From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933911Ab3GWTEg (ORCPT ); Tue, 23 Jul 2013 15:04:36 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:56428 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756943Ab3GWTEf (ORCPT ); Tue, 23 Jul 2013 15:04:35 -0400 Date: Tue, 23 Jul 2013 14:04:26 -0500 From: Serge Hallyn To: Tejun Heo Cc: "Eric W. Biederman" , lkml , Containers Subject: Re: [RFC PATCH 1/2] devices cgroup: allow can_attach() if ns_capable Message-ID: <20130723190426.GA9577@tp> References: <20130723181606.GA6342@sergelap> <20130723183018.GF21100@mtj.dyndns.org> <20130723183841.GA9021@tp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Tejun Heo (tj@kernel.org): > On Tue, Jul 23, 2013 at 2:38 PM, Serge Hallyn wrote: > > This doesn't delegate it into the container. It allows me, on the host, > > to set the cgroup for a container. > > Hmmm? I'm a bit confused. Isn't the description saying that the patch > allows pseudo-root in userns to change cgroup membership even if it > isn't actually root? If task A is uid 1000 on the host, and creates task B as uid X in a new user namespace, then task A, still being uid 1000 on the host, is privileged with respect to B and his namespace - i.e. ns_capable(B->userns, CAP_SYS_ADMIN) is true. > Besides, I find the whole check rather bogus and would actually much > prefer just nuking the check and just follow the standard permission > checks. I'd be ok with that - but there's one case I'm not sure about: If PAM sets me up with /sys/fs/cgroup/devices/serge owned by me, then if I'm thinking right, removing can_attach would mean I could move init into /sys/fs/cgroup/devices/serge... Is there something else stopping that from happening? -serge