Staging: batman-adv: Don't use net_dev after dev_put

dev_put allows a device to be freed when all its references are dropped.
After that we are not allowed to access that information anymore. Access
to the data structure of a net_device must be surrounded a dev_hold
and ended using dev_put.

batman-adv adds a device to its own management structure in
hardif_add_interface and will release it in hardif_remove_interface.
Thus it must hold a reference all the time between those functions to
prevent any access to the already released net_device structure.
Reported-by: Tim Glaremin <Tim.Glaremin@web.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/batman-adv/hard-interface.c

@@ -194,8 +194,6 @@ static void hardif_activate_interface(struct net_device *net_dev,
 	if (batman_if->if_status != IF_INACTIVE)
 		return;
 
-	dev_hold(batman_if->net_dev);
-
 	update_mac_addresses(batman_if);
 	batman_if->if_status = IF_TO_BE_ACTIVATED;
 
@@ -222,8 +220,6 @@ static void hardif_deactivate_interface(struct net_device *net_dev,
 	   (batman_if->if_status != IF_TO_BE_ACTIVATED))
 		return;
 
-	dev_put(batman_if->net_dev);
-
 	batman_if->if_status = IF_INACTIVE;
 
 	bat_info(net_dev, "Interface deactivated: %s\n", batman_if->dev);
@@ -318,11 +314,13 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev)
 	if (ret != 1)
 		goto out;
 
+	dev_hold(net_dev);
+
 	batman_if = kmalloc(sizeof(struct batman_if), GFP_ATOMIC);
 	if (!batman_if) {
 		pr_err("Can't add interface (%s): out of memory\n",
 		       net_dev->name);
-		goto out;
+		goto release_dev;
 	}
 
 	batman_if->dev = kstrdup(net_dev->name, GFP_ATOMIC);
@@ -346,6 +344,8 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev)
 	kfree(batman_if->dev);
 free_if:
 	kfree(batman_if);
+release_dev:
+	dev_put(net_dev);
 out:
 	return NULL;
 }
@@ -374,6 +374,7 @@ static void hardif_remove_interface(struct batman_if *batman_if)
 	batman_if->if_status = IF_TO_BE_REMOVED;
 	list_del_rcu(&batman_if->list);
 	sysfs_del_hardif(&batman_if->hardif_obj);
+	dev_put(batman_if->net_dev);
 	call_rcu(&batman_if->rcu, hardif_free_interface);
 }