batman-adv: Fix debugfs path for renamed softif

batman-adv is creating special debugfs directories in the init
net_namespace for each created soft-interface (batadv net_device). But it
is possible to rename a net_device to a completely different name then the
original one.

It can therefore happen that a user registers a new batadv net_device with
the name "bat0". batman-adv is then also adding a new directory under
$debugfs/batman-adv/ with the name "wlan0".

The user then decides to rename this device to "bat1" and registers a
different batadv device with the name "bat0". batman-adv will then try to
create a directory with the name "bat0" under $debugfs/batman-adv/ again.
But there already exists one with this name under this path and thus this
fails. batman-adv will detect a problem and rollback the registering of
this device.

batman-adv must therefore take care of renaming the debugfs directories for
soft-interfaces whenever it detects such a net_device rename.

Fixes: c6c8fea2 ("net: Add batman-adv meshing protocol")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/debugfs.c

@@ -433,6 +433,26 @@ int batadv_debugfs_add_meshif(struct net_device *dev)
 	return -ENOMEM;
 }
 
+/**
+ * batadv_debugfs_rename_meshif() - Fix debugfs path for renamed softif
+ * @dev: net_device which was renamed
+ */
+void batadv_debugfs_rename_meshif(struct net_device *dev)
+{
+	struct batadv_priv *bat_priv = netdev_priv(dev);
+	const char *name = dev->name;
+	struct dentry *dir;
+	struct dentry *d;
+
+	dir = bat_priv->debug_dir;
+	if (!dir)
+		return;
+
+	d = debugfs_rename(dir->d_parent, dir, dir->d_parent, name);
+	if (!d)
+		pr_err("Can't rename debugfs dir to %s\n", name);
+}
+
 /**
  * batadv_debugfs_del_meshif() - Remove interface dependent debugfs entries
  * @dev: netdev struct of the soft interface

net/batman-adv/debugfs.h

@@ -30,6 +30,7 @@ struct net_device;
 void batadv_debugfs_init(void);
 void batadv_debugfs_destroy(void);
 int batadv_debugfs_add_meshif(struct net_device *dev);
+void batadv_debugfs_rename_meshif(struct net_device *dev);
 void batadv_debugfs_del_meshif(struct net_device *dev);
 int batadv_debugfs_add_hardif(struct batadv_hard_iface *hard_iface);
 void batadv_debugfs_rename_hardif(struct batadv_hard_iface *hard_iface);
@@ -50,6 +51,10 @@ static inline int batadv_debugfs_add_meshif(struct net_device *dev)
 	return 0;
 }
 
+static inline void batadv_debugfs_rename_meshif(struct net_device *dev)
+{
+}
+
 static inline void batadv_debugfs_del_meshif(struct net_device *dev)
 {
 }

net/batman-adv/hard-interface.c

@@ -989,6 +989,32 @@ void batadv_hardif_remove_interfaces(void)
 	rtnl_unlock();
 }
 
+/**
+ * batadv_hard_if_event_softif() - Handle events for soft interfaces
+ * @event: NETDEV_* event to handle
+ * @net_dev: net_device which generated an event
+ *
+ * Return: NOTIFY_* result
+ */
+static int batadv_hard_if_event_softif(unsigned long event,
+				       struct net_device *net_dev)
+{
+	struct batadv_priv *bat_priv;
+
+	switch (event) {
+	case NETDEV_REGISTER:
+		batadv_sysfs_add_meshif(net_dev);
+		bat_priv = netdev_priv(net_dev);
+		batadv_softif_create_vlan(bat_priv, BATADV_NO_FLAGS);
+		break;
+	case NETDEV_CHANGENAME:
+		batadv_debugfs_rename_meshif(net_dev);
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int batadv_hard_if_event(struct notifier_block *this,
 				unsigned long event, void *ptr)
 {
@@ -997,12 +1023,8 @@ static int batadv_hard_if_event(struct notifier_block *this,
 	struct batadv_hard_iface *primary_if = NULL;
 	struct batadv_priv *bat_priv;
 
-	if (batadv_softif_is_valid(net_dev) && event == NETDEV_REGISTER) {
-		batadv_sysfs_add_meshif(net_dev);
-		bat_priv = netdev_priv(net_dev);
-		batadv_softif_create_vlan(bat_priv, BATADV_NO_FLAGS);
-		return NOTIFY_DONE;
-	}
+	if (batadv_softif_is_valid(net_dev))
+		return batadv_hard_if_event_softif(event, net_dev);
 
 	hard_iface = batadv_hardif_get_by_netdev(net_dev);
 	if (!hard_iface && (event == NETDEV_REGISTER ||