[PATCH v2 2/2] mac80211: implement support for 4-address frames for AP and client mode

[Felix Fietkau <nbd@openwrt.org>]

In some situations it might be useful to run a network with an
Access Point and multiple clients, but with each client bridged
to a network behind it. For this to work, both the client and the
AP need to transmit 4-address frames, containing both source and
destination MAC addresses.
With this patch, you can configure a client to communicate using
only 4-address frames for data traffic.
On the AP side you can enable 4-address frames for individual
clients by isolating them in separate AP VLANs which are configured
in 4-address mode.
Such an AP VLAN will be limited to one client only, and this client
will be used as the destination for all traffic on its interface,
regardless of the destination MAC address in the packet headers.
The advantage of this mode compared to regular WDS mode is that it's
easier to configure and does not require a static list of peer MAC
addresses on any side.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
---
v2: 
  - minor coding style cleanups
  - better return code when trying to add a sta to a used 4-addr vlan
  - check interface type before setting 4-addr mode and reset the mode
    on interface type changes

--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -208,6 +208,9 @@ struct ieee80211_if_wds {
 
 struct ieee80211_if_vlan {
 	struct list_head list;
+
+	/* used for all tx if the VLAN is configured to 4-addr mode */
+	struct sta_info *sta;
 };
 
 struct mesh_stats {
@@ -457,6 +460,8 @@ struct ieee80211_sub_if_data {
 	int force_unicast_rateidx; /* forced TX rateidx for unicast frames */
 	int max_ratectrl_rateidx; /* max TX rateidx for rate control */
 
+	bool use_4addr; /* use 4-address frames */
+
 	union {
 		struct ieee80211_if_ap ap;
 		struct ieee80211_if_wds wds;
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -36,6 +36,24 @@ static bool nl80211_type_check(enum nl80
 	}
 }
 
+static bool nl80211_params_check(enum nl80211_iftype type,
+				 struct vif_params *params)
+{
+	if (!nl80211_type_check(type))
+		return false;
+
+	if (params->use_4addr > 0) {
+		switch(type) {
+		case NL80211_IFTYPE_AP_VLAN:
+		case NL80211_IFTYPE_STATION:
+			break;
+		default:
+			return false;
+		}
+	}
+	return true;
+}
+
 static int ieee80211_add_iface(struct wiphy *wiphy, char *name,
 			       enum nl80211_iftype type, u32 *flags,
 			       struct vif_params *params)
@@ -45,7 +63,7 @@ static int ieee80211_add_iface(struct wi
 	struct ieee80211_sub_if_data *sdata;
 	int err;
 
-	if (!nl80211_type_check(type))
+	if (!nl80211_params_check(type, params))
 		return -EINVAL;
 
 	err = ieee80211_if_add(local, name, &dev, type, params);
@@ -75,7 +93,7 @@ static int ieee80211_change_iface(struct
 	if (netif_running(dev))
 		return -EBUSY;
 
-	if (!nl80211_type_check(type))
+	if (!nl80211_params_check(type, params))
 		return -EINVAL;
 
 	sdata = IEEE80211_DEV_TO_SUB_IF(dev);
@@ -89,6 +107,9 @@ static int ieee80211_change_iface(struct
 					    params->mesh_id_len,
 					    params->mesh_id);
 
+	if (params->use_4addr >= 0)
+		sdata->use_4addr = !!params->use_4addr;
+
 	if (sdata->vif.type != NL80211_IFTYPE_MONITOR || !flags)
 		return 0;
 
@@ -806,6 +827,13 @@ static int ieee80211_change_station(stru
 			return -EINVAL;
 		}
 
+		if (vlansdata->use_4addr) {
+			if (vlansdata->u.vlan.sta)
+				return -EBUSY;
+
+			rcu_assign_pointer(vlansdata->u.vlan.sta, sta);
+		}
+
 		sta->sdata = vlansdata;
 		ieee80211_send_layer2_update(sta);
 	}
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -489,6 +489,9 @@ static void __sta_info_unlink(struct sta
 	local->num_sta--;
 	local->sta_generation++;
 
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
+		rcu_assign_pointer(sdata->u.vlan.sta, NULL);
+
 	if (local->ops->sta_notify) {
 		if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
 			sdata = container_of(sdata->bss,
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1046,7 +1046,10 @@ ieee80211_tx_prepare(struct ieee80211_su
 
 	hdr = (struct ieee80211_hdr *) skb->data;
 
-	tx->sta = sta_info_get(local, hdr->addr1);
+	if ((sdata->vif.type == NL80211_IFTYPE_AP_VLAN) && sdata->use_4addr)
+		tx->sta = rcu_dereference(sdata->u.vlan.sta);
+	if (!tx->sta)
+		tx->sta = sta_info_get(local, hdr->addr1);
 
 	if (tx->sta && ieee80211_is_data_qos(hdr->frame_control) &&
 	    (local->hw.flags & IEEE80211_HW_AMPDU_AGGREGATION)) {
@@ -1608,7 +1611,7 @@ netdev_tx_t ieee80211_subif_start_xmit(s
 	const u8 *encaps_data;
 	int encaps_len, skip_header_bytes;
 	int nh_pos, h_pos;
-	struct sta_info *sta;
+	struct sta_info *sta = NULL;
 	u32 sta_flags = 0;
 
 	if (unlikely(skb->len < ETH_HLEN)) {
@@ -1625,8 +1628,25 @@ netdev_tx_t ieee80211_subif_start_xmit(s
 	fc = cpu_to_le16(IEEE80211_FTYPE_DATA | IEEE80211_STYPE_DATA);
 
 	switch (sdata->vif.type) {
-	case NL80211_IFTYPE_AP:
 	case NL80211_IFTYPE_AP_VLAN:
+		rcu_read_lock();
+		if (sdata->use_4addr)
+			sta = rcu_dereference(sdata->u.vlan.sta);
+		if (sta) {
+			fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS | IEEE80211_FCTL_TODS);
+			/* RA TA DA SA */
+			memcpy(hdr.addr1, sta->sta.addr, ETH_ALEN);
+			memcpy(hdr.addr2, dev->dev_addr, ETH_ALEN);
+			memcpy(hdr.addr3, skb->data, ETH_ALEN);
+			memcpy(hdr.addr4, skb->data + ETH_ALEN, ETH_ALEN);
+			hdrlen = 30;
+			sta_flags = get_sta_flags(sta);
+		}
+		rcu_read_unlock();
+		if (sta)
+			break;
+		/* fall through */
+	case NL80211_IFTYPE_AP:
 		fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS);
 		/* DA BSSID SA */
 		memcpy(hdr.addr1, skb->data, ETH_ALEN);
@@ -1700,12 +1720,21 @@ netdev_tx_t ieee80211_subif_start_xmit(s
 		break;
 #endif
 	case NL80211_IFTYPE_STATION:
-		fc |= cpu_to_le16(IEEE80211_FCTL_TODS);
-		/* BSSID SA DA */
 		memcpy(hdr.addr1, sdata->u.mgd.bssid, ETH_ALEN);
-		memcpy(hdr.addr2, skb->data + ETH_ALEN, ETH_ALEN);
-		memcpy(hdr.addr3, skb->data, ETH_ALEN);
-		hdrlen = 24;
+		if (sdata->use_4addr && ethertype != ETH_P_PAE) {
+			fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS | IEEE80211_FCTL_TODS);
+			/* RA TA DA SA */
+			memcpy(hdr.addr2, dev->dev_addr, ETH_ALEN);
+			memcpy(hdr.addr3, skb->data, ETH_ALEN);
+			memcpy(hdr.addr4, skb->data + ETH_ALEN, ETH_ALEN);
+			hdrlen = 30;
+		} else {
+			fc |= cpu_to_le16(IEEE80211_FCTL_TODS);
+			/* BSSID SA DA */
+			memcpy(hdr.addr2, skb->data + ETH_ALEN, ETH_ALEN);
+			memcpy(hdr.addr3, skb->data, ETH_ALEN);
+			hdrlen = 24;
+		}
 		break;
 	case NL80211_IFTYPE_ADHOC:
 		/* DA SA BSSID */
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -772,6 +772,7 @@ int ieee80211_if_change_type(struct ieee
 		ieee80211_mandatory_rates(sdata->local,
 			sdata->local->hw.conf.channel->band);
 	sdata->drop_unencrypted = 0;
+	sdata->use_4addr = 0;
 
 	return 0;
 }
@@ -853,6 +854,9 @@ int ieee80211_if_add(struct ieee80211_lo
 					    params->mesh_id_len,
 					    params->mesh_id);
 
+	if (params && params->use_4addr >= 0)
+		sdata->use_4addr = !!params->use_4addr;
+
 	mutex_lock(&local->iflist_mtx);
 	list_add_tail_rcu(&sdata->list, &local->interfaces);
 	mutex_unlock(&local->iflist_mtx);
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1237,6 +1237,13 @@ __ieee80211_data_to_8023(struct ieee8021
 {
 	struct net_device *dev = rx->dev;
 	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
+	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
+
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN && !sdata->use_4addr &&
+	    ieee80211_has_a4(hdr->frame_control))
+		return -1;
+	if (sdata->use_4addr && is_multicast_ether_addr(hdr->addr1))
+		return -1;
 
 	return ieee80211_data_to_8023(rx->skb, dev->dev_addr, sdata->vif.type);
 }
@@ -1590,6 +1597,7 @@ ieee80211_rx_h_data(struct ieee80211_rx_
 {
 	struct net_device *dev = rx->dev;
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
+	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 	__le16 fc = hdr->frame_control;
 	int err;
 
@@ -1599,6 +1607,14 @@ ieee80211_rx_h_data(struct ieee80211_rx_
 	if (unlikely(!ieee80211_is_data_present(hdr->frame_control)))
 		return RX_DROP_MONITOR;
 
+	/*
+	 * Allow the cooked monitor interface of an AP to see 4-addr frames so
+	 * that a 4-addr station can be detected and moved into a separate VLAN
+	 */
+	if (ieee80211_has_a4(hdr->frame_control) &&
+	    sdata->vif.type == NL80211_IFTYPE_AP)
+		return RX_DROP_MONITOR;
+
 	err = __ieee80211_data_to_8023(rx);
 	if (unlikely(err))
 		return RX_DROP_UNUSABLE;
@@ -2039,7 +2055,7 @@ static int prepare_for_handlers(struct i
 
 	switch (sdata->vif.type) {
 	case NL80211_IFTYPE_STATION:
-		if (!bssid)
+		if (!bssid && !sdata->use_4addr)
 			return 0;
 		if (!multicast &&
 		    compare_ether_addr(sdata->dev->dev_addr, hdr->addr1) != 0) {
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -320,7 +320,9 @@ int ieee80211_data_to_8023(struct sk_buf
 		break;
 	case cpu_to_le16(IEEE80211_FCTL_TODS | IEEE80211_FCTL_FROMDS):
 		if (unlikely(iftype != NL80211_IFTYPE_WDS &&
-			     iftype != NL80211_IFTYPE_MESH_POINT))
+			     iftype != NL80211_IFTYPE_MESH_POINT &&
+			     iftype != NL80211_IFTYPE_AP_VLAN &&
+			     iftype != NL80211_IFTYPE_STATION))
 			return -1;
 		if (iftype == NL80211_IFTYPE_MESH_POINT) {
 			struct ieee80211s_hdr *meshdr =