[FFmpeg-devel] [PATCH V3] lavfi/nlmeans: Checking number precision when computing integral images

[mypopy at gmail.com]

On Fri, Mar 8, 2019 at 4:28 AM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Thu, Mar 07, 2019 at 09:18:42PM +0100, Michael Niedermayer wrote:
> > On Thu, Mar 07, 2019 at 09:45:12AM +0800, Jun Zhao wrote:
> > > From: Jun Zhao <barryjzhao at tencent.com>
> > >
> > > accumulation of 8-bits uint_8 (uint8_t *src) into 32-bits (uint32_t
> *ii)
> > > data type, it will have a risk of an integral value becoming larger
> than
> > > the 32-bits integer capacity and resulting in an integer overflow. For
> > > this risk, add a checking with warning message.
> > >
> > > Signed-off-by: Jun Zhao <barryjzhao at tencent.com>
> > > ---
> > >  libavfilter/vf_nlmeans.c |    7 +++++++
> > >  1 files changed, 7 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/libavfilter/vf_nlmeans.c b/libavfilter/vf_nlmeans.c
> > > index dcb5a03..9876aae 100644
> > > --- a/libavfilter/vf_nlmeans.c
> > > +++ b/libavfilter/vf_nlmeans.c
> > > @@ -236,6 +236,13 @@ static void compute_ssd_integral_image(const
> NLMeansDSPContext *dsp,
> > >      // adjusted end x position of the safe area after width of the
> safe area gets aligned
> > >      const int endx_safe = startx_safe + safe_pw;
> > >
> > > +    // accumulation of 8-bits uint_8 (uint8_t *src) into 32-bits
> (uint32_t *ii)
> > > +    // data type, it will have a risk of an integral value becoming
> larger than
> > > +    // the 32-bits integer capacity and resulting in an integer
> overflow.
> > > +    if ((UINT32_MAX / (uint64_t)w) < (255 * (uint64_t)h))
> > > +        av_log(NULL, AV_LOG_WARNING,
> > > +               "image (%d x %d) integral value may overflow.\n", w
> ,h);
> >
> > Printing a warning is not an adequate response for a integer overflow.
> > Such thing is undefined behavior (in case signed of signed int) and must
> > not occur.
>
> And if no signed ints are involved, while this is then not undefined it
> still
> gives the wrong result. Thats a bug, the bug should be fixed not a warning
> be printed that the bug might be triggered
>
> Thanks
>
>
Will give a stricter w * h check for this case, Tks