[FFmpeg-devel] [PATCH] Fix issue when invalid nb_index_entries value is read - SPONSORED BY INA (Institut National de l'Audiovisuel)

[Cédric Le Barz]

We have several samples but these are big files: about 7 GB. Is it OK to 
share such a file size ?

Thanks for you answer,

Regards,

Cédric

Le 16/03/2023 à 21:28, Marton Balint a écrit :
>
>
> On Thu, 16 Mar 2023, Cédric Le Barz wrote:
>
>> Hi,
>>
>> By "invalid", I mean that the written nb_index_entries value does not
>> match with the real number of entries in the table. The number of
>> entries in the table is lower than the specified one. This is a bug in
>> commercial MXFTk software (at least version V 2.8.0.0.1). It exists a
>> lot a MXF files with this problem.
>
> Please share a sample. Or better yet, open a ticket for this issue and
> attach a sample there for future reference.
>
> Thanks,
> Marton
>
>>
>> Best regards,
>>
>> Cédric
>>
>> -----Message d'origine-----
>> De : ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> De la part de 
>> Marton Balint
>> Envoyé : mercredi 8 mars 2023 23:06
>> À : FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
>> Objet : Re: [FFmpeg-devel] [PATCH] Fix issue when invalid 
>> nb_index_entries value is read - SPONSORED BY INA (Institut National 
>> de l'Audiovisuel)
>>
>>
>>
>> On Wed, 8 Mar 2023, Cédric Le Barz wrote:
>>
>>>
>>> Fix issue when invalid nb_index_entries value is read : in case of
>>> false nb_index_entries value, ffmpeg exit. This patch fix this problem.
>>
>> What do you mean invalid? Is the value wrong, or is the file 
>> truncated in the middle of the index segment? From the patch it looks 
>> like the latter.
>>
>> Is there a single unluckily truncated file that you want to fix with 
>> this patch, or multiple files can be affected by this fix because 
>> e.g. they are written by the same broken muxer?
>>
>> Overall I am not sure if we want this applied, the user can also opt 
>> to avoid parsing all partitions with -seekable 0 and read / remux the 
>> file sequentially ignoring any index, so if somebody wants to rescue 
>> the data, it can be done as is.
>>
>> Regards,
>> Marton
>>
>>>
>>>
>>> Signed-off-by: Cedric Le Barz <clebarz at ektacom.com>
>>> ---
>>>  ffmpeg/libavformat/mxfdec.c | 14 ++++++++++++--
>>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/ffmpeg/libavformat/mxfdec.c b/ffmpeg/libavformat/mxfdec.c
>>> index 4530617..ffc8987 100644
>>> --- a/ffmpeg/libavformat/mxfdec.c
>>> +++ b/ffmpeg/libavformat/mxfdec.c
>>> @@ -1221,8 +1221,18 @@ static int
>>> mxf_read_index_entry_array(AVIOContext *pb, MXFIndexTableSegment *seg
>>>      }
>>>      for (i = 0; i < segment->nb_index_entries; i++) {
>>> -        if(avio_feof(pb))
>>> -            return AVERROR_INVALIDDATA;
>>> +
>>> +        if(avio_feof(pb)) {
>>> +            if (i == 0) {
>>> +                return AVERROR_INVALIDDATA;
>>> +            } else {
>>> +                /* To be more robust to invalid nb_index_entries 
>>> value,
>>> +                   fix the index entry number according to read 
>>> entries */
>>> +                segment->nb_index_entries = i;
>>> +                return 0;
>>> +            }
>>> +        }
>>> +
>>>          segment->temporal_offset_entries[i] = avio_r8(pb);
>>>          avio_r8(pb); /*
>>> KeyFrameOffset */
>>>         segment->flag_entries[i] = avio_r8(pb);
>>> -- 
>>> 2.34.1
>>>
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>>>
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