From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932344AbcERP4v (ORCPT ); Wed, 18 May 2016 11:56:51 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:42573 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753421AbcERP4r (ORCPT ); Wed, 18 May 2016 11:56:47 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Seth Forshee Cc: Alexander Viro , Greg Kroah-Hartman , Jeff Layton , "J. Bruce Fields" , Tejun Heo , Li Zefan , Johannes Weiner , Serge Hallyn , Richard Weinberger , Austin S Hemmelgarn , Miklos Szeredi , Pavel Tikhomirov , linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.sourceforge.net, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, cgroups@vger.kernel.org References: <1461699046-30485-1-git-send-email-seth.forshee@canonical.com> <1461699046-30485-4-git-send-email-seth.forshee@canonical.com> <87shxgxqai.fsf@x220.int.ebiederm.org> <20160517235834.GA104031@ubuntu-hedt> Date: Wed, 18 May 2016 10:45:31 -0500 In-Reply-To: <20160517235834.GA104031@ubuntu-hedt> (Seth Forshee's message of "Tue, 17 May 2016 18:58:34 -0500") Message-ID: <8760ubs738.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX19fWt8j5OVvedZb4BEqAjkOroQLeOcf/vQ= X-SA-Exim-Connect-IP: 97.119.107.188 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 TVD_RCVD_IP Message was received from an IP address * 0.7 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa03 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Seth Forshee X-Spam-Relay-Country: X-Spam-Timing: total 1943 ms - load_scoreonly_sql: 0.06 (0.0%), signal_user_changed: 4.0 (0.2%), b_tie_ro: 2.9 (0.2%), parse: 1.26 (0.1%), extract_message_metadata: 109 (5.6%), get_uri_detail_list: 12 (0.6%), tests_pri_-1000: 36 (1.9%), tests_pri_-950: 2.0 (0.1%), tests_pri_-900: 14 (0.7%), tests_pri_-400: 75 (3.8%), check_bayes: 69 (3.6%), b_tokenize: 24 (1.2%), b_tok_get_all: 18 (0.9%), b_comp_prob: 6 (0.3%), b_tok_touch_all: 16 (0.8%), b_finish: 1.16 (0.1%), tests_pri_0: 1673 (86.1%), check_dkim_signature: 0.87 (0.0%), check_dkim_adsp: 24 (1.2%), tests_pri_500: 22 (1.1%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH v4 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Seth Forshee writes: > On Tue, May 17, 2016 at 05:39:33PM -0500, Eric W. Biederman wrote: >> Seth Forshee writes: >> >> > Both of these filesystems already have use cases for mounting the >> > same super block from multiple user namespaces. For sysfs this >> > happens when using criu for snapshotting a container, where sysfs >> > is mnounted in the containers network ns but the hosts user ns. >> > The cgroup filesystem shares the same super block for all mounts >> > of the same hierarchy regardless of the namespace. >> > >> > As a result, the restriction on mounting a super block from a >> > single user namespace creates regressions for existing uses of >> > these filesystems. For these specific filesystems this >> > restriction isn't really necessary since the backing store is >> > objects in kernel memory and thus the ids assigned from inodes >> > is not subject to translation relative to s_user_ns. >> > >> > Add a new filesystem flag, FS_USERNS_SHARE_SB, which when set >> > causes sget_userns() to skip the check of s_user_ns. Set this >> > flag for the sysfs and cgroup filesystems to fix the >> > regressions. >> >> So this one needs to be sget_userns(..., &init_user_ns, ...). >> And not a new special case. > > This is actually what I wanted to do, but based on a previous discussion > where I had suggested doing this (for a different reason) I came away > thinking you did not want it that way. So I'm happy with that change. Yeah. Somedays it seems like there are a lot of pieces in play here. The security labels on sysfs seems to be a very compelling case. > But if we do that it violates some of the assumptions of the patch to > rework MNT_NODEV on your testing branch (and also those behind patch 2 > in this series). Something will need to be changed there to prevent a > regression in mount behavior when a user ns tries to mount without > MNT_NODEV when the mount inherited from its parent has it set. Thank you for pointing that out. I will look into that. I believe I know exactly what you are talking about. Of the choices I think it is better to a minor localized change in the fs_fully_visible logic than it is to cause problems elsewhere. >> Apologies for not catching this earlier. > > Actually this is a more recent patch, so you possibly hadn't seen it > before. > >> I am looking at folding all of this into the patch that introduces >> sget_userns so that even bisects won't have regresssions. > > That's fine with me. And thank you for keeping everything as separate patches. That is at least helping me catch up. Even if I don't agree that these things should be separate come merge time. Eric