[PATCH v2] regulator: core: fix race condition in regulator_put()

[PATCH v2] regulator: core: fix race condition in regulator_put()

[Ashay Jaiswal]

The regulator framework maintains a list of consumer regulators
for a regulator device and protects it from concurrent access using
the regulator device's mutex lock.

In the case of regulator_put() the consumer is removed and regulator
device's parameters are updated without holding the regulator device's
mutex. This would lead to a race condition between the regulator_put()
and any function which traverses the consumer list or modifies regulator
device's parameters.
Fix this race condition by holding the regulator device's mutex in case
of regulator_put.

Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
---
 Changes:
 V1-->V2:
	- Updated comment on top of _regulator_put function
	- Updated lock region

 drivers/regulator/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index c2554d8..f70a02c 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1488,7 +1488,7 @@ struct regulator *regulator_get_optional(struct device *dev, const char *id)
 }
 EXPORT_SYMBOL_GPL(regulator_get_optional);

-/* Locks held by regulator_put() */
+/* regulator_list_mutex lock held by regulator_put() */
 static void _regulator_put(struct regulator *regulator)
 {
 	struct regulator_dev *rdev;
@@ -1503,12 +1503,14 @@ static void _regulator_put(struct regulator *regulator)
 	/* remove any sysfs entries */
 	if (regulator->dev)
 		sysfs_remove_link(&rdev->dev.kobj, regulator->supply_name);
+	mutex_lock(&rdev->mutex);
 	kfree(regulator->supply_name);
 	list_del(&regulator->list);
 	kfree(regulator);

 	rdev->open_count--;
 	rdev->exclusive = 0;
+	mutex_unlock(&rdev->mutex);

 	module_put(rdev->owner);
 }
--
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Re: [PATCH v2] regulator: core: fix race condition in regulator_put()

[Mark Brown]

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On Thu, Jan 08, 2015 at 06:54:25PM +0530, Ashay Jaiswal wrote:
> The regulator framework maintains a list of consumer regulators
> for a regulator device and protects it from concurrent access using
> the regulator device's mutex lock.

Applied, thanks but...

> +	mutex_lock(&rdev->mutex);
>  	kfree(regulator->supply_name);
>  	list_del(&regulator->list);
>  	kfree(regulator);
> 
>  	rdev->open_count--;
>  	rdev->exclusive = 0;
> +	mutex_unlock(&rdev->mutex);

I'll do a followup which moves the frees out of the locked region
(reordering things a bit) - they're the main bit I was worried about
with time, they should be fast since they're just frees but it's easy
enough to avoid having to think about it.

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