mac80211: Encrypt "Group addressed privacy" action frames

Previously, the action frames to group address was not encrypted. But
[1] "Table 8-38 Category values" indicates "Mesh" and "Multihop" category
action frames should be encrypted (Group addressed privacy == yes). And the
encyption key should be MGTK ([1] 10.13 Group addressed robust management frame
procedures). So this patch modifies the code to make it suitable for spec.

[1] IEEE Std 802.11-2012
Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

include/linux/ieee80211.h

@@ -19,6 +19,7 @@
 
 #include <linux/types.h>
 #include <linux/if_ether.h>
+#include <linux/etherdevice.h>
 #include <asm/byteorder.h>
 #include <asm/unaligned.h>
 
@@ -2486,6 +2487,35 @@ static inline bool ieee80211_is_public_action(struct ieee80211_hdr *hdr,
 	return mgmt->u.action.category == WLAN_CATEGORY_PUBLIC;
 }
 
+/**
+ * _ieee80211_is_group_privacy_action - check if frame is a group addressed
+ * privacy action frame
+ * @hdr: the frame
+ */
+static inline bool _ieee80211_is_group_privacy_action(struct ieee80211_hdr *hdr)
+{
+	struct ieee80211_mgmt *mgmt = (void *)hdr;
+
+	if (!ieee80211_is_action(hdr->frame_control) ||
+	    !is_multicast_ether_addr(hdr->addr1))
+		return false;
+
+	return mgmt->u.action.category == WLAN_CATEGORY_MESH_ACTION ||
+	       mgmt->u.action.category == WLAN_CATEGORY_MULTIHOP_ACTION;
+}
+
+/**
+ * ieee80211_is_group_privacy_action - check if frame is a group addressed
+ * privacy action frame
+ * @skb: the skb containing the frame, length will be checked
+ */
+static inline bool ieee80211_is_group_privacy_action(struct sk_buff *skb)
+{
+	if (skb->len < IEEE80211_MIN_ACTION_SIZE)
+		return false;
+	return _ieee80211_is_group_privacy_action((void *)skb->data);
+}
+
 /**
  * ieee80211_tu_to_usec - convert time units (TU) to microseconds
  * @tu: the TUs

net/mac80211/rx.c

@@ -1624,8 +1624,13 @@ ieee80211_rx_h_decrypt(struct ieee80211_rx_data *rx)
 		if (mmie_keyidx < NUM_DEFAULT_KEYS ||
 		    mmie_keyidx >= NUM_DEFAULT_KEYS + NUM_DEFAULT_MGMT_KEYS)
 			return RX_DROP_MONITOR; /* unexpected BIP keyidx */
-		if (rx->sta)
+		if (rx->sta) {
+			if (ieee80211_is_group_privacy_action(skb) &&
+			    test_sta_flag(rx->sta, WLAN_STA_MFP))
+				return RX_DROP_MONITOR;
+
 			rx->key = rcu_dereference(rx->sta->gtk[mmie_keyidx]);
+		}
 		if (!rx->key)
 			rx->key = rcu_dereference(rx->sdata->keys[mmie_keyidx]);
 	} else if (!ieee80211_has_protected(fc)) {

net/mac80211/tx.c

@@ -593,6 +593,9 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 	else if (tx->sta &&
 		 (key = rcu_dereference(tx->sta->ptk[tx->sta->ptk_idx])))
 		tx->key = key;
+	else if (ieee80211_is_group_privacy_action(tx->skb) &&
+		(key = rcu_dereference(tx->sdata->default_multicast_key)))
+		tx->key = key;
 	else if (ieee80211_is_mgmt(hdr->frame_control) &&
 		 is_multicast_ether_addr(hdr->addr1) &&
 		 ieee80211_is_robust_mgmt_frame(tx->skb) &&
@@ -625,7 +628,8 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 		case WLAN_CIPHER_SUITE_GCMP_256:
 			if (!ieee80211_is_data_present(hdr->frame_control) &&
 			    !ieee80211_use_mfp(hdr->frame_control, tx->sta,
-					       tx->skb))
+					       tx->skb) &&
+			    !ieee80211_is_group_privacy_action(tx->skb))
 				tx->key = NULL;
 			else
 				skip_hw = (tx->key->conf.flags &