[PATCH] drm: add a check for x/y in drm_mode_setcrtc

[Daniel Vetter]

On Tue, Jul 07, 2015 at 04:21:50PM +0800, John Hunter wrote:
> From: Zhao Junwang <zhjwpku at gmail.com>
> 
> legacy setcrtc ioctl does take a 32 bit value which might indeed
> overflow
> 
> the checks of crtc_req->x > INT_MAX and crtc_req->y > INT_MAX aren't
> needed any more with this
> 
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Zhao Junwang <zhjwpku at gmail.com>
> ---
>  drivers/gpu/drm/drm_crtc.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index b69ed97..c307435 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -2706,8 +2706,11 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
>  	if (!drm_core_check_feature(dev, DRIVER_MODESET))
>  		return -EINVAL;
>  
> -	/* For some reason crtc x/y offsets are signed internally. */
> -	if (crtc_req->x > INT_MAX || crtc_req->y > INT_MAX)
> +	/*
> +	 * Legacy setcrtc ioctl does take a 32 bit value which might
> +	 * overflow

That legacy takes 32bit is clear, the important part to mention is that
atomic only takes a 16.16 fixed point for this. And to avoid surprises in
for atomic drivers it's better to check this here. Actually this even
holds for just universal planes, no need for full-blown atomic. So what
about instead

	/*
	 * Universal lane src offsets are only 16.16, prevent havoc for
	 * drivers using universal plane code internally.
	 */
-Daniel
> +	 */
> +	if (crtc_req->x & 0xffff0000 || crtc_req->y & 0xffff0000)
>  		return -ERANGE;
>  
>  	drm_modeset_lock_all(dev);
> -- 
> 1.7.10.4
> 
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch