Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752555AbdGRXNw (ORCPT ); Tue, 18 Jul 2017 19:13:52 -0400 Received: from h2.hallyn.com ([78.46.35.8]:49298 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751505AbdGRXNv (ORCPT ); Tue, 18 Jul 2017 19:13:51 -0400 Date: Tue, 18 Jul 2017 18:13:50 -0500 From: "Serge E. Hallyn" To: "Eric W. Biederman" Cc: Stefan Berger , James Morris , "Theodore Ts'o" , "Serge E. Hallyn" , containers@lists.linux-foundation.org, lkp@01.org, linux-kernel@vger.kernel.org, zohar@linux.vnet.ibm.com, tycho@docker.com, James.Bottomley@HansenPartnership.com, vgoyal@redhat.com, christian.brauner@mailbox.org, amir73il@gmail.com, linux-security-module@vger.kernel.org, casey@schaufler-ca.com Subject: Re: [PATCH v2] xattr: Enable security.capability in user namespaces Message-ID: <20170718231350.GA20787@mail.hallyn.com> References: <20170712170346.GA17974@mail.hallyn.com> <877ezdgsey.fsf@xmission.com> <74664cc8-bc3e-75d6-5892-f8934404349f@linux.vnet.ibm.com> <20170713011554.xwmrgkzfwnibvgcu@thunk.org> <87y3rscz9j.fsf@xmission.com> <20170713164012.brj2flnkaaks2oci@thunk.org> <29fdda5e-ed4a-bcda-e3cc-c06ab87973ce@linux.vnet.ibm.com> <871spdj2pe.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <871spdj2pe.fsf@xmission.com> 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: 1403 Lines: 31 Quoting Eric W. Biederman (ebiederm@xmission.com): > Stefan Berger writes: > > > On 07/18/2017 03:01 AM, James Morris wrote: > >> On Thu, 13 Jul 2017, Stefan Berger wrote: > >> > >>> A file shared by 2 containers, one mapping root to uid=1000, the other mapping > >>> root to uid=2000, will show these two xattrs on the host (init_user_ns) once > >>> these containers set xattrs on that file. > >> I may be missing something here, but what happens when say the uid=2000 > >> container and associated user is deleted from the system, then another is > >> created with the same uid? > >> > >> Won't this mean that you have unexpected capabilities turning up in the > >> new container? > >> > > > > Yes, that's right. I don't know any solution for that. We would have to walk the > > filesystems and find all 'stale' xattrs with such a uid. This is independent of > > whether the uid is encoded on the name side, as in this patch, or on the value > > side, as in Serge's original proposal. And uids of a mapped container root user > > don't necessarily have to have an account on the host so that an account > > deletion could trigger that. > > This problem is actually independent of this piece of code entirely. > Any lingering files owned by that uid have the same issue. In particular, any setuid-root files in that container have the precisely analogous issue. -serge