mac80211: fix debugfs default key links

Due to the way the default key links are created,
it happens that a link is left dangling:
 * both unicast/multicast links are created
 * unicast link is destroyed, and the links
   are updated
 * during this update, adding the multicast
   link again fails because it is present,
   destroying the debugfs pointer
 * removing the multicast link won't work as
   the pointer has been destroyed

Fix this by always removing the links and then
re-creating them if needed.
Reported-by: Marek Lindner <lindner_marek@yahoo.de>
Reported-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/debugfs_key.c

@@ -283,6 +283,11 @@ void ieee80211_debugfs_key_update_default(struct ieee80211_sub_if_data *sdata)
 
 	lockdep_assert_held(&sdata->local->key_mtx);
 
+	if (sdata->debugfs.default_unicast_key) {
+		debugfs_remove(sdata->debugfs.default_unicast_key);
+		sdata->debugfs.default_unicast_key = NULL;
+	}
+
 	if (sdata->default_unicast_key) {
 		key = key_mtx_dereference(sdata->local,
 					  sdata->default_unicast_key);
@@ -290,9 +295,11 @@ void ieee80211_debugfs_key_update_default(struct ieee80211_sub_if_data *sdata)
 		sdata->debugfs.default_unicast_key =
 			debugfs_create_symlink("default_unicast_key",
 					       sdata->debugfs.dir, buf);
-	} else {
-		debugfs_remove(sdata->debugfs.default_unicast_key);
-		sdata->debugfs.default_unicast_key = NULL;
+	}
+
+	if (sdata->debugfs.default_multicast_key) {
+		debugfs_remove(sdata->debugfs.default_multicast_key);
+		sdata->debugfs.default_multicast_key = NULL;
 	}
 
 	if (sdata->default_multicast_key) {
@@ -302,9 +309,6 @@ void ieee80211_debugfs_key_update_default(struct ieee80211_sub_if_data *sdata)
 		sdata->debugfs.default_multicast_key =
 			debugfs_create_symlink("default_multicast_key",
 					       sdata->debugfs.dir, buf);
-	} else {
-		debugfs_remove(sdata->debugfs.default_multicast_key);
-		sdata->debugfs.default_multicast_key = NULL;
 	}
 }