Re: [PATCH] media: mediatek: vcodec: Fix potential array out-of-bounds in decoder queue_setup

[Nicolas Dufresne]

Hi,

Le mardi 28 mars 2023 à 10:09 +0000, Wei Chen a écrit :
> variable *nplanes is provided by user via system call argument. The
> possible value of q_data->fmt->num_planes is 1-3, while the value
> of *nplanes can be 1-8. The array access by index i can cause array
> out-of-bounds.
> 
> Fix this bug by checking *nplanes against the array size.
> 
> Signed-off-by: Wei Chen <harperchen1110@xxxxxxxxx>
> ---
>  drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec.c b/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec.c
> index 641f533c417f..cae34cc7c807 100644
> --- a/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec.c
> +++ b/drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec.c
> @@ -753,6 +753,13 @@ int vb2ops_vdec_queue_setup(struct vb2_queue *vq, unsigned int *nbuffers,
>  	}
>  
>  	if (*nplanes) {
> +		if (vq->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE)
> +			if (*nplanes != q_data->fmt->num_planes)
> +				return -EINVAL;
> +		else
> +			if (*nplanes != 1)
> +				return -EINVAL;
> +
>  		for (i = 0; i < *nplanes; i++) {
>  			if (sizes[i] < q_data->sizeimage[i])
>  				return -EINVAL;


A bit of context, *nplanes is non zero only when called from VIDIOC_CREATE_BUFS.
I think this highlights a bigger problem around the format in
VIDIOC_CREATE_BUFS. The format should be validated through TRY_FMT in some ways,
notably to apply the HW required alignment, but also to avoid having to validate
that lower in the stack.

Nicolas