linux-kernel - Re: Current state of CLONE

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Date:	Fri, 21 Nov 2008 09:07:10 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	mtk.manpages@...il.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?

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

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 :)

-serge
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