On Mon, Jun 08, 2015 at 11:31:15PM +0200, Andreas Cadhalpun wrote:
> ffmpeg | branch: master | Andreas Cadhalpun
> <andreas.cadhal...@googlemail.com> | Mon Jun 8 22:38:29 2015 +0200|
> [6fdbaa2b7fb56623ab2163f861952bc1408c39b3] | committer: Andreas Cadhalpun
>
> vp8: change mv_{min,max}.{x,y} type to int
>
> If one of the dimensions is larger than 8176, s->mb_width or
> s->mb_height is larger than 511, leading to an int16_t overflow of
> s->mv_max.{x,y}. This then causes av_clip to be called with amin > amax.
>
> Changing the type to int avoids the overflow and has no negative
> effect, because s->mv_max is only used in clamp_mv for clipping.
> Since mv_max.{x,y} is positive and mv_min.{x,y} negative, av_clip can't
> increase the absolute value. The input to av_clip is an int16_t, and
> thus the output fits into int16_t as well.
>
> For additional safety, s->mv_{min,max}.{x,y} are clipped to int16_t range
> before use.
>
> Reviewed-by: Ronald S. Bultje <rsbul...@gmail.com>
> Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
>
> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=6fdbaa2b7fb56623ab2163f861952bc1408c39b3
> ---
>
> libavcodec/vp8.c | 6 ++++--
> libavcodec/vp8.h | 9 +++++++--
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c
> index dbba568..becbb2c 100644
> --- a/libavcodec/vp8.c
> +++ b/libavcodec/vp8.c
> @@ -757,8 +757,10 @@ static int vp8_decode_frame_header(VP8Context *s, const
> uint8_t *buf, int buf_si
> static av_always_inline
> void clamp_mv(VP8Context *s, VP56mv *dst, const VP56mv *src)
> {
> - dst->x = av_clip(src->x, s->mv_min.x, s->mv_max.x);
> - dst->y = av_clip(src->y, s->mv_min.y, s->mv_max.y);
> + dst->x = av_clip(src->x, av_clip(s->mv_min.x, INT16_MIN, INT16_MAX),
> + av_clip(s->mv_max.x, INT16_MIN, INT16_MAX));
> + dst->y = av_clip(src->y, av_clip(s->mv_min.y, INT16_MIN, INT16_MAX),
> + av_clip(s->mv_max.y, INT16_MIN, INT16_MAX));Sorry I might have missed something, but why not use av_clip_int16()? [...] -- Clément B.
pgpJPhWjpFzV9.pgp
Description: PGP signature
_______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
