[NETNS]: Namespace stop vs 'ip r l' race.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 02cf848..ddbdde8 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1368,25 +1368,14 @@ 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 (file)
--- 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 (file)
--- 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);