Re: [FFmpeg-devel] [PATCH 4/7] avformat/nistspheredec: Check bits_per_coded_sample and channels

[Michael Niedermayer]

On Mon, Jan 18, 2021 at 09:06:10PM +0100, Anton Khirnov wrote:
> Quoting Michael Niedermayer (2021-01-17 00:07:26)
> > Fixes: signed integer overflow: 80 * 92233009 cannot be represented in type 
> > 'int'
> > Fixes: 
> > 26910/clusterfuzz-testcase-minimized-ffmpeg_dem_NISTSPHERE_fuzzer-6669100654919680
> > 
> > Found-by: continuous fuzzing process 
> > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> > ---
> >  libavformat/nistspheredec.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/nistspheredec.c b/libavformat/nistspheredec.c
> > index 079369929f..fec5c88892 100644
> > --- a/libavformat/nistspheredec.c
> > +++ b/libavformat/nistspheredec.c
> > @@ -80,7 +80,9 @@ static int nist_read_header(AVFormatContext *s)
> >  
> >              avpriv_set_pts_info(st, 64, 1, st->codecpar->sample_rate);
> >  
> > -            st->codecpar->block_align = 
> > st->codecpar->bits_per_coded_sample * st->codecpar->channels / 8;
> > +            if (st->codecpar->bits_per_coded_sample * 
> > (uint64_t)st->codecpar->channels / 8 > INT_MAX)
> > +                return AVERROR_INVALIDDATA;
> > +            st->codecpar->block_align = 
> > st->codecpar->bits_per_coded_sample * (uint64_t)st->codecpar->channels / 8;
> >  
> >              if (avio_tell(s->pb) > header_size)
> >                  return AVERROR_INVALIDDATA;
> > -- 
> > 2.17.1
> 
> Both bits_per_coded_sample and channels seem to be arbitrary ints, so
> you are assuming sizeof(int) < sizeof(int64)

I wonder if we shouldnt limit these 2 fields in a platform independant way
But if we dont then the change below should do more correct checks

@@ -80,7 +80,11 @@ static int nist_read_header(AVFormatContext *s)
 
             avpriv_set_pts_info(st, 64, 1, st->codecpar->sample_rate);
 
-            st->codecpar->block_align = st->codecpar->bits_per_coded_sample * 
st->codecpar->channels / 8;
+            if (st->codecpar->bits_per_coded_sample < 0 || 
st->codecpar->channels <= 0 ||
+                st->codecpar->bits_per_coded_sample > UINT64_MAX / 
st->codecpar->channels ||
+                st->codecpar->bits_per_coded_sample * 
(uint64_t)st->codecpar->channels / 8 > INT_MAX)
+                return AVERROR_INVALIDDATA;
+            st->codecpar->block_align = st->codecpar->bits_per_coded_sample * 
(uint64_t)st->codecpar->channels / 8;
 
             if (avio_tell(s->pb) > header_size)
                 return AVERROR_INVALIDDATA;


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

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway

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