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thermal: max77620: fix device-node reference imbalance

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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: ec4664b3fd ("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>
This commit is contained in:
Johan Hovold 2017-06-06 17:59:03 +02:00 committed by Greg Kroah-Hartman
parent 2bf6986712
commit c592fafbdb
1 changed files with 8 additions and 2 deletions
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10
drivers/thermal/max77620_thermal.c
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@ -104,8 +104,6 @@ static int max77620_thermal_probe(struct platform_device *pdev)
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 platform_device *pdev)
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)) {