gpio: sysfs: fix gpio attribute-creation race

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>

2 files changed, 40 insertions, 22 deletions

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index fd4d9423f6e6..f62aa115d79a 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -356,12 +356,44 @@ 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/
@@ -550,8 +582,11 @@ 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);
@@ -567,27 +602,10 @@ 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);
@@ -711,6 +729,7 @@ 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;
@@ -719,8 +738,6 @@ 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);
         }
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index e3a52113a541..550a5eafbd38 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -77,6 +77,7 @@ 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 */