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

[Lino Sanfilippo]

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@xxxxxxxxxx>
>> Cc: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
>> ---
>>  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!