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

[Marton Balint]

On Mon, 20 Mar 2023, Cédric Le Barz wrote:

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

I kind of hoped you have access to the broken muxer and can remux a 
small file which can be made public.

If not, then simply upload it somewhere so I can take a look. If the 
sample can't be made public, just share it with me privately.

Thanks,
Marton

>
> 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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