Bluetooth: Disconnect if E0 is used for Level 4

E0 is not allowed with Level 4:

BLUETOOTH CORE SPECIFICATION Version 5.2 | Vol 3, Part C page 1319:

  '128-bit equivalent strength for link and encryption keys
   required using FIPS approved algorithms (E0 not allowed,
   SAFER+ not allowed, and P-192 not allowed; encryption key
   not shortened'

SC enabled:

> HCI Event: Read Remote Extended Features (0x23) plen 13
        Status: Success (0x00)
        Handle: 256
        Page: 1/2
        Features: 0x0b 0x00 0x00 0x00 0x00 0x00 0x00 0x00
          Secure Simple Pairing (Host Support)
          LE Supported (Host)
          Secure Connections (Host Support)
> HCI Event: Encryption Change (0x08) plen 4
        Status: Success (0x00)
        Handle: 256
        Encryption: Enabled with AES-CCM (0x02)

SC disabled:

> HCI Event: Read Remote Extended Features (0x23) plen 13
        Status: Success (0x00)
        Handle: 256
        Page: 1/2
        Features: 0x03 0x00 0x00 0x00 0x00 0x00 0x00 0x00
          Secure Simple Pairing (Host Support)
          LE Supported (Host)
> HCI Event: Encryption Change (0x08) plen 4
        Status: Success (0x00)
        Handle: 256
        Encryption: Enabled with E0 (0x01)
[May 8 20:23] Bluetooth: hci0: Invalid security: expect AES but E0 was used
< HCI Command: Disconnect (0x01|0x0006) plen 3
        Handle: 256
        Reason: Authentication Failure (0x05)
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/hci_core.h

@@ -1481,11 +1481,13 @@ static inline void hci_encrypt_cfm(struct hci_conn *conn, __u8 status)
 	else
 		encrypt = 0x01;
 
-	if (conn->sec_level == BT_SECURITY_SDP)
-		conn->sec_level = BT_SECURITY_LOW;
+	if (!status) {
+		if (conn->sec_level == BT_SECURITY_SDP)
+			conn->sec_level = BT_SECURITY_LOW;
 
-	if (conn->pending_sec_level > conn->sec_level)
-		conn->sec_level = conn->pending_sec_level;
+		if (conn->pending_sec_level > conn->sec_level)
+			conn->sec_level = conn->pending_sec_level;
+	}
 
 	mutex_lock(&hci_cb_list_lock);
 	list_for_each_entry(cb, &hci_cb_list, list) {

net/bluetooth/hci_conn.c

@@ -1322,6 +1322,23 @@ int hci_conn_check_link_mode(struct hci_conn *conn)
 			return 0;
 	}
 
+	 /* AES encryption is required for Level 4:
+	  *
+	  * BLUETOOTH CORE SPECIFICATION Version 5.2 | Vol 3, Part C
+	  * page 1319:
+	  *
+	  * 128-bit equivalent strength for link and encryption keys
+	  * required using FIPS approved algorithms (E0 not allowed,
+	  * SAFER+ not allowed, and P-192 not allowed; encryption key
+	  * not shortened)
+	  */
+	if (conn->sec_level == BT_SECURITY_FIPS &&
+	    !test_bit(HCI_CONN_AES_CCM, &conn->flags)) {
+		bt_dev_err(conn->hdev,
+			   "Invalid security: Missing AES-CCM usage");
+		return 0;
+	}
+
 	if (hci_conn_ssp_enabled(conn) &&
 	    !test_bit(HCI_CONN_ENCRYPT, &conn->flags))
 		return 0;

net/bluetooth/hci_event.c

@@ -3065,27 +3065,23 @@ static void hci_encrypt_change_evt(struct hci_dev *hdev, struct sk_buff *skb)
 
 	clear_bit(HCI_CONN_ENCRYPT_PEND, &conn->flags);
 
+	/* Check link security requirements are met */
+	if (!hci_conn_check_link_mode(conn))
+		ev->status = HCI_ERROR_AUTH_FAILURE;
+
 	if (ev->status && conn->state == BT_CONNECTED) {
 		if (ev->status == HCI_ERROR_PIN_OR_KEY_MISSING)
 			set_bit(HCI_CONN_AUTH_FAILURE, &conn->flags);
 
+		/* Notify upper layers so they can cleanup before
+		 * disconnecting.
+		 */
+		hci_encrypt_cfm(conn, ev->status);
 		hci_disconnect(conn, HCI_ERROR_AUTH_FAILURE);
 		hci_conn_drop(conn);
 		goto unlock;
 	}
 
-	/* 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 (hci_dev_test_flag(hdev, HCI_SC_ONLY) &&
-	    (!test_bit(HCI_CONN_AES_CCM, &conn->flags) ||
-	     conn->key_type != HCI_LK_AUTH_COMBINATION_P256)) {
-		hci_connect_cfm(conn, HCI_ERROR_AUTH_FAILURE);
-		hci_conn_drop(conn);
-		goto unlock;
-	}
-
 	/* Try reading the encryption key size for encrypted ACL links */
 	if (!ev->status && ev->encrypt && conn->type == ACL_LINK) {
 		struct hci_cp_read_enc_key_size cp;