linux-kernel - Re: [PATCH v3 3/6] serial: core: fix sanitizing check for RTS settings

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Date:   Mon, 16 Oct 2023 12:10:02 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Lino Sanfilippo <l.sanfilippo@...bus.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, shawnguo@...nel.org,
        s.hauer@...gutronix.de, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, cniedermaier@...electronics.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 v3 3/6] serial: core: fix sanitizing check for RTS
 settings



On 16.10.23 12:05, Ilpo Järvinen wrote:
> On Sat, 14 Oct 2023, Lino Sanfilippo wrote:
>> On 13.10.23 12:24, Ilpo Järvinen wrote:
>>> On Thu, 12 Oct 2023, Lino Sanfilippo wrote:
>>>> On 12.10.23 15:10, Ilpo Järvinen wrote:
>>>>> On Wed, 11 Oct 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 697c36dc7ec8..f4feebf8200f 100644
>>>>>> --- a/drivers/tty/serial/serial_core.c
>>>>>> +++ b/drivers/tty/serial/serial_core.c
>>>>>> @@ -1370,19 +1370,27 @@ 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;
>>>>>
>>>>> So if neither of the flags is supported, what will happen? You might want
>>>>> add if after that else?
>>>>>
>>>>
>>>> I would consider this a bug in the driver, as at least one of both modes
>>>> has to be supported. If the driver does not have at least one of both flags
>>>> set in rs485_supported.flags we could print a warning though. Would you prefer that?
>>>
>>> 8250_exar.c needs to fixed then?
>> I was taking these as things one can
>>> "configure" even if when there's support only for a one of them there's
>>> not that much to configure. As there was neither in 8250_exar's code, I
>>> didn't add either flag.
>>
>>> But I suppose your interpretation of those flag makes more sense.
>>
>> IMHO this is consistent with what we have in uart_get_rs485_mode(). This function
>> ensures that we have at least one RTS mode set (with default to RTS_ON_SEND). So
>> concerning 8250_exar.c, I think it should be fixed (havent noticed the missing
>> RTS mode though until you mentioned it). Would you like to provide a fix for this
>> or shall I include one into the next version of this series?
>
> Just create that fix yourself thank you and include it into your series,
> I'm busy with other stuff currently.
>
>

Sure, will do.

BR,
Lino