[FFmpeg-devel] [PATCH 5/9] avcodec/cbs_h266_syntax_template: Check bit depth with range extension

[Michael Niedermayer]

On Thu, Sep 19, 2024 at 08:53:07PM -0300, James Almer wrote:
> On 9/19/2024 7:56 PM, Michael Niedermayer wrote:
> > Fixes: shift exponent 62 is too large for 32-bit type 'int'
> > Fixes: 71020/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VVC_fuzzer-6444916325023744
> > 
> > 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/cbs_h266_syntax_template.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/libavcodec/cbs_h266_syntax_template.c b/libavcodec/cbs_h266_syntax_template.c
> > index a8f5af04d02..1c111126563 100644
> > --- a/libavcodec/cbs_h266_syntax_template.c
> > +++ b/libavcodec/cbs_h266_syntax_template.c
> > @@ -1041,6 +1041,9 @@ static int FUNC(sps_range_extension)(CodedBitstreamContext *ctx, RWContext *rw,
> >   {
> >       int err;
> > +    if (current->sps_bitdepth_minus8 < 10)
> 
> sps_bitdepth_minus8 can only be between 0 and 8, so this is basically making
> it abort on any and every sample with SPS range extension.

+ if (current->sps_bitdepth_minus8 < 10 - 8)

Its supposed to check this:
"When BitDepth is less
 than or equal to 10, the value of sps_range_extension_flag shall be equal to 0."


> 
> Also, it doesn't seem to be used here at all, so i don't see how this is
> fixing anything. Can you share the sample?

its used here:
libavcodec/vvc/ctu.c:            persistent_rice_adaptation_enabled_flag ? 2 * (av_log2(bit_depth - 10)) : 0;

I can send you the file but i think this case is quite clear

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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