Bluetooth: hci_sync: Fix queuing commands when HCI_UNREGISTER is set

hci_cmd_sync_queue shall return an error if HCI_UNREGISTER flag has
been set as that means hci_unregister_dev has been called so it will
likely cause a uaf after the timeout as the hdev will be freed.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/hci_sync.c

@@ -382,6 +382,9 @@ int hci_cmd_sync_queue(struct hci_dev *hdev, hci_cmd_sync_work_func_t func,
 {
 	struct hci_cmd_sync_work_entry *entry;
 
+	if (hci_dev_test_flag(hdev, HCI_UNREGISTER))
+		return -ENODEV;
+
 	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
 	if (!entry)
 		return -ENOMEM;