pidns: Add a limit on the number of pid namespaces

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 918b117..34cce96 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -40,6 +40,7 @@
 	struct fs_pin *bacct;
 #endif
 	struct user_namespace *user_ns;
+	struct ucounts *ucounts;
 	struct work_struct proc_work;
 	kgid_t pid_gid;
 	int hide_pid;