mac80211: fix rx->key NULL dereference during mic failure

Sometimes when reporting a MIC failure rx->key may be unset. This
code path is hit when receiving a packet meant for a multicast
address, and decryption is performed in HW.

Fortunately, the failing key_idx is not used for anything up to
(and including) usermode, so we allow ourselves to drop it on the
way up when a key cannot be retrieved.
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/cfg80211.h

@@ -2688,7 +2688,7 @@ void cfg80211_send_unprot_disassoc(struct net_device *dev, const u8 *buf,
  * @dev: network device
  * @addr: The source MAC address of the frame
  * @key_type: The key type that the received frame used
- * @key_id: Key identifier (0..3)
+ * @key_id: Key identifier (0..3). Can be -1 if missing.
  * @tsc: The TSC value of the frame that generated the MIC failure (6 octets)
  * @gfp: allocation flags
  *

net/mac80211/wpa.c

@@ -154,7 +154,13 @@ ieee80211_rx_h_michael_mic_verify(struct ieee80211_rx_data *rx)
 	return RX_CONTINUE;
 
 mic_fail:
-	mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
+	/*
+	 * In some cases the key can be unset - e.g. a multicast packet, in
+	 * a driver that supports HW encryption. Send up the key idx only if
+	 * the key is set.
+	 */
+	mac80211_ev_michael_mic_failure(rx->sdata,
+					rx->key ? rx->key->conf.keyidx : -1,
 					(void *) skb->data, NULL, GFP_ATOMIC);
 	return RX_DROP_UNUSABLE;
 }

net/wireless/nl80211.c

@@ -6463,6 +6463,7 @@ void nl80211_michael_mic_failure(struct cfg80211_registered_device *rdev,
 	if (addr)
 		NLA_PUT(msg, NL80211_ATTR_MAC, ETH_ALEN, addr);
 	NLA_PUT_U32(msg, NL80211_ATTR_KEY_TYPE, key_type);
+	if (key_id != -1)
 		NLA_PUT_U8(msg, NL80211_ATTR_KEY_IDX, key_id);
 	if (tsc)
 		NLA_PUT(msg, NL80211_ATTR_KEY_SEQ, 6, tsc);