[FFmpeg-devel] [PATCH 5/5] avformat/mxfdec: fix and enhance RIP KLV length checks

[Tomas Härdin]

sön 2019-04-28 klockan 22:17 +0200 skrev Marton Balint:
> 
> On Sun, 14 Apr 2019, Tomas Härdin wrote:
> 
> > fre 2019-04-12 klockan 01:09 +0200 skrev Marton Balint:
> > > KLV length is BER encoded (variable size), but the code assumed the encoding to
> > > always use 4 bytes.
> > > 
> > > Fixes parsing Random Index Pack in samples/MXF/issue2160/PW0805A0V01.4C5B5636.EFA330.mxf.
> > > 
> > > > Signed-off-by: Marton Balint <cus at passwd.hu>
> > > 
> > > ---
> > >  libavformat/mxfdec.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > > index 6f0f87763d..a69f2f1996 100644
> > > --- a/libavformat/mxfdec.c
> > > +++ b/libavformat/mxfdec.c
> > > @@ -3126,9 +3126,12 @@ static void mxf_read_random_index_pack(AVFormatContext *s)
> > >          goto end;
> > >      avio_seek(s->pb, file_size - length, SEEK_SET);
> > >      if (klv_read_packet(&klv, s->pb) < 0 ||
> > > -        !IS_KLV_KEY(klv.key, mxf_random_index_pack_key) ||
> > > -        klv.length != length - 20)
> > > +        !IS_KLV_KEY(klv.key, mxf_random_index_pack_key))
> > >          goto end;
> > > +    if (klv.next_klv != file_size || klv.length <= 4 || (klv.length - 4) % 12) {
> > > +        av_log(s, AV_LOG_WARNING, "Invalid RIP KLV length\n");
> > > +        goto end;
> > > +    }
> > 
> > Looks OK.
> 
> Thanks, applied.
> 
> > 
> > Aside: Looking at klv_read_packet(), I'm suspicious of its use of
> > mxf_read_sync(). That feels like something that only belongs in
> > mxf_read_header(), to deal with run-in. Baptiste added it in
> > cabe2527ef3. FATE passes without it.
> 
> I wonder if it is there to allow some byte based seeking or handle damaged 
> files more gracefully? I agree it is strange a bit, maybe Baptise can chip 
> in...

I *suspect* it has something to do with seeking in frame wrapped files
with crappy or non-existing indexes. But then it would be best if it
were used only in mxf_read_seek()

/Tomas