Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752743AbbKQBN4 (ORCPT ); Mon, 16 Nov 2015 20:13:56 -0500 Received: from h2.hallyn.com ([78.46.35.8]:52580 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751053AbbKQBNy (ORCPT ); Mon, 16 Nov 2015 20:13:54 -0500 Date: Mon, 16 Nov 2015 19:13:49 -0600 From: "Serge E. Hallyn" To: "Eric W. Biederman" Cc: "Serge E. Hallyn" , Richard Weinberger , Richard Weinberger , LKML , "open list:ABI/API" , Linux Containers , LXC development mailing-list , Tejun Heo , cgroups mailinglist , Andrew Morton Subject: Re: CGroup Namespaces (v4) Message-ID: <20151117011349.GA1958@mail.hallyn.com> References: <1447703505-29672-1-git-send-email-serge@hallyn.com> <20151116204606.GA30681@mail.hallyn.com> <564A41AF.4040208@nod.at> <20151116205452.GA30975@mail.hallyn.com> <87y4dxh9b8.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y4dxh9b8.fsf@x220.int.ebiederm.org> 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 Content-Length: 4508 Lines: 120 On Mon, Nov 16, 2015 at 04:24:27PM -0600, Eric W. Biederman wrote: > "Serge E. Hallyn" writes: > > > On Mon, Nov 16, 2015 at 09:50:55PM +0100, Richard Weinberger wrote: > >> Am 16.11.2015 um 21:46 schrieb Serge E. Hallyn: > >> > On Mon, Nov 16, 2015 at 09:41:15PM +0100, Richard Weinberger wrote: > >> >> Serge, > >> >> > >> >> On Mon, Nov 16, 2015 at 8:51 PM, wrote: > >> >>> To summarize the semantics: > >> >>> > >> >>> 1. CLONE_NEWCGROUP re-uses 0x02000000, which was previously CLONE_STOPPED > >> >>> > >> >>> 2. unsharing a cgroup namespace makes all your current cgroups your new > >> >>> cgroup root. > >> >>> > >> >>> 3. /proc/pid/cgroup always shows cgroup paths relative to the reader's > >> >>> cgroup namespce root. A task outside of your cgroup looks like > >> >>> > >> >>> 8:memory:/../../.. > >> >>> > >> >>> 4. when a task mounts a cgroupfs, the cgroup which shows up as root depends > >> >>> on the mounting task's cgroup namespace. > >> >>> > >> >>> 5. setns to a cgroup namespace switches your cgroup namespace but not > >> >>> your cgroups. > >> >>> > >> >>> With this, using github.com/hallyn/lxc #2015-11-09/cgns (and > >> >>> github.com/hallyn/lxcfs #2015-11-10/cgns) we can start a container in a full > >> >>> proper cgroup namespace, avoiding either cgmanager or lxcfs cgroup bind mounts. > >> >>> > >> >>> This is completely backward compatible and will be completely invisible > >> >>> to any existing cgroup users (except for those running inside a cgroup > >> >>> namespace and looking at /proc/pid/cgroup of tasks outside their > >> >>> namespace.) > >> >>> cgroupns-root. > >> >> > >> >> IIRC one downside of this series was that only the new "sane" cgroup > >> >> layout was supported > >> >> and hence it was useless for everything which expected the default layout. > >> >> Hence, still no systemd for us. :) > >> >> > >> >> Is this now different? > >> > > >> > Yes, all hierachies are no supported. > >> > > >> > >> Should read "now"? :-) > >> If so, *awesome*! > > > > D'oh! Yes, now :-) > > I am glad to see multiple hierarchy support, that is something people > can use today. > > A couple of quick questions before I delve into a review. > > Does this allow mixing of cgroupfs and cgroupfs2? That is can I: "mount > -t cgroupfs" inside a container and "mount -t cgroupfs2" outside a > container? and still have reasonable things happen? I suspect the > semantics of cgroups prevent this but I am interested to know what happens. As Tejun said, this is not an issue. There's not an actual separate cgroupfs2 filesystem, it's just a separate hierarchy which controllers can be bound to or not, which has its own set of semantics (like no tasks on leafnodes). So a legacy application would never be able to run on the unified hierarchy, but this does not change that. > Similary have you considered what it required to be able to safely set > FS_USERNS_MOUNT? I think the only thing we need to do is 1. go through and make sure that any ability to change mount flags is under capable() (which I have not yet done). The cgroup_mount() itself checks that flags are not changed, but there may be some subtle way to effect a change that I'm not aware of yet. 2. Make sure that to bind a new controller you must be true root. It's possible that a patch like the one below would suffice. -serge >From 37699aa868cba3efb6ea0aa2e53e0b85b619f02d Mon Sep 17 00:00:00 2001 From: Serge Hallyn Date: Mon, 16 Nov 2015 19:11:07 -0600 Subject: [PATCH 1/1] Don't allow user namespaces to bind new subsystems If memory was not mounted on the host, then root in a container should not be able to mount it. Signed-off-by: Serge Hallyn --- kernel/cgroup.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 0a3e893..db514b4 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2102,6 +2102,11 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, goto out_unlock; } + if (!opts.none && !capable(CAP_SYS_ADMIN)) { + ret = -EPERM; + goto out_unlock; + } + root = kzalloc(sizeof(*root), GFP_KERNEL); if (!root) { ret = -ENOMEM; -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/