linux-kernel - Re: [PATCH] Forbid invocation of kexec_load() outside initial PID namespace

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Date:	Sat, 04 Aug 2012 18:15:35 -0500
From:	Serge Hallyn <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Daniel P. Berrange" <berrange@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] Forbid invocation of kexec_load() outside initial PID
	namespace

Eric,

during the container reboot discussion, the agreement was reached that rebooting for real fron non-init pid ns is not safe.  Restarting userspace (in pidns caller owns) is.  I argue the same reasoning supports this.

I haven't had a chance to review the patch, but the idea gets my ack.  I'll look at the patch asap.

I'm also fine with splitting cap_sys_boot into a user and system caps.  The former would only be needed targeted to the userns of the init pid, while the latter would be required to init_user_ns.  Then containers could safely be given cap_sys_restart or whatever, but not cap_sys_boot which authorizes kexec and machine reset/poweroff.

----- Original message -----
> "Daniel P. Berrange" <berrange@...hat.com> wrote:
> 
> > On Fri, Aug 03, 2012 at 05:45:40AM -0700, Eric W. Biederman wrote:
> > > The solution is to use user namespaces and to only test ns_capable on
> > the magic reboot path.
> > > 
> > > For the 3.7 timeframe that should be a realistic solution.
> > 
> > Hmm, that would imply that if LXC wants to allow reboot()/CAP_SYS_BOOT
> > they will be forced to use CLONE_NEWUSER. I was rather looking for a
> > way
> > to allow the container to keep CAP_SYS_BOOT, without also mandating use
> > of user namespaces.
> 
> If we remove the use of CAP_SYS_BOOT on the container reboot path
> perhaps.
> 
> But you have hit one small issue in the huge pile of issues why giving
> contaners capabilities is generally a bad idea.
> 
> This is the reason I have been insisting on a reasonable version of user
> namespaces for a long time.
> 
> When the security issues become important it is time for user
> namespaces.     That is their purpose.
> 
> Eric
> 
> 
> 
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