bridge: implement BPDU blocking

This is Linux bridge implementation of STP protection
(Cisco BPDU guard/Juniper BPDU block). BPDU block disables
the bridge port if a STP BPDU packet is received.

Why would you want to do this?
If running Spanning Tree on bridge, hostile devices on the network
may send BPDU and cause network failure. Enabling bpdu block
will detect and stop this.

How to recover the port?
The port will be restarted if link is brought down, or
removed and reattached.  For example:
 # ip li set dev eth0 down; ip li set dev eth0 up
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/if_link.h

@@ -216,6 +216,7 @@ enum {
 	IFLA_BRPORT_PRIORITY,	/* "             priority  */
 	IFLA_BRPORT_COST,	/* "             cost      */
 	IFLA_BRPORT_MODE,	/* mode (hairpin)          */
+	IFLA_BRPORT_GUARD,	/* bpdu guard              */
 	__IFLA_BRPORT_MAX
 };
 #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)

net/bridge/br_netlink.c

@@ -26,6 +26,7 @@ static inline size_t br_port_info_size(void)
 		+ nla_total_size(2)	/* IFLA_BRPORT_PRIORITY */
 		+ nla_total_size(4)	/* IFLA_BRPORT_COST */
 		+ nla_total_size(1)	/* IFLA_BRPORT_MODE */
+		+ nla_total_size(1)	/* IFLA_BRPORT_GUARD */
 		+ 0;
 }
 
@@ -49,7 +50,8 @@ static int br_port_fill_attrs(struct sk_buff *skb,
 	if (nla_put_u8(skb, IFLA_BRPORT_STATE, p->state) ||
 	    nla_put_u16(skb, IFLA_BRPORT_PRIORITY, p->priority) ||
 	    nla_put_u32(skb, IFLA_BRPORT_COST, p->path_cost) ||
-	    nla_put_u8(skb, IFLA_BRPORT_MODE, mode))
+	    nla_put_u8(skb, IFLA_BRPORT_MODE, mode) ||
+	    nla_put_u8(skb, IFLA_BRPORT_GUARD, !!(p->flags & BR_BPDU_GUARD)))
 		return -EMSGSIZE;
 
 	return 0;
@@ -162,6 +164,7 @@ static const struct nla_policy ifla_brport_policy[IFLA_BRPORT_MAX + 1] = {
 	[IFLA_BRPORT_COST]	= { .type = NLA_U32 },
 	[IFLA_BRPORT_PRIORITY]	= { .type = NLA_U16 },
 	[IFLA_BRPORT_MODE]	= { .type = NLA_U8 },
+	[IFLA_BRPORT_GUARD]	= { .type = NLA_U8 },
 };
 
 /* Change the state of the port and notify spanning tree */
@@ -203,6 +206,7 @@ static int br_setport(struct net_bridge_port *p, struct nlattr *tb[])
 	int err;
 
 	br_set_port_flag(p, tb, IFLA_BRPORT_MODE, BR_HAIRPIN_MODE);
+	br_set_port_flag(p, tb, IFLA_BRPORT_GUARD, BR_BPDU_GUARD);
 
 	if (tb[IFLA_BRPORT_COST]) {
 		err = br_stp_set_path_cost(p, nla_get_u32(tb[IFLA_BRPORT_COST]));

net/bridge/br_private.h

@@ -135,6 +135,7 @@ struct net_bridge_port
 
 	unsigned long 			flags;
 #define BR_HAIRPIN_MODE		0x00000001
+#define BR_BPDU_GUARD           0x00000002
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	u32				multicast_startup_queries_sent;

net/bridge/br_stp_bpdu.c

@@ -170,6 +170,13 @@ void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
 	if (!ether_addr_equal(dest, br->group_addr))
 		goto out;
 
+	if (p->flags & BR_BPDU_GUARD) {
+		br_notice(br, "BPDU received on blocked port %u(%s)\n",
+			  (unsigned int) p->port_no, p->dev->name);
+		br_stp_disable_port(p);
+		goto out;
+	}
+
 	buf = skb_pull(skb, 3);
 
 	if (buf[0] == BPDU_TYPE_CONFIG) {

net/bridge/br_sysfs_if.c

@@ -156,6 +156,7 @@ static int store_flush(struct net_bridge_port *p, unsigned long v)
 static BRPORT_ATTR(flush, S_IWUSR, NULL, store_flush);
 
 BRPORT_ATTR_FLAG(hairpin_mode, BR_HAIRPIN_MODE);
+BRPORT_ATTR_FLAG(bpdu_guard, BR_BPDU_GUARD);
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 static ssize_t show_multicast_router(struct net_bridge_port *p, char *buf)
@@ -189,6 +190,7 @@ static const struct brport_attribute *brport_attrs[] = {
 	&brport_attr_hold_timer,
 	&brport_attr_flush,
 	&brport_attr_hairpin_mode,
+	&brport_attr_bpdu_guard,
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	&brport_attr_multicast_router,
 #endif