linux-kernel - Re: [PATCH v2 tty-next 1/3] 8250: microchip: pci1xxxx: Add driver for quad-uart support.

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Message-ID: <61826266-3f02-bc04-bd98-6391fe5d9fa6@wanadoo.fr>
Date:   Wed, 26 Oct 2022 22:10:40 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Tharunkumar.Pasumarthi@...rochip.com, jk@...abs.org,
        Kumaravel.Thiagarajan@...rochip.com, gregkh@...uxfoundation.org,
        ilpo.jarvinen@...ux.intel.com, wander@...hat.com,
        u.kleine-koenig@...gutronix.de, etremblay@...tech-controls.com,
        macro@...am.me.uk, jirislaby@...nel.org, johan@...nel.org,
        andy.shevchenko@...il.com, geert+renesas@...der.be,
        phil.edworthy@...esas.com, lukas@...ner.de
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH v2 tty-next 1/3] 8250: microchip: pci1xxxx: Add driver for
 quad-uart support.

Le 26/10/2022 à 13:12, Tharunkumar.Pasumarthi@...rochip.com a écrit :
> On Mon, 2022-10-03 at 21:36 +0200, Christophe JAILLET wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
>> content is safe
>>> +             }
>>> +             priv->line[i] = serial8250_register_8250_port(&uart);
>>
>> In case of error, this should be undone in an error handling path in the
>> probe, as done in the remove() function below.
>>
>> If we break, we still continue and return success. But the last
>> priv->line[i] are still 0. Is it an issue when pci1xxxx_serial_remove()
>> is called?
> 
> This will not cause a problem in pci1xxxx_serial_remove as this condition 'priv-
>> line[i] >= 0' will be checked for each of the ports before calling
> serial8250_unregister_port API.

Yes, this is my point.

We check for >=0 in pci1xxxx_serial_remove(), but if we have an error in 
the "for (i = 0; i < nr_ports; i++)" loop, some line[i] we'll still be 
zeroed because 'priv' is zalloc'ed.

In such a case, the probe still succeeds.

So, if pci1xxxx_serial_remove() is called later, we potentially call 
serial8250_unregister_port(0) several times.

This can lead to double (or more) free in serial8250_em485_destroy() 
(but maybe this path can't be taken here?) or maybe some other troubles 
elsewhere (I've not checked all the logic in uart_remove_one_port() to 
make sure that calling several times this function with the same args is 
fine).

So my point is maybe just a "can't happen" case.
If so, apologize for the noise.

CJ

> 
> 
> Thanks,
> Tharun Kumar P