[FFmpeg-devel] [PATCH] avcodec/vvcdec: check pred flag to fix undefined beavhiours

[Nuo Mi]

On Sun, Mar 3, 2024 at 2:43 PM Andreas Rheinhardt <
andreas.rheinhardt at outlook.com> wrote:

> Nuo Mi:
> > libavcodec/vvc/vvc_inter.c:823:18: runtime error: signed integer
> overflow: 1426128896 + 1426128896 cannot be represented in type 'int'
> > SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
> libavcodec/vvc/vvc_inter.c:823:18
> > ---
> >  libavcodec/vvc/vvc_inter.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/vvc/vvc_inter.c b/libavcodec/vvc/vvc_inter.c
> > index d5be32aa14..48c566b097 100644
> > --- a/libavcodec/vvc/vvc_inter.c
> > +++ b/libavcodec/vvc/vvc_inter.c
> > @@ -816,13 +816,16 @@ static void derive_affine_mvc(MvField *mvc, const
> VVCFrameContext *fc, const MvF
> >      const int hs = fc->ps.sps->hshift[1];
> >      const int vs = fc->ps.sps->vshift[1];
> >      const MvField* mv2 = ff_vvc_get_mvf(fc, x0 + hs * sbw, y0 + vs *
> sbh);
> > +
> >      *mvc = *mv;
> > -    mvc->mv[0].x += mv2->mv[0].x;
> > -    mvc->mv[0].y += mv2->mv[0].y;
> > -    mvc->mv[1].x += mv2->mv[1].x;
> > -    mvc->mv[1].y += mv2->mv[1].y;
> > -    ff_vvc_round_mv(mvc->mv + 0, 0, 1);
> > -    ff_vvc_round_mv(mvc->mv + 1, 0, 1);
> > +    for (int i = L0; i <= L1; i++) {
> > +        PredFlag mask = 1 << i;
> > +        if (mv2->pred_flag & mask) {
> > +            mvc->mv[i].x += mv2->mv[i].x;
> > +            mvc->mv[i].y += mv2->mv[i].y;
> > +            ff_vvc_round_mv(mvc->mv + i, 0, 1);
> > +        }
> > +    }
> >  }
> >
> >  static void pred_affine_blk(VVCLocalContext *lc)
>
> This adds branches; the UB alone could also be fixed/suppressed with
> casting to unsigned. Would the latter cause any problems or are the
> values set here unused lateron?
>
It will not be used later.
sent a new patch based on your suggestion.
thank you

>
> - Andreas
>
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