Patch "thermal: max77620: fix device-node reference imbalance" has been added to the 4.9-stable tree

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

thermal: max77620: fix device-node reference imbalance

to the 4.9-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:
thermal-max77620-fix-device-node-reference-imbalance.patch
and it can be found in the queue-4.9 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, 6 Jun 2017 17:59:03 +0200
Subject: thermal: max77620: fix device-node reference imbalance

From: Johan Hovold <[email protected]>

commit c592fafbdbb6b1279b76a54722d1465ca77e5bde upstream.

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).

---
 drivers/thermal/max77620_thermal.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

@@ -104,8 +104,6 @@ static int max77620_thermal_probe(struct
 		return -EINVAL;
 	}
 
-	pdev->dev.of_node = pdev->dev.parent->of_node;
-
 	mtherm->dev = &pdev->dev;
 	mtherm->rmap = dev_get_regmap(pdev->dev.parent, NULL);
 	if (!mtherm->rmap) {

@@ -113,6 +111,14 @@ static int max77620_thermal_probe(struct
 		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, &max77620_thermal_ops);
 	if (IS_ERR(mtherm->tz_device)) {

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

queue-4.9/nfc-nfcmrvl-use-nfc-device-for-firmware-download.patch queue-4.9/nfc-nfcmrvl-fix-firmware-management-initialisation.patch queue-4.9/nfc-nfcmrvl-do-not-use-device-managed-resources.patch queue-4.9/thermal-max77620-fix-device-node-reference-imbalance.patch queue-4.9/nfc-nfcmrvl_uart-add-missing-tty-device-sanity-check.patch queue-4.9/nfc-fix-broken-device-allocation.patch