Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754233AbdFWQA2 (ORCPT ); Fri, 23 Jun 2017 12:00:28 -0400 Received: from h2.hallyn.com ([78.46.35.8]:56626 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754109AbdFWQA0 (ORCPT ); Fri, 23 Jun 2017 12:00:26 -0400 Date: Fri, 23 Jun 2017 11:00:26 -0500 From: "Serge E. Hallyn" To: Amir Goldstein Cc: Stefan Berger , "Eric W. Biederman" , Linux Containers , lkp@01.org, xiaolong.ye@intel.com, linux-kernel , Mimi Zohar , "Serge E. Hallyn" , Tycho Andersen , James Bottomley , christian.brauner@mailbox.org, Vivek Goyal , LSM List Subject: Re: [PATCH 0/3] Enable namespaced file capabilities Message-ID: <20170623160026.GA18257@mail.hallyn.com> References: <1498157989-11814-1-git-send-email-stefanb@linux.vnet.ibm.com> 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 Content-Length: 1927 Lines: 37 Quoting Amir Goldstein (amir73il@gmail.com): > On Thu, Jun 22, 2017 at 9:59 PM, Stefan Berger > wrote: > > This series of patches primary goal is to enable file capabilities > > in user namespaces without affecting the file capabilities that are > > effective on the host. This is to prevent that any unprivileged user > > on the host maps his own uid to root in a private namespace, writes > > the xattr, and executes the file with privilege on the host. > > > > We achieve this goal by writing extended attributes with a different > > name when a user namespace is used. If for example the root user > > in a user namespace writes the security.capability xattr, the name > > of the xattr that is actually written is encoded as > > security.capability@uid=1000 for root mapped to uid 1000 on the host. > > When listing the xattrs on the host, the existing security.capability > > as well as the security.capability@uid=1000 will be shown. Inside the > > namespace only 'security.capability', with the value of > > security.capability@uid=1000, is visible. > > > > Am I the only one who thinks that suffix is perhaps not the best grammar > to use for this namespace? You're the only one to have mentioned it so far. > xattrs are clearly namespaced by prefix, so it seems right to me to keep > it that way - define a new special xattr namespace "ns" and only if that > prefix exists, the @uid suffix will be parsed. > This could be either ns.security.capability@uid=1000 or > ns@uid=1000.security.capability. The latter seems more correct to me, > because then we will be able to namespace any xattr without having to > protect from "unprivileged xattr injection", i.e.: > setfattr -n "user.whatever.foo@uid=0" I like it for simplifying the parser code. One concern I have is that, since ns.* is currently not gated, one could write ns.* on an older kernel and then exploit it on a newer one.