[PATCH 1/3] mac80211: use nullfunc frames for 4-addr sta detection

[Felix Fietkau <nbd@openwrt.org>]

To detect incoming 4-addr stations, hostapd needs to receive a 4-addr 
data frame from the remote station, so that it can create the AP VLAN 
for it. With this patch, the mlme code emits a 4-addr nullfunc frame 
immediately after assoc. On the AP side it also drops 4-addr nullfunc 
frames to the cooked monitor mode interface, if the interface hasn't 
been fully set up to receive 4-addr data frames yet.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

---
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -312,6 +312,38 @@ void ieee80211_send_nullfunc(struct ieee
 	ieee80211_tx_skb(sdata, skb);
 }
 
+static void ieee80211_send_4addr_nullfunc(struct ieee80211_local *local,
+					  struct ieee80211_sub_if_data *sdata)
+{
+	struct sk_buff *skb;
+	struct ieee80211_hdr *nullfunc;
+	__le16 fc;
+
+	if (WARN_ON(sdata->vif.type != NL80211_IFTYPE_STATION))
+		return;
+
+	skb = dev_alloc_skb(local->hw.extra_tx_headroom + 30);
+	if (!skb) {
+		printk(KERN_DEBUG "%s: failed to allocate buffer for 4addr "
+		       "nullfunc frame\n", sdata->name);
+		return;
+	}
+	skb_reserve(skb, local->hw.extra_tx_headroom);
+
+	nullfunc = (struct ieee80211_hdr *) skb_put(skb, 30);
+	memset(nullfunc, 0, 30);
+	fc = cpu_to_le16(IEEE80211_FTYPE_DATA | IEEE80211_STYPE_NULLFUNC |
+			 IEEE80211_FCTL_FROMDS | IEEE80211_FCTL_TODS);
+	nullfunc->frame_control = fc;
+	memcpy(nullfunc->addr1, sdata->u.mgd.bssid, ETH_ALEN);
+	memcpy(nullfunc->addr2, sdata->vif.addr, ETH_ALEN);
+	memcpy(nullfunc->addr3, sdata->u.mgd.bssid, ETH_ALEN);
+	memcpy(nullfunc->addr4, sdata->vif.addr, ETH_ALEN);
+
+	IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_INTFL_DONT_ENCRYPT;
+	ieee80211_tx_skb(sdata, skb);
+}
+
 /* spectrum management related things */
 static void ieee80211_chswitch_work(struct work_struct *work)
 {
@@ -1120,6 +1152,13 @@ static bool ieee80211_assoc_success(stru
 	ieee80211_set_associated(sdata, cbss, changed);
 
 	/*
+	 * If we're using 4-addr mode, let the AP know that we're
+	 * doing so, so that it can create the STA VLAN on its side
+	 */
+	if (ifmgd->use_4addr)
+		ieee80211_send_4addr_nullfunc(local, sdata);
+
+	/*
 	 * Start timer to probe the connection to the AP now.
 	 * Also start the timer that will detect beacon loss.
 	 */
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1111,6 +1111,18 @@ ieee80211_rx_h_sta_process(struct ieee80
 	if (ieee80211_is_nullfunc(hdr->frame_control) ||
 	    ieee80211_is_qos_nullfunc(hdr->frame_control)) {
 		I802_DEBUG_INC(rx->local->rx_handlers_drop_nullfunc);
+
+		/*
+		 * If we receive a 4-addr nullfunc frame from a STA
+		 * that was not moved to a 4-addr STA vlan yet, drop
+		 * the frame to the monitor interface, to make sure
+		 * that hostapd sees it
+		 */
+		if (ieee80211_has_a4(hdr->frame_control) &&
+		    (rx->sdata->vif.type == NL80211_IFTYPE_AP ||
+		     (rx->sdata->vif.type == NL80211_IFTYPE_AP_VLAN &&
+		      !rx->sdata->u.vlan.sta)))
+			return RX_DROP_MONITOR;
 		/*
 		 * Update counter and free packet here to avoid
 		 * counting this as a dropped packed.