linux-kernel - Re: [PATCH] user namespace: make signal.c respect user namespaces

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Date:	Tue, 20 Sep 2011 14:22:02 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, richard@....at,
	Andrew Morton <akpm@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>, serge@...lyn.com
Subject: Re: [PATCH] user namespace: make signal.c respect user namespaces

On 09/19, Serge E. Hallyn wrote:
>
> __send_signal: convert the uid being sent in SI_USER to the target task's
> user namespace.
>
> do_notify_parent and do_notify_parent_cldstop: map task's uid to parent's
>  user namespace
>
> ptrace_signal: map parent's uid into current's user namespace before
> including in signal to current.

And all of them follow the same pattern,

> @@ -1073,7 +1074,8 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
>  			q->info.si_code = SI_USER;
>  			q->info.si_pid = task_tgid_nr_ns(current,
>  							task_active_pid_ns(t));
> -			q->info.si_uid = current_uid();
> +			q->info.si_uid = user_ns_map_uid(task_cred_xxx(t, user_ns),
> +					current_cred(), current_uid());

Up to you, but may be we can add a helper? Something like

	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);
	}

As for __send_signal() in particular, I guess we could do

		q->info.si_uid = from_ancestor_ns ? 0 : current_uid();

instead, but otoh perhaps it is better to use user_ns_map_uid() anyway
for consistency.

> @@ -2118,11 +2124,16 @@ static int ptrace_signal(int signr, siginfo_t *info,
>  	 * have updated *info via PTRACE_SETSIGINFO.
>  	 */
>  	if (signr != info->si_signo) {
> +		const struct cred *pcred;
>  		info->si_signo = signr;
>  		info->si_errno = 0;
>  		info->si_code = SI_USER;
>  		info->si_pid = task_pid_vnr(current->parent);
> -		info->si_uid = task_uid(current->parent);
> +		rcu_read_lock();

In this case please add rcu_read_lock() earlier, before task_pid_vnr().
It has the same (theoretical) reasons for rcu lock.

Oleg.

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