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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ppp/pppoe.c

···
 	 * 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) {