Re: [FFmpeg-devel] [PATCH v2 1/2] avformat/mov: add validate_box_size

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2021-12-22 06:43 pm, Nicolas George wrote:
> Gyan Doshi (12021-12-22):
>> Helper function to check if stored box size is correct and looks
>> to be fully available.
>> ---
>>   libavformat/mov.c | 34 ++++++++++++++++++++++++++++++++++
>>   1 file changed, 34 insertions(+)
>>
>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>> index 2aed6e80ef..7de95b7ab0 100644
>> --- a/libavformat/mov.c
>> +++ b/libavformat/mov.c
>> @@ -80,6 +80,40 @@ static int mov_read_mfra(MOVContext *c, AVIOContext *f);
>>   static int64_t add_ctts_entry(MOVCtts** ctts_data, unsigned int* ctts_count, unsigned int* allocated_size,
>>                                 int count, int duration);
>>   
>> +/**  Check if the box size meets the requirements passed in limit and constraint_type.
>> + *   If input avio_size is valid, it checks if box size appears to be available.
>> + *
>> + *   constraint_type may be
>> + *   0  if the box size has to be exactly equal to limit
>> + *  -1  if the box size has to be at most limit
>> + *   1  if the box size has to be at least limit
>> + *
>> + *   Returns 0 if size meets requirements.
>> + */
>> +static int validate_box_size(MOVContext *c, MOVAtom atom, AVIOContext *pb,
>> +                             int64_t pos, int64_t limit, int constraint_type)
>> +{
>> +    int size_fit;
>> +    int64_t input_size = avio_size(pb);
>> +
>> +    if (input_size > 0 &&
>> +        input_size - pos < atom.size) {
>> +        av_log(c->fc, AV_LOG_ERROR, "Box %s is truncated\n", av_fourcc2str(atom.type));
>> +        return AVERROR_INVALIDDATA;
>> +    }
>> +
>> +    if (FFABS(constraint_type) > 1)
>> +        return AVERROR_BUG;
> av_assert() whould have been the right choice here.

Will change.

>
>> +
>> +    switch(constraint_type) {
>> +    case  0: size_fit = atom.size == limit; break;
>> +    case -1: size_fit = atom.size <= limit; break;
>> +    case  1: size_fit = atom.size >= limit; break;
> This code is unused, AFAICS. Not a good idea.

I'll call this function in other box readers. Their requirements are 
different.
That's why I made the check a separate function.

Regards,
Gyan
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