af_netlink.c: make netlink_capable userns-aware

netlink_capable should check for permissions against the user
namespace owning the socket in question.

Changelog:
  Per Eric Dumazet advice, use sock_net(sk) instead of #ifdef.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0a4db02..3cc0bbe 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -580,8 +580,9 @@
 
 static inline int netlink_capable(struct socket *sock, unsigned int flag)
 {
-	return (nl_table[sock->sk->sk_protocol].nl_nonroot & flag) ||
-	       capable(CAP_NET_ADMIN);
+	if (nl_table[sock->sk->sk_protocol].nl_nonroot & flag)
+		return 1;
+	return ns_capable(sock_net(sock->sk)->user_ns, CAP_NET_ADMIN);
 }
 
 static void