pppoe: Lacks DST MAC address check

A pppoe session is identified by its session ID and MAC address.
Currently pppoe does not check if the received pkg has the correct
MAC address. This is a problem when the eth I/F is in promisc mode
as then any DST MAC address is accepted.
Signed-off-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp/pppoe.c

@@ -380,6 +380,9 @@ static int pppoe_rcv_core(struct sock *sk, struct sk_buff *skb)
 	 * can't change.
 	 */
 
+	if (skb->pkt_type == PACKET_OTHERHOST)
+		goto abort_kfree;
+
 	if (sk->sk_state & PPPOX_BOUND) {
 		ppp_input(&po->chan, skb);
 	} else if (sk->sk_state & PPPOX_RELAY) {