[FFmpeg-devel] [PATCH 6/7] avformat/lxfdec: Fix multiple integer overflows related to track_size

[Tomas Härdin]

lör 2021-01-16 klockan 00:22 +0100 skrev Michael Niedermayer:
> On Fri, Jan 15, 2021 at 09:48:38AM +0100, Tomas Härdin wrote:
> > tor 2021-01-14 klockan 23:51 +0100 skrev Michael Niedermayer:
> > > Fixes: signed integer overflow: 538976288 * 8 cannot be represented in type 'int'
> > > Fixes: 26910/clusterfuzz-testcase-minimized-ffmpeg_dem_LXF_fuzzer-6634030636335104
> > > 
> > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > > ---
> > >  libavformat/lxfdec.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/libavformat/lxfdec.c b/libavformat/lxfdec.c
> > > index fa84ceea78..509d19fe7f 100644
> > > --- a/libavformat/lxfdec.c
> > > +++ b/libavformat/lxfdec.c
> > > @@ -195,7 +195,7 @@ static int get_packet_header(AVFormatContext *s)
> > >              return AVERROR_PATCHWELCOME;
> > >          }
> > >  
> > > -        samples = track_size * 8 / st->codecpar->bits_per_coded_sample;
> > > +        samples = track_size * 8LL / st->codecpar->bits_per_coded_sample;
> > >  
> > >          //use audio packet size to determine video standard
> > >          //for NTSC we have one 8008-sample audio frame per five video frames
> > > @@ -210,6 +210,8 @@ static int get_packet_header(AVFormatContext *s)
> > >              avpriv_set_pts_info(s->streams[0], 64, 1, 25);
> > >          }
> > >  
> > > +        if (av_popcount(channels) * (uint64_t)track_size > INT_MAX)
> > > +            return AVERROR_INVALIDDATA;
> > >          //TODO: warning if track mask != (1 << channels) - 1?
> > >          ret = av_popcount(channels) * track_size;
> > 
> > What happens if channels == 0 ? Probably gets caught in
> > av_new_packet(), just making sure
> 
> Probably would produce a 0 sized packet.
> That could be checked for too but seems unrelated to the integer overflow
> are there any other constraints i should check for ?
> The code suggests  mask != (1 << channels) - 1
> what level of warning vs. error do you prefer for the different odd
> possibilities?

I haven't seen LXF files in quite a while, so I can't really say
whether we should warn or not. Probably best not to increase nag in
this case.

/Tomas