[PATCH] [NETNS 4/4 net-2.6.25] Namespace stop vs 'ip r l' race.

["Denis V. Lunev" <den@openvz.org>]

During network namespace stop process kernel side netlink sockets belonging
to a namespace should be closed. They should not prevent namespace to stop,
so they do not increment namespace usage counter. Though this counter will
be put during last sock_put.

The raplacement of the correct netns for init_ns solves the problem only
partial as socket to be stoped until proper stop is a valid netlink kernel
socket and can be looked up by the user processes. This is not a problem
until it resides in initial namespace (no processes inside this net), but
this is not true for init_net.

So, hold the referrence for a socket, remove it from lookup tables and only
after that change namespace and perform a last put.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Tested-by: Alexey Dobriyan <adobriyan@openvz.org>
---
 net/core/rtnetlink.c     |   15 ++-------------
 net/ipv4/fib_frontend.c  |    7 +------
 net/netlink/af_netlink.c |   15 +++++++++++++++
 3 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 2ef9480..aafc34d 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1365,25 +1365,14 @@ static int rtnetlink_net_init(struct net *net)
 				   rtnetlink_rcv, &rtnl_mutex, THIS_MODULE);
 	if (!sk)
 		return -ENOMEM;
-
-	/* Don't hold an extra reference on the namespace */
-	put_net(sk->sk_net);
 	net->rtnl = sk;
 	return 0;
 }
 
 static void rtnetlink_net_exit(struct net *net)
 {
-	struct sock *sk = net->rtnl;
-	if (sk) {
-		/* At the last minute lie and say this is a socket for the
-		 * initial network namespace.  So the socket will be safe to
-		 * free.
-		 */
-		sk->sk_net = get_net(&init_net);
-		netlink_kernel_release(net->rtnl);
-		net->rtnl = NULL;
-	}
+	netlink_kernel_release(net->rtnl);
+	net->rtnl = NULL;
 }
 
 static struct pernet_operations rtnetlink_net_ops = {
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index e787d21..62bd791 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -869,19 +869,14 @@ static int nl_fib_lookup_init(struct net *net)
 				   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)
 {
-	/* 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);
 	netlink_kernel_release(net->ipv4.fibnl);
+	net->ipv4.fibnl = NULL;
 }
 
 static void fib_disable_ip(struct net_device *dev, int force)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 626a582..6b178e1 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1396,6 +1396,9 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
 	}
 	netlink_table_ungrab();
 
+	/* Do not hold an extra referrence to a namespace as this socket is
+	 * internal to a namespace and does not prevent it to stop. */
+	put_net(net);
 	return sk;
 
 out_sock_release:
@@ -1411,7 +1414,19 @@ netlink_kernel_release(struct sock *sk)
 {
 	if (sk == NULL || sk->sk_socket == NULL)
 		return;
+
+	/*
+	 * Last sock_put should drop referrence to sk->sk_net. It has already
+	 * been dropped in netlink_kernel_create. Taking referrence to stopping
+	 * namespace is not an option.
+	 * Take referrence to a socket to remove it from netlink lookup table
+	 * _alive_ and after that destroy it in the context of init_net.
+	 */
+	sock_hold(sk);
 	sock_release(sk->sk_socket);
+
+	sk->sk_net = get_net(&init_net);
+	sock_put(sk);
 }
 EXPORT_SYMBOL(netlink_kernel_release);
 
-- 
1.5.3.rc5