[NET]: Make netlink_kernel_release publically available as sk_release_kernel.

This staff will be needed for non-netlink kernel sockets, which should
also not pin a namespace like tcp_socket and icmp_socket.
Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -850,6 +850,7 @@ extern struct sock		*sk_alloc(struct net *net, int family,
 					  gfp_t priority,
 					  struct proto *prot);
 extern void			sk_free(struct sock *sk);
+extern void			sk_release_kernel(struct sock *sk);
 extern struct sock		*sk_clone(const struct sock *sk,
 					  const gfp_t priority);
 
@@ -1333,6 +1334,18 @@ static inline void sk_eat_skb(struct sock *sk, struct sk_buff *skb, int copied_e
 }
 #endif
 
+/*
+ * Kernel sockets, f.e. rtnl or icmp_socket, are a part of a namespace.
+ * They should not hold a referrence to a namespace in order to allow
+ * to stop it.
+ * Sockets after sk_change_net should be released using sk_release_kernel
+ */
+static inline void sk_change_net(struct sock *sk, struct net *net)
+{
+	put_net(sk->sk_net);
+	sk->sk_net = net;
+}
+
 extern void sock_enable_timestamp(struct sock *sk);
 extern int sock_get_timestamp(struct sock *, struct timeval __user *);
 extern int sock_get_timestampns(struct sock *, struct timespec __user *);

net/core/sock.c

@@ -987,6 +987,24 @@ void sk_free(struct sock *sk)
 	sk_prot_free(sk->sk_prot_creator, sk);
 }
 
+/*
+ * Last sock_put should drop referrence to sk->sk_net. It has already
+ * been dropped in sk_change_net. Taking referrence to stopping namespace
+ * is not an option.
+ * Take referrence to a socket to remove it from hash _alive_ and after that
+ * destroy it in the context of init_net.
+ */
+void sk_release_kernel(struct sock *sk)
+{
+	if (sk == NULL || sk->sk_socket == NULL)
+		return;
+
+	sock_hold(sk);
+	sock_release(sk->sk_socket);
+	sk->sk_net = get_net(&init_net);
+	sock_put(sk);
+}
+
 struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
 {
 	struct sock *newsk;

net/netlink/af_netlink.c

@@ -1372,8 +1372,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
 		goto out_sock_release_nosk;
 
 	sk = sock->sk;
-	put_net(sk->sk_net);
-	sk->sk_net = net;
+	sk_change_net(sk, net);
 
 	if (groups < 32)
 		groups = 32;
@@ -1421,20 +1420,7 @@ EXPORT_SYMBOL(netlink_kernel_create);
 void
 netlink_kernel_release(struct sock *sk)
 {
-	/*
-	 * 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.
-	 */
-	if (sk == NULL || sk->sk_socket == NULL)
-		return;
-
-	sock_hold(sk);
-	sock_release(sk->sk_socket);
-	sk->sk_net = get_net(&init_net);
-	sock_put(sk);
+	sk_release_kernel(sk);
 }
 EXPORT_SYMBOL(netlink_kernel_release);