linux-kernel - Re: [PATCH v2] gpio: Restrict usage of gc irq members before initialization

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Message-ID: <CAHp75VdoN+iSu1GLnxWW9BtL-p9uF1sfAw3ZxkFWNpoo44+bZg@mail.gmail.com>
Date:   Tue, 15 Mar 2022 13:00:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Shreeya Patel <shreeya.patel@...labora.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>, krisman@...labora.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>
Subject: Re: [PATCH v2] gpio: Restrict usage of gc irq members before initialization

On Tue, Mar 15, 2022 at 12:38 PM Shreeya Patel
<shreeya.patel@...labora.com> wrote:

Thanks for the update, my comments below.

> gc irq members are exposed before they could be completely

gc --> GPIO chip


> initialized and this leads to race conditions.

Any example here. like ~3-4 lines of the Oops in question?

> One such issue was observed for the gc->irq.domain variable which
> was accessed through the I2C interface in gpiochip_to_irq() before
> it could be initialized by gpiochip_add_irqchip(). This resulted in
> Kernel NULL pointer dereference.
>
> To avoid such scenarios, restrict usage of gc irq members before

gc --> GPIO chip

> they are completely initialized.

...

> +       /*
> +        * Using barrier() here to prevent compiler from reordering
> +        * gc->irq.gc_irq_initialized before initialization of above
> +        * gc irq members.
> +        */
> +       barrier();
> +
> +       gc->irq.gc_irq_initialized = true;

There are too many duplications. Why not simply call it 'initialized'?

> -       if (gc->to_irq) {
> +       if (gc->to_irq && gc->irq.gc_irq_initialized) {

Why can't this check be added into gpiochip_to_irq() ?

    if (!gc->irq.initialized)
        return -ENXIO;

...

> +       bool gc_irq_initialized;

Can you move it closer to .init_hw so it will be weakly grouped by
logic similarities?
Also see above.

-- 
With Best Regards,
Andy Shevchenko