linux-kernel - Re: [PATCH] pidns: Limit kill -1 and cap_set

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Message-ID: <m1pryxpzsb.fsf@ebiederm.dsl.xmission.com>
Date:	Mon, 29 Oct 2007 11:59:48 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Linux Containers <containers@...ts.osdl.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Sukadev Bhattiprolu [imap]" <sukadev@...ibm.com>
Subject: Re: [PATCH] pidns: Limit kill -1 and cap_set_all

Dave Hansen <haveblue@...ibm.com> writes:

> On Fri, 2007-10-26 at 14:37 -0600, Eric W. Biederman wrote:
>> 
>> +static int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)
>> +{
>> +       return pid && (ns->level <= pid->level) &&
>> +               pid->numbers[ns->level].ns == ns;
>> +}
>
> Could we blow this out a little bit?  (I think the blown-out version
> lends itself to being better commented, and easier to read.)  Also, can
> we think of any better name for this?  It seems a bit funky that:
>
> 	pid_in_pid_ns(mypid, &init_pid_ns);
>
> would _ever_ return 0.

It can't.

> So, it isn't truly a test for belonging *in* a
> namespace, but having that namespace be the lowest level one. 

No.  It is precisely a test for being in a namespace.
We first check ns->level to make certain it doesn't fall out
of the array, and then we check to see if the namespace we
are looking for is at that level.

pid->numbers[0].ns == &init_pid_ns.

> I think
> Suka toyed with calling it an "active" or "primary" pid namespace.  That
> differentiated mere membership in a pid namespace from the one that
> actually molds that pid's view of the world.

What we want for the test is a test for membership.


> static int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)
> {
> 	if (!pid)
> 		return 0;
> 	if (ns->level > pid->level)
> 		return 0;
> 	if (pid->numbers[ns->level].ns != ns)
> 		return 0;
> 	return 1;
> }

I don't have a problem with that.  The rest of the checks for
this in kernel/pid.c are in the same form.

Eric

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