[PATCH] drm: Make integer overflow checking cover universal cursor updates (v2)

[Matt Roper]

Our legacy SetPlane updates perform integer overflow checking on a
plane's destination rectangle in drm_mode_setplane(), and atomic updates
handled as part of a drm_atomic_state transaction do the same checking
in drm_atomic_plane_check().  However legacy cursor updates that get
routed through universal plane interfaces may bypass this overflow
checking if the driver's .update_plane is serviced by the transitional
plane helpers rather than the full atomic plane helpers.

Move the check for destination rectangle integer overflow from the
drm_mode_setplane() to __setplane_internal() so that it also covers
cursor operations.

This fixes an issue first noticed with i915 commit:

        commit ff42e093e9c9c17a6e1d6aab24875a36795f926e
        Author: Daniel Vetter <daniel.vetter at 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.

v2: Move check from setplane ioctl to setplane_internal rather than
    adding an additional copy of the checks to the transitional plane
    helpers.  (Daniel)

Cc: Daniel Vetter <daniel at ffwll.ch>
Testcase: igt/kms_cursor_crc
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84269
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/drm_crtc.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index b914882..160647a 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -2507,6 +2507,17 @@ static int __setplane_internal(struct drm_plane *plane,
 		goto out;
 	}
 
+	/* Give drivers some help against integer overflows */
+	if (crtc_w > INT_MAX ||
+	    crtc_x > INT_MAX - (int32_t) crtc_w ||
+	    crtc_h > INT_MAX ||
+	    crtc_y > INT_MAX - (int32_t) crtc_h) {
+		DRM_DEBUG_KMS("Invalid CRTC coordinates %ux%u+%d+%d\n",
+			      crtc_w, crtc_h, crtc_x, crtc_y);
+		return -ERANGE;
+	}
+
+
 	fb_width = fb->width << 16;
 	fb_height = fb->height << 16;
 
@@ -2591,17 +2602,6 @@ int drm_mode_setplane(struct drm_device *dev, void *data,
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;
 
-	/* Give drivers some help against integer overflows */
-	if (plane_req->crtc_w > INT_MAX ||
-	    plane_req->crtc_x > INT_MAX - (int32_t) plane_req->crtc_w ||
-	    plane_req->crtc_h > INT_MAX ||
-	    plane_req->crtc_y > INT_MAX - (int32_t) plane_req->crtc_h) {
-		DRM_DEBUG_KMS("Invalid CRTC coordinates %ux%u+%d+%d\n",
-			      plane_req->crtc_w, plane_req->crtc_h,
-			      plane_req->crtc_x, plane_req->crtc_y);
-		return -ERANGE;
-	}
-
 	/*
 	 * First, find the plane, crtc, and fb objects.  If not available,
 	 * we don't bother to call the driver.
-- 
1.8.5.1