do_move_mount(): don't leak MNTNS_PROPAGATING on failures

as it is, a failed move_mount(2) from anon namespace breaks
all further propagation into that namespace, including normal
mounts in non-anon namespaces that would otherwise propagate
there.

Fixes: 064fe6e ("mount: handle mount propagation for detached mount trees")
Reviewed-by: Christian Brauner <[email protected]>
Signed-off-by: Al Viro <[email protected]>

Author: Al Viro

fs/namespace.c

@@ -3715,15 +3715,14 @@ static int do_move_mount(struct path *old_path,
 	if (err)
 		goto out;
 
-	if (is_anon_ns(ns))
-		ns->mntns_flags &= ~MNTNS_PROPAGATING;
-
 	/* if the mount is moved, it should no longer be expire
 	 * automatically */
 	list_del_init(&old->mnt_expire);
 	if (attached)
 		put_mountpoint(old_mp);
 out:
+	if (is_anon_ns(ns))
+		ns->mntns_flags &= ~MNTNS_PROPAGATING;
 	unlock_mount(mp);
 	if (!err) {
 		if (attached) {