[3.13.y-ckt stable] Patch "gpio: sysfs: fix memory leaks and device hotplug" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    gpio: sysfs: fix memory leaks and device hotplug

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 750c80fac19f6ef000956276e0f79ef1291cada8 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan at kernel.org>
Date: Tue, 21 Apr 2015 17:42:09 +0200
Subject: gpio: sysfs: fix memory leaks and device hotplug

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).

Fixes: d8f388d8dc8d ("gpio: sysfs interface")
Signed-off-by: Johan Hovold <johan at kernel.org>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
[ kamal: backport to 3.13-stable: applied to drivers/gpio/gpiolib.c; context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpio/gpiolib.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e90efc0..e1b4878 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -781,6 +781,7 @@ 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;
@@ -798,8 +799,16 @@ 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)) {
@@ -1043,12 +1052,15 @@ 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 = 0;
 		status = 0;
 	} else
@@ -1058,6 +1070,13 @@ static void gpiochip_unexport(struct gpio_chip *chip)
 	if (status)
 		pr_debug("%s: chip %s status %d\n", __func__,
 				chip->label, 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)
--
1.9.1