[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>

1 files changed, 1 insertions, 6 deletions

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)