bridge: Add support for IEEE 802.11 Proxy ARP

This feature is defined in IEEE Std 802.11-2012, 10.23.13. It allows
the AP devices to keep track of the hardware-address-to-IP-address
mapping of the mobile devices within the WLAN network.

The AP will learn this mapping via observing DHCP, ARP, and NS/NA
frames. When a request for such information is made (i.e. ARP request,
Neighbor Solicitation), the AP will respond on behalf of the
associated mobile device. In the process of doing so, the AP will drop
the multicast request frame that was intended to go out to the wireless
medium.

It was recommended at the LKS workshop to do this implementation in
the bridge layer. vxlan.c is already doing something very similar.
The DHCP snooping code will be added to the userspace application
(hostapd) per the recommendation.

This RFC commit is only for IPv4. A similar approach in the bridge
layer will be taken for IPv6 as well.

Signed-off-by: Kyeyoon Park <kyeyoonp@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 60 insertions, 0 deletions

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 6fd5522df696..1f1de715197c 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -16,6 +16,8 @@
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/netfilter_bridge.h>
+#include <linux/neighbour.h>
+#include <net/arp.h>
 #include <linux/export.h>
 #include <linux/rculist.h>
 #include "br_private.h"
@@ -57,6 +59,60 @@ static int br_pass_frame_up(struct sk_buff *skb)
 		       netif_receive_skb);
 }
 
+static void br_do_proxy_arp(struct sk_buff *skb, struct net_bridge *br,
+			    u16 vid)
+{
+	struct net_device *dev = br->dev;
+	struct neighbour *n;
+	struct arphdr *parp;
+	u8 *arpptr, *sha;
+	__be32 sip, tip;
+
+	if (dev->flags & IFF_NOARP)
+		return;
+
+	if (!pskb_may_pull(skb, arp_hdr_len(dev))) {
+		dev->stats.tx_dropped++;
+		return;
+	}
+	parp = arp_hdr(skb);
+
+	if (parp->ar_pro != htons(ETH_P_IP) ||
+	    parp->ar_op != htons(ARPOP_REQUEST) ||
+	    parp->ar_hln != dev->addr_len ||
+	    parp->ar_pln != 4)
+		return;
+
+	arpptr = (u8 *)parp + sizeof(struct arphdr);
+	sha = arpptr;
+	arpptr += dev->addr_len;	/* sha */
+	memcpy(&sip, arpptr, sizeof(sip));
+	arpptr += sizeof(sip);
+	arpptr += dev->addr_len;	/* tha */
+	memcpy(&tip, arpptr, sizeof(tip));
+
+	if (ipv4_is_loopback(tip) ||
+	    ipv4_is_multicast(tip))
+		return;
+
+	n = neigh_lookup(&arp_tbl, &tip, dev);
+	if (n) {
+		struct net_bridge_fdb_entry *f;
+
+		if (!(n->nud_state & NUD_VALID)) {
+			neigh_release(n);
+			return;
+		}
+
+		f = __br_fdb_get(br, n->ha, vid);
+		if (f)
+			arp_send(ARPOP_REPLY, ETH_P_ARP, sip, skb->dev, tip,
+				 sha, n->ha, sha);
+
+		neigh_release(n);
+	}
+}
+
 /* note: already called with rcu_read_lock */
 int br_handle_frame_finish(struct sk_buff *skb)
 {
@@ -98,6 +154,10 @@ int br_handle_frame_finish(struct sk_buff *skb)
 	dst = NULL;
 
 	if (is_broadcast_ether_addr(dest)) {
+		if (p->flags & BR_PROXYARP &&
+		    skb->protocol == htons(ETH_P_ARP))
+			br_do_proxy_arp(skb, br, vid);
+
 		skb2 = skb;
 		unicast = false;
 	} else if (is_multicast_ether_addr(dest)) {