mac80211: 802.11w - Add BIP (AES-128-CMAC)

Implement Broadcast/Multicast Integrity Protocol for management frame
protection. This patch adds the needed definitions for the new
information element (MMIE) and implementation for the new "encryption"
type (though, BIP is actually not encrypting data, it provides only
integrity protection). These routines will be used by a follow-on patch
that enables BIP for multicast/broadcast robust management frames.

Signed-off-by: Jouni Malinen <j@w1.fi>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 125 insertions, 0 deletions

diff --git a/net/mac80211/wpa.c b/net/mac80211/wpa.c
index aff46ad..53e11e6 100644
--- a/net/mac80211/wpa.c
+++ b/net/mac80211/wpa.c
@@ -1,5 +1,6 @@
 /*
  * Copyright 2002-2004, Instant802 Networks, Inc.
+ * Copyright 2008, Jouni Malinen <j@w1.fi>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -19,6 +20,7 @@
 #include "michael.h"
 #include "tkip.h"
 #include "aes_ccm.h"
+#include "aes_cmac.h"
 #include "wpa.h"
 
 ieee80211_tx_result
@@ -491,3 +493,126 @@ ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
 
 	return RX_CONTINUE;
 }
+
+
+static void bip_aad(struct sk_buff *skb, u8 *aad)
+{
+	/* BIP AAD: FC(masked) || A1 || A2 || A3 */
+
+	/* FC type/subtype */
+	aad[0] = skb->data[0];
+	/* Mask FC Retry, PwrMgt, MoreData flags to zero */
+	aad[1] = skb->data[1] & ~(BIT(4) | BIT(5) | BIT(6));
+	/* A1 || A2 || A3 */
+	memcpy(aad + 2, skb->data + 4, 3 * ETH_ALEN);
+}
+
+
+static inline void bip_ipn_swap(u8 *d, const u8 *s)
+{
+	*d++ = s[5];
+	*d++ = s[4];
+	*d++ = s[3];
+	*d++ = s[2];
+	*d++ = s[1];
+	*d = s[0];
+}
+
+
+ieee80211_tx_result
+ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
+{
+	struct sk_buff *skb = tx->skb;
+	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	struct ieee80211_key *key = tx->key;
+	struct ieee80211_mmie *mmie;
+	u8 *pn, aad[20];
+	int i;
+
+	if (tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE) {
+		/* hwaccel */
+		info->control.hw_key = &tx->key->conf;
+		return 0;
+	}
+
+	if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
+		return TX_DROP;
+
+	mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
+	mmie->element_id = WLAN_EID_MMIE;
+	mmie->length = sizeof(*mmie) - 2;
+	mmie->key_id = cpu_to_le16(key->conf.keyidx);
+
+	/* PN = PN + 1 */
+	pn = key->u.aes_cmac.tx_pn;
+
+	for (i = sizeof(key->u.aes_cmac.tx_pn) - 1; i >= 0; i--) {
+		pn[i]++;
+		if (pn[i])
+			break;
+	}
+	bip_ipn_swap(mmie->sequence_number, pn);
+
+	bip_aad(skb, aad);
+
+	/*
+	 * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
+	 */
+	ieee80211_aes_cmac(key->u.aes_cmac.tfm, key->u.aes_cmac.tx_crypto_buf,
+			   aad, skb->data + 24, skb->len - 24, mmie->mic);
+
+	return TX_CONTINUE;
+}
+
+
+ieee80211_rx_result
+ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
+{
+	struct sk_buff *skb = rx->skb;
+	struct ieee80211_key *key = rx->key;
+	struct ieee80211_mmie *mmie;
+	u8 aad[20], mic[8], ipn[6];
+	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+
+	if (!ieee80211_is_mgmt(hdr->frame_control))
+		return RX_CONTINUE;
+
+	if ((rx->status->flag & RX_FLAG_DECRYPTED) &&
+	    (rx->status->flag & RX_FLAG_IV_STRIPPED))
+		return RX_CONTINUE;
+
+	if (skb->len < 24 + sizeof(*mmie))
+		return RX_DROP_UNUSABLE;
+
+	mmie = (struct ieee80211_mmie *)
+		(skb->data + skb->len - sizeof(*mmie));
+	if (mmie->element_id != WLAN_EID_MMIE ||
+	    mmie->length != sizeof(*mmie) - 2)
+		return RX_DROP_UNUSABLE; /* Invalid MMIE */
+
+	bip_ipn_swap(ipn, mmie->sequence_number);
+
+	if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
+		key->u.aes_cmac.replays++;
+		return RX_DROP_UNUSABLE;
+	}
+
+	if (!(rx->status->flag & RX_FLAG_DECRYPTED)) {
+		/* hardware didn't decrypt/verify MIC */
+		bip_aad(skb, aad);
+		ieee80211_aes_cmac(key->u.aes_cmac.tfm,
+				   key->u.aes_cmac.rx_crypto_buf, aad,
+				   skb->data + 24, skb->len - 24, mic);
+		if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
+			key->u.aes_cmac.icverrors++;
+			return RX_DROP_UNUSABLE;
+		}
+	}
+
+	memcpy(key->u.aes_cmac.rx_pn, ipn, 6);
+
+	/* Remove MMIE */
+	skb_trim(skb, skb->len - sizeof(*mmie));
+
+	return RX_CONTINUE;
+}