static void __exit hci_uart_exit(void)
{
	int err;

#ifdef CONFIG_BT_HCIUART_H4
	h4_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_BCSP
	bcsp_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_LL
	ll_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_ATH3K
	ath_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_3WIRE
	h5_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_INTEL
	intel_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_BCM
	bcm_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_QCA
	qca_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_AG6XX
	ag6xx_deinit();
#endif
#ifdef CONFIG_BT_HCIUART_MRVL
	mrvl_deinit();
#endif

	/* Release tty registration of line discipline */
	err = tty_unregister_ldisc(N_HCI);
	if (err)
		BT_ERR("Can't unregister HCI line discipline (%d)", 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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.