[PATCH 3.2 117/152] gpio: sysfs: fix gpio attribute-creation race

Ben Hutchings
2015-02-17T01:46:53Z

From: Johan Hovold <johan@kernel.org>

commit ebbeba120ab2ec6ac5f3afc1425ec6ff0b77ad6f upstream.

Fix attribute-creation race with userspace by using the default group
to create also the contingent gpio device attributes.

Fixes: d8f388d8dc8d ("gpio: sysfs interface")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[bwh: Backported to 3.2:
- Adjust filenames, context
- Use gpio_to_desc(), not gpiod_to_desc(), in gpio_is_visible()
- gpio_is_visible() must return mode_t]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -58,6 +58,7 @@ struct gpio_desc {
#define FLAG_TRIG_FALL 5 /* trigger on falling edge */
#define FLAG_TRIG_RISE 6 /* trigger on rising edge */
#define FLAG_ACTIVE_LOW 7 /* sysfs value has active low */
+#define FLAG_SYSFS_DIR 10 /* show sysfs direction attribute */

#define ID_SHIFT 16 /* add new flags before this one */

@@ -543,12 +544,45 @@ static ssize_t gpio_active_low_store(str
static DEVICE_ATTR(active_low, 0644,
gpio_active_low_show, gpio_active_low_store);

+static mode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
+ int n)
+{
+ struct device *dev = container_of(kobj, struct device, kobj);
+ struct gpio_desc *desc = dev_get_drvdata(dev);
+ unsigned gpio = desc - gpio_desc;
+ mode_t mode = attr->mode;
+ bool show_direction = test_bit(FLAG_SYSFS_DIR, &desc->flags);
+
+ if (attr == &dev_attr_direction.attr) {
+ if (!show_direction)
+ mode = 0;
+ } else if (attr == &dev_attr_edge.attr) {
+ if (gpio_to_irq(gpio) < 0)
+ mode = 0;
+ if (!show_direction && test_bit(FLAG_IS_OUT, &desc->flags))
+ mode = 0;
+ }
+
+ return mode;
+}
+
static struct attribute *gpio_attrs[] = {
+ &dev_attr_direction.attr,
+ &dev_attr_edge.attr,
&dev_attr_value.attr,
&dev_attr_active_low.attr,
NULL,
};
-ATTRIBUTE_GROUPS(gpio);
+
+static const struct attribute_group gpio_group = {
+ .attrs = gpio_attrs,
+ .is_visible = gpio_is_visible,
+};
+
+static const struct attribute_group *gpio_groups[] = {
+ &gpio_group,
+ NULL
+};

/*
* /sys/class/gpio/gpiochipN/
@@ -723,8 +757,11 @@ int gpio_export(unsigned gpio, bool dire
return -EPERM;
}

- if (!desc->chip->direction_input || !desc->chip->direction_output)
- direction_may_change = false;
+ if (desc->chip->direction_input && desc->chip->direction_output &&
+ direction_may_change) {
+ set_bit(FLAG_SYSFS_DIR, &desc->flags);
+ }
+
spin_unlock_irqrestore(&gpio_lock, flags);

if (desc->chip->names && desc->chip->names[gpio - desc->chip->base])
@@ -738,27 +775,10 @@ int gpio_export(unsigned gpio, bool dire
goto fail_unlock;
}

- if (direction_may_change) {
- status = device_create_file(dev, &dev_attr_direction);
- if (status)
- goto fail_unregister_device;
- }
-
- if (gpio_to_irq(gpio) >= 0 && (direction_may_change ||
- !test_bit(FLAG_IS_OUT, &desc->flags))) {
- status = device_create_file(dev, &dev_attr_edge);
- if (status)
- goto fail_remove_attr_direction;
- }
-
set_bit(FLAG_EXPORT, &desc->flags);
mutex_unlock(&sysfs_lock);
return 0;

-fail_remove_attr_direction:
- device_remove_file(dev, &dev_attr_direction);
-fail_unregister_device:
- device_unregister(dev);
fail_unlock:
mutex_unlock(&sysfs_lock);
pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
@@ -889,6 +909,7 @@ void gpio_unexport(unsigned gpio)
dev = class_find_device(&gpio_class, NULL, desc, match_export);
if (dev) {
gpio_setup_irq(desc, dev, 0);
+ clear_bit(FLAG_SYSFS_DIR, &desc->flags);
clear_bit(FLAG_EXPORT, &desc->flags);
} else
status = -ENODEV;
@@ -896,8 +917,6 @@ void gpio_unexport(unsigned gpio)

mutex_unlock(&sysfs_lock);
if (dev) {
- device_remove_file(dev, &dev_attr_edge);
- device_remove_file(dev, &dev_attr_direction);
device_unregister(dev);
put_device(dev);
}