batman-adv: Fix debugfs path for renamed hardif

BugLink: https://bugs.launchpad.net/bugs/1868629

commit 36dc621c upstream.

batman-adv is creating special debugfs directories in the init
net_namespace for each valid hard-interface (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 net_device which gets
the name "wlan0" assigned by default. batman-adv is also adding a new
directory under $debugfs/batman-adv/ with the name "wlan0".

The user then decides to rename this device to "wl_pri" and registers a
different device. The kernel may now decide to use the name "wlan0" again
for this new device. batman-adv will detect it as a valid net_device and
tries to create a directory with the name "wlan0" under
$debugfs/batman-adv/. 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 hard-interfaces whenever it detects such a net_device rename.

Fixes: 5bc7c1eb ("batman-adv: add debugfs structure for information per interface")
Reported-by: John Soros <sorosj@gmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/batman-adv/debugfs.c

@@ -19,6 +19,7 @@
 #include "main.h"
 
 #include <linux/compiler.h>
+#include <linux/dcache.h>
 #include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/errno.h>
@@ -506,6 +507,25 @@ int batadv_debugfs_add_hardif(struct batadv_hard_iface *hard_iface)
 	return -ENOMEM;
 }
 
+/**
+ * batadv_debugfs_rename_hardif() - Fix debugfs path for renamed hardif
+ * @hard_iface: hard interface which was renamed
+ */
+void batadv_debugfs_rename_hardif(struct batadv_hard_iface *hard_iface)
+{
+	const char *name = hard_iface->net_dev->name;
+	struct dentry *dir;
+	struct dentry *d;
+
+	dir = hard_iface->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_hardif - delete the base directory for a hard interface
  *  in debugfs.

net/batman-adv/debugfs.h

@@ -33,6 +33,7 @@ void batadv_debugfs_destroy(void);
 int batadv_debugfs_add_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);
 void batadv_debugfs_del_hardif(struct batadv_hard_iface *hard_iface);
 
 #else
@@ -60,6 +61,11 @@ int batadv_debugfs_add_hardif(struct batadv_hard_iface *hard_iface)
 	return 0;
 }
 
+static inline
+void batadv_debugfs_rename_hardif(struct batadv_hard_iface *hard_iface)
+{
+}
+
 static inline
 void batadv_debugfs_del_hardif(struct batadv_hard_iface *hard_iface)
 {

net/batman-adv/hard-interface.c

@@ -780,6 +780,9 @@ static int batadv_hard_if_event(struct notifier_block *this,
 		if (hard_iface == primary_if)
 			batadv_primary_if_update_addr(bat_priv, NULL);
 		break;
+	case NETDEV_CHANGENAME:
+		batadv_debugfs_rename_hardif(hard_iface);
+		break;
 	default:
 		break;
 	}