Commit c592fafb authored Jun 06, 2017 by Johan Hovold Committed by Greg Kroah-Hartman Jun 13, 2017

thermal: max77620: fix device-node reference imbalance



The thermal child device reuses the parent MFD-device device-tree node
when registering a thermal zone, but did not take a reference to the
node.

This leads to a reference imbalance, and potential use-after-free, when
the node reference is dropped by the platform-bus device destructor
(once for the child and later again for the parent).

Fix this by dropping any reference already held to a device-tree node
and getting a reference to the parent's node which will be balanced on
reprobe or on platform-device release, whichever comes first.

Note that simply clearing the of_node pointer on probe errors and on
driver unbind would not allow the use of device-managed resources as
specifically thermal_zone_of_sensor_unregister() claims that a valid
device-tree node pointer is needed during deregistration (even if it
currently does not seem to use it).

Fixes: ec4664b3 ("thermal: max77620: Add thermal driver for reporting junction temp")
Cc: stable <stable@vger.kernel.org>     # 4.9
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 2bf69867

drivers/thermal/max77620_thermal.c

+8 −2

Original line number	Original line	Diff line number	Diff line
	@@ -104,8 +104,6 @@ static int max77620_thermal_probe(struct platform_device *pdev)
	return -EINVAL;		return -EINVAL;
	}		}

	pdev->dev.of_node = pdev->dev.parent->of_node;

	mtherm->dev = &pdev->dev;		mtherm->dev = &pdev->dev;
	mtherm->rmap = dev_get_regmap(pdev->dev.parent, NULL);		mtherm->rmap = dev_get_regmap(pdev->dev.parent, NULL);
	if (!mtherm->rmap) {		if (!mtherm->rmap) {
	@@ -113,6 +111,14 @@ static int max77620_thermal_probe(struct platform_device *pdev)
	return -ENODEV;		return -ENODEV;
	}		}

			/*
			* Drop any current reference to a device-tree node and get a
			* reference to the parent's node which will be balanced on reprobe or
			* on platform-device release.
			*/
			of_node_put(pdev->dev.of_node);
			pdev->dev.of_node = of_node_get(pdev->dev.parent->of_node);

	mtherm->tz_device = devm_thermal_zone_of_sensor_register(&pdev->dev, 0,		mtherm->tz_device = devm_thermal_zone_of_sensor_register(&pdev->dev, 0,
	mtherm, &max77620_thermal_ops);		mtherm, &max77620_thermal_ops);
	if (IS_ERR(mtherm->tz_device)) {		if (IS_ERR(mtherm->tz_device)) {