[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>

3 files changed, 18 insertions, 19 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 02cf848f71d2..ddbdde82a700 100644
--- 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 e787d2151152..62bd791c204e 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 626a58206298..6b178e1247b5 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);