Re: [FFmpeg-devel] [PATCH v2 1/3] avcodec/x86/vvc/vvc_alf: fix integer overflow

["Ronald S. Bultje" <rsbultje@gmail.com>]

Hi Andreas,

On Thu, May 30, 2024 at 2:33 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> toqsxw@outlook.com:
> > From: Wu Jianhua <toqsxw@outlook.com>
> >
> > Some tests fails with certain seeds
> >
> > tests/checkasm/checkasm 2325607578 --test=vvc_alf
> > checkasm: using random seed 2325607578
> > AVX2:
> >     vvc_alf_filter_luma_120x20_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x24_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x28_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x32_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x36_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x40_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x44_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x48_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x52_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x56_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x60_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x64_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x68_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x72_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x76_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x80_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x84_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x88_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x92_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x96_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x100_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x104_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x108_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x112_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x116_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x120_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x124_12_avx2 (vvc_alf.c:104)
> >     vvc_alf_filter_luma_120x128_12_avx2 (vvc_alf.c:104)
> >   - vvc_alf.alf_filter   [FAILED]
> >   - vvc_alf.alf_classify [OK]
> > checkasm: 28 of 9216 tests have failed
> >
> > Reported-by: James Almer <jamrial@gmail.com>
> > Signed-off-by: Wu Jianhua <toqsxw@outlook.com>
> > ---
> >  libavcodec/x86/vvc/vvc_alf.asm | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/x86/vvc/vvc_alf.asm
> b/libavcodec/x86/vvc/vvc_alf.asm
> > index 71e821c27b..f7b3e2a6cc 100644
> > --- a/libavcodec/x86/vvc/vvc_alf.asm
> > +++ b/libavcodec/x86/vvc/vvc_alf.asm
> > @@ -356,7 +356,8 @@ SECTION .text
> >
> >      FILTER_VB         xq
> >
> > -    paddw             m0, m2
> > +    ; sum += curr
> > +    paddsw             m0, m2
> >
> >      ; clip to pixel
> >      CLIPW             m0, m14, m15
>
> And can I get an answer to the question of whether the issue is present
> when used by the actual decoder and not only the checkasm test?
>

From my reading of the source code, this could happen in a crafted (e.g.
fuzzed) stream.

Ronald
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