[B.A.T.M.A.N.] [PATCHv4 5/7] batman-adv: Distributed ARP Table - add snooping functions for ARP messages

Antonio Quartulli
2011-11-24T22:21:17Z

In case of an ARP message going in or out the soft_iface, it is intercepted and
a special action is performed. In particular the DHT helper functions previously
implemented are used to store all the ARP entries belonging to the network in
order to provide a fast and unicast lookup instead of the classic broadcast flooding
mechanism.
Each node stores the entries it is responsible for (following the DHT rules) in
its soft_iface ARP table. This makes it possible to reuse the kernel data
structures and functions for ARP management.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
---
distributed-arp-table.c | 226 +++++++++++++++++++++++++++++++++++++++++++++++
distributed-arp-table.h | 10 ++
main.h | 2 +
send.c | 6 ++
soft-interface.c | 16 +++-
5 files changed, 259 insertions(+), 1 deletions(-)

diff --git a/distributed-arp-table.c b/distributed-arp-table.c
index 6cb60b0..a1deb79 100644
--- a/distributed-arp-table.c
+++ b/distributed-arp-table.c
@@ -21,6 +21,8 @@

#include <linux/if_ether.h>
#include <linux/if_arp.h>
+/* needed to use arp_tbl */
+#include <net/arp.h>

#include "main.h"
#include "distributed-arp-table.h"
@@ -197,6 +199,31 @@ out:
return ret;
}

+/* Update the neighbour entry corresponding to the IP passed as parameter with
+ * the hw address hw. If the neighbour entry doesn't exists, then it will be
+ * created */
+static void arp_neigh_update(struct bat_priv *bat_priv, uint32_t ip,
+ uint8_t *hw)
+{
+ struct neighbour *n = NULL;
+ struct hard_iface *primary_if = primary_if_get_selected(bat_priv);
+ if (!primary_if)
+ goto out;
+
+ n = __neigh_lookup(&arp_tbl, &ip, primary_if->soft_iface, 1);
+ if (!n)
+ goto out;
+
+ bat_dbg(DBG_ARP, bat_priv, "Updating neighbour: %pI4 - %pM\n", &ip, hw);
+
+ neigh_update(n, hw, NUD_CONNECTED, NEIGH_UPDATE_F_OVERRIDE);
+out:
+ if (n && !IS_ERR(n))
+ neigh_release(n);
+ if (primary_if)
+ hardif_free_ref(primary_if);
+}
+
/* Returns arphdr->ar_op if the skb contains a valid ARP packet, otherwise
* returns 0 */
static uint16_t arp_get_type(struct bat_priv *bat_priv, struct sk_buff *skb)
@@ -239,3 +266,202 @@ static uint16_t arp_get_type(struct bat_priv *bat_priv, struct sk_buff *skb)
out:
return type;
}
+
+/* return true if the message has been sent to the dht candidates, false
+ * otherwise. In case of true the message has to be enqueued to permit the
+ * fallback */
+bool arp_snoop_outgoing_request(struct bat_priv *bat_priv, struct sk_buff *skb)
+{
+ uint16_t type = 0;
+ uint32_t ip_dst, ip_src;
+ uint8_t *hw_src;
+ bool ret = false;
+ struct neighbour *n = NULL;
+ struct hard_iface *primary_if = NULL;
+ struct sk_buff *skb_new;
+
+ type = arp_get_type(bat_priv, skb);
+ /* If we get an ARP_REQUEST we have to send the unicast message to the
+ * selected DHT candidates */
+ if (type != ARPOP_REQUEST)
+ goto out;
+
+ bat_dbg(DBG_ARP, bat_priv, "Snooped outgoing ARP request\n");
+
+ ip_src = ARP_IP_SRC(skb);
+ hw_src = ARP_HW_SRC(skb);
+ ip_dst = ARP_IP_DST(skb);
+
+ primary_if = primary_if_get_selected(bat_priv);
+ if (!primary_if)
+ goto out;
+
+ arp_neigh_update(bat_priv, ip_src, hw_src);
+
+ n = neigh_lookup(&arp_tbl, &ip_dst, primary_if->soft_iface);
+ /* check if it is a valid neigh entry */
+ if (n && (n->nud_state & NUD_CONNECTED)) {
+ skb_new = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_src,
+ primary_if->soft_iface, ip_dst, hw_src,
+ n->ha, hw_src);
+ if (!skb_new)
+ goto out;
+
+ skb_reset_mac_header(skb_new);
+ skb_new->protocol = eth_type_trans(skb_new,
+ primary_if->soft_iface);
+ bat_priv->stats.rx_packets++;
+ bat_priv->stats.rx_bytes += skb->len + sizeof(struct ethhdr);
+ primary_if->soft_iface->last_rx = jiffies;
+
+ netif_rx(skb_new);
+ bat_dbg(DBG_ARP, bat_priv, "ARP request replied locally\n");
+ } else
+ /* Send the request on the DHT */
+ ret = dht_send_data(bat_priv, skb, ip_dst);
+out:
+ if (n)
+ neigh_release(n);
+ if (primary_if)
+ hardif_free_ref(primary_if);
+ return ret;
+}
+
+/* This function is meant to be invoked for an ARP request which is coming into
+ * the bat0 interfaces from the mesh network. It will check for the needed data
+ * into the local table. If found, an ARP reply is sent immediately, otherwise
+ * the caller has to deliver the ARP request to the upper layer */
+bool arp_snoop_incoming_request(struct bat_priv *bat_priv, struct sk_buff *skb)
+{
+ uint16_t type;
+ uint32_t ip_src, ip_dst;
+ uint8_t *hw_src;
+ struct hard_iface *primary_if = NULL;
+ struct sk_buff *skb_new;
+ struct neighbour *n = NULL;
+ bool ret = false;
+
+ type = arp_get_type(bat_priv, skb);
+ if (type != ARPOP_REQUEST)
+ goto out;
+
+ hw_src = ARP_HW_SRC(skb);
+ ip_src = ARP_IP_SRC(skb);
+ ip_dst = ARP_IP_DST(skb);
+
+ bat_dbg(DBG_ARP, bat_priv, "Snooped incoming ARP request\n");
+
+ primary_if = primary_if_get_selected(bat_priv);
+ if (!primary_if)
+ goto out;
+
+ arp_neigh_update(bat_priv, ip_src, hw_src);
+
+ n = neigh_lookup(&arp_tbl, &ip_dst, primary_if->soft_iface);
+ /* check if it is a valid neigh entry */
+ if (!n || !(n->nud_state & NUD_CONNECTED))
+ goto out;
+
+ skb_new = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_src,
+ primary_if->soft_iface, ip_dst, hw_src, n->ha,
+ hw_src);
+
+ if (!skb_new)
+ goto out;
+
+ unicast_send_skb(skb_new, bat_priv);
+
+ ret = true;
+out:
+ if (n)
+ neigh_release(n);
+ if (primary_if)
+ hardif_free_ref(primary_if);
+ if (ret)
+ kfree_skb(skb);
+ return ret;
+}
+
+/* This function is meant to be invoked on an ARP reply packet going into the
+ * soft interface. The related neighbour entry has to be updated and the DHT has
+ * to be populated as well */
+bool arp_snoop_outgoing_reply(struct bat_priv *bat_priv, struct sk_buff *skb)
+{
+ uint16_t type;
+ uint32_t ip_src, ip_dst;
+ uint8_t *hw_src, *hw_dst;
+ bool ret = false;
+
+ type = arp_get_type(bat_priv, skb);
+ if (type != ARPOP_REPLY)
+ goto out;
+
+ bat_dbg(DBG_ARP, bat_priv, "Snooped outgoing ARP reply\n");
+
+ hw_src = ARP_HW_SRC(skb);
+ ip_src = ARP_IP_SRC(skb);
+ hw_dst = ARP_HW_DST(skb);
+ ip_dst = ARP_IP_DST(skb);
+
+ arp_neigh_update(bat_priv, ip_src, hw_src);
+ arp_neigh_update(bat_priv, ip_dst, hw_dst);
+
+ /* Send the ARP reply to the candidates for both the IP addresses we
+ * fetched from the ARP reply */
+ dht_send_data(bat_priv, skb, ip_src);
+ dht_send_data(bat_priv, skb, ip_dst);
+ ret = true;
+out:
+ return ret;
+}
+
+/* This function has to be invoked on an ARP reply coming into the soft
+ * interface from the mesh network. The local table has to be updated */
+bool arp_snoop_incoming_reply(struct bat_priv *bat_priv, struct sk_buff *skb)
+{
+ uint16_t type;
+ uint32_t ip_src, ip_dst;
+ uint8_t *hw_src, *hw_dst;
+ bool ret = false;
+
+ type = arp_get_type(bat_priv, skb);
+ if (type != ARPOP_REPLY)
+ goto out;
+
+ bat_dbg(DBG_ARP, bat_priv, "Snooped incoming ARP reply\n");
+
+ hw_src = ARP_HW_SRC(skb);
+ ip_src = ARP_IP_SRC(skb);
+ hw_dst = ARP_HW_DST(skb);
+ ip_dst = ARP_IP_DST(skb);
+
+ /* Update our internal cache with both the IP addresses we fetched from
+ * the ARP reply */
+ arp_neigh_update(bat_priv, ip_src, hw_src);
+ arp_neigh_update(bat_priv, ip_dst, hw_dst);
+
+ ret = true;
+out:
+ return ret;
+}
+
+bool arp_drop_broadcast_packet(struct bat_priv *bat_priv,
+ struct forw_packet *forw_packet)
+{
+ struct neighbour *n;
+
+ /* If this packet is an ARP_REQUEST and we already have the information
+ * that it is going to ask, we can drop the packet */
+ if (!forw_packet->num_packets &&
+ (arp_get_type(bat_priv, forw_packet->skb) ==
+ ARPOP_REQUEST)) {
+ n = neigh_lookup(&arp_tbl, &ARP_IP_DST(forw_packet->skb),
+ forw_packet->if_incoming->soft_iface);
+ /* check if we already know this neigh */
+ if (n && (n->nud_state & NUD_CONNECTED))
+ return true;
+
+ bat_dbg(DBG_ARP, bat_priv, "ARP request: fallback\n");
+ }
+ return false;
+}
diff --git a/distributed-arp-table.h b/distributed-arp-table.h
index 3e0f5c6..3747aad 100644
--- a/distributed-arp-table.h
+++ b/distributed-arp-table.h
@@ -27,6 +27,7 @@
#include <linux/if_arp.h>

struct bat_priv;
+struct forw_packet;

/*
* dat_addr_t is the type used for all DHT indexes. If it is changed,
@@ -43,6 +44,15 @@ struct bat_priv;
#define ARP_HW_DST(skb) (ARP_HW_SRC(skb) + ETH_ALEN + 4)
#define ARP_IP_DST(skb) (*(uint32_t *)(ARP_HW_SRC(skb) + ETH_ALEN * 2 + 4))

+bool arp_snoop_outgoing_request(struct bat_priv *bat_priv,
+ struct sk_buff *skb);
+bool arp_snoop_incoming_request(struct bat_priv *bat_priv,
+ struct sk_buff *skb);
+bool arp_snoop_outgoing_reply(struct bat_priv *bat_priv, struct sk_buff *skb);
+bool arp_snoop_incoming_reply(struct bat_priv *bat_priv, struct sk_buff *skb);
+bool arp_drop_broadcast_packet(struct bat_priv *bat_priv,
+ struct forw_packet *forw_packet);
+
/* hash function to choose an entry in a hash table of given size */
/* hash algorithm from http://en.wikipedia.org/wiki/Hash_table */
static inline uint32_t hash_ipv4(const void *data, uint32_t size)
diff --git a/main.h b/main.h
index e129b01..a915db6 100644
--- a/main.h
+++ b/main.h
@@ -64,6 +64,8 @@

#define NULL_IFINDEX 0 /* dummy ifindex used to avoid iface checks */

+/* msecs after which an ARP_REQUEST is sent in broadcast as fallback */
+#define ARP_REQ_DELAY 250
/* numbers of originator to contact for any STORE/GET DHT operation */
#define DHT_CANDIDATES_NUM 3

diff --git a/send.c b/send.c
index b00a0f5..d625998 100644
--- a/send.c
+++ b/send.c
@@ -20,6 +20,7 @@
*/

#include "main.h"
+#include "distributed-arp-table.h"
#include "send.h"
#include "routing.h"
#include "translation-table.h"
@@ -30,6 +31,8 @@
#include "originator.h"
#include "bat_ogm.h"

+#include <net/arp.h>
+
static void send_outstanding_bcast_packet(struct work_struct *work);

/* send out an already prepared packet to the given address via the
@@ -275,6 +278,9 @@ static void send_outstanding_bcast_packet(struct work_struct *work)
if (atomic_read(&bat_priv->mesh_state) == MESH_DEACTIVATING)
goto out;

+ if (arp_drop_broadcast_packet(bat_priv, forw_packet))
+ goto out;
+
/* rebroadcast packet */
rcu_read_lock();
list_for_each_entry_rcu(hard_iface, &hardif_list, list) {
diff --git a/soft-interface.c b/soft-interface.c
index 962ee8d..21991e1 100644
--- a/soft-interface.c
+++ b/soft-interface.c
@@ -22,6 +22,7 @@
#include "main.h"
#include "soft-interface.h"
#include "hard-interface.h"
+#include "distributed-arp-table.h"
#include "routing.h"
#include "send.h"
#include "bat_debugfs.h"
@@ -567,6 +568,7 @@ static int interface_tx(struct sk_buff *skb, struct net_device *soft_iface)
int data_len = skb->len, ret;
short vid = -1;
bool do_bcast = false;
+ unsigned long brd_delay = 1;

if (atomic_read(&bat_priv->mesh_state) != MESH_ACTIVE)
goto dropped;
@@ -587,6 +589,8 @@ static int interface_tx(struct sk_buff *skb, struct net_device *soft_iface)
goto end;
}

+ skb_reset_mac_header(skb);
+
/**
* if we have a another chosen mesh exit node in range
* it will transport the packets to the mesh
@@ -628,6 +632,9 @@ static int interface_tx(struct sk_buff *skb, struct net_device *soft_iface)
if (!primary_if)
goto dropped;

+ if (arp_snoop_outgoing_request(bat_priv, skb))
+ brd_delay = msecs_to_jiffies(ARP_REQ_DELAY);
+
if (my_skb_head_push(skb, sizeof(*bcast_packet)) < 0)
goto dropped;

@@ -647,7 +654,7 @@ static int interface_tx(struct sk_buff *skb, struct net_device *soft_iface)
bcast_packet->seqno =
htonl(atomic_inc_return(&bat_priv->bcast_seqno));

- add_bcast_packet_to_list(bat_priv, skb, 1);
+ add_bcast_packet_to_list(bat_priv, skb, brd_delay);

/* a copy is stored in the bcast list, therefore removing
* the original skb. */
@@ -661,6 +668,8 @@ static int interface_tx(struct sk_buff *skb, struct net_device *soft_iface)
goto dropped;
}

+ arp_snoop_outgoing_reply(bat_priv, skb);
+
ret = unicast_send_skb(skb, bat_priv);
if (ret != 0)
goto dropped_freed;
@@ -716,6 +725,11 @@ void interface_rx(struct net_device *soft_iface,
goto dropped;
}

+ if (arp_snoop_incoming_request(bat_priv, skb))
+ goto out;
+
+ arp_snoop_incoming_reply(bat_priv, skb);
+
/**
* if we have a another chosen mesh exit node in range
* it will transport the packets to the non-mesh network
--
1.7.3.4