Bluetooth: Enforce validation on max value of connection interval

Right now Linux BT stack cannot pass test case "GAP/CONN/CPUP/BV-05-C
'Connection Parameter Update Procedure Invalid Parameters Central
Responder'" in Bluetooth Test Suite revision GAP.TS.p44. [0]

That was revoled by commit c49a8682 ("Bluetooth: validate BLE
connection interval updates"), but later got reverted due to devices
like keyboards and mice may require low connection interval.

So only validate the max value connection interval to pass the Test
Suite, and let devices to request low connection interval if needed.

[0] https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=229869

Fixes: 68d19d7d ("Revert "Bluetooth: validate BLE connection interval updates"")
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/hci_event.c

@@ -6797,6 +6797,10 @@ static void hci_le_remote_conn_param_req_evt(struct hci_dev *hdev, void *data,
 		return send_conn_param_neg_reply(hdev, handle,
 						 HCI_ERROR_UNKNOWN_CONN_ID);
 
+	if (max > hcon->le_conn_max_interval)
+		return send_conn_param_neg_reply(hdev, handle,
+						 HCI_ERROR_INVALID_LL_PARAMS);
+
 	if (hci_check_conn_params(min, max, latency, timeout))
 		return send_conn_param_neg_reply(hdev, handle,
 						 HCI_ERROR_INVALID_LL_PARAMS);

net/bluetooth/l2cap_core.c

@@ -5613,7 +5613,13 @@ static inline int l2cap_conn_param_update_req(struct l2cap_conn *conn,
 
 	memset(&rsp, 0, sizeof(rsp));
 
-	err = hci_check_conn_params(min, max, latency, to_multiplier);
+	if (max > hcon->le_conn_max_interval) {
+		BT_DBG("requested connection interval exceeds current bounds.");
+		err = -EINVAL;
+	} else {
+		err = hci_check_conn_params(min, max, latency, to_multiplier);
+	}
+
 	if (err)
 		rsp.result = cpu_to_le16(L2CAP_CONN_PARAM_REJECTED);
 	else