gpio: reject invalid gpio before getting gpio_desc

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.

Fixes: 0e9a5edf5d01 ("gpio: fix deferred probe detection for legacy API")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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 +456,7 @@ static ssize_t export_store(struct class *class,
 	if (status < 0)
 		goto done;
 
-	desc = gpio_to_desc(gpio);
+	desc = gpio_to_valid_desc(gpio);
 	/* reject invalid GPIOs */
 	if (!desc) {
 		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
@@ -493,7 +499,7 @@ static ssize_t unexport_store(struct class *class,
 	if (status < 0)
 		goto done;
 
-	desc = gpio_to_desc(gpio);
+	desc = gpio_to_valid_desc(gpio);
 	/* reject bogus commands (gpio_unexport ignores them) */
 	if (!desc) {
 		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);