linux-kernel - Re: Current state of CLONE

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Date:	Tue, 25 Nov 2008 10:54:49 -0500
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Subrata Modak" <subrata@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>, linux-man@...r.kernel.org,
	clg@...ibm.com, herbert@...hfloor.at, dev@...ru
Subject: Re: Current state of CLONE_NEWUSER?

Hi Serge,

On Fri, Nov 21, 2008 at 10:07 AM, Serge E. Hallyn <serue@...ibm.com> wrote:
> Quoting Eric W. Biederman (ebiederm@...ssion.com):
>> "Michael Kerrisk" <mtk.manpages@...glemail.com> writes:
>>
>> > Hi Eric,
>> >
>> > On Wed, Nov 19, 2008 at 8:41 PM, Eric W. Biederman
>> > <ebiederm@...ssion.com> wrote:
>> >> "Michael Kerrisk" <mtk.manpages@...glemail.com> writes:
>> >>
>> >>> Hi Serge,
>> >>>
>> >>> What is the current status of CLONE_NEWUSER?  I'm currently trying to
>> >>> test this flag in preparation for documenting it in the clone(2) man
>> >>> page, but am running into an ENOMEM error from the clone() call, which
>> >>> seems to occur after a failure in kobject_init_and_add() in the
>> >>> following call sequence:
>> >>>
>> >>> clone_user_ns() --> alloc_uid() --> uids_user_create() -->
>> >>> kobject_init_and_add()
>> >>>
>> >>> Are there already some test programs somewhere?  Is there any
>> >>> documentation already available for this flag?
>> >>
>> >> This code is definitely still under development.
>> >>
>> >> When complete it should be able to create a new uid namespace,
>> >> as an unprivileged user.  Creating a new process with uid == gid == 0.
>> >> Have a full set of caps.  And have permission to do nothing on the system
>> >> except read world readable files and write world writable files.
>> >
>> > Thanks for the info,
>> >
>> > So the error I described is expected?
>>
>> I don't think so.  Serge?
>
> I suspect you have the fair scheduler compiled in
> (CONFIG_FAIR_GROUP_SCHED).

True.

> So when you create a new user namespace, it
> tries to create a new /sys/kernel/uids/0 (or thereabouts) directory
> which sysfs refuses.

Okay.

> The fix for this was rolled in as the last patch in the rejected large
> network namespace/sysfs rework.  So we'll need another fix.  I suspect
> following the same path as we did for making network namespaces work is
> the best path for now.  (This being my last day of a week-long vacation
> I won't be sending a patch today :)

Yep, I saw your patch, thanks.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
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