Bluetooth: hci_ldisc: require CAP_NET_ADMIN to attach N_HCI ldisc

Any unprivileged user can attach N_HCI ldisc and send packets coming from a
virtual controller by using PTYs.

Require initial namespace CAP_NET_ADMIN to do that.
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -479,6 +479,9 @@ static int hci_uart_tty_open(struct tty_struct *tty)
 
 	BT_DBG("tty %p", tty);
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	/* Error if the tty has no write op instead of leaving an exploitable
 	 * hole
 	 */