[NETNS]: Provide correct namespace for fibnl netlink socket.

This patch makes the netlink socket to be per namespace. That allows
to have each namespace its own socket for routing queries.
Acked-by: Benjamin Thery <benjamin.thery@bull.net>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netns/ipv4.h

@@ -9,6 +9,7 @@ struct ctl_table_header;
 struct ipv4_devconf;
 struct fib_rules_ops;
 struct hlist_head;
+struct sock;
 
 struct netns_ipv4 {
 #ifdef CONFIG_SYSCTL
@@ -20,5 +21,6 @@ struct netns_ipv4 {
 	struct fib_rules_ops	*rules_ops;
 #endif
 	struct hlist_head	*fib_table_hash;
+	struct sock		*fibnl;
 };
 #endif

net/ipv4/fib_frontend.c

@@ -49,8 +49,6 @@
 
 #define FFprint(a...) printk(KERN_DEBUG a)
 
-static struct sock *fibnl;
-
 #ifndef CONFIG_IP_MULTIPLE_TABLES
 
 static int __net_init fib4_rules_init(struct net *net)
@@ -845,11 +843,13 @@ static void nl_fib_lookup(struct fib_result_nl *frn, struct fib_table *tb )
 
 static void nl_fib_input(struct sk_buff *skb)
 {
+	struct net *net;
 	struct fib_result_nl *frn;
 	struct nlmsghdr *nlh;
 	struct fib_table *tb;
 	u32 pid;
 
+	net = skb->sk->sk_net;
 	nlh = nlmsg_hdr(skb);
 	if (skb->len < NLMSG_SPACE(0) || skb->len < nlh->nlmsg_len ||
 	    nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*frn)))
@@ -861,28 +861,36 @@ static void nl_fib_input(struct sk_buff *skb)
 	nlh = nlmsg_hdr(skb);
 
 	frn = (struct fib_result_nl *) NLMSG_DATA(nlh);
-	tb = fib_get_table(&init_net, frn->tb_id_in);
+	tb = fib_get_table(net, frn->tb_id_in);
 
 	nl_fib_lookup(frn, tb);
 
 	pid = NETLINK_CB(skb).pid;       /* pid of sending process */
 	NETLINK_CB(skb).pid = 0;         /* from kernel */
 	NETLINK_CB(skb).dst_group = 0;  /* unicast */
-	netlink_unicast(fibnl, skb, pid, MSG_DONTWAIT);
+	netlink_unicast(net->ipv4.fibnl, skb, pid, MSG_DONTWAIT);
 }
 
 static int nl_fib_lookup_init(struct net *net)
 {
-	fibnl = netlink_kernel_create(net, NETLINK_FIB_LOOKUP, 0,
-				      nl_fib_input, NULL, THIS_MODULE);
-	if (fibnl == NULL)
+	struct sock *sk;
+	sk = netlink_kernel_create(net, NETLINK_FIB_LOOKUP, 0,
+				   nl_fib_input, NULL, THIS_MODULE);
+	if (sk == NULL)
 		return -EAFNOSUPPORT;
+	/* Don't hold an extra reference on the namespace */
+	put_net(sk->sk_net);
+	net->ipv4.fibnl = sk;
 	return 0;
 }
 
 static void nl_fib_lookup_exit(struct net *net)
 {
-	sock_put(fibnl);
+	/* At the last minute lie and say this is a socket for the
+	 * initial network namespace. So the socket will  be safe to free.
+	 */
+	net->ipv4.fibnl->sk_net = get_net(&init_net);
+	sock_put(net->ipv4.fibnl);
 }
 
 static void fib_disable_ip(struct net_device *dev, int force)