mac80211: drop robust management frames from unknown TA

When receiving a robust management frame, drop it if we don't have
rx->sta since then we don't have a security association and thus
couldn't possibly validate the frame.

Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -3831,6 +3831,8 @@ static bool ieee80211_accept_frame(struct ieee80211_rx_data *rx)
 	case NL80211_IFTYPE_STATION:
 		if (!bssid && !sdata->u.mgd.use_4addr)
 			return false;
+		if (ieee80211_is_robust_mgmt_frame(skb) && !rx->sta)
+			return false;
 		if (multicast)
 			return true;
 		return ether_addr_equal(sdata->vif.addr, hdr->addr1);