[PATCH 3.16.y-ckt 161/183] gpio: sysfs: fix gpio attribute-creation race

From: Luis Henriques
Date: Fri Mar 06 2015 - 05:10:34 EST


3.16.7-ckt8 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
[ luis: backported to 3.16:
- all changes in drivers/gpio/gpiolib.c
- adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
drivers/gpio/gpiolib.c | 62 ++++++++++++++++++++++++++++++++------------------
1 file changed, 40 insertions(+), 22 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index afdca5a6b2a6..d9b8844e2715 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -60,6 +60,7 @@ struct gpio_desc {
#define FLAG_OPEN_DRAIN 7 /* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 8 /* Gpio is open source type */
#define FLAG_USED_AS_IRQ 9 /* GPIO is connected to an IRQ */
+#define FLAG_SYSFS_DIR 10 /* show sysfs direction attribute */

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

@@ -637,12 +638,44 @@ static ssize_t gpio_active_low_store(struct device *dev,
static DEVICE_ATTR(active_low, 0644,
gpio_active_low_show, gpio_active_low_store);

+static umode_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);
+ umode_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 (gpiod_to_irq(desc) < 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/
@@ -831,8 +864,11 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
goto fail_unlock;
}

- 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);

offset = gpio_chip_hwgpio(desc);
@@ -848,27 +884,10 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
goto fail_unlock;
}

- if (direction_may_change) {
- status = device_create_file(dev, &dev_attr_direction);
- if (status)
- goto fail_unregister_device;
- }
-
- if (gpiod_to_irq(desc) >= 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);
gpiod_dbg(desc, "%s: status %d\n", __func__, status);
@@ -994,6 +1013,7 @@ void gpiod_unexport(struct gpio_desc *desc)
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;
@@ -1002,8 +1022,6 @@ void gpiod_unexport(struct gpio_desc *desc)
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);
}
--
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