drm: Use array_size() when creating lease

Passing an object_count of sufficient size will make
object_count * 4 wrap around to be very small, then a later function
will happily iterate off the end of the object_ids array.  Using
array_size() will saturate at SIZE_MAX, the kmalloc() will fail and
we'll return an -ENOMEM to the norty userspace.

Fixes: 62884cd386b8 ("drm: Add four ioctls for managing drm mode object leases [v7]")
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v4.15+
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c
index 99cba8e..5df1256 100644
--- a/drivers/gpu/drm/drm_lease.c
+++ b/drivers/gpu/drm/drm_lease.c
@@ -528,7 +528,8 @@
 	object_count = cl->object_count;
-	object_ids = memdup_user(u64_to_user_ptr(cl->object_ids), object_count * sizeof(__u32));
+	object_ids = memdup_user(u64_to_user_ptr(cl->object_ids),
+			array_size(object_count, sizeof(__u32)));
 	if (IS_ERR(object_ids))
 		return PTR_ERR(object_ids);