Re: [FFmpeg-devel] [PATCH 2/2] avformat/matroskaenc: Fix and simplify check for invalid crop values

[James Almer <jamrial@gmail.com>]

On 7/8/2024 2:24 PM, Andreas Rheinhardt wrote:
> The check "left >= INT_MAX - right" is supposed to check for
> whether left + right does not overflow/wraparound, but given that
> left and top are uint32_t INT_MAX - right can already wraparound
> for big values of right (and ordinary 32-bit ints):
> If right == UINT32_MAX, INT_MAX - right is INT_MAX + 1;
> for left in 0..par->width both checks will be passed.
> 
> Fix this and simplify the check by using 64-bit types,
> where the addition is guaranteed not to overflow.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>   libavformat/matroskaenc.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index e1adc0eba6..4b91283119 100644
> --- a/libavformat/matroskaenc.c
> +++ b/libavformat/matroskaenc.c
> @@ -1786,16 +1786,14 @@ static int mkv_write_track_video(AVFormatContext *s, MatroskaMuxContext *mkv,
>                                    st->codecpar->nb_coded_side_data,
>                                    AV_PKT_DATA_FRAME_CROPPING);
>       if (sd && sd->size == sizeof(uint32_t) * 4) {
> -        uint32_t top, bottom, left, right;
> +        uint64_t top, bottom, left, right;
>   
>           top    = AV_RL32(sd->data +  0);
>           bottom = AV_RL32(sd->data +  4);
>           left   = AV_RL32(sd->data +  8);
>           right  = AV_RL32(sd->data + 12);
>   
> -        if (left >= INT_MAX - right ||
> -            top >= INT_MAX - bottom ||
> -            (left + right) >= par->width ||
> +        if ((left + right) >= par->width ||
>               (top + bottom) >= par->height) {
>               av_log(s, AV_LOG_ERROR, "Invalid cropping dimensions in stream side data\n");
>               return AVERROR(EINVAL);

LGTM.
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