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

[Michael Niedermayer <michael@niedermayer.cc>]

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On Thu, Jun 27, 2024 at 08:40:00AM +0200, Paul B Mahol wrote:
> 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?

Iam not sure how. Maybe there is a way ...


> Or there is some silly loop that goes unchecked up to INT32_MAX ?

there are multiple loops
one is in
av_channel_layout_custom_init()

another is in av_channel_layout_describe_bprint()

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin

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