[PATCH 3/8] gpiolib: sanitize the return value of gpio_chip::set_config()

[Bartosz Golaszewski <brgl@xxxxxxxx>]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

The return value of the set_config() callback may be propagated to
user-space. If a bad driver returns a positive number, it may confuse
user programs. Tighten the API contract and check for positive numbers
returned by GPIO controllers.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
 drivers/gpio/gpiolib.c      | 3 +++
 include/linux/gpio/driver.h | 3 ++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 42625da7e797..95ea300da109 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2575,6 +2575,9 @@ int gpio_do_set_config(struct gpio_desc *desc, unsigned long config)
 		return -ENOTSUPP;
 
 	ret = guard.gc->set_config(guard.gc, gpio_chip_hwgpio(desc), config);
+	if (ret > 0)
+		ret = -EBADE;
+
 #ifdef CONFIG_GPIO_CDEV
 	/*
 	 * Special case - if we're setting debounce period, we need to store
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 26fcddcb74b8..81c06fc8dcda 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -348,7 +348,8 @@ struct gpio_irq_chip {
  * @set: assigns output value for signal "offset"
  * @set_multiple: assigns output values for multiple signals defined by "mask"
  * @set_config: optional hook for all kinds of settings. Uses the same
- *	packed config format as generic pinconf.
+ *	packed config format as generic pinconf. Must return 0 on success and
+ *	a negative error number on failure.
  * @to_irq: optional hook supporting non-static gpiod_to_irq() mappings;
  *	implementation may not sleep
  * @dbg_show: optional routine to show contents in debugfs; default code

-- 
2.45.2