batman-adv: fix duplicate MAC address check

batadv_check_known_mac_addr() is both too lenient and too strict:

- It is called from batadv_hardif_add_interface(), which means that it
  checked interfaces that are not used for batman-adv at all. Move it
  to batadv_hardif_enable_interface(). Also, restrict it to hardifs of
  the same mesh interface; different mesh interfaces should not interact
  at all. The batadv_check_known_mac_addr() argument is changed from
  `struct net_device` to `struct batadv_hard_iface` to achieve this.
- The check only cares about hardifs in BATADV_IF_ACTIVE and
  BATADV_IF_TO_BE_ACTIVATED states, but interfaces in BATADV_IF_INACTIVE
  state should be checked as well, or the following steps will not
  result in a warning then they should:

  - Add two interfaces in down state with different MAC addresses to
    a mesh as hardifs
  - Change the MAC addresses so they conflict
  - Set interfaces to up state

  Now there will be two active hardifs with the same MAC address, but no
  warning. Fix by only ignoring hardifs in BATADV_IF_NOT_IN_USE state.

The RCU lock can be dropped, as we're holding RTNL anyways when the
function is called.

Fixes: c6c8fea ("net: Add batman-adv meshing protocol")
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/hard-interface.c

@@ -506,28 +506,32 @@ batadv_hardif_is_iface_up(const struct batadv_hard_iface *hard_iface)
 	return false;
 }
 
-static void batadv_check_known_mac_addr(const struct net_device *net_dev)
+static void batadv_check_known_mac_addr(const struct batadv_hard_iface *hard_iface)
 {
-	const struct batadv_hard_iface *hard_iface;
+	const struct net_device *mesh_iface = hard_iface->mesh_iface;
+	const struct batadv_hard_iface *tmp_hard_iface;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(hard_iface, &batadv_hardif_list, list) {
-		if (hard_iface->if_status != BATADV_IF_ACTIVE &&
-		    hard_iface->if_status != BATADV_IF_TO_BE_ACTIVATED)
+	if (!mesh_iface)
+		return;
+
+	list_for_each_entry(tmp_hard_iface, &batadv_hardif_list, list) {
+		if (tmp_hard_iface == hard_iface)
+			continue;
+
+		if (tmp_hard_iface->mesh_iface != mesh_iface)
 			continue;
 
-		if (hard_iface->net_dev == net_dev)
+		if (tmp_hard_iface->if_status == BATADV_IF_NOT_IN_USE)
 			continue;
 
-		if (!batadv_compare_eth(hard_iface->net_dev->dev_addr,
-					net_dev->dev_addr))
+		if (!batadv_compare_eth(tmp_hard_iface->net_dev->dev_addr,
+					hard_iface->net_dev->dev_addr))
 			continue;
 
 		pr_warn("The newly added mac address (%pM) already exists on: %s\n",
-			net_dev->dev_addr, hard_iface->net_dev->name);
+			hard_iface->net_dev->dev_addr, tmp_hard_iface->net_dev->name);
 		pr_warn("It is strongly recommended to keep mac addresses unique to avoid problems!\n");
 	}
-	rcu_read_unlock();
 }
 
 /**
@@ -764,6 +768,8 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
 			    hard_iface->net_dev->name, hardif_mtu,
 			    required_mtu);
 
+	batadv_check_known_mac_addr(hard_iface);
+
 	if (batadv_hardif_is_iface_up(hard_iface))
 		batadv_hardif_activate_interface(hard_iface);
 	else
@@ -902,7 +908,6 @@ batadv_hardif_add_interface(struct net_device *net_dev)
 
 	batadv_v_hardif_init(hard_iface);
 
-	batadv_check_known_mac_addr(hard_iface->net_dev);
 	kref_get(&hard_iface->refcount);
 	list_add_tail_rcu(&hard_iface->list, &batadv_hardif_list);
 	batadv_hardif_generation++;
@@ -989,7 +994,7 @@ static int batadv_hard_if_event(struct notifier_block *this,
 		if (hard_iface->if_status == BATADV_IF_NOT_IN_USE)
 			goto hardif_put;
 
-		batadv_check_known_mac_addr(hard_iface->net_dev);
+		batadv_check_known_mac_addr(hard_iface);
 
 		bat_priv = netdev_priv(hard_iface->mesh_iface);
 		bat_priv->algo_ops->iface.update_mac(hard_iface);