Re: [FFmpeg-devel] [PATCH 7/8] avcodec/svq3: Check that for 8 byte space before subtracting

[Michael Niedermayer <michael@niedermayer.cc>]

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On Wed, May 14, 2025 at 06:34:25PM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > No testcase
> > 
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/svq3.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavcodec/svq3.c b/libavcodec/svq3.c
> > index f730358e2f9..30bc9334af7 100644
> > --- a/libavcodec/svq3.c
> > +++ b/libavcodec/svq3.c
> > @@ -1173,7 +1173,7 @@ static av_cold int svq3_decode_init(AVCodecContext *avctx)
> >          int w,h;
> >  
> >          size = AV_RB32(&extradata[4]);
> > -        if (size > extradata_end - extradata - 8)
> > +        if (extradata_end - extradata < 8 || size > extradata_end - extradata - 8)
> >              return AVERROR_INVALIDDATA;
> >          init_get_bits(&gb, extradata + 8, size * 8);
> >  
> 
> Can't be triggered: This code is only executed iff marker_found is 1;
> and given the "m + 8 < avctx->extradata_size" check in the loop it is
> guaranteed that there are at least eight bytes of extradata available.

True

Did we ever had someone miss such distributed checks and
produce buggy code through a change ?
If not then i think you are correct here and lets skip adding an
explicit check, its ugly to have such redundant checks

thx

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The day soldiers stop bringing you their problems is the day you have stopped 
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you do not care. Either case is a failure of leadership. - Colin Powell

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