Patch "gpio: sysfs: fix memory leaks and device hotplug" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

gpio: sysfs: fix memory leaks and device hotplug

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
gpio-sysfs-fix-memory-leaks-and-device-hotplug.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Johan Hovold <[email protected]>
Date: Tue, 21 Apr 2015 17:42:09 +0200
Subject: gpio: sysfs: fix memory leaks and device hotplug

From: Johan Hovold <[email protected]>

commit 483d821108791092798f5d230686868112927044 upstream.

Unregister GPIOs requested through sysfs at chip remove to avoid leaking the associated memory and sysfs entries.

The stale sysfs entries prevented the gpio numbers from being exported when the gpio range was later reused (e.g. at device reconnect).

This also fixes the related module-reference leak.

Note that kernfs makes sure that any on-going sysfs operations finish before the class devices are unregistered and that further accesses fail.

The chip exported flag is used to prevent gpiod exports during removal. This also makes it harder to trigger, but does not fix, the related race between gpiochip_remove and export_store, which is really a race with gpiod_request that needs to be addressed separately.

Also note that this would prevent the crashes (e.g. NULL-dereferences) at reconnect that affects pre-3.18 kernels, as well as use-after-free on operations on open attribute files on pre-3.14 kernels (prior to kernfs).

---
 drivers/gpio/gpiolib.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

@@ -800,6 +800,7 @@ static struct class gpio_class = {
  */
 int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 {
+	struct gpio_chip	*chip;
 	unsigned long		flags;
 	int			status;
 	const char		*ioname = NULL;

@@ -817,8 +818,16 @@ int gpiod_export(struct gpio_desc *desc,
 		return -EINVAL;
 	}
 
+	chip = desc->chip;
+
 	mutex_lock(&sysfs_lock);
 
+	/* check if chip is being removed */
+	if (!chip || !chip->exported) {
+		status = -ENODEV;
+		goto fail_unlock;
+	}
+
 	spin_lock_irqsave(&gpio_lock, flags);
 	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
 	     test_bit(FLAG_EXPORT, &desc->flags)) {

@@ -1057,12 +1066,15 @@ static void gpiochip_unexport(struct gpi
 {
 	int			status;
 	struct device		*dev;
+	struct gpio_desc *desc;
+	unsigned int i;
 
 	mutex_lock(&sysfs_lock);
 	dev = class_find_device(&gpio_class, NULL, chip, match_export);
 	if (dev) {
 		put_device(dev);
 		device_unregister(dev);
+		/* prevent further gpiod exports */
 		chip->exported = false;
 		status = 0;
 	} else

@@ -1071,6 +1083,13 @@ static void gpiochip_unexport(struct gpi
 
 	if (status)
 		chip_dbg(chip, "%s: status %d\n", __func__, status);
+
+	/* unregister gpiod class devices owned by sysfs */
+	for (i = 0; i < chip->ngpio; i++) {
+		desc = &chip->desc[i];
+		if (test_and_clear_bit(FLAG_SYSFS, &desc->flags))
+			gpiod_free(desc);
+	}
 }
 
 static int __init gpiolib_sysfs_init(void)

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/gpio-sysfs-fix-memory-leaks-and-device-hotplug.patch

Your backport looks good, but this one depends on commit 01cca93a9491 ("gpio: unregister gpiochip device before removing it") which needs to be backported as well. I tried to convey this in the stable tag:

	Cc: stable <[email protected]> # v2.6.27: 01cca93a9491

I'll respond to this message with a tested backport of both patches.

Thanks,
Johan

commit 01cca93a9491ed95992523ff7e79dd9bfcdea8e0 upstream.

Unregister gpiochip device (used to export information through sysfs) before removing it internally. This way removal will reverse addition.

---
 drivers/gpio/gpiolib.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

index f1fc14c33be5..7fc186c6927d 100644
@@ -1265,6 +1265,8 @@ int gpiochip_remove(struct gpio_chip *chip)
 	int		status = 0;
 	unsigned	id;
 
+	gpiochip_unexport(chip);
+
 	spin_lock_irqsave(&gpio_lock, flags);
 
 	gpiochip_remove_pin_ranges(chip);

@@ -1286,9 +1288,6 @@ int gpiochip_remove(struct gpio_chip *chip)
 
 	spin_unlock_irqrestore(&gpio_lock, flags);
 
-	if (status == 0)
-		gpiochip_unexport(chip);
-
 	return status;
 }
 EXPORT_SYMBOL_GPL(gpiochip_remove);

2.3.6

commit 483d821108791092798f5d230686868112927044 upstream.

Unregister GPIOs requested through sysfs at chip remove to avoid leaking the associated memory and sysfs entries.

The stale sysfs entries prevented the gpio numbers from being exported when the gpio range was later reused (e.g. at device reconnect).

This also fixes the related module-reference leak.

Note that kernfs makes sure that any on-going sysfs operations finish before the class devices are unregistered and that further accesses fail.

The chip exported flag is used to prevent gpiod exports during removal. This also makes it harder to trigger, but does not fix, the related race between gpiochip_remove and export_store, which is really a race with gpiod_request that needs to be addressed separately.

Also note that this would prevent the crashes (e.g. NULL-dereferences) at reconnect that affects pre-3.18 kernels, as well as use-after-free on operations on open attribute files on pre-3.14 kernels (prior to kernfs).

---
 drivers/gpio/gpiolib.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

index 7fc186c6927d..a03e18f5e562 100644
@@ -800,6 +800,7 @@ static struct class gpio_class = {
  */
 int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 {
+	struct gpio_chip	*chip;
 	unsigned long		flags;
 	int			status;
 	const char		*ioname = NULL;

@@ -817,8 +818,16 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 		return -EINVAL;
 	}
 
+	chip = desc->chip;
+
 	mutex_lock(&sysfs_lock);
 
+	/* check if chip is being removed */
+	if (!chip || !chip->exported) {
+		status = -ENODEV;
+		goto fail_unlock;
+	}
+
 	spin_lock_irqsave(&gpio_lock, flags);
 	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
 	     test_bit(FLAG_EXPORT, &desc->flags)) {

@@ -1057,12 +1066,15 @@ static void gpiochip_unexport(struct gpio_chip *chip)
 {
 	int			status;
 	struct device		*dev;
+	struct gpio_desc *desc;
+	unsigned int i;
 
 	mutex_lock(&sysfs_lock);
 	dev = class_find_device(&gpio_class, NULL, chip, match_export);
 	if (dev) {
 		put_device(dev);
 		device_unregister(dev);
+		/* prevent further gpiod exports */
 		chip->exported = false;
 		status = 0;
 	} else

@@ -1071,6 +1083,13 @@ static void gpiochip_unexport(struct gpio_chip *chip)
 
 	if (status)
 		chip_dbg(chip, "%s: status %d\n", __func__, status);
+
+	/* unregister gpiod class devices owned by sysfs */
+	for (i = 0; i < chip->ngpio; i++) {
+		desc = &chip->desc[i];
+		if (test_and_clear_bit(FLAG_SYSFS, &desc->flags))
+			gpiod_free(desc);
+	}
 }
 
 static int __init gpiolib_sysfs_init(void)

2.3.6

You did that correctly, I didn't read it properly, it's my fault here, sorry about that.

Thanks for the patches, I'll go queue them up now.

greg k-h