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

[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...

Regards,
Marton