mac80211: allow rx of mesh eapol frames with default rx key

Without this patch, eapol frames cannot be received in mesh
mode, when 802.1X should be used. Initially only a MGTK is
defined, which is found and set as rx->key, when there are
no other keys set. ieee80211_drop_unencrypted would then
drop these eapol frames, as they are data frames without
encryption and there exists some rx->key.

Fix this by differentiating between mesh eapol frames and
other data frames with existing rx->key. Allow mesh mesh
eapol frames only if they are for our vif address.

With this patch in-place, ieee80211_rx_h_mesh_fwding continues
after the ieee80211_drop_unencrypted check and notices, that
these eapol frames have to be delivered locally, as they should.
Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
Link: https://lore.kernel.org/r/20200625104214.50319-1-markus.theil@tu-ilmenau.de
[small code cleanups]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -2396,6 +2396,7 @@ static int ieee80211_802_1x_port_control(struct ieee80211_rx_data *rx)
 
 static int ieee80211_drop_unencrypted(struct ieee80211_rx_data *rx, __le16 fc)
 {
+	struct ieee80211_hdr *hdr = (void *)rx->skb->data;
 	struct sk_buff *skb = rx->skb;
 	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 
@@ -2406,6 +2407,31 @@ static int ieee80211_drop_unencrypted(struct ieee80211_rx_data *rx, __le16 fc)
 	if (status->flag & RX_FLAG_DECRYPTED)
 		return 0;
 
+	/* check mesh EAPOL frames first */
+	if (unlikely(rx->sta && ieee80211_vif_is_mesh(&rx->sdata->vif) &&
+		     ieee80211_is_data(fc))) {
+		struct ieee80211s_hdr *mesh_hdr;
+		u16 hdr_len = ieee80211_hdrlen(fc);
+		u16 ethertype_offset;
+		__be16 ethertype;
+
+		if (!ether_addr_equal(hdr->addr1, rx->sdata->vif.addr))
+			goto drop_check;
+
+		/* make sure fixed part of mesh header is there, also checks skb len */
+		if (!pskb_may_pull(rx->skb, hdr_len + 6))
+			goto drop_check;
+
+		mesh_hdr = (struct ieee80211s_hdr *)(skb->data + hdr_len);
+		ethertype_offset = hdr_len + ieee80211_get_mesh_hdrlen(mesh_hdr) +
+				   sizeof(rfc1042_header);
+
+		if (skb_copy_bits(rx->skb, ethertype_offset, &ethertype, 2) == 0 &&
+		    ethertype == rx->sdata->control_port_protocol)
+			return 0;
+	}
+
+drop_check:
 	/* Drop unencrypted frames if key is set. */
 	if (unlikely(!ieee80211_has_protected(fc) &&
 		     !ieee80211_is_any_nullfunc(fc) &&