mac80211: drop non-auth 3-addr data frames when running as a 4-addr station

When running as a 4-addr station against an AP that has the 4-addr VLAN
interface and the main 3-addr AP interface bridged together, sometimes
frames originating from the station were looping back from the 3-addr AP
interface, causing the bridge code to emit warnings about receiving frames
with its own source address.
I'm not sure why this is happening yet, but I think it's a good idea to
drop all frames (except 802.1x/EAP frames) that do not match the configured
addressing mode, including 4-address frames sent to a 3-address station.
User test reports indicate that the problem goes away with this patch.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -1556,17 +1556,36 @@ __ieee80211_data_to_8023(struct ieee80211_rx_data *rx)
 {
 	struct ieee80211_sub_if_data *sdata = rx->sdata;
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
+	bool check_port_control = false;
+	struct ethhdr *ehdr;
+	int ret;
 
 	if (ieee80211_has_a4(hdr->frame_control) &&
 	    sdata->vif.type == NL80211_IFTYPE_AP_VLAN && !sdata->u.vlan.sta)
 		return -1;
 
+	if (sdata->vif.type == NL80211_IFTYPE_STATION &&
+	    !!sdata->u.mgd.use_4addr != !!ieee80211_has_a4(hdr->frame_control)) {
+
+		if (!sdata->u.mgd.use_4addr)
+			return -1;
+		else
+			check_port_control = true;
+	}
+
 	if (is_multicast_ether_addr(hdr->addr1) &&
-	    ((sdata->vif.type == NL80211_IFTYPE_AP_VLAN && sdata->u.vlan.sta) ||
-	     (sdata->vif.type == NL80211_IFTYPE_STATION && sdata->u.mgd.use_4addr)))
+	    sdata->vif.type == NL80211_IFTYPE_AP_VLAN && sdata->u.vlan.sta)
 		return -1;
 
-	return ieee80211_data_to_8023(rx->skb, sdata->vif.addr, sdata->vif.type);
+	ret = ieee80211_data_to_8023(rx->skb, sdata->vif.addr, sdata->vif.type);
+	if (ret < 0 || !check_port_control)
+		return ret;
+
+	ehdr = (struct ethhdr *) rx->skb->data;
+	if (ehdr->h_proto != rx->sdata->control_port_protocol)
+		return -1;
+
+	return 0;
 }
 
 /*