Bluetooth: Enforce strict Secure Connections Only mode security

In Secure Connections Only mode, it is required that Secure Connections
is used for pairing and that the link key is encrypted with AES-CCM using
a P-256 authenticated combination key. If this is not the case, then new
connection shall be refused or existing connections shall be dropped.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

net/bluetooth/hci_conn.c

@@ -781,6 +781,17 @@ int hci_conn_check_link_mode(struct hci_conn *conn)
 {
 	BT_DBG("hcon %p", conn);
 
+	/* In Secure Connections Only mode, it is required that Secure
+	 * Connections is used and the link is encrypted with AES-CCM
+	 * using a P-256 authenticated combination key.
+	 */
+	if (test_bit(HCI_SC_ONLY, &conn->hdev->flags)) {
+		if (!hci_conn_sc_enabled(conn) ||
+		    !test_bit(HCI_CONN_AES_CCM, &conn->flags) ||
+		    conn->key_type != HCI_LK_AUTH_COMBINATION_P256)
+			return 0;
+	}
+
 	if (hci_conn_ssp_enabled(conn) && !(conn->link_mode & HCI_LM_ENCRYPT))
 		return 0;
 

net/bluetooth/hci_event.c

@@ -2183,6 +2183,18 @@ static void hci_encrypt_change_evt(struct hci_dev *hdev, struct sk_buff *skb)
 		if (!ev->status)
 			conn->state = BT_CONNECTED;
 
+		/* In Secure Connections Only mode, do not allow any
+		 * connections that are not encrypted with AES-CCM
+		 * using a P-256 authenticated combination key.
+		 */
+		if (test_bit(HCI_SC_ONLY, &hdev->dev_flags) &&
+		    (!test_bit(HCI_CONN_AES_CCM, &conn->flags) ||
+		     conn->key_type != HCI_LK_AUTH_COMBINATION_P256)) {
+			hci_proto_connect_cfm(conn, HCI_ERROR_AUTH_FAILURE);
+			hci_conn_drop(conn);
+			goto unlock;
+		}
+
 		hci_proto_connect_cfm(conn, ev->status);
 		hci_conn_drop(conn);
 	} else