linux-kernel - Re: [RFC][PATCH 6/7][v4] SI_USER: Masquerade si

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Date:	Wed, 24 Dec 2008 13:08:55 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	ebiederm@...ssion.com, roland@...hat.com, bastian@...di.eu.org,
	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 6/7][v4] SI_USER: Masquerade si_pid when crossing
	pid ns boundary

Oleg Nesterov [oleg@...hat.com] wrote:
| On 12/24, Sukadev Bhattiprolu wrote:
| >
| > +static void masquerade_si_pid(struct task_struct *t, siginfo_t *info)
| > +{
| > +	if (is_si_special(info) || SI_FROMKERNEL(info))
| > +		return;

Grr, This needs to go. I started with a general function but then
got specific to SI_USER.

| > +
| > +	/*
| > +	 * When crossing pid namespace boundary, SI_USER signal can only
| > +	 * go from ancestor to descendant ns but not the other way. So,
| > +	 * just ->si_pid to 0 since, the sender will not have a pid in
| > +	 * the receiver's namespace.
| > +	 */
| > +	if (info->si_code == SI_USER)
| > +		info->si_pid = 0;
| > +}
| > +
| >  static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
| >  			int group)
| >  {
| > @@ -946,6 +974,8 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
| >  			break;
| >  		default:
| >  			copy_siginfo(&q->info, info);
| > +			if (from_ancestor_ns)
| > +				masquerade_si_pid(t, &q->info);
| >  			break;
| >  		}
| >  	} else if (!is_si_special(info)) {
| > @@ -2343,7 +2373,7 @@ sys_kill(pid_t pid, int sig)
| >  	info.si_signo = sig;
| >  	info.si_errno = 0;
| >  	info.si_code = SI_USER;
| > -	info.si_pid = task_tgid_vnr(current);
| > +	info.si_pid = 0;	/* masquerade in send_signal() */
| >  	info.si_uid = current_uid();

Yes, I will undo this...

| 
| Can't understand this patch. First of all, it looks wrong. Looks like
| we never set .si_pid != 0 when the signal is set by sys_kill() ?
| 
| But more importantly, unless I missed something, this patch is unnecessary
| complication.
| 
| We call masquerade_si_pid() only when from_ancestor_ns == T, this is correct.
| But this means that (!is_si_special(info) && SI_FROMUSER(info)) == T, why
| do we re-check in masquerade_si_pid() ?
| 
| And why can't we just do
| 
| 	 default:
| 	 	copy_siginfo(&q->info, info);
| 	 	if (from_ancestor_ns)
| 	 		info->si_pid = 0;

and go with this.

| 
| ? Why should we check SI_USER and change sys_kill() ?
| 
| see also the comment for the next 7/7 patch.
| 
| Oleg.
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