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

From: Nicolas George <george@nsup.org>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v2 1/2] avformat/mov: add validate_box_size
Date: Wed, 22 Dec 2021 14:13:45 +0100
Message-ID: <YcMkiYg6LdIyh3FP@phare.normalesup.org> (raw)
In-Reply-To: <20211222124728.7300-1-ffmpeg@gyani.pro>

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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.

> +
> +    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.

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

I think the changes belong in a single patch.

Regards,

-- 
  Nicolas George

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