drm: Detect overflow in drm_mm_reserve_node()

Protect ourselves from a caller passing in node.start + node.size that
will overflow and trick us into reserving that node.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161222083641.2691-24-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_mm.c

@@ -308,10 +308,9 @@ int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
 	u64 hole_start, hole_end;
 	u64 adj_start, adj_end;
 
-	if (WARN_ON(node->size == 0))
-		return -EINVAL;
-
 	end = node->start + node->size;
+	if (unlikely(end <= node->start))
+		return -ENOSPC;
 
 	/* Find the relevant hole to add our node to */
 	hole = drm_mm_interval_tree_iter_first(&mm->interval_tree,