Re: [PATCH v2 1/2] signal: avoid shared siginfo namespace rewrites

[Oleg Nesterov <oleg@redhat.com>]

On 06/24, Bradley Morgan wrote:
>
> Hey you two, sorry to impede in your conversation, but could we write
> your "conflicting" patch over my Patch 2?
>
> It's fine if you don't want to, it kind of kills two birds with one stone.

No, sorry, I don't ;) at least right now. Because I don't really like the
changes it adds into send_signal_locked(). But perhaps I didn't read it
carefully.

Can we return to it later? There is another reason... Currently I am very
busy but I am thinking about another change on top of your 1/2. Something
like below. Not sure it makes a lot of sense though.

Eric, do you think this optimization on top of 1/2 makes sense?

Oleg.

int send_signal_locked(int sig, struct kernel_siginfo *info,
		       struct task_struct *t, enum pid_type type)
{
	/* Should SIGKILL or SIGSTOP be received by a pid namespace init? */
	struct kernel_siginfo __info;
	bool force = false;

	if (info == SEND_SIG_NOINFO) {
		/* Force if sent from an ancestor pid namespace */
		force = !task_pid_nr_ns(current, task_active_pid_ns(t));
	} else if (info == SEND_SIG_PRIV) {
		/* Don't ignore kernel generated signals */
		force = true;
	} else if (has_si_pid_and_uid(info)) {
		/* SIGKILL and SIGSTOP is special or has ids */
		struct user_namespace *t_user_ns;

#ifdef CONFIG_USER_NS
		rcu_read_lock();
		t_user_ns = task_cred_xxx(t, user_ns);
		if (current_user_ns() != t_user_ns) {
			__info = *info;
			info = &__info;
			kuid_t uid = make_kuid(current_user_ns(), info->si_uid);
			info->si_uid = from_kuid_munged(t_user_ns, uid);
		}
		rcu_read_unlock();
#endif
		/* A kernel generated signal? */
		force = (info->si_code == SI_KERNEL);

#ifdef CONFIG_PID_NS
		/* From an ancestor pid namespace? */
		if (!task_pid_nr_ns(current, task_active_pid_ns(t))) {
			if (info != &__info) {
				__info = *info;
				info = &__info;
			}
			info->si_pid = 0;
			force = true;
		}
#endif
	}
	return __send_signal_locked(sig, info, t, type, force);
}