From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <548625E3.6020400@nod.at> Date: Mon, 08 Dec 2014 23:27:47 +0100 From: Richard Weinberger MIME-Version: 1.0 To: Andy Lutomirski CC: "Eric W. Biederman" , 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> <5486237D.4060304@nod.at> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: Am 08.12.2014 um 23:25 schrieb Andy Lutomirski: > On Mon, Dec 8, 2014 at 2:17 PM, Richard Weinberger wrote: >> 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? >> > > See my other comment -- the ordering will matter at the end of the series. But ns->gid_map.nr_extents is not atomic, it is a plain u32. This confuses me. Thanks, //richard