Re: [FFmpeg-devel] [PATCH 1/3] avformat/cafdec: sanity check channels and bps

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

On Thu, Jun 27, 2024 at 1:50 AM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> On Tue, Jun 25, 2024 at 09:27:55PM +0200, Anton Khirnov wrote:
> > Quoting Michael Niedermayer (2024-06-25 21:25:46)
> > > On Thu, Mar 28, 2024 at 12:27:02AM +0100, Michael Niedermayer wrote:
> > > > On Wed, Mar 27, 2024 at 08:39:17AM +0100, Anton Khirnov wrote:
> > > > > Quoting Michael Niedermayer (2024-03-23 00:08:16)
> > > > > > Fixes: Timeout
> > > > > > Fixes:
> 67044/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-5791144363491328
> > > > > >
> > > > > > Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > > > > > ---
> > > > > >  libavformat/cafdec.c | 5 +++++
> > > > > >  1 file changed, 5 insertions(+)
> > > > > >
> > > > > > diff --git a/libavformat/cafdec.c b/libavformat/cafdec.c
> > > > > > index 426c56b9bd..334077efb5 100644
> > > > > > --- a/libavformat/cafdec.c
> > > > > > +++ b/libavformat/cafdec.c
> > > > > > @@ -33,6 +33,7 @@
> > > > > >  #include "isom.h"
> > > > > >  #include "mov_chan.h"
> > > > > >  #include "libavcodec/flac.h"
> > > > > > +#include "libavcodec/internal.h"
> > > > > >  #include "libavutil/intreadwrite.h"
> > > > > >  #include "libavutil/intfloat.h"
> > > > > >  #include "libavutil/dict.h"
> > > > > > @@ -87,6 +88,10 @@ static int read_desc_chunk(AVFormatContext *s)
> > > > > >      st->codecpar->ch_layout.nb_channels = avio_rb32(pb);
> > > > > >      st->codecpar->bits_per_coded_sample = avio_rb32(pb);
> > > > > >
> > > > > > +    if (st->codecpar->ch_layout.nb_channels >
> FF_SANE_NB_CHANNELS ||
> > > > >
> > > > > I dislike this.
> > > >
> > > > I dislike it too
> > >
> > > so what do we do about this ?
> >
> > About what? What is the actual problem that needs addressed?
>
> 67044/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-5791144363491328
>
>
> >
> > > any objections to apply this ?
> >
> > yes, FF_SANE_NB_CHANNELS is a hack that should be removed, not spread
>
> a maximum number for each theoretically unlimited parameter is desirable
> This can be a user setable value or a compile time value when such is
> preferred.
>

Cant you check if so many channels are actually available in stream?
Or there is some silly loop that goes unchecked up to INT32_MAX ?


>
> We can take this to the TC if you want.
>
> The same way as the number of files or number of bytes used by some cache
> needs limits, so do channels, and number of pixels.
>
> One can remove them but users and companies concious about security and
> efficiency with untrusted input in an (semi-) automated environment will
> likely
> choose the codebase providing such features.
>

"Sure."


>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> The day soldiers stop bringing you their problems is the day you have
> stopped
> leading them. They have either lost confidence that you can help or
> concluded
> you do not care. Either case is a failure of leadership. - Colin Powell
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