linux-kernel - Re: [PATCH v5 3/7] serial: core: fix sanitizing check for RTS settings

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Date:   Mon, 11 Dec 2023 12:40:53 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Lino Sanfilippo <l.sanfilippo@...bus.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        u.kleine-koenig@...gutronix.de, shawnguo@...nel.org,
        s.hauer@...gutronix.de, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, cniedermaier@...electronics.com,
        hugo@...ovil.com, LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LinoSanfilippo@....de, Lukas Wunner <lukas@...ner.de>,
        p.rosenberger@...bus.com, stable@...r.kernel.org
Subject: Re: [PATCH v5 3/7] serial: core: fix sanitizing check for RTS
 settings

On Sat, 9 Dec 2023, Lino Sanfilippo wrote:

> Among other things uart_sanitize_serial_rs485() tests the sanity of the RTS
> settings in a RS485 configuration that has been passed by userspace.
> If RTS-on-send and RTS-after-send are both set or unset the configuration
> is adjusted and RTS-after-send is disabled and RTS-on-send enabled.
> 
> This however makes only sense if both RTS modes are actually supported by
> the driver.
> 
> With commit be2e2cb1d281 ("serial: Sanitize rs485_struct") the code does
> take the driver support into account but only checks if one of both RTS
> modes are supported. This may lead to the errorneous result of RTS-on-send
> being set even if only RTS-after-send is supported.
> 
> Fix this by changing the implemented logic: First clear all unsupported
> flags in the RS485 configuration, then adjust an invalid RTS setting by
> taking into account which RTS mode is supported.
> 
> Cc: stable@...r.kernel.org
> Fixes: be2e2cb1d281 ("serial: Sanitize rs485_struct")
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/tty/serial/serial_core.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index c254e88c8452..4eae1406cb6c 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1371,19 +1371,27 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
>  		return;
>  	}
>  
> +	rs485->flags &= supported_flags;
> +
>  	/* Pick sane settings if the user hasn't */
> -	if ((supported_flags & (SER_RS485_RTS_ON_SEND|SER_RS485_RTS_AFTER_SEND)) &&
> -	    !(rs485->flags & SER_RS485_RTS_ON_SEND) ==
> +	if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
>  	    !(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
> -		dev_warn_ratelimited(port->dev,
> -			"%s (%d): invalid RTS setting, using RTS_ON_SEND instead\n",
> -			port->name, port->line);
> -		rs485->flags |= SER_RS485_RTS_ON_SEND;
> -		rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
> -		supported_flags |= SER_RS485_RTS_ON_SEND|SER_RS485_RTS_AFTER_SEND;
> -	}
> +		if (supported_flags & SER_RS485_RTS_ON_SEND) {
> +			rs485->flags |= SER_RS485_RTS_ON_SEND;
> +			rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
>  
> -	rs485->flags &= supported_flags;
> +			dev_warn_ratelimited(port->dev,
> +				"%s (%d): invalid RTS setting, using RTS_ON_SEND instead\n",
> +				port->name, port->line);
> +		} else {
> +			rs485->flags |= SER_RS485_RTS_AFTER_SEND;
> +			rs485->flags &= ~SER_RS485_RTS_ON_SEND;
> +
> +			dev_warn_ratelimited(port->dev,
> +				"%s (%d): invalid RTS setting, using RTS_AFTER_SEND instead\n",
> +				port->name, port->line);
> +		}
> +	}

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.