Re: [PATCH] gpio: Do not trigger WARN() with sysfs gpio export/unexport

[Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>]

On Wed, Nov 4, 2020 at 12:53 PM Damien Le Moal <damien.lemoal@xxxxxxx> wrote:
>
> If a user tries to export or unexport an invalid gpio (e.g. gpio number
> >= ARCH_NR_GPIOS), gpio_to_desc() will trigger a register dump through a
> WARN() call. Avoid this rather scary error message by first checking the
> validity of the gpio number before calling gpio_to_desc() in
> export_store() and unexport_store(). The user gets a normal error
> message to signal his/her error without any possible confusion with a
> kernel bug.
>
> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
> ---
>  drivers/gpio/gpiolib-sysfs.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
> index 728f6c687182..b6fd0d82757a 100644
> --- a/drivers/gpio/gpiolib-sysfs.c
> +++ b/drivers/gpio/gpiolib-sysfs.c
> @@ -3,6 +3,7 @@
>  #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>
> @@ -456,14 +457,15 @@ static ssize_t export_store(struct class *class,
>                                 const char *buf, size_t len)
>  {
>         long                    gpio;
> -       struct gpio_desc        *desc;
> +       struct gpio_desc        *desc = NULL;
>         int                     status;
>
>         status = kstrtol(buf, 0, &gpio);
>         if (status < 0)
>                 goto done;
>
> -       desc = gpio_to_desc(gpio);
> +       if (gpio_is_valid(gpio))
> +               desc = gpio_to_desc(gpio);
>         /* reject invalid GPIOs */
>         if (!desc) {
>                 pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
> @@ -503,14 +505,15 @@ static ssize_t unexport_store(struct class *class,
>                                 const char *buf, size_t len)
>  {
>         long                    gpio;
> -       struct gpio_desc        *desc;
> +       struct gpio_desc        *desc = NULL;
>         int                     status;
>
>         status = kstrtol(buf, 0, &gpio);
>         if (status < 0)
>                 goto done;
>
> -       desc = gpio_to_desc(gpio);
> +       if (gpio_is_valid(gpio))
> +               desc = gpio_to_desc(gpio);
>         /* reject bogus commands (gpio_unexport ignores them) */
>         if (!desc) {
>                 pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
> --
> 2.28.0
>

How about we change that to an unconditional WARN() everytime the user
tries to export a GPIO over sysfs so that people switch over to the
character device?

I'm joking a bit but I think it's time to start discouraging people
from using sysfs and a warning may be a good start.

Bartosz