block.c
> > > +++ b/libavcodec/vp9block.c
> > > @@ -915,9 +915,9 @@ skip_eob:
> > >          if (!--band_left)
> > >              band_left = band_counts[++band];
> > >          if (is_tx32x32)
> > > -            STORE_COEF(coef, rc, ((vp8_rac_get(c) ? -val : val) *
> > > qmul[!!i]) / 2);
> > > +            STORE_COEF(coef, rc, (int)((vp8_rac_get(c) ? -val : val) *
> > > (unsigned)qmul[!!i]) / 2);
> > >          else
> > > -            STORE_COEF(coef, rc, (vp8_rac_get(c) ? -val : val) *
> > > qmul[!!i]);
> > > +            STORE_COEF(coef, rc, (vp8_rac_get(c) ? -val : val) *
> > > (unsigned)qmul[!!i]);
> > >          nnz = (1 + cache[nb[i][0]] + cache[nb[i][1]]) >> 1;
> > >          tp = p[band][nnz];
> > >      } while (++i < n_coeffs);
> > > --
> > > 2.13.0
> > 
> > 
> > Since this is the only use of qmul[], why don't you make the array unsigned
> > instead? That saves a cast.
> 
> will change and apply

actually, no i cant do that
qmul is int16_t *, uint16_t * will be "promoted" to signed int

do you see another way ?

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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