bridge: notify user space after fdb update

There has been a number incidents recently where customers running KVM have reported that VM hosts on different Hypervisors are unreachable. Based on pcap traces we found that the bridge was broadcasting the ARP request out onto the network. However some NICs have an inbuilt switch which on occasions were broadcasting the VMs ARP request back through the physical NIC on the Hypervisor. This resulted in the bridge changing ports and incorrectly learning that the VMs mac address was external. As a result the ARP reply was directed back onto the external network and VM never updated it's ARP cache. This patch will notify the bridge command, after a fdb has been updated to identify such port toggling.

Signed-off-by Jon Maxwell <[email protected]>

---
  net/bridge/br_fdb.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

net/bridge/br_fdb.c +0 -0

index 9203d5a..f3ee2da 100644

There has been a number incidents recently where customers running KVM have reported that VM hosts on different Hypervisors are unreachable. Based on pcap traces we found that the bridge was broadcasting the ARP request out onto the network. However some NICs have an inbuilt switch which on occasions were broadcasting the VMs ARP request back through the physical NIC on the Hypervisor. This resulted in the bridge changing ports and incorrectly learning that the VMs mac address was external. As a result the ARP reply was directed back onto the external network and VM never updated it's ARP cache. This patch will notify the bridge command, after a fdb has been updated to identify such port toggling.

Signed-off-by Jon Maxwell <[email protected]>

---
 net/bridge/br_fdb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

net/bridge/br_fdb.c +1 -0

index 9203d5a..f3ee2da 100644
@@ -487,6 +487,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 {
 	struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
 	struct net_bridge_fdb_entry *fdb;
+	bool fdb_modified = 0;
 
 	/* some users want to always flood. */
 	if (hold_time(br) == 0)

net/bridge/br_fdb.c +2 -0

 			fdb->updated = jiffies;
 			if (unlikely(added_by_user))
 				fdb->added_by_user = 1;
+			if (unlikely(fdb_modified))
+				fdb_notify(br, fdb, RTM_NEWNEIGH);
 		}
 	} else {
 		spin_lock(&br->hash_lock);