bridge: Extend Proxy ARP design to allow optional rules for Wi-Fi

This extends the design in commit 958501163ddd ("bridge: Add support for
IEEE 802.11 Proxy ARP") with optional set of rules that are needed to
meet the IEEE 802.11 and Hotspot 2.0 requirements for ProxyARP. The
previously added BR_PROXYARP behavior is left as-is and a new
BR_PROXYARP_WIFI alternative is added so that this behavior can be
configured from user space when required.

In addition, this enables proxyarp functionality for unicast ARP
requests for both BR_PROXYARP and BR_PROXYARP_WIFI since it is possible
to use unicast as well as broadcast for these frames.

The key differences in functionality:

BR_PROXYARP:
- uses the flag on the bridge port on which the request frame was
received to determine whether to reply
- block bridge port flooding completely on ports that enable proxy ARP

BR_PROXYARP_WIFI:
- uses the flag on the bridge port to which the target device of the
request belongs
- block bridge port flooding selectively based on whether the proxyarp
functionality replied

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

include/linux/if_bridge.h

···
 #define BR_PROMISC		BIT(7)
 #define BR_PROXYARP		BIT(8)
 #define BR_LEARNING_SYNC	BIT(9)
+#define BR_PROXYARP_WIFI	BIT(10)
 
 extern void brioctl_set(int (*ioctl_hook)(struct net *, unsigned int, void __user *));
 

include/uapi/linux/if_link.h

···
 	IFLA_BRPORT_UNICAST_FLOOD, /* flood unicast traffic */
 	IFLA_BRPORT_PROXYARP,	/* proxy ARP */
 	IFLA_BRPORT_LEARNING_SYNC, /* mac learning sync from device */
+	IFLA_BRPORT_PROXYARP_WIFI, /* proxy ARP for Wi-Fi */
 	__IFLA_BRPORT_MAX
 };
 #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)

net/bridge/br_forward.c

···
 		/* Do not flood to ports that enable proxy ARP */
 		if (p->flags & BR_PROXYARP)
 			continue;
+		if ((p->flags & BR_PROXYARP_WIFI) &&
+		    BR_INPUT_SKB_CB(skb)->proxyarp_replied)
+			continue;
 
 		prev = maybe_deliver(prev, p, skb, __packet_hook);
 		if (IS_ERR(prev))

net/bridge/br_input.c

···
 }
 
 static void br_do_proxy_arp(struct sk_buff *skb, struct net_bridge *br,
-			    u16 vid)
+			    u16 vid, struct net_bridge_port *p)
 {
 	struct net_device *dev = br->dev;
 	struct neighbour *n;
 	struct arphdr *parp;
 	u8 *arpptr, *sha;
 	__be32 sip, tip;
+
+	BR_INPUT_SKB_CB(skb)->proxyarp_replied = false;
 
 	if (dev->flags & IFF_NOARP)
 		return;
···
 		}
 
 		f = __br_fdb_get(br, n->ha, vid);
-		if (f)
+		if (f && ((p->flags & BR_PROXYARP) ||
+			  (f->dst && (f->dst->flags & BR_PROXYARP_WIFI)))) {
 			arp_send(ARPOP_REPLY, ETH_P_ARP, sip, skb->dev, tip,
 				 sha, n->ha, sha);
+			BR_INPUT_SKB_CB(skb)->proxyarp_replied = true;
+		}
 
 		neigh_release(n);
 	}
···
 
 	dst = NULL;
 
-	if (is_broadcast_ether_addr(dest)) {
-		if (IS_ENABLED(CONFIG_INET) &&
-		    p->flags & BR_PROXYARP &&
-		    skb->protocol == htons(ETH_P_ARP))
-			br_do_proxy_arp(skb, br, vid);
+	if (IS_ENABLED(CONFIG_INET) && skb->protocol == htons(ETH_P_ARP))
+		br_do_proxy_arp(skb, br, vid, p);
 
+	if (is_broadcast_ether_addr(dest)) {
 		skb2 = skb;
 		unicast = false;
 	} else if (is_multicast_ether_addr(dest)) {

net/bridge/br_netlink.c

···
 	    nla_put_u8(skb, IFLA_BRPORT_FAST_LEAVE, !!(p->flags & BR_MULTICAST_FAST_LEAVE)) ||
 	    nla_put_u8(skb, IFLA_BRPORT_LEARNING, !!(p->flags & BR_LEARNING)) ||
 	    nla_put_u8(skb, IFLA_BRPORT_UNICAST_FLOOD, !!(p->flags & BR_FLOOD)) ||
-	    nla_put_u8(skb, IFLA_BRPORT_PROXYARP, !!(p->flags & BR_PROXYARP)))
+	    nla_put_u8(skb, IFLA_BRPORT_PROXYARP, !!(p->flags & BR_PROXYARP)) ||
+	    nla_put_u8(skb, IFLA_BRPORT_PROXYARP_WIFI,
+		       !!(p->flags & BR_PROXYARP_WIFI)))
 		return -EMSGSIZE;
 
 	return 0;
···
 	br_set_port_flag(p, tb, IFLA_BRPORT_LEARNING, BR_LEARNING);
 	br_set_port_flag(p, tb, IFLA_BRPORT_UNICAST_FLOOD, BR_FLOOD);
 	br_set_port_flag(p, tb, IFLA_BRPORT_PROXYARP, BR_PROXYARP);
+	br_set_port_flag(p, tb, IFLA_BRPORT_PROXYARP_WIFI, BR_PROXYARP_WIFI);
 
 	if (tb[IFLA_BRPORT_COST]) {
 		err = br_stp_set_path_cost(p, nla_get_u32(tb[IFLA_BRPORT_COST]));

net/bridge/br_private.h

···
 #endif
 
 	u16 frag_max_size;
+	bool proxyarp_replied;
 
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 	bool vlan_filtered;

net/bridge/br_sysfs_if.c

···
 BRPORT_ATTR_FLAG(learning, BR_LEARNING);
 BRPORT_ATTR_FLAG(unicast_flood, BR_FLOOD);
 BRPORT_ATTR_FLAG(proxyarp, BR_PROXYARP);
+BRPORT_ATTR_FLAG(proxyarp_wifi, BR_PROXYARP_WIFI);
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 static ssize_t show_multicast_router(struct net_bridge_port *p, char *buf)
···
 	&brport_attr_multicast_fast_leave,
 #endif
 	&brport_attr_proxyarp,
+	&brport_attr_proxyarp_wifi,
 	NULL
 };