Date:	Fri, 20 Apr 2012 20:56:09 +0200
From:	Jiri Bohac <jbohac@...e.cz>
To:	Jay Vosburgh <fubar@...ibm.com>
Cc:	jbohac@...e.cz, Andy Gospodarek <andy@...yhouse.net>,
	netdev@...r.kernel.org
Subject: Re: [PATCH][RFC] bonding: delete migrated IP addresses from the rlb
 hash table

I finally got back to this, sorry for such a long delay ...
Start of this thread is here:
http://thread.gmane.org/gmane.linux.network/222233

On Wed, Mar 07, 2012 at 05:02:16PM +0100, Jiri Bohac wrote:
> On Wed, Feb 29, 2012 at 06:12:20PM -0800, Jay Vosburgh wrote:
> > 	I've done some initial testing with this, and so far I'm seeing
> > one problem: every time the local host (with bonding) sends a broadcast
> > ARP, that ends up flushing the entire RLB table.  Well, all entries that
> > match the IP on the bond that's sending an ARP request, which is just
> > one address in my testing.
> > 
> > 	Anyway, this happens because the switch forwards the broadcast
> > ARP back around to one of the other bond slaves, and then that
> > "incoming" ARP bears an ip_src of our already-in-use IP address, and
> > that matches everything in the table.
> 
> Good catch! I did not notice this.
> 
> > 	Perhaps a check that the ip_src being flushed is not actually in
> > use locally is warranted?
> 
> This would not work for the setups where the bonding master is
> bridget to some other network. I think it would be better to also
> store the source (server) MAC address in struct client_info and
> only flush the hash table entries if the MAC address from the
> incoming APR packet and the source MAC address stored in the hash
> table differ.
> 
> Updated patch follows (compile-tested only) I also
> fixed the coding style problems you pointed out. As for the
> forward/reverse naming, it's your call. Should I change it to
> src/dst?

I now thoroughly tested this updated patch in a real setup. It
works as intended - it does not purge the entries when receiving the
looped-back ARP requests. It correctly purges the offending
entries when an ARP packet arrives with a its SRC IP address
matching a SRC IP address in the table and having differrent MAC
address -- exactly the case that would cause the ARP cache
poisoning if not purged from the table.

Jay, would you please consider applying this? Or do you want me
to somehow rename the RLB table forward/reverse elements?

Re-sending the fixed patch with the original description:

------


Bonding in balance-alb mode records information from ARP packets
passing through the bond in a hash table (rx_hashtbl).

At certain situations (e.g. link change of a slave),
rlb_update_rx_clients() will send out ARP packets to update ARP
caches of other hosts on the network to achieve RX load balancing.

The problem is that once an IP address is recorded in the hash
table, it stays there indefinitely. If this IP address is
migrated to a different host in the network, bonding still sends
out ARP packets that poison other systems' ARP caches with
invalid information.

This patch solves this by looking at all incoming ARP packets,
and checking if the source IP address is one of the source
addresses stored in the rx_hashtbl. If it is, the corresponding
hash table entries are removed. Thus, when an IP address is
migrated, the first ARP broadcast by its new owner will purge the
offending entries of rx_hashtbl.

The hash table is hashed by ip_dst. To be able to do the above
check efficiently (not walking the whole hash table), we need a
reverse mapping (by ip_src).

I added three new members in struct rlb_client_info:
   rx_hashtbl[x].reverse_first will point to the start of a list of
      entries for which hash(ip_src) == x.
   The list is linked with reverse_next and reverse_prev.

When an incoming ARP packet arrives at rlb_arp_recv()
rlb_purge_src_ip() can quickly walk only the entries on the
corresponding lists, i.e. the entries that are likely to contain
the offending IP address.

Signed-off-by: Jiri Bohac <jbohac@...e.cz>

diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index f820b26..a938ab6 100644
--- a/drivers/net/bonding/bond_alb.c
+++ b/drivers/net/bonding/bond_alb.c
@@ -84,6 +84,9 @@ static inline struct arp_pkt *arp_pkt(const struct sk_buff *skb)
 
 /* Forward declaration */
 static void alb_send_learning_packets(struct slave *slave, u8 mac_addr[]);
+static void rlb_purge_src_ip(struct bonding *bond, struct arp_pkt *arp);
+static void rlb_delete_table_entry_reverse(struct bonding *bond, u32 index);
+static void rlb_set_reverse_entry(struct bonding *bond, u32 ip_src_hash, u32 ip_dst_hash);
 
 static inline u8 _simple_hash(const u8 *hash_start, int hash_size)
 {
@@ -366,6 +369,17 @@ static void rlb_arp_recv(struct sk_buff *skb, struct bonding *bond,
 		return;
 	}
 
+	/* We received an ARP from arp->ip_src.
+	 * We might have used this IP address previously (on the bonding host
+	 * itself or on a system that is bridged together with the bond).
+	 * However, if arp->mac_src is different than what is stored in
+	 * rx_hashtbl, some other host is now using the IP and we must prevent
+	 * sending out client updates with this IP address as the source.
+	 * Clean up all hash table entries that have this address as ip_src but
+	 * have a dirrerent mac_src.
+	 */
+	rlb_purge_src_ip(bond, arp);
+
 	if (arp->op_code == htons(ARPOP_REPLY)) {
 		/* update rx hash table for this ARP */
 		rlb_update_entry_from_arp(bond, arp);
@@ -635,6 +649,7 @@ static struct slave *rlb_choose_channel(struct sk_buff *skb, struct bonding *bon
 				/* update mac address from arp */
 				memcpy(client_info->mac_dst, arp->mac_dst, ETH_ALEN);
 			}
+			memcpy(client_info->mac_src, arp->mac_src, ETH_ALEN);
 
 			assigned_slave = client_info->slave;
 			if (assigned_slave) {
@@ -657,6 +672,13 @@ static struct slave *rlb_choose_channel(struct sk_buff *skb, struct bonding *bon
 	assigned_slave = rlb_next_rx_slave(bond);
 
 	if (assigned_slave) {
+		if (!(client_info->assigned && client_info->ip_src == arp->ip_src)) {
+			/* ip_src is going to be updated, fix the reverse hashing */
+			u32 hash_src = _simple_hash((u8 *)&arp->ip_src, sizeof(arp->ip_src));
+			rlb_delete_table_entry_reverse(bond, hash_index);
+			rlb_set_reverse_entry(bond, hash_src, hash_index);
+		}
+
 		client_info->ip_src = arp->ip_src;
 		client_info->ip_dst = arp->ip_dst;
 		/* arp->mac_dst is broadcast for arp reqeusts.
@@ -664,6 +686,7 @@ static struct slave *rlb_choose_channel(struct sk_buff *skb, struct bonding *bon
 		 * upon receiving an arp reply.
 		 */
 		memcpy(client_info->mac_dst, arp->mac_dst, ETH_ALEN);
+		memcpy(client_info->mac_src, arp->mac_src, ETH_ALEN);
 		client_info->slave = assigned_slave;
 
 		if (compare_ether_addr_64bits(client_info->mac_dst, mac_bcast)) {
@@ -769,11 +792,109 @@ static void rlb_rebalance(struct bonding *bond)
 }
 
 /* Caller must hold rx_hashtbl lock */
-static void rlb_init_table_entry(struct rlb_client_info *entry)
+static void rlb_init_table_entry_forward(struct rlb_client_info *entry)
 {
-	memset(entry, 0, sizeof(struct rlb_client_info));
 	entry->next = RLB_NULL_INDEX;
 	entry->prev = RLB_NULL_INDEX;
+	entry->assigned = 0;
+	entry->slave = NULL;
+	entry->tag = 0;
+}
+static void rlb_init_table_entry_reverse(struct rlb_client_info *entry)
+{
+	entry->reverse_first = RLB_NULL_INDEX;
+	entry->reverse_prev = RLB_NULL_INDEX;
+	entry->reverse_next = RLB_NULL_INDEX;
+}
+
+static void rlb_init_table_entry(struct rlb_client_info *entry)
+{
+	memset(entry, 0, sizeof(struct rlb_client_info));
+	rlb_init_table_entry_forward(entry);
+	rlb_init_table_entry_reverse(entry);
+}
+
+static void rlb_delete_table_entry_forward(struct bonding *bond, u32 index)
+{
+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
+	u32 next_index = bond_info->rx_hashtbl[index].next;
+	u32 prev_index = bond_info->rx_hashtbl[index].prev;
+
+	if (index == bond_info->rx_hashtbl_head)
+		bond_info->rx_hashtbl_head = next_index;
+	if (prev_index != RLB_NULL_INDEX)
+		bond_info->rx_hashtbl[prev_index].next = next_index;
+	if (next_index != RLB_NULL_INDEX)
+		bond_info->rx_hashtbl[next_index].prev = prev_index;
+}
+
+static void rlb_delete_table_entry_reverse(struct bonding *bond, u32 index)
+{
+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
+	u32 next_index = bond_info->rx_hashtbl[index].reverse_next;
+	u32 prev_index = bond_info->rx_hashtbl[index].reverse_prev;
+
+	bond_info->rx_hashtbl[index].reverse_next = RLB_NULL_INDEX;
+	bond_info->rx_hashtbl[index].reverse_prev = RLB_NULL_INDEX;
+
+	if (next_index != RLB_NULL_INDEX)
+		bond_info->rx_hashtbl[next_index].reverse_prev = prev_index;
+
+	if (prev_index == RLB_NULL_INDEX)
+		return;
+
+	/* is prev_index pointing to the head of this chain? */
+	if (bond_info->rx_hashtbl[prev_index].reverse_first == index)
+		bond_info->rx_hashtbl[prev_index].reverse_first = next_index;
+	else
+		bond_info->rx_hashtbl[prev_index].reverse_next = next_index;
+
+}
+
+static void rlb_delete_table_entry(struct bonding *bond, u32 index)
+{
+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
+	struct rlb_client_info *entry = &(bond_info->rx_hashtbl[index]);
+
+	rlb_delete_table_entry_forward(bond, index);
+	rlb_init_table_entry_forward(entry);
+
+	rlb_delete_table_entry_reverse(bond, index);
+}
+
+static void rlb_set_reverse_entry(struct bonding *bond, u32 ip_src_hash, u32 ip_dst_hash)
+{
+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
+	u32 next;
+
+	bond_info->rx_hashtbl[ip_dst_hash].reverse_prev = ip_src_hash;
+	next = bond_info->rx_hashtbl[ip_src_hash].reverse_first;
+	bond_info->rx_hashtbl[ip_dst_hash].reverse_next = next;
+	if (next != RLB_NULL_INDEX)
+		bond_info->rx_hashtbl[next].reverse_prev = ip_dst_hash;
+	bond_info->rx_hashtbl[ip_src_hash].reverse_first = ip_dst_hash;
+}
+
+/* deletes all rx_hashtbl entries with  arp->ip_src if their mac_src does
+ * not match arp->mac_src */
+static void rlb_purge_src_ip(struct bonding *bond, struct arp_pkt *arp)
+{
+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
+	u32 ip_src_hash = _simple_hash((u8*)&(arp->ip_src), sizeof(arp->ip_src));
+	u32 index;
+
+	_lock_rx_hashtbl_bh(bond);
+
+	index = bond_info->rx_hashtbl[ip_src_hash].reverse_first;
+	while (index != RLB_NULL_INDEX) {
+		struct rlb_client_info *entry = &(bond_info->rx_hashtbl[index]);
+		u32 next_index = entry->reverse_next;
+		if (entry->ip_src == arp->ip_src &&
+		    compare_ether_addr_64bits(arp->mac_src, entry->mac_src))
+				rlb_delete_table_entry(bond, index);
+		index = next_index;
+	}
+	_unlock_rx_hashtbl_bh(bond);
 }
 
 static int rlb_initialize(struct bonding *bond)
@@ -831,21 +952,9 @@ static void rlb_clear_vlan(struct bonding *bond, unsigned short vlan_id)
 	while (curr_index != RLB_NULL_INDEX) {
 		struct rlb_client_info *curr = &(bond_info->rx_hashtbl[curr_index]);
 		u32 next_index = bond_info->rx_hashtbl[curr_index].next;
-		u32 prev_index = bond_info->rx_hashtbl[curr_index].prev;
-
-		if (curr->tag && (curr->vlan_id == vlan_id)) {
-			if (curr_index == bond_info->rx_hashtbl_head) {
-				bond_info->rx_hashtbl_head = next_index;
-			}
-			if (prev_index != RLB_NULL_INDEX) {
-				bond_info->rx_hashtbl[prev_index].next = next_index;
-			}
-			if (next_index != RLB_NULL_INDEX) {
-				bond_info->rx_hashtbl[next_index].prev = prev_index;
-			}
 
-			rlb_init_table_entry(curr);
-		}
+		if (curr->tag && (curr->vlan_id == vlan_id))
+			rlb_delete_table_entry(bond, curr_index);
 
 		curr_index = next_index;
 	}
diff --git a/drivers/net/bonding/bond_alb.h b/drivers/net/bonding/bond_alb.h
index 90f140a..8286df52 100644
--- a/drivers/net/bonding/bond_alb.h
+++ b/drivers/net/bonding/bond_alb.h
@@ -100,6 +100,7 @@ struct tlb_client_info {
 struct rlb_client_info {
 	__be32 ip_src;		/* the server IP address */
 	__be32 ip_dst;		/* the client IP address */
+	u8  mac_src[ETH_ALEN];	/* the server MAC address */
 	u8  mac_dst[ETH_ALEN];	/* the client MAC address */
 	u32 next;		/* The next Hash table entry index */
 	u32 prev;		/* The previous Hash table entry index */
@@ -108,6 +109,9 @@ struct rlb_client_info {
 	struct slave *slave;	/* the slave assigned to this client */
 	u8 tag;			/* flag - need to tag skb */
 	unsigned short vlan_id;	/* VLAN tag associated with IP address */
+	u32 reverse_next;	/* next entry with same hash(ip_src) */
+	u32 reverse_prev;	/* prev entry with same hash(ip_src) */
+	u32 reverse_first;	/* first entry with hash(ip_src) == this entry's index */
 };
 
 struct tlb_slave_info {

 

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, SUSE CZ

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