linux-kernel - Re: [PATCH v3 2/4] serial: mctrl_gpio: Add a NULL check to mctrl_gpio_to

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Date:   Mon, 5 Aug 2019 09:01:39 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-imx@....com" <linux-imx@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "geert+renesas@...der.be" <geert+renesas@...der.be>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/4] serial: mctrl_gpio: Add a NULL check to
 mctrl_gpio_to_gpiod()

On 02.08.19 14:12, Uwe Kleine-König wrote:
> On Fri, Aug 02, 2019 at 10:04:10AM +0000, Schrempf Frieder wrote:
>> From: Frieder Schrempf <frieder.schrempf@...tron.de>
>>
>> As it is allowed to use the mctrl_gpio_* functions before
>> initialization (as the 8250 driver does according to 434be0ae7aa7),
> 
> Actually I was surprised some time ago that 8250 used serial_mctrl
> without first initializing it and expecting it to work. I didn't look in
> detail, but I wouldn't go so far to call this "allowed". The commit
> itself calls it "workaround" which seems a better match.

Ok, but if this is considered to be a workaround and as the 8250 driver 
does not use mctrl_gpio_to_gpiod(), we should maybe just drop this patch 
instead of encouraging others to use mctrl_gpio before initialization.

I'm really not sure what's best, so depending on what you will propose, 
I'll send a new version of this patch with adjusted commit message or not.

By the way, Uwe and Fabio: Thanks for your reviews!

> 
>> it seems appropriate to have a NULL check in all of the functions.
>> Otherwise the mctrl_gpio_to_gpiod() function is prone to be used
>> in a context that can lead to a NULL pointer dereference.
>>
>> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> 
> Best regards
> Uwe
>