mac80211: Don't memset RXCB prior to PAE intercept

In ieee80211_deliver_skb_to_local_stack intercepts EAPoL frames if
mac80211 is configured to do so and forwards the contents over nl80211.
During this process some additional data is also forwarded, including
whether the frame was received encrypted or not.  Unfortunately just
prior to the call to ieee80211_deliver_skb_to_local_stack, skb->cb is
cleared, resulting in incorrect data being exposed over nl80211.

Fixes: 018f6fbf54 ("mac80211: Send control port frames over nl80211")
Cc: stable@vger.kernel.org
Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Link: https://lore.kernel.org/r/20190827224120.14545-2-denkenz@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -2452,6 +2452,8 @@ static void ieee80211_deliver_skb_to_local_stack(struct sk_buff *skb,
 		cfg80211_rx_control_port(dev, skb, noencrypt);
 		dev_kfree_skb(skb);
 	} else {
+		memset(skb->cb, 0, sizeof(skb->cb));
+
 		/* deliver to local stack */
 		if (rx->napi)
 			napi_gro_receive(rx->napi, skb);
@@ -2546,8 +2548,6 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)
 
 	if (skb) {
 		skb->protocol = eth_type_trans(skb, dev);
-		memset(skb->cb, 0, sizeof(skb->cb));
-
 		ieee80211_deliver_skb_to_local_stack(skb, rx);
 	}