[Disco][SRU][PATCH] mac80211: Do not send Layer 2 Update frame before authorization

[Connor Kuehl]

From: Jouni Malinen <jouni at codeaurora.org>

CVE-2019-5108

The Layer 2 Update frame is used to update bridges when a station roams
to another AP even if that STA does not transmit any frames after the
reassociation. This behavior was described in IEEE Std 802.11F-2003 as
something that would happen based on MLME-ASSOCIATE.indication, i.e.,
before completing 4-way handshake. However, this IEEE trial-use
recommended practice document was published before RSN (IEEE Std
802.11i-2004) and as such, did not consider RSN use cases. Furthermore,
IEEE Std 802.11F-2003 was withdrawn in 2006 and as such, has not been
maintained amd should not be used anymore.

Sending out the Layer 2 Update frame immediately after association is
fine for open networks (and also when using SAE, FT protocol, or FILS
authentication when the station is actually authenticated by the time
association completes). However, it is not appropriate for cases where
RSN is used with PSK or EAP authentication since the station is actually
fully authenticated only once the 4-way handshake completes after
authentication and attackers might be able to use the unauthenticated
triggering of Layer 2 Update frame transmission to disrupt bridge
behavior.

Fix this by postponing transmission of the Layer 2 Update frame from
station entry addition to the point when the station entry is marked
authorized. Similarly, send out the VLAN binding update only if the STA
entry has already been authorized.

Signed-off-by: Jouni Malinen <jouni at codeaurora.org>
Reviewed-by: Johannes Berg <johannes at sipsolutions.net>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 3e493173b7841259a08c5c8e5cbe90adb349da7e)
Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>
---
 net/mac80211/cfg.c      | 14 ++++----------
 net/mac80211/sta_info.c |  4 ++++
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 28027952769b..d1a71b3305b9 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1474,7 +1474,6 @@ static int ieee80211_add_station(struct wiphy *wiphy, struct net_device *dev,
 	struct sta_info *sta;
 	struct ieee80211_sub_if_data *sdata;
 	int err;
-	int layer2_update;
 
 	if (params->vlan) {
 		sdata = IEEE80211_DEV_TO_SUB_IF(params->vlan);
@@ -1518,18 +1517,12 @@ static int ieee80211_add_station(struct wiphy *wiphy, struct net_device *dev,
 	    test_sta_flag(sta, WLAN_STA_ASSOC))
 		rate_control_rate_init(sta);
 
-	layer2_update = sdata->vif.type == NL80211_IFTYPE_AP_VLAN ||
-		sdata->vif.type == NL80211_IFTYPE_AP;
-
 	err = sta_info_insert_rcu(sta);
 	if (err) {
 		rcu_read_unlock();
 		return err;
 	}
 
-	if (layer2_update)
-		cfg80211_send_layer2_update(sta->sdata->dev, sta->sta.addr);
-
 	rcu_read_unlock();
 
 	return 0;
@@ -1627,10 +1620,11 @@ static int ieee80211_change_station(struct wiphy *wiphy,
 		sta->sdata = vlansdata;
 		ieee80211_check_fast_xmit(sta);
 
-		if (test_sta_flag(sta, WLAN_STA_AUTHORIZED))
+		if (test_sta_flag(sta, WLAN_STA_AUTHORIZED)) {
 			ieee80211_vif_inc_num_mcast(sta->sdata);
-
-		cfg80211_send_layer2_update(sta->sdata->dev, sta->sta.addr);
+			cfg80211_send_layer2_update(sta->sdata->dev,
+						    sta->sta.addr);
+		}
 	}
 
 	err = sta_apply_parameters(local, sta, params);
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 463abfbbcccf..9ed035720b5d 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -1911,6 +1911,10 @@ int sta_info_move_state(struct sta_info *sta,
 			ieee80211_check_fast_xmit(sta);
 			ieee80211_check_fast_rx(sta);
 		}
+		if (sta->sdata->vif.type == NL80211_IFTYPE_AP_VLAN ||
+		    sta->sdata->vif.type == NL80211_IFTYPE_AP)
+			cfg80211_send_layer2_update(sta->sdata->dev,
+						    sta->sta.addr);
 		break;
 	default:
 		break;
-- 
2.20.1