From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out01.mta.xmission.com ([166.70.13.231]:52756 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751329AbcGWWJ6 (ORCPT ); Sat, 23 Jul 2016 18:09:58 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: "W. Trevor King" Cc: James Bottomley , Andrey Vagin , Serge Hallyn , linux-api@vger.kernel.org, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Alexander Viro , criu@openvz.org, linux-fsdevel@vger.kernel.org, "Michael Kerrisk \(man-pages\)" References: <1468520419-28220-1-git-send-email-avagin@openvz.org> <20160723211414.GA25371@odin.tremily.us> <1469309936.2332.35.camel@HansenPartnership.com> <20160723215802.GO24913@odin.tremily.us> Date: Sat, 23 Jul 2016 16:56:44 -0500 In-Reply-To: <20160723215802.GO24913@odin.tremily.us> (W. Trevor King's message of "Sat, 23 Jul 2016 14:58:02 -0700") Message-ID: <87mvl8nhlv.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Sender: linux-fsdevel-owner@vger.kernel.org List-ID: "W. Trevor King" writes: 2> On Sat, Jul 23, 2016 at 02:38:56PM -0700, James Bottomley wrote: >> On Sat, 2016-07-23 at 14:14 -0700, W. Trevor King wrote: >> > namespaces(7) and clone(2) both have: >> > >> > When a network namespace is freed (i.e., when the last process >> > in the namespace terminates), its physical network devices are >> > moved back to the initial network namespace (not to the parent >> > of the process). >> > >> > So the initial network namespace (the head of net_namespace_list?) >> > is special [1]. To understand how physical network devices will >> > be handled, it seems like we want to treat network devices as a >> > depth-1 tree, with all non-initial net namespaces as children of >> > the initial net namespace. Can we extend this series' >> > NS_GET_PARENT to return: >> > >> > * EPERM for an unprivileged caller (like this series currently does >> > for PID namespaces), >> > * ENOENT when called on net_namespace_list, and >> > * net_namespace_list when called on any other net namespace. >> >> What's the practical application of this? independent net >> namespaces are managed by the ip netns command. It pins them by a >> bind mount in a flat fashion; if we make them hierarchical the tool >> would probably need updating to reflect this, so we're going to need >> a reason to give the network people. Just having the interfaces not >> go back to root when you do an ip netns delete doesn't seem very >> compelling. > > I'm not suggesting we add support for deeper nesting, I'm suggesting > we use NS_GET_PARENT to allow sufficiently privileged users to > determine if a given net namespace is the initial net namespace. You > could do this already with something like: > > 1. Create a new net namespace. > 2. Add a physical network device to that namespace. > 3. Delete that namespace. > 4. See if the physical network device shows up in your > initial-net-namespace candidate. > 5. Delete the physical network device (hopefully it ended up somewhere > you can find it ;). > > But using an NS_GET_PARENT call seems much safer and easier. Have you had the problem in practice where you can't tell which network namespace is the initial network namespace. This all seems like a theoretical problem rather than a real one. Eric