Re: [PATCH v2] [BUGFIX] gpio: reject invalid gpio before getting gpio_desc

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Mon, Jul 31, 2017 at 4:57 AM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> Check user-given gpio number and reject it before
> calling gpio_to_desc() because gpio_to_desc() is
> for kernel driver and it expects given gpio number
> is valid (means 0 to 511).
> If given number is invalid, gpio_to_desc() calls
> WARN() and dump registers and stack for debug.
> This means user can easily kick WARN() just by
> writing invalid gpio number (e.g. 512) to
> /sys/class/gpio/export.
>

Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>

(2 bikesheds below)

> Fixes: 0e9a5edf5d01 ("gpio: fix deferred probe detection for legacy API")
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
>   Changes in v2:
>    - Add gpio_to_valid_desc() according to Andy's comment (Thanks!).
>    - Fix patch description.
> ---
>  drivers/gpio/gpiolib-sysfs.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
> index 4b44dd97c07f..819f36258925 100644
> --- a/drivers/gpio/gpiolib-sysfs.c
> +++ b/drivers/gpio/gpiolib-sysfs.c
> @@ -2,6 +2,7 @@
>  #include <linux/mutex.h>
>  #include <linux/device.h>
>  #include <linux/sysfs.h>
> +#include <linux/gpio.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/gpio/driver.h>
>  #include <linux/interrupt.h>
> @@ -432,6 +433,11 @@ static struct attribute *gpiochip_attrs[] = {
>  };
>  ATTRIBUTE_GROUPS(gpiochip);
>
> +static struct gpio_desc *gpio_to_valid_desc(int gpio)
> +{
> +       return gpio_is_valid(gpio) ? gpio_to_desc(gpio) : NULL;
> +}
> +
>  /*
>   * /sys/class/gpio/export ... write-only
>   *     integer N ... number of GPIO to export (full access)
> @@ -450,7 +456,8 @@ static ssize_t export_store(struct class *class,
>         if (status < 0)
>                 goto done;
>
> -       desc = gpio_to_desc(gpio);
> +       desc = gpio_to_valid_desc(gpio);

> +

No need, if you wish better to put modified line after comment.

>         /* reject invalid GPIOs */
>         if (!desc) {
>                 pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
> @@ -492,7 +499,8 @@ static ssize_t unexport_store(struct class *class,
>         if (status < 0)
>                 goto done;
>
> -       desc = gpio_to_desc(gpio);
> +       desc = gpio_to_valid_desc(gpio);

> +


Ditto.

>         /* reject bogus commands (gpio_unexport ignores them) */
>         if (!desc) {
>                 pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
>



-- 
With Best Regards,
Andy Shevchenko
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