bridge: ignore bogus STP config packets

If the message_age is already greater than the max_age, then the
BPDU is bogus. Linux won't generate BPDU, but conformance tester
or buggy implementation might.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_stp_bpdu.c

@@ -210,6 +210,17 @@ void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
 		bpdu.hello_time = br_get_ticks(buf+28);
 		bpdu.forward_delay = br_get_ticks(buf+30);
 
+		if (bpdu.message_age > bpdu.max_age) {
+			if (net_ratelimit())
+				br_notice(p->br,
+					  "port %u config from %pM"
+					  " (message_age %ul > max_age %ul)\n",
+					  p->port_no,
+					  eth_hdr(skb)->h_source,
+					  bpdu.message_age, bpdu.max_age);
+			goto out;
+		}
+
 		br_received_config_bpdu(p, &bpdu);
 	}