[MAC80211]: fix software decryption

When doing key selection for software decryption, mac80211 gets
a few things wrong: it always uses pairwise keys if configured,
even if the frame is addressed to a multicast address. Also, it
doesn't allow using a key index of zero if a pairwise key has
also been found.

This patch changes the key selection code to be (more) in line
with the 802.11 specification. I have confirmed that with this,
multicast frames are correctly decrypted and I've tested with
WEP as well.

While at it, I've cleaned up the semantics of the hardware flags
IEEE80211_HW_WEP_INCLUDE_IV and IEEE80211_HW_DEVICE_HIDES_WEP
and clarified them in the mac80211.h header; it is also now
allowed to set the IEEE80211_HW_DEVICE_HIDES_WEP option even if
it only applies to frames that have been decrypted by the hw,
unencrypted frames must be dropped but encrypted frames that
the hardware couldn't handle can be passed up unmodified.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 70 insertions, 43 deletions

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index b0959c2..08ca066 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -310,52 +310,77 @@ static ieee80211_txrx_result
 ieee80211_rx_h_load_key(struct ieee80211_txrx_data *rx)
 {
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
-	int always_sta_key;
+	int keyidx;
+	int hdrlen;
 
-	if (rx->sdata->type == IEEE80211_IF_TYPE_STA)
-		always_sta_key = 0;
-	else
-		always_sta_key = 1;
+	/*
+	 * Key selection 101
+	 *
+	 * There are three types of keys:
+	 *  - GTK (group keys)
+	 *  - PTK (pairwise keys)
+	 *  - STK (station-to-station pairwise keys)
+	 *
+	 * When selecting a key, we have to distinguish between multicast
+	 * (including broadcast) and unicast frames, the latter can only
+	 * use PTKs and STKs while the former always use GTKs. Unless, of
+	 * course, actual WEP keys ("pre-RSNA") are used, then unicast
+	 * frames can also use key indizes like GTKs. Hence, if we don't
+	 * have a PTK/STK we check the key index for a WEP key.
+	 *
+	 * There is also a slight problem in IBSS mode: GTKs are negotiated
+	 * with each station, that is something we don't currently handle.
+	 */
+
+	if (!(rx->fc & IEEE80211_FCTL_PROTECTED))
+		return TXRX_CONTINUE;
 
-	if (rx->sta && rx->sta->key && always_sta_key) {
+	/*
+	 * No point in finding a key if the frame is neither
+	 * addressed to us nor a multicast frame.
+	 */
+	if (!rx->u.rx.ra_match)
+		return TXRX_CONTINUE;
+
+	if (!is_multicast_ether_addr(hdr->addr1) && rx->sta && rx->sta->key) {
 		rx->key = rx->sta->key;
 	} else {
-		if (rx->sta && rx->sta->key)
-			rx->key = rx->sta->key;
-		else
-			rx->key = rx->sdata->default_key;
+		/*
+		 * The device doesn't give us the IV so we won't be
+		 * able to look up the key. That's ok though, we
+		 * don't need to decrypt the frame, we just won't
+		 * be able to keep statistics accurate.
+		 * Except for key threshold notifications, should
+		 * we somehow allow the driver to tell us which key
+		 * the hardware used if this flag is set?
+		 */
+		if (!(rx->local->hw.flags & IEEE80211_HW_WEP_INCLUDE_IV))
+			return TXRX_CONTINUE;
 
-		if ((rx->local->hw.flags & IEEE80211_HW_WEP_INCLUDE_IV) &&
-		    rx->fc & IEEE80211_FCTL_PROTECTED) {
-			int keyidx = ieee80211_wep_get_keyidx(rx->skb);
+		hdrlen = ieee80211_get_hdrlen(rx->fc);
 
-			if (keyidx >= 0 && keyidx < NUM_DEFAULT_KEYS &&
-			    (!rx->sta || !rx->sta->key || keyidx > 0))
-				rx->key = rx->sdata->keys[keyidx];
+		if (rx->skb->len < 8 + hdrlen)
+			return TXRX_DROP; /* TODO: count this? */
 
-			if (!rx->key) {
-				if (!rx->u.rx.ra_match)
-					return TXRX_DROP;
-				if (net_ratelimit())
-					printk(KERN_DEBUG "%s: RX WEP frame "
-					       "with unknown keyidx %d "
-					       "(A1=" MAC_FMT
-					       " A2=" MAC_FMT
-					       " A3=" MAC_FMT ")\n",
-					       rx->dev->name, keyidx,
-					       MAC_ARG(hdr->addr1),
-					       MAC_ARG(hdr->addr2),
-					       MAC_ARG(hdr->addr3));
-				/*
-				 * TODO: notify userspace about this
-				 * via cfg/nl80211
-				 */
-				return TXRX_DROP;
-			}
-		}
+		/*
+		 * no need to call ieee80211_wep_get_keyidx,
+		 * it verifies a bunch of things we've done already
+		 */
+		keyidx = rx->skb->data[hdrlen + 3] >> 6;
+
+		rx->key = rx->sdata->keys[keyidx];
+
+		/*
+		 * RSNA-protected unicast frames should always be sent with
+		 * pairwise or station-to-station keys, but for WEP we allow
+		 * using a key index as well.
+		 */
+		if (rx->key && rx->key->alg != ALG_WEP &&
+		    !is_multicast_ether_addr(hdr->addr1))
+			rx->key = NULL;
 	}
 
-	if (rx->fc & IEEE80211_FCTL_PROTECTED && rx->key && rx->u.rx.ra_match) {
+	if (rx->key) {
 		rx->key->tx_rx_count++;
 		if (unlikely(rx->local->key_tx_rx_threshold &&
 			     rx->key->tx_rx_count >
@@ -516,10 +541,6 @@ ieee80211_rx_h_wep_weak_iv_detection(struct ieee80211_txrx_data *rx)
 static ieee80211_txrx_result
 ieee80211_rx_h_wep_decrypt(struct ieee80211_txrx_data *rx)
 {
-	/* If the device handles decryption totally, skip this test */
-	if (rx->local->hw.flags & IEEE80211_HW_DEVICE_HIDES_WEP)
-		return TXRX_CONTINUE;
-
 	if ((rx->key && rx->key->alg != ALG_WEP) ||
 	    !(rx->fc & IEEE80211_FCTL_PROTECTED) ||
 	    ((rx->fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA &&
@@ -871,8 +892,14 @@ ieee80211_rx_h_802_1x_pae(struct ieee80211_txrx_data *rx)
 static ieee80211_txrx_result
 ieee80211_rx_h_drop_unencrypted(struct ieee80211_txrx_data *rx)
 {
-	/*  If the device handles decryption totally, skip this test */
-	if (rx->local->hw.flags & IEEE80211_HW_DEVICE_HIDES_WEP)
+	/*
+	 * Pass through unencrypted frames if the hardware might have
+	 * decrypted them already without telling us, but that can only
+	 * be true if we either didn't find a key or the found key is
+	 * uploaded to the hardware.
+	 */
+	if ((rx->local->hw.flags & IEEE80211_HW_DEVICE_HIDES_WEP) &&
+	    (!rx->key || !rx->key->force_sw_encrypt))
 		return TXRX_CONTINUE;
 
 	/* Drop unencrypted frames if key is set. */