ipvlan: improvise dev_id generation logic in IPvlan

The patch 009146d117b ("ipvlan: assign unique dev-id for each slave
device.") used ida_simple_get() to generate dev_ids assigned to the
slave devices. However (Eric has pointed out that) there is a shortcoming
with that approach as it always uses the first available ID. This
becomes a problem when a slave gets deleted and a new slave gets added.
The ID gets reassigned causing the new slave to get the same link-local
address. This side-effect is undesirable.

This patch adds a per-port variable that keeps track of the IDs
assigned and used as the stat-base for the IDR api. This base will be
wrapped around when it reaches the MAX (0xFFFE) value possibly on a
busy system where slaves are added and deleted routinely.

Fixes: 009146d117b ("ipvlan: assign unique dev-id for each slave device.")
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
CC: Eric Dumazet <edumazet@google.com>
CC: David Miller <davem@davemloft.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
index 1cdb8c5ec403..92b221a03350 100644
--- a/drivers/net/ipvlan/ipvlan_main.c
+++ b/drivers/net/ipvlan/ipvlan_main.c
@@ -120,6 +120,7 @@ static int ipvlan_port_create(struct net_device *dev)
         skb_queue_head_init(&port->backlog);
         INIT_WORK(&port->wq, ipvlan_process_multicast);
         ida_init(&port->ida);
+        port->dev_id_start = 1;
 
         err = netdev_rx_handler_register(dev, ipvlan_handle_frame, port);
         if (err)
@@ -534,15 +535,25 @@ static int ipvlan_link_new(struct net *src_net, struct net_device *dev,
         ipvlan_adjust_mtu(ipvlan, phy_dev);
         INIT_LIST_HEAD(&ipvlan->addrs);
 
+        /* If the port-id base is at the MAX value, then wrap it around and
+         * begin from 0x1 again. This may be due to a busy system where lots
+         * of slaves are getting created and deleted.
+         */
+        if (port->dev_id_start == 0xFFFE)
+                port->dev_id_start = 0x1;
+
         /* Since L2 address is shared among all IPvlan slaves including
          * master, use unique 16 bit dev-ids to diffentiate among them.
          * Assign IDs between 0x1 and 0xFFFE (used by the master) to each
          * slave link [see addrconf_ifid_eui48()].
          */
-        err = ida_simple_get(&port->ida, 1, 0xFFFE, GFP_KERNEL);
+        err = ida_simple_get(&port->ida, port->dev_id_start, 0xFFFE,
+                             GFP_KERNEL);
         if (err < 0)
                 goto destroy_ipvlan_port;
         dev->dev_id = err;
+        /* Increment id-base to the next slot for the future assignment */
+        port->dev_id_start = err + 1;
 
         /* TODO Probably put random address here to be presented to the
          * world but keep using the physical-dev address for the outgoing