Bluetooth: Allow re-encryption with LTK when STK is in use

If we're encrypted with the STK we should allow re-encryption with an
LTK even though the achieved security level is the same. This patch adds
the necessary logic to the smp_sufficient_security function which is
used to determine whether to proceed with encryption or not.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/smp.c

@@ -868,6 +868,14 @@ bool smp_sufficient_security(struct hci_conn *hcon, u8 sec_level)
 	if (sec_level == BT_SECURITY_LOW)
 		return true;
 
+	/* If we're encrypted with an STK always claim insufficient
+	 * security. This way we allow the connection to be re-encrypted
+	 * with an LTK, even if the LTK provides the same level of
+	 * security.
+	 */
+	if (test_bit(HCI_CONN_STK_ENCRYPT, &hcon->flags))
+		return false;
+
 	if (hcon->sec_level >= sec_level)
 		return true;