wifi: mac80211: lock wiphy in IP address notifier

Lock the wiphy in the IP address notifier as another
place that should have it locked before calling into
the driver. This needs a bit of attention since the
notifier can be called while the wiphy is already
locked, when we remove an interface. Handle this by
not running the notifier in this case, and instead
calling out to the driver directly.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

@@ -2284,6 +2284,20 @@ void ieee80211_remove_interfaces(struct ieee80211_local *local)
 	list_for_each_entry_safe(sdata, tmp, &unreg_list, list) {
 		bool netdev = sdata->dev;
 
+		/*
+		 * Remove IP addresses explicitly, since the notifier will
+		 * skip the callbacks if wdev->registered is false, since
+		 * we can't acquire the wiphy_lock() again there if already
+		 * inside this locked section.
+		 */
+		sdata_lock(sdata);
+		sdata->vif.cfg.arp_addr_cnt = 0;
+		if (sdata->vif.type == NL80211_IFTYPE_STATION &&
+		    sdata->u.mgd.associated)
+			ieee80211_vif_cfg_change_notify(sdata,
+							BSS_CHANGED_ARP_FILTER);
+		sdata_unlock(sdata);
+
 		list_del(&sdata->list);
 		cfg80211_unregister_wdev(&sdata->wdev);
 

net/mac80211/main.c

@@ -437,7 +437,7 @@ static int ieee80211_ifa_changed(struct notifier_block *nb,
 	if (!wdev)
 		return NOTIFY_DONE;
 
-	if (wdev->wiphy != local->hw.wiphy)
+	if (wdev->wiphy != local->hw.wiphy || !wdev->registered)
 		return NOTIFY_DONE;
 
 	sdata = IEEE80211_DEV_TO_SUB_IF(ndev);
@@ -452,6 +452,25 @@ static int ieee80211_ifa_changed(struct notifier_block *nb,
 		return NOTIFY_DONE;
 
 	ifmgd = &sdata->u.mgd;
+
+	/*
+	 * The nested here is needed to convince lockdep that this is
+	 * all OK. Yes, we lock the wiphy mutex here while we already
+	 * hold the notifier rwsem, that's the normal case. And yes,
+	 * we also acquire the notifier rwsem again when unregistering
+	 * a netdev while we already hold the wiphy mutex, so it does
+	 * look like a typical ABBA deadlock.
+	 *
+	 * However, both of these things happen with the RTNL held
+	 * already. Therefore, they can't actually happen, since the
+	 * lock orders really are ABC and ACB, which is fine due to
+	 * the RTNL (A).
+	 *
+	 * We still need to prevent recursion, which is accomplished
+	 * by the !wdev->registered check above.
+	 */
+	mutex_lock_nested(&local->hw.wiphy->mtx, 1);
+	__acquire(&local->hw.wiphy->mtx);
 	sdata_lock(sdata);
 
 	/* Copy the addresses to the vif config list */
@@ -470,6 +489,7 @@ static int ieee80211_ifa_changed(struct notifier_block *nb,
 		ieee80211_vif_cfg_change_notify(sdata, BSS_CHANGED_ARP_FILTER);
 
 	sdata_unlock(sdata);
+	wiphy_unlock(local->hw.wiphy);
 
 	return NOTIFY_OK;
 }