linux-kernel - Re: [PATCH v3 23/23] drm/qxl: add overflow checks to qxl_mode_dumb

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Date:   Fri, 18 Jan 2019 16:49:44 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 23/23] drm/qxl: add overflow checks to
 qxl_mode_dumb_create()

On Fri, Jan 18, 2019 at 01:20:20PM +0100, Gerd Hoffmann wrote:
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>

We already do all reasonable overflow checks in drm_mode_create_dumb(). If
you don't trust them I think would be better time spent typing an igt to
test this than adding redundant check in all drivers.

You're also missing one check for bpp underflows :-)
-Daniel

> ---
>  drivers/gpu/drm/qxl/qxl_dumb.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/qxl/qxl_dumb.c b/drivers/gpu/drm/qxl/qxl_dumb.c
> index 272d19b677..bed6d06ee4 100644
> --- a/drivers/gpu/drm/qxl/qxl_dumb.c
> +++ b/drivers/gpu/drm/qxl/qxl_dumb.c
> @@ -37,11 +37,13 @@ int qxl_mode_dumb_create(struct drm_file *file_priv,
>  	uint32_t handle;
>  	int r;
>  	struct qxl_surface surf;
> -	uint32_t pitch, format;
> +	uint32_t pitch, size, format;
>  
> -	pitch = args->width * ((args->bpp + 1) / 8);
> -	args->size = pitch * args->height;
> -	args->size = ALIGN(args->size, PAGE_SIZE);
> +	if (check_mul_overflow(args->width, ((args->bpp + 1) / 8), &pitch))
> +		return -EINVAL;
> +	if (check_mul_overflow(pitch, args->height, &size))
> +		return -EINVAL;
> +	args->size = ALIGN(size, PAGE_SIZE);
>  
>  	switch (args->bpp) {
>  	case 16:
> -- 
> 2.9.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch