static int hci_uart_register_dev(struct hci_uart *hu)
{
	struct hci_dev *hdev;
	int err;

	BT_DBG("");

	/* Initialize and register HCI device */
	hdev = hci_alloc_dev();
	if (!hdev) {
		BT_ERR("Can't allocate HCI device");
		return -ENOMEM;
	}

	hu->hdev = hdev;

	hdev->bus = HCI_UART;
	hci_set_drvdata(hdev, hu);

	/* Only when vendor specific setup callback is provided, consider
	 * the manufacturer information valid. This avoids filling in the
	 * value for Ericsson when nothing is specified.
	 */
	if (hu->proto->setup)
		hdev->manufacturer = hu->proto->manufacturer;

	hdev->open  = hci_uart_open;
	hdev->close = hci_uart_close;
	hdev->flush = hci_uart_flush;
	hdev->send  = hci_uart_send_frame;
	hdev->setup = hci_uart_setup;
	SET_HCIDEV_DEV(hdev, hu->tty->dev);

	if (test_bit(HCI_UART_RAW_DEVICE, &hu->hdev_flags))
		set_bit(HCI_QUIRK_RAW_DEVICE, &hdev->quirks);

	if (test_bit(HCI_UART_EXT_CONFIG, &hu->hdev_flags))
		set_bit(HCI_QUIRK_EXTERNAL_CONFIG, &hdev->quirks);

	if (!test_bit(HCI_UART_RESET_ON_INIT, &hu->hdev_flags))
		set_bit(HCI_QUIRK_RESET_ON_CLOSE, &hdev->quirks);

	if (test_bit(HCI_UART_CREATE_AMP, &hu->hdev_flags))
		hdev->dev_type = HCI_AMP;
	else
		hdev->dev_type = HCI_PRIMARY;

	/* Only call open() for the protocol after hdev is fully initialized as
	 * open() (or a timer/workqueue it starts) may attempt to reference it.
	 */
	err = hu->proto->open(hu);
	if (err) {
		hu->hdev = NULL;
		hci_free_dev(hdev);
		return err;
	}

	if (test_bit(HCI_UART_INIT_PENDING, &hu->hdev_flags))
		return 0;

	if (hci_register_dev(hdev) < 0) {
		BT_ERR("Can't register HCI device");
		hu->proto->close(hu);
		hu->hdev = NULL;
		hci_free_dev(hdev);
		return -ENODEV;
	}

	set_bit(HCI_UART_REGISTERED, &hu->flags);

	return 0;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.