linux-kernel - [PATCH] software node: Handle software node injection to an existing device properly

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Message-Id: <20210623131421.15159-1-heikki.krogerus@linux.intel.com>
Date:   Wed, 23 Jun 2021 16:14:21 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [PATCH] software node: Handle software node injection to an existing device properly

The function software_node_notify() - the function that creates
and removes the symlinks between the node and the device - was
called unconditionally in device_add_software_node() and
device_remove_software_node(), but it needs to be called in
those functions only in the special case where the node is
added to a device that has already been registered.

This fixes NULL pointer dereference that happens if
device_remove_software_node() is used with device that was
never registered.

Fixes: b622b24519f5 ("software node: Allow node addition to already existing device")
Reported-and-tested-by: Dominik Brodowski <linux@...inikbrodowski.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
---
 drivers/base/swnode.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index 3cc11b813f28c..d1f1a82401207 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -1045,7 +1045,15 @@ int device_add_software_node(struct device *dev, const struct software_node *nod
 	}
 
 	set_secondary_fwnode(dev, &swnode->fwnode);
-	software_node_notify(dev, KOBJ_ADD);
+
+	/*
+	 * If the device has been fully registered by the time this function is
+	 * called, software_node_notify() must be called separately so that the
+	 * symlinks get created and the reference count of the node is kept in
+	 * balance.
+	 */
+	if (device_is_registered(dev))
+		software_node_notify(dev, KOBJ_ADD);
 
 	return 0;
 }
@@ -1065,7 +1073,8 @@ void device_remove_software_node(struct device *dev)
 	if (!swnode)
 		return;
 
-	software_node_notify(dev, KOBJ_REMOVE);
+	if (device_is_registered(dev))
+		software_node_notify(dev, KOBJ_REMOVE);
 	set_secondary_fwnode(dev, NULL);
 	kobject_put(&swnode->kobj);
 }
@@ -1119,8 +1128,7 @@ int software_node_notify(struct device *dev, unsigned long action)
 
 	switch (action) {
 	case KOBJ_ADD:
-		ret = sysfs_create_link_nowarn(&dev->kobj, &swnode->kobj,
-					       "software_node");
+		ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
 		if (ret)
 			break;
 
-- 
2.30.2