Re: [FFmpeg-devel] [PATCH 02/13] avformat/mxfdec: Check run_in to fit in int and be valid

From: "Tomas Härdin" <tjoppen@acc.umu.se>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 02/13] avformat/mxfdec: Check run_in to fit in int and be valid
Date: Tue, 20 Sep 2022 13:20:00 +0200
Message-ID: <5b3fa2ba445e5fae04459c5ea4f5d982d3a0a0eb.camel@acc.umu.se> (raw)
In-Reply-To: <ab75bceca060624fe9b4efc49b8601d51ec131b0.camel@acc.umu.se>

tis 2022-09-20 klockan 13:07 +0200 skrev Tomas Härdin:
> sön 2022-09-18 klockan 19:13 +0200 skrev Michael Niedermayer:
> > Fixes: signed integer overflow: 9223372036854775807 - -2146905566
> > cannot be represented in type 'long'
> > Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-
> > 6570996594769920
> > 
> > Found-by: continuous fuzzing process 
> > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavformat/mxfdec.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > index e63e803aa56..da81fea3bc1 100644
> > --- a/libavformat/mxfdec.c
> > +++ b/libavformat/mxfdec.c
> > @@ -3681,6 +3681,7 @@ static int mxf_read_header(AVFormatContext
> > *s)
> >      KLVPacket klv;
> >      int64_t essence_offset = 0;
> >      int ret;
> > +    int64_t run_in;
> >  
> >      mxf->last_forward_tell = INT64_MAX;
> >  
> > @@ -3690,7 +3691,10 @@ static int mxf_read_header(AVFormatContext
> > *s)
> >      }
> >      avio_seek(s->pb, -14, SEEK_CUR);
> >      mxf->fc = s;
> > -    mxf->run_in = avio_tell(s->pb);
> > +    run_in = avio_tell(s->pb);
> > +    if (run_in < 0 || run_in != (int)run_in)
> 
> run_in > INT_MAX is more clear
> 
> It strikes me that run_in is also used in lots of places in the
> demuxer
> without checking for overflow

I went and checked S377m and the run-in sequence "shall be less than
65536 bytes long". Both the 2004 and 2009 version of the spec agree on
this. So we should reject run_in >= 65536, and mxf_probe() should be
similarly adjusted.

/Tomas

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