From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34FB6C433DB for ; Wed, 27 Jan 2021 06:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 039112064B for ; Wed, 27 Jan 2021 06:10:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233090AbhA0GKD (ORCPT ); Wed, 27 Jan 2021 01:10:03 -0500 Received: from mail.hallyn.com ([178.63.66.53]:60370 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233843AbhA0FwB (ORCPT ); Wed, 27 Jan 2021 00:52:01 -0500 Received: by mail.hallyn.com (Postfix, from userid 1001) id 55466864; Tue, 26 Jan 2021 23:50:12 -0600 (CST) Date: Tue, 26 Jan 2021 23:50:12 -0600 From: "Serge E. Hallyn" To: Christian Brauner Cc: "Eric W. Biederman" , Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, John Johansen , James Morris , Mimi Zohar , Dmitry Kasatkin , Stephen Smalley , Casey Schaufler , Arnd Bergmann , Andreas Dilger , OGAWA Hirofumi , Geoffrey Thomas , Mrunal Patel , Josh Triplett , Andy Lutomirski , Theodore Tso , Alban Crequy , Tycho Andersen , David Howells , James Bottomley , Seth Forshee , =?iso-8859-1?Q?St=E9phane?= Graber , Linus Torvalds , Aleksa Sarai , Lennart Poettering , smbarber@chromium.org, Phil Estes , Serge Hallyn , Kees Cook , Todd Kjos , Paul Moore , Jonathan Corbet , containers@lists.linux-foundation.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org Subject: Re: [PATCH v6 23/40] exec: handle idmapped mounts Message-ID: <20210127055012.GA32153@mail.hallyn.com> References: <20210121131959.646623-1-christian.brauner@ubuntu.com> <20210121131959.646623-24-christian.brauner@ubuntu.com> <875z3l0y56.fsf@x220.int.ebiederm.org> <20210125164404.aullgl3vlajgkef3@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210125164404.aullgl3vlajgkef3@wittgenstein> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Mon, Jan 25, 2021 at 05:44:04PM +0100, Christian Brauner wrote: > On Mon, Jan 25, 2021 at 10:39:01AM -0600, Eric W. Biederman wrote: > > Christian Brauner writes: > > > > > When executing a setuid binary the kernel will verify in bprm_fill_uid() > > > that the inode has a mapping in the caller's user namespace before > > > setting the callers uid and gid. Let bprm_fill_uid() handle idmapped > > > mounts. If the inode is accessed through an idmapped mount it is mapped > > > according to the mount's user namespace. Afterwards the checks are > > > identical to non-idmapped mounts. If the initial user namespace is > > > passed nothing changes so non-idmapped mounts will see identical > > > behavior as before. > > > > This does not handle the v3 capabilites xattr with embeds a uid. > > So at least at that level you are missing some critical conversions. > > Thanks for looking. Vfs v3 caps are handled earlier in the series. I'm > not sure what you're referring to here. There are tests in xfstests that > verify vfs3 capability behavior. > > Christian So fwiw I just tested it manually as well. Scenario: uid 1000 user ubuntu uid 1001 user u2 sudo ./mount-idmapped --map-mount b:1000:1001:1 /home/ubuntu/ /mnt su - u2 cp /usr/bin/id /mnt/ unshare -Urm setcap cap_setuid=pe /mnt/id At this point, from init_user_ns, ubuntu@fscaps:~/mount-idmapped$ /home/u2/rcap /mnt/id v3, rootid is 1001 ubuntu@fscaps:~/mount-idmapped$ /home/u2/rcap //home/ubuntu/id v3, rootid is 1000 -serge