drm/i915: Update the restrict check to filter out wrong Ring ID passed by user-space

Signed-off-by: NZhao Yakui <yakui.zhao@intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1037,7 +1037,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	if (args->flags & I915_EXEC_IS_PINNED)
 		flags |= I915_DISPATCH_PINNED;
 
-	if ((args->flags & I915_EXEC_RING_MASK) > I915_NUM_RINGS) {
+	if ((args->flags & I915_EXEC_RING_MASK) > LAST_USER_RING) {
 		DRM_DEBUG("execbuf with unknown ring: %d\n",
 			  (int)(args->flags & I915_EXEC_RING_MASK));
 		return -EINVAL;

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -63,6 +63,7 @@ struct  intel_ring_buffer {
 		VECS,
 	} id;
 #define I915_NUM_RINGS 4
+#define LAST_USER_RING (VECS + 1)
 	u32		mmio_base;
 	void		__iomem *virtual_start;
 	struct		drm_device *dev;