Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754305AbaLHWRm (ORCPT ); Mon, 8 Dec 2014 17:17:42 -0500 Received: from a.ns.miles-group.at ([95.130.255.143]:65279 "EHLO radon.swed.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331AbaLHWRk (ORCPT ); Mon, 8 Dec 2014 17:17:40 -0500 Message-ID: <5486237D.4060304@nod.at> Date: Mon, 08 Dec 2014 23:17:33 +0100 From: Richard Weinberger User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.0 MIME-Version: 1.0 To: "Eric W. Biederman" , Andy Lutomirski CC: Linux Containers , Josh Triplett , Andrew Morton , Kees Cook , Michael Kerrisk-manpages , Linux API , linux-man , "linux-kernel@vger.kernel.org" , LSM , Casey Schaufler , "Serge E. Hallyn" , Kenton Varda , stable Subject: Re: [CFT][PATCH 2/7] userns: Don't allow setgroups until a gid mapping has been setablished References: <52e0643bd47b1e5c65921d6e00aea1f724bb510a.1417281801.git.luto@amacapital.net> <87h9xez20g.fsf@x220.int.ebiederm.org> <87mw75ygwp.fsf@x220.int.ebiederm.org> <87fvcxyf28.fsf_-_@x220.int.ebiederm.org> <874mtdyexp.fsf_-_@x220.int.ebiederm.org> <87a935u3nj.fsf@x220.int.ebiederm.org> <87388xodlj.fsf@x220.int.ebiederm.org> <87h9x5re41.fsf_-_@x220.int.ebiederm.org> <87bnndre2h.fsf_-_@x220.int.ebiederm.org> In-Reply-To: <87bnndre2h.fsf_-_@x220.int.ebiederm.org> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 08.12.2014 um 23:07 schrieb Eric W. Biederman: > > setgroups is unique in not needing a valid mapping before it can be called, > in the case of setgroups(0, NULL) which drops all supplemental groups. > > The design of the user namespace assumes that CAP_SETGID can not actually > be used until a gid mapping is established. Therefore add a helper function > to see if the user namespace gid mapping has been established and call > that function in the setgroups permission check. > > This is part of the fix for CVE-2014-8989, being able to drop groups > without privilege using user namespaces. > > Cc: stable@vger.kernel.org > Signed-off-by: "Eric W. Biederman" > --- > include/linux/user_namespace.h | 9 +++++++++ > kernel/groups.c | 7 ++++++- > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > index e95372654f09..41cc26e5a350 100644 > --- a/include/linux/user_namespace.h > +++ b/include/linux/user_namespace.h > @@ -37,6 +37,15 @@ struct user_namespace { > > extern struct user_namespace init_user_ns; > > +static inline bool userns_gid_mappings_established(const struct user_namespace *ns) > +{ > + bool established; > + smp_mb__before_atomic(); > + established = ACCESS_ONCE(ns->gid_map.nr_extents) != 0; > + smp_mb__after_atomic(); > + return established; > +} > + Maybe this is a stupid question, but why do we need all this magic around established = ... ? The purpose of this code is to check whether ns->gid_map.nr_extents != 0 in a lock-free manner? Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/