linux-kernel - Re: [PATCH v5 4/7] serial: core: make sure RS485 cannot be enabled when it is not supported

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Date:   Wed, 13 Dec 2023 23:23:03 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        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>,
        Lukas Wunner <lukas@...ner.de>, p.rosenberger@...bus.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v5 4/7] serial: core: make sure RS485 cannot be enabled
 when it is not supported



On 11.12.23 11:53, Ilpo Järvinen wrote:
> On Sat, 9 Dec 2023, Lino Sanfilippo wrote:
>
>> Some uart drivers specify a rs485_config() function and then decide later
>> to disable RS485 support for some reason (e.g. imx and ar933).
>>
>> In these cases userspace may be able to activate RS485 via TIOCSRS485
>> nevertheless, since in uart_set_rs485_config() an existing rs485_config()
>> function indicates that RS485 is supported.
>>
>> Make sure that this is not longer possible by checking the uarts
>> rs485_supported.flags instead and bailing out if SER_RS485_ENABLED is not
>> set.
>>
>> Furthermore instead of returning an empty structure return -ENOTTY if the
>> RS485 configuration is requested via TIOCGRS485 but RS485 is not supported.
>> This has a small impact on userspace visibility but it is consistent with
>> the -ENOTTY error for TIOCGRS485.
>>
>> Fixes: e849145e1fdd ("serial: ar933x: Fill in rs485_supported")
>> Fixes: 55e18c6b6d42 ("serial: imx: Remove serial_rs485 sanitization")
>> Cc: Shawn Guo <shawnguo@...nel.org>
>> Cc: Sascha Hauer <s.hauer@...gutronix.de>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>> ---
>>  drivers/tty/serial/serial_core.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
>> index 4eae1406cb6c..661074ab8edb 100644
>> --- a/drivers/tty/serial/serial_core.c
>> +++ b/drivers/tty/serial/serial_core.c
>> @@ -1448,6 +1448,9 @@ static int uart_get_rs485_config(struct uart_port *port,
>>  	unsigned long flags;
>>  	struct serial_rs485 aux;
>>
>> +	if (!(port->rs485_supported.flags & SER_RS485_ENABLED))
>> +		return -ENOTTY;
>> +
>>  	uart_port_lock_irqsave(port, &flags);
>>  	aux = port->rs485;
>>  	uart_port_unlock_irqrestore(port, flags);
>> @@ -1465,7 +1468,7 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
>>  	int ret;
>>  	unsigned long flags;
>>
>> -	if (!port->rs485_config)
>> +	if (!(port->rs485_supported.flags & SER_RS485_ENABLED))
>>  		return -ENOTTY;
>>
>>  	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
>
> Looking through debian code search entries for TIOCGRS485, this might
> actually fly... I'd suggest splitting this into two patches though.

Ok. I will split this into two patches or maybe even leave the change for uart_get_rs485_config()
completely out of this series (which is only about bug fixes) for now. Thanks!