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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2CEC1C433E7 for ; Sun, 11 Oct 2020 20:53:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EFD7220678 for ; Sun, 11 Oct 2020 20:53:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729466AbgJKUxV (ORCPT ); Sun, 11 Oct 2020 16:53:21 -0400 Received: from relay6-d.mail.gandi.net ([217.70.183.198]:53575 "EHLO relay6-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729321AbgJKUxV (ORCPT ); Sun, 11 Oct 2020 16:53:21 -0400 X-Originating-IP: 67.5.25.97 Received: from localhost (unknown [67.5.25.97]) (Authenticated sender: josh@joshtriplett.org) by relay6-d.mail.gandi.net (Postfix) with ESMTPSA id 499F2C0004; Sun, 11 Oct 2020 20:53:08 +0000 (UTC) Date: Sun, 11 Oct 2020 13:53:06 -0700 From: Josh Triplett To: "Serge E. Hallyn" Cc: Christian Brauner , containers@lists.linux-foundation.org, Alexander Mihalicyn , Mrunal Patel , Wat Lim , Aleksa Sarai , Pavel Tikhomirov , Geoffrey Thomas , "Eric W. Biederman" , Joseph Christopher Sible , =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , Vivek Goyal , Giuseppe Scrivano , Andy Lutomirski , Stephane Graber , Kees Cook , Sargun Dhillon , linux-kernel@vger.kernel.org Subject: Re: LPC 2020 Hackroom Session: summary and next steps for isolated user namespaces Message-ID: <20201011205306.GC17441@localhost> References: <20200830143959.rhosiunyz5yqbr35@wittgenstein> <20201010042606.GA30062@mail.hallyn.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201010042606.GA30062@mail.hallyn.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 09, 2020 at 11:26:06PM -0500, Serge E. Hallyn wrote: > > 3. Find a way to allow setgroups() in a user namespace while keeping > > in mind the case of groups used for negative access control. > > This was suggested by Josh Triplett and Geoffrey Thomas. Their idea was to > > investigate adding a prctl() to allow setgroups() to be called in a user > > namespace at the cost of restricting paths to the most restrictive > > permission. So if something is 0707 it needs to be treated as if it's 0000 > > even though the caller is not in its owning group which is used for negative > > access control (how these new semantics will interact with ACLs will also > > need to be looked into). > > I should probably think this through more, but for this problem, would it > not suffice to add a new prevgroups grouplist to the struct cred, maybe > struct group_info *locked_groups, and every time an unprivileged task creates > a new user namespace, add all its current groups to this list? So, effectively, you would be allowed to drop permissions, but locked_groups would still be checked for restrictions? That seems like it'd introduce a new level of complexity (a new facet of permission) to manage. Not opposed, but it does seem more complex than just opting out of using groups for negative permissions.