static int hci_uart_tty_ioctl(struct tty_struct *tty, struct file *file,
			      unsigned int cmd, unsigned long arg)
{
	struct hci_uart *hu = tty->disc_data;
	int err = 0;

	BT_DBG("");

	/* Verify the status of the device */
	if (!hu)
		return -EBADF;

	switch (cmd) {
	case HCIUARTSETPROTO:
		if (!test_and_set_bit(HCI_UART_PROTO_SET, &hu->flags)) {
			err = hci_uart_set_proto(hu, arg);
			if (err)
				clear_bit(HCI_UART_PROTO_SET, &hu->flags);
		} else
			err = -EBUSY;
		break;

	case HCIUARTGETPROTO:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = hu->proto->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTGETDEVICE:
		if (test_bit(HCI_UART_REGISTERED, &hu->flags))
			err = hu->hdev->id;
		else
			err = -EUNATCH;
		break;

	case HCIUARTSETFLAGS:
		if (test_bit(HCI_UART_PROTO_SET, &hu->flags))
			err = -EBUSY;
		else
			err = hci_uart_set_flags(hu, arg);
		break;

	case HCIUARTGETFLAGS:
		err = hu->hdev_flags;
		break;

	default:
		err = n_tty_ioctl_helper(tty, file, cmd, arg);
		break;
	}

	return err;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.