xfs: also reject BULKSTAT_SINGLE in a mount user namespace

BULKSTAT_SINGLE exposed the ondisk uids/gids just like bulkstat, and can
be called on any inode, including ones not visible in the current mount.

Fixes: f736d93d ("xfs: support idmapped mounts")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_itable.c

@@ -168,6 +168,12 @@ xfs_bulkstat_one(
 	};
 	int			error;
 
+	if (breq->mnt_userns != &init_user_ns) {
+		xfs_warn_ratelimited(breq->mp,
+			"bulkstat not supported inside of idmapped mounts.");
+		return -EINVAL;
+	}
+
 	ASSERT(breq->icount == 1);
 
 	bc.buf = kmem_zalloc(sizeof(struct xfs_bulkstat),