linux-kernel - Re: [PATCH] NFC: nci: uart: Set tty->disc

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Message-ID: <2025061838-frustrate-operative-bd34@gregkh>
Date: Wed, 18 Jun 2025 09:44:56 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Vincent Cuissard <cuissard@...vell.com>,
	Samuel Ortiz <sameo@...ux.intel.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] NFC: nci: uart: Set tty->disc_data only in success path

On Wed, Jun 18, 2025 at 09:36:50AM +0200, Krzysztof Kozlowski wrote:
> Setting tty->disc_data before opening the NCI device means we need to
> clean it up on error paths.  This also opens some short window if device
> starts sending data, even before NCIUARTSETDRIVER IOCTL succeeded
> (broken hardware?).  Close the window by exposing tty->disc_data only on
> the success path, when opening of the NCI device and try_module_get()
> succeeds.
> 
> The code differs in error path in one aspect: tty->disc_data won't be
> ever assigned thus NULL-ified.  This however should not be relevant
> difference, because of "tty->disc_data=NULL" in nci_uart_tty_open().
> 
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: Linus Torvalds <torvalds@...uxfoundation.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Fixes: 9961127d4bce ("NFC: nci: add generic uart support")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---
>  net/nfc/nci/uart.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/nfc/nci/uart.c b/net/nfc/nci/uart.c
> index ed1508a9e093..aab107727f18 100644
> --- a/net/nfc/nci/uart.c
> +++ b/net/nfc/nci/uart.c
> @@ -119,22 +119,22 @@ static int nci_uart_set_driver(struct tty_struct *tty, unsigned int driver)
>  
>  	memcpy(nu, nci_uart_drivers[driver], sizeof(struct nci_uart));
>  	nu->tty = tty;
> -	tty->disc_data = nu;
>  	skb_queue_head_init(&nu->tx_q);
>  	INIT_WORK(&nu->write_work, nci_uart_write_work);
>  	spin_lock_init(&nu->rx_lock);
>  
>  	ret = nu->ops.open(nu);
>  	if (ret) {
> -		tty->disc_data = NULL;
>  		kfree(nu);
> +		return ret;
>  	} else if (!try_module_get(nu->owner)) {
>  		nu->ops.close(nu);
> -		tty->disc_data = NULL;
>  		kfree(nu);
>  		return -ENOENT;
>  	}
> -	return ret;
> +	tty->disc_data = nu;
> +
> +	return 0;
>  }

Looks good, thanks for cleaning this up:

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>