Netlink protocol table is global for all namespaces. Some netlink protocols
have been virtualized, i.e. they have per/namespace netlink socket. This
difference can easily lead to double free if more than 1 namespace is
started. Count the number of kernel netlink sockets to track that this
table is not used any more.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Tested-by: Alexey Dobriyan <adobriyan@openvz.org>
---
 net/netlink/af_netlink.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 21f9e30..29fef55 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -498,9 +498,12 @@ static int netlink_release(struct socket *sock)
 
 	netlink_table_grab();
 	if (netlink_is_kernel(sk)) {
-		kfree(nl_table[sk->sk_protocol].listeners);
-		nl_table[sk->sk_protocol].module = NULL;
-		nl_table[sk->sk_protocol].registered = 0;
+		BUG_ON(nl_table[sk->sk_protocol].registered == 0);
+		if (--nl_table[sk->sk_protocol].registered == 0) {
+			kfree(nl_table[sk->sk_protocol].listeners);
+			nl_table[sk->sk_protocol].module = NULL;
+			nl_table[sk->sk_protocol].registered = 0;
+		}
 	} else if (nlk->subscriptions)
 		netlink_update_listeners(sk);
 	netlink_table_ungrab();
@@ -1389,6 +1392,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
 		nl_table[unit].registered = 1;
 	} else {
 		kfree(listeners);
+		nl_table[unit].registered++;
 	}
 	netlink_table_ungrab();
 
-- 
1.5.3.rc5