[FFmpeg-devel] [PATCH] avformat/matroskadec: Check parents remaining length

[Dale Curtis]

Sent http://ffmpeg.org/pipermail/ffmpeg-devel/2019-February/240418.html -
which passes fate and fixes the issue with our test clip.

- dale

On Fri, Feb 22, 2019 at 12:31 PM Dale Curtis <dalecurtis at chromium.org>
wrote:

> +steve who submitted the original patch.
>
> - dale
>
>
> On Thu, Feb 21, 2019 at 2:30 PM Dale Curtis <dalecurtis at chromium.org>
> wrote:
>
>> One of our test clips is behaving differently after this patch:
>>
>> https://cs.chromium.org/chromium/src/media/test/data/bear-320x240-live.webm
>>
>> The printed log message is:
>> [matroska,webm @ 0x1516c84f4e00] Invalid length 0xffffffffffffff >
>> 0x10000000000002f in parent
>>
>> Looking through the code I'm unsure which of the mixed usage
>> "(uint64_t)-1" and "2**56-1" as marker values is correct. Changing the code
>> to:
>> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
>> index 9b706ab4e0..3015a0b230 100644
>> --- a/libavformat/matroskadec.c
>> +++ b/libavformat/matroskadec.c
>> @@ -1205,7 +1205,7 @@ static int ebml_parse_elem(MatroskaDemuxContext
>> *matroska,
>>              MatroskaLevel *level =
>> &matroska->levels[matroska->num_levels - 1];
>>              AVIOContext *pb = matroska->ctx->pb;
>>              int64_t pos = avio_tell(pb);
>> -            if (level->length != (uint64_t) -1 &&
>> +            if (level->length != 0xffffffffffffffULL &&
>>                  (pos + length) > (level->start + level->length)) {
>>                  av_log(matroska->ctx, AV_LOG_ERROR,
>>                         "Invalid length 0x%"PRIx64" > 0x%"PRIx64" in
>> parent\n",
>>
>> Resolves our issues. Should all other length tests be done the same way?
>>
>> - dale
>>
>> On Sun, Feb 17, 2019 at 12:45 AM Michael Niedermayer <michaelni at gmx.at>
>> wrote:
>>
>>> On Wed, Feb 13, 2019 at 01:41:31PM +0100, Michael Niedermayer wrote:
>>> > Reported-by: Steve Lhomme
>>> > This was found through the Hacker One program on VLC but is not a
>>> security issue in libavformat
>>> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>>> > ---
>>> >  libavformat/matroskadec.c | 21 +++++++++++++++++++++
>>> >  1 file changed, 21 insertions(+)
>>>
>>> will apply an equivalent variant from steve
>>>
>>> [...]
>>> --
>>> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>>>
>>> Asymptotically faster algorithms should always be preferred if you have
>>> asymptotical amounts of data
>>> _______________________________________________
>>> ffmpeg-devel mailing list
>>> ffmpeg-devel at ffmpeg.org
>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>>
>>