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

[Michael Niedermayer <michael@niedermayer.cc>]

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On Tue, Sep 20, 2022 at 01:20:00PM +0200, Tomas Härdin wrote:
> 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.

ok, will do

thx for checking

i will change the patch by:
@@ -3717,7 +3717,7 @@ static int mxf_read_header(AVFormatContext *s)
     avio_seek(s->pb, -14, SEEK_CUR);
     mxf->fc = s;
     run_in = avio_tell(s->pb);
-    if (run_in < 0 || run_in != (int)run_in)
+    if (run_in < 0 || run_in > 65535)
         return AVERROR_INVALIDDATA;
     mxf->run_in = run_in;
 
@@ -4125,7 +4125,7 @@ static int mxf_read_close(AVFormatContext *s)
 
 static int mxf_probe(const AVProbeData *p) {
     const uint8_t *bufp = p->buf;
-    const uint8_t *end = p->buf + p->buf_size;
+    const uint8_t *end = p->buf + FFMIN(p->buf_size, 65536 + sizeof(mxf_header_partition_pack_key));
 
     if (p->buf_size < sizeof(mxf_header_partition_pack_key))
         return 0;

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

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates

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