fork: allow CLONE_NEWTIME in clone3 flags

Currently, calling clone3() with CLONE_NEWTIME in clone_args->flags
fails with -EINVAL. This is because CLONE_NEWTIME intersects with
CSIGNAL. However, CSIGNAL was deprecated when clone3 was introduced in
commit 7f192e3c ("fork: add clone3"), allowing re-use of that part
of clone flags.

Fix this by explicitly allowing CLONE_NEWTIME in clone3_args_valid. This
is also in line with the respective check in check_unshare_flags which
allow CLONE_NEWTIME for unshare().

Fixes: 769071ac ("ns: Introduce Time Namespace")
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

kernel/fork.c

@@ -2936,7 +2936,7 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
 	 * - make the CLONE_DETACHED bit reusable for clone3
 	 * - make the CSIGNAL bits reusable for clone3
 	 */
-	if (kargs->flags & (CLONE_DETACHED | CSIGNAL))
+	if (kargs->flags & (CLONE_DETACHED | (CSIGNAL & (~CLONE_NEWTIME))))
 		return false;
 
 	if ((kargs->flags & (CLONE_SIGHAND | CLONE_CLEAR_SIGHAND)) ==