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

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Date:	Mon, 6 Aug 2012 19:20:40 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Serge Hallyn <serge@...lyn.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	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

Quoting Serge Hallyn (serge@...lyn.com):
> 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.

Splitting the cap up into CAP_RESTART (restart /sbin/init) and CAP_BOOT
(reboot hardware or kexec kernel) has the advantage that the capabilities
each remain simpler to parse, no 'in this context it means that'.
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