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

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Dec 22, 2021, at 7:30 PM, Gyan Doshi <ffmpeg@gyani.pro> wrote:
> 
> Helper function to check if stored box size is correct and looks
> to be fully available.
> ---
> libavformat/mov.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 2aed6e80ef..2cc9e699de 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -80,6 +80,38 @@ 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;
> +    }
> +
> +    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;
> +    default: return AVERROR_INVALIDDATA;

The default case doesn’t come from invalid data, I prefer assert and
return AVERROR(EINVAL) or AVERROR_BUG.

> +    }
> +
> +   return !size_fit;
> +}
> +
> static int mov_metadata_track_or_disc_number(MOVContext *c, AVIOContext *pb,
>                                              unsigned len, const char *key)
> {
> -- 
> 2.33.0
> 
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