[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, 15 insertions, 0 deletions

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);