Re: [FFmpeg-devel] [PATCH v2] avcodec/mv30: Check the input length before allocation

[Paul B Mahol <onemda@gmail.com>]

On Thu, Aug 10, 2023 at 5:46 PM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> On Thu, Aug 10, 2023 at 12:12:51PM +0200, Paul B Mahol wrote:
> > On Thu, Aug 10, 2023 at 11:34 AM Michael Niedermayer <
> michael@niedermayer.cc>
> > wrote:
> >
> > > On Wed, Aug 09, 2023 at 11:20:43PM +0200, Paul B Mahol wrote:
> > > > On Wed, Aug 9, 2023 at 9:30 PM Michael Niedermayer <
> > > michael@niedermayer.cc>
> > > > wrote:
> > > >
> > > > > Hi Paul
> > > > >
> > > > > On Wed, Aug 09, 2023 at 08:53:03PM +0200, Paul B Mahol wrote:
> > > > > > This is not correct, and please stop writing such patches.
> Thanks.
> > > > >
> > > > > If there is a problem in the bugfix, please explain what the
> problem
> > > is.
> > > > > If you do not like the specific fix, you can fix it differently
> too or
> > > > > tell me what you prefer.
> > > > > Simply saying "no" with no explanation repeatedly is rude
> > > > >
> > > >
> > > > Patch breaks valid files.
> > >
> > > Does the patch break files you create intentionally or files
> > > pre-existing ?
> > > The check can fail if 2 data segments overlap, one can craft
> > > a file with that. The previous patches are implemented differently
> > > and dont have that behavior, you rejected them too and at the time
> > > you did call them "hacky" and did not mention that they break anything
> > > and also ignored all further questions
> > >
> > > I just implemented this one differently as the other way was rejected
> > > by you with no comment
> > >
> > > Also please provide the files this breaks so the issue can be
> > > fixed
> > >
> > >
> > Why not same thing for AV1 codec?
> > Just reduce max resolutions for mv30 to 32x32 and be done.
>
> Limiting the resolution to max 32x32 would break real samples
> for example V-codecs/mv30.avi
>
> if you suggest to limit it only for the fuzzer, well, that would not
> fix the timeout outside the fuzzer.
> For some decoders limiting the resolution in the fuzzer is the only
> practical
> option. But for mv30 this timeout really occurs because the input is not
> checked/validated.
>

But mv30 bitstream is not so trivial and can not be checked that easily
with your patches.

Also whole fuzzing idea of your work is flawed.


>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> In a rich man's house there is no place to spit but his face.
> -- Diogenes of Sinope
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