tor 2019-10-10 klockan 11:47 +0200 skrev Andreas Rheinhardt:
> zmbvenc allocates a buffer for a picture with padding on all four sides:
> The stride is choosen so large that it already contains padding on the
> right; the height also includes padding rows. The padding on the right
> of each row is also reused as padding for the left of the next row. So
> one still needs to add padding on the left for the first row. This is done
> by offsetting the actual pointer used to access the picture from the
> pointer returned by av_mallocz and the formula for this offset was
> wrong, because it ignored that a pixel can take more than one byte when
> calculating the offset resulting from the left padding of the first row.
>
> This fixes accesses outside of the allocated buffer that were reported
> in tickets #7980 and #7994. No writes were ever attempted outside of
> the buffer.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
> ---
> libavcodec/zmbvenc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/zmbvenc.c b/libavcodec/zmbvenc.c
> index 0e22ce687f..319381dd48 100644
> --- a/libavcodec/zmbvenc.c
> +++ b/libavcodec/zmbvenc.c
> @@ -409,7 +409,7 @@ static av_cold int encode_init(AVCodecContext *avctx)
> */
> c->pstride = FFALIGN((avctx->width + c->lrange) * c->bypp, 16);
> prev_size = FFALIGN(c->lrange * c->bypp, 16) + c->pstride * (c->lrange +
> avctx->height + c->urange);
> - prev_offset = FFALIGN(c->lrange, 16) + c->pstride * c->lrange;
> + prev_offset = FFALIGN(c->lrange * c->bypp, 16) + c->pstride * c->lrange;
> if (!(c->prev_buf = av_mallocz(prev_size))) {
> av_log(avctx, AV_LOG_ERROR, "Can't allocate picture.\n");
> return AVERROR(ENOMEM);
Looks OK.
Perhaps there should be a static function in some header to get a
pointer to the start of a given line in a picture. That'd cut down on
bugs like this..
/Tomas
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