[BRIDGE]: prevent bad forwarding table updates

Avoid poisoning of the bridge forwarding table by frames that have been
dropped by filtering. This prevents spoofed source addresses on hostile
side of bridge from causing packet leakage, a small but possible security
risk.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_input.c

@@ -54,6 +54,9 @@ int br_handle_frame_finish(struct sk_buff *skb)
 	struct net_bridge_fdb_entry *dst;
 	int passedup = 0;
 
+	/* insert into forwarding database after filtering to avoid spoofing */
+	br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
+
 	if (br->dev->flags & IFF_PROMISC) {
 		struct sk_buff *skb2;
 
@@ -108,8 +111,7 @@ int br_handle_frame(struct net_bridge_port *p, struct sk_buff **pskb)
 	if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
 		goto err;
 
-	if (p->state == BR_STATE_LEARNING ||
-	    p->state == BR_STATE_FORWARDING)
+	if (p->state == BR_STATE_LEARNING)
 		br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
 
 	if (p->br->stp_enabled &&

net/bridge/br_stp_bpdu.c

@@ -140,6 +140,9 @@ int br_stp_handle_bpdu(struct sk_buff *skb)
 	struct net_bridge *br = p->br;
 	unsigned char *buf;
 
+	/* insert into forwarding database after filtering to avoid spoofing */
+	br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
+
 	/* need at least the 802 and STP headers */
 	if (!pskb_may_pull(skb, sizeof(header)+1) ||
 	    memcmp(skb->data, header, sizeof(header)))