linux-kernel - Re: [PATCH] gpio: Initialize gc->irq.domain before setting gc->to

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Date:   Mon, 15 Nov 2021 14:53:49 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Emil Velikov <emil.velikov@...labora.com>
Cc:     Shreeya Patel <shreeya.patel@...labora.com>,
        linus.walleij@...aro.org, brgl@...ev.pl,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH] gpio: Initialize gc->irq.domain before setting gc->to_irq

Emil Velikov <emil.velikov@...labora.com> writes:

> Hi Shreeya, all,
>
> On 2021/11/09, Shreeya Patel wrote:
>> There is a race in registering of gc->irq.domain when
>> probing the I2C driver.
>> This sometimes leads to a Kernel NULL pointer dereference
>> in gpiochip_to_irq function which uses the domain variable.
>> 
>> To avoid this issue, set gc->to_irq after domain is
>> initialized. This will make sure whenever gpiochip_to_irq
>> is called, it has domain already initialized.
>> 
>
> What is stopping the next developer to moving the assignment to the
> incorrect place? Aka should we add an inline comment about this?

I agree with Emil.  The patch seems like a workaround that doesn't
really solve the underlying issue.  I'm not familiar with this code, but
it seems that gc is missing a lock during this initialization, to prevent
it from exposing a partially initialized gc->irq.

-- 
Gabriel Krisman Bertazi