netns: Add a limit on the number of net namespaces

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/ucount.c

@@ -71,6 +71,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_pid_namespaces"),
 	UCOUNT_ENTRY("max_uts_namespaces"),
 	UCOUNT_ENTRY("max_ipc_namespaces"),
+	UCOUNT_ENTRY("max_net_namespaces"),
 	UCOUNT_ENTRY("max_cgroup_namespaces"),
 	{ }
 };