Re: [FFmpeg-devel] [PATCH 4/5] avformat/mxfdec: Check index_edit_rate

[Marton Balint <cus@passwd.hu>]

On Tue, 9 Apr 2024, Tomas Härdin wrote:

> mån 2024-04-08 klockan 21:46 +0200 skrev Marton Balint:
>> 
>> 
>> On Mon, 8 Apr 2024, Tomas Härdin wrote:
>> 
>> > tor 2024-04-04 klockan 00:51 +0200 skrev Michael Niedermayer:
>> > > Fixes: Assertion b >=0 failed at libavutil/mathematics.c:62
>> > > Fixes: 67811/clusterfuzz-testcase-minimized-
>> > > ffmpeg_dem_MXF_fuzzer-
>> > > 5108429687422976
>> > > 
>> > > 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 | 3 +++
>> > >  1 file changed, 3 insertions(+)
>> > > 
>> > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
>> > > index 04de4c1d5e3..233d614f783 100644
>> > > --- a/libavformat/mxfdec.c
>> > > +++ b/libavformat/mxfdec.c
>> > > @@ -1264,6 +1264,9 @@ static int
>> > > mxf_read_index_table_segment(void
>> > > *arg, AVIOContext *pb, int tag, int
>> > >      case 0x3F0B:
>> > >          segment->index_edit_rate.num = avio_rb32(pb);
>> > >          segment->index_edit_rate.den = avio_rb32(pb);
>> > > +        if (segment->index_edit_rate.num <= 0 ||
>> > > +            segment->index_edit_rate.den <= 0)
>> > > +            return AVERROR_INVALIDDATA;
>> > 
>> > mxf_compute_index_tables() has a check for index_edit_rate that you
>> > probably want to remove as well. It was introduced in c6fff3d, but
>> > the
>> > files it supposedly fixes aren't in FATE. We shouldn't encourage
>> > broken
>> > muxers.
>> 
>> I don't quite get what FATE has to do with it. And the samples
>> mentioned 
>> in the patch has valid index segment edit rates, only they are
>> different 
>> from the track edit rate, and the patch was intended to fix that
>> case.
>
> Then why does it check against 0/0?

Probably to avoid divison by zero.

Regards,
Marton
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