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

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Date:   Thu, 10 Mar 2022 16:44:53 +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] gpio: Restrict usage of gc irq members before initialization

On Thu, Mar 10, 2022 at 3:22 PM Shreeya Patel
<shreeya.patel@...labora.com> wrote:
>
> gc irq members are exposed before they could be completely
> initialized and this leads to race conditions.
>
> 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
> they are completely initialized.

Fixes tag?

...

> +bool gc_irq_initialized;

Non-static?

Why is it global?

...

> @@ -1593,6 +1594,8 @@ static int gpiochip_add_irqchip(struct gpio_chip *gc,
>
>         acpi_gpiochip_request_interrupts(gc);
>
> +       gc_irq_initialized = true;

This is wrong. Imagine a system where you have more than one GPIO chip.

...

> -       if (gc->to_irq) {
> +       if (gc->to_irq && gc_irq_initialized) {
>                 int retirq = gc->to_irq(gc, offset);

Shouldn't it rather be something like

  if (gc->to_irq) {
    if (! ..._initialized)
      return -EPROBE_DEFER;
    ...
  }

?

--
With Best Regards,
Andy Shevchenko