(Was: user namespace: make signal.c respect user namespaces)

Quoted 11 lines · Serge E. Hallyn

Quoted 8 lines · Oleg Nesterov

	static inline uid_t good_name(struct task_struct *from, struct task_struct *to)
	{
		// the caller does rcu_read_lock() if needed
		const struct cred *from_cred = __task_cred(from);
		return user_ns_map_uid(task_cred_xxx(to, user_ns),
					from_cred, from_cred->uid);
	}

Quoted 3 lines

That looks great, thanks. I couldn't think it up myself, but now that I see it in your email, I see this would be very valuable in helping make this code more readable :)

Damn ;) The problem is, "the caller does rcu_read_lock() if needed" can't shut up __rcu_dereference_check(). current_cred() passes c == true to do this.

This reminds me, __task_cred()->task_is_dead() should go away. Probably we can replace it with (__t == current). Otherwise send_signal() needs rcu_read_lock() to avoid the warning from lockdep, or the helper needs the unconditional rcu_read_lock().