linux-kernel - Re: [PATCH] gpiolib: Fix crash when exporting non-existant gpio

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Message-ID: <CACRpkdYTytiOd=Lhb84XTKZpOWe20sqFxzwNf_0U8hvoy5deUA@mail.gmail.com>
Date:	Thu, 29 Aug 2013 11:52:44 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Daniel Santos <daniel.santos@...ox.com>,
	Alexandre Courbot <acourbot@...dia.com>
Cc:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [PATCH] gpiolib: Fix crash when exporting non-existant gpio

On Sat, Aug 24, 2013 at 10:48 PM,  <danielfsantos@....net> wrote:

> [  222.961384] Unable to handle kernel NULL pointer dereference at
> virtual address 00000044
> [  222.969486] pgd = d97d0000
> [  222.972190] [00000044] *pgd=1aaca831, *pte=00000000, *ppte=00000000
> [  222.978483] Internal error: Oops: 17 [#1] PREEMPT ARM
> ---
>  drivers/gpio/gpiolib.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index d6413b2..db7c6bb 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -123,7 +123,8 @@ static int gpio_chip_hwgpio(const struct gpio_desc *desc)
>   */
>  static struct gpio_desc *gpio_to_desc(unsigned gpio)
>  {
> -       if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
> +       if (WARN(!gpio_is_valid(gpio) || !gpio_desc[gpio].chip,
> +                       "invalid GPIO %d\n", gpio))
>                 return NULL;
>         else
>                 return &gpio_desc[gpio];
> @@ -1406,8 +1407,7 @@ static int gpiod_request(struct gpio_desc *desc, const char *label)
>         spin_lock_irqsave(&gpio_lock, flags);
>
>         chip = desc->chip;
> -       if (chip == NULL)
> -               goto done;
> +       BUG_ON(!chip);

It'd be good if Alexandre took a look at this.

BUG_ON() is pretty nasty, atleast replace it with
a warning.

Yours,
Linus Walleij
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