Subject: [PATCH] bridge: add knob for filtering rx/tx BPDU packets on a port
From: Felix Fietkau <[email-masked]>
Date: Fri, 27 Aug 2021 12:22:32 +0200

Some devices (e.g. wireless APs) can't have devices behind them be part of
a bridge topology with redundant links, due to address limitations.
Additionally, broadcast traffic on these devices is somewhat expensive, due to
the low data rate and wakeups of clients in powersave mode.
This knob can be used to ensure that BPDU packets are never sent or forwarded
to/from these devices

Signed-off-by: Felix Fietkau <[email-masked]>
---

--- a/include/linux/if_bridge.h
+++ b/include/linux/if_bridge.h
@@ -56,6 +56,7 @@ struct br_ip_list {
 #define BR_MRP_AWARE		BIT(17)
 #define BR_MRP_LOST_CONT	BIT(18)
 #define BR_MRP_LOST_IN_CONT	BIT(19)
+#define BR_BPDU_FILTER		BIT(20)
 
 #define BR_DEFAULT_AGEING_TIME	(300 * HZ)
 
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -191,6 +191,7 @@ out:
 void br_flood(struct net_bridge *br, struct sk_buff *skb,
 	      enum br_pkt_type pkt_type, bool local_rcv, bool local_orig)
 {
+	const unsigned char *dest = eth_hdr(skb)->h_dest;
 	struct net_bridge_port *prev = NULL;
 	struct net_bridge_port *p;
 
@@ -206,6 +207,10 @@ void br_flood(struct net_bridge *br, str
 		case BR_PKT_MULTICAST:
 			if (!(p->flags & BR_MCAST_FLOOD) && skb->dev != br->dev)
 				continue;
+			if ((p->flags & BR_BPDU_FILTER) &&
+			    unlikely(is_link_local_ether_addr(dest) &&
+				     dest[5] == 0))
+				continue;
 			break;
 		case BR_PKT_BROADCAST:
 			if (!(p->flags & BR_BCAST_FLOOD) && skb->dev != br->dev)
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -312,6 +312,8 @@ static rx_handler_result_t br_handle_fra
 		fwd_mask |= p->group_fwd_mask;
 		switch (dest[5]) {
 		case 0x00:	/* Bridge Group Address */
+			if (p->flags & BR_BPDU_FILTER)
+				goto drop;
 			/* If STP is turned off,
 			   then must forward to keep loop detection */
 			if (p->br->stp_enabled == BR_NO_STP ||
--- a/net/bridge/br_sysfs_if.c
+++ b/net/bridge/br_sysfs_if.c
@@ -233,6 +233,7 @@ BRPORT_ATTR_FLAG(multicast_flood, BR_MCA
 BRPORT_ATTR_FLAG(broadcast_flood, BR_BCAST_FLOOD);
 BRPORT_ATTR_FLAG(neigh_suppress, BR_NEIGH_SUPPRESS);
 BRPORT_ATTR_FLAG(isolated, BR_ISOLATED);
+BRPORT_ATTR_FLAG(bpdu_filter, BR_BPDU_FILTER);
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 static ssize_t show_multicast_router(struct net_bridge_port *p, char *buf)
@@ -285,6 +286,7 @@ static const struct brport_attribute *br
 	&brport_attr_group_fwd_mask,
 	&brport_attr_neigh_suppress,
 	&brport_attr_isolated,
+	&brport_attr_bpdu_filter,
 	&brport_attr_backup_port,
 	NULL
 };
--- a/net/bridge/br_stp_bpdu.c
+++ b/net/bridge/br_stp_bpdu.c
@@ -80,7 +80,8 @@ void br_send_config_bpdu(struct net_brid
 {
 	unsigned char buf[35];
 
-	if (p->br->stp_enabled != BR_KERNEL_STP)
+	if (p->br->stp_enabled != BR_KERNEL_STP ||
+	    (p->flags & BR_BPDU_FILTER))
 		return;
 
 	buf[0] = 0;
@@ -127,7 +128,8 @@ void br_send_tcn_bpdu(struct net_bridge_
 {
 	unsigned char buf[4];
 
-	if (p->br->stp_enabled != BR_KERNEL_STP)
+	if (p->br->stp_enabled != BR_KERNEL_STP ||
+	    (p->flags & BR_BPDU_FILTER))
 		return;
 
 	buf[0] = 0;
@@ -172,6 +174,9 @@ void br_stp_rcv(const struct stp_proto *
 	if (!(br->dev->flags & IFF_UP))
 		goto out;
 
+	if (p->flags & BR_BPDU_FILTER)
+		goto out;
+
 	if (p->state == BR_STATE_DISABLED)
 		goto out;
 
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -524,6 +524,7 @@ enum {
 	IFLA_BRPORT_BACKUP_PORT,
 	IFLA_BRPORT_MRP_RING_OPEN,
 	IFLA_BRPORT_MRP_IN_OPEN,
+	IFLA_BRPORT_BPDU_FILTER,
 	__IFLA_BRPORT_MAX
 };
 #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -137,6 +137,7 @@ static inline size_t br_port_info_size(v
 		+ nla_total_size(1)	/* IFLA_BRPORT_VLAN_TUNNEL */
 		+ nla_total_size(1)	/* IFLA_BRPORT_NEIGH_SUPPRESS */
 		+ nla_total_size(1)	/* IFLA_BRPORT_ISOLATED */
+		+ nla_total_size(1)	/* IFLA_BRPORT_BPDU_FILTER */
 		+ nla_total_size(sizeof(struct ifla_bridge_id))	/* IFLA_BRPORT_ROOT_ID */
 		+ nla_total_size(sizeof(struct ifla_bridge_id))	/* IFLA_BRPORT_BRIDGE_ID */
 		+ nla_total_size(sizeof(u16))	/* IFLA_BRPORT_DESIGNATED_PORT */
@@ -220,7 +221,8 @@ static int br_port_fill_attrs(struct sk_
 							  BR_MRP_LOST_CONT)) ||
 	    nla_put_u8(skb, IFLA_BRPORT_MRP_IN_OPEN,
 		       !!(p->flags & BR_MRP_LOST_IN_CONT)) ||
-	    nla_put_u8(skb, IFLA_BRPORT_ISOLATED, !!(p->flags & BR_ISOLATED)))
+	    nla_put_u8(skb, IFLA_BRPORT_ISOLATED, !!(p->flags & BR_ISOLATED)) ||
+	    nla_put_u8(skb, IFLA_BRPORT_BPDU_FILTER, !!(p->flags & BR_BPDU_FILTER)))
 		return -EMSGSIZE;
 
 	timerval = br_timer_value(&p->message_age_timer);
@@ -728,6 +730,7 @@ static const struct nla_policy br_port_p
 	[IFLA_BRPORT_NEIGH_SUPPRESS] = { .type = NLA_U8 },
 	[IFLA_BRPORT_ISOLATED]	= { .type = NLA_U8 },
 	[IFLA_BRPORT_BACKUP_PORT] = { .type = NLA_U32 },
+	[IFLA_BRPORT_BPDU_FILTER] = { .type = NLA_U8 },
 };
 
 /* Change the state of the port and notify spanning tree */
@@ -826,6 +829,10 @@ static int br_setport(struct net_bridge_
 	if (err)
 		return err;
 
+	err = br_set_port_flag(p, tb, IFLA_BRPORT_BPDU_FILTER, BR_BPDU_FILTER);
+	if (err)
+		return err;
+
 	br_vlan_tunnel_old = (p->flags & BR_VLAN_TUNNEL) ? true : false;
 	err = br_set_port_flag(p, tb, IFLA_BRPORT_VLAN_TUNNEL, BR_VLAN_TUNNEL);
 	if (err)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -55,7 +55,7 @@
 #include <net/net_namespace.h>
 
 #define RTNL_MAX_TYPE		50
-#define RTNL_SLAVE_MAX_TYPE	36
+#define RTNL_SLAVE_MAX_TYPE	37
 
 struct rtnl_link {
 	rtnl_doit_func		doit;
@@ -4717,7 +4717,9 @@ int ndo_dflt_bridge_getlink(struct sk_bu
 	    brport_nla_put_flag(skb, flags, mask,
 				IFLA_BRPORT_MCAST_FLOOD, BR_MCAST_FLOOD) ||
 	    brport_nla_put_flag(skb, flags, mask,
-				IFLA_BRPORT_BCAST_FLOOD, BR_BCAST_FLOOD)) {
+				IFLA_BRPORT_BCAST_FLOOD, BR_BCAST_FLOOD) ||
+	    brport_nla_put_flag(skb, flags, mask,
+				IFLA_BRPORT_BPDU_FILTER, BR_BPDU_FILTER)) {
 		nla_nest_cancel(skb, protinfo);
 		goto nla_put_failure;
 	}