[Bluetooth] Restrict well known PSM to privileged users

The PSM values below 0x1001 of L2CAP are reserved for well known
services. Restrict the possibility to bind them to privileged
users.

Signed-off-by: Marcel Holtmann <[e-mail]>

net/bluetooth/l2cap.c

···
 		goto done;
 	}
 
+	if (la->l2_psm > 0 && btohs(la->l2_psm) < 0x1001 &&
+				!capable(CAP_NET_BIND_SERVICE)) {
+		err = -EACCES;
+		goto done;
+	}
+		
 	write_lock_bh(&l2cap_sk_list.lock);
 
 	if (la->l2_psm && __l2cap_get_sock_by_addr(la->l2_psm, &la->l2_bdaddr)) {