Re: [PATCH] drm: Add integer overflow checking to transitional plane helpers

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 03, 2015 at 02:27:46PM -0700, Matt Roper wrote:
> Add tests for destination rectangle integer overflow before calling the
> driver's check function.  This will ensure that the transitional plane
> helpers match the behavior of the full atomic helpers by always
> returning -ERANGE for planes positioned beyond INT_MAX.
> 
> Note that the legacy SetPlane ioctl itself also includes similar tests
> for integer overflow, so the only case where this check really matters
> is when legacy cursor operations get routed through the universal plane
> interface internally.
> 
> This issue was first noticed with i915 commit:
> 
>         commit ff42e093e9c9c17a6e1d6aab24875a36795f926e
>         Author: Daniel Vetter <daniel.vetter@ffwll.ch>
>         Date:   Mon Mar 2 16:35:20 2015 +0100
> 
>             Revert "drm/i915: Switch planes from transitional helpers to full
>             atomic helpers"
> 
> The above revert switched us from full atomic helpers back to the
> transitional helpers, and in doing so we lost the overflow checking here
> for universal cursor updates.  Even though such extreme cursor positions
> are unlikely to actually happen in the wild, we still don't want there
> to be a change of behavior when drivers switch from transitional helpers
> to full helpers.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84269
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

Since this is just for the cursor ioctl ... shouldn't we instead move
these checks from drm_mode_setplane to __setplane_internal? That way other
drivers also can rely upon these guarantees when implementing universal
cursor support and we won't have a mismatch in what kind of plane
properties can sneak through to drivers.
-Daniel

> ---
>  drivers/gpu/drm/drm_plane_helper.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
> index 33807e0..1e9e105 100644
> --- a/drivers/gpu/drm/drm_plane_helper.c
> +++ b/drivers/gpu/drm/drm_plane_helper.c
> @@ -417,6 +417,20 @@ int drm_plane_helper_commit(struct drm_plane *plane,
>  	for (i = 0; i < 2; i++)
>  		crtc_funcs[i] = crtc[i] ? crtc[i]->helper_private : NULL;
>  
> +	/*
> +	 * Give drivers some help against integer overflows (and match the
> +	 * behavior of the full atomic helpers).
> +	 */
> +	if (plane_state->crtc_w > INT_MAX ||
> +	    plane_state->crtc_x > INT_MAX - (int32_t) plane_state->crtc_w ||
> +	    plane_state->crtc_h > INT_MAX ||
> +	    plane_state->crtc_y > INT_MAX - (int32_t) plane_state->crtc_h) {
> +		DRM_DEBUG_ATOMIC("Invalid CRTC coordinates %ux%u+%d+%d\n",
> +				 plane_state->crtc_w, plane_state->crtc_h,
> +				 plane_state->crtc_x, plane_state->crtc_y);
> +		return -ERANGE;
> +	}
> +
>  	if (plane_funcs->atomic_check) {
>  		ret = plane_funcs->atomic_check(plane, plane_state);
>  		if (ret)
> -- 
> 1.8.5.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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