Re: [FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation

[Michael Niedermayer <michael@niedermayer.cc>]

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On Fri, Dec 23, 2022 at 12:47:02PM +0100, Tomas Härdin wrote:
> fre 2022-12-23 klockan 00:25 +0100 skrev Michael Niedermayer:
> > On Wed, Nov 16, 2022 at 12:49:10PM +0100, Tomas Härdin wrote:
> > > sön 2022-11-13 klockan 00:44 +0100 skrev Michael Niedermayer:
> > > > Fixes: signed integer overflow: -3741319169 - 9223372036823449370
> > > > cannot be represented in type 'long'
> > > > Fixes: 51896/clusterfuzz-testcase-minimized-
> > > > ffmpeg_dem_MXF_fuzzer-
> > > > 513039428681728
> > > > 
> > > > 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 | 10 +++++++---
> > > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > > > index e6118e141d..42109cb43a 100644
> > > > --- a/libavformat/mxfdec.c
> > > > +++ b/libavformat/mxfdec.c
> > > > @@ -100,7 +100,7 @@ typedef struct MXFPartition {
> > > >      uint64_t previous_partition;
> > > >      int index_sid;
> > > >      int body_sid;
> > > > -    int64_t this_partition;
> > > > +    uint64_t this_partition;
> > > >      int64_t essence_offset;         ///< absolute offset of
> > > > essence
> > > >      int64_t essence_length;
> > > >      int32_t kag_size;
> > > > @@ -3519,8 +3519,12 @@ static void
> > > > mxf_compute_essence_containers(AVFormatContext *s)
> > > >              p->essence_offset = p->first_essence_klv.offset;
> > > >  
> > > >              /* essence container spans to the next partition */
> > > > -            if (x < mxf->partitions_count - 1)
> > > > -                p->essence_length = mxf-
> > > > > partitions[x+1].this_partition - p->essence_offset;
> > > > +            if (x < mxf->partitions_count - 1) {
> > > > +                if (mxf->partitions[x+1].this_partition < p-
> > > > > essence_offset) {
> > > > +                    p->essence_length = -1;
> > > > +                } else
> > > > +                    p->essence_length = mxf-
> > > > > partitions[x+1].this_partition - p->essence_offset;
> > > > +            }
> > > 
> > > A better solution might be to record the actual offset of the
> > > partitions rather than relying on ThisPartition. Then we can
> > > guarantee
> > > that they are strictly increasing.
> > 
> > do you mean that pack_ofs could be used here ?
> 
> this_partition should be == pack_ofs - run_in. I think we can just nuke
> this_partition in the struct and use pack_ofs - run_in everywhere. Emit
> a warning or bail out if any partition does not obey this contraint,
> since such files have likely been written by bad muxers.

ill post a patch doing that

thx

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

Elect your leaders based on what they did after the last election, not
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