static int hci_uart_tty_open(struct tty_struct *tty)
{
	struct hci_uart *hu;

	BT_DBG("tty %p", tty);

	/* Error if the tty has no write op instead of leaving an exploitable
	 * hole
	 */
	if (tty->ops->write == NULL)
		return -EOPNOTSUPP;

	hu = kzalloc(sizeof(struct hci_uart), GFP_KERNEL);
	if (!hu) {
		BT_ERR("Can't allocate control structure");
		return -ENFILE;
	}

	tty->disc_data = hu;
	hu->tty = tty;
	tty->receive_room = 65536;

	/* disable alignment support by default */
	hu->alignment = 1;
	hu->padding = 0;

	INIT_WORK(&hu->init_ready, hci_uart_init_work);
	INIT_WORK(&hu->write_work, hci_uart_write_work);

	percpu_init_rwsem(&hu->proto_lock);

	/* Flush any pending characters in the driver */
	tty_driver_flush_buffer(tty);

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.