From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: [CFT][PATCH 2/7] userns: Don't allow setgroups until a gid mapping has been setablished Date: Mon, 08 Dec 2014 16:07:02 -0600 Message-ID: <87bnndre2h.fsf_-_@x220.int.ebiederm.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87h9x5re41.fsf_-_-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org> (Eric W. Biederman's message of "Mon, 08 Dec 2014 16:06:06 -0600") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Andy Lutomirski Cc: linux-man , Kees Cook , Linux API , Linux Containers , Josh Triplett , stable , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Kenton Varda , LSM , Michael Kerrisk-manpages , Richard Weinberger , Casey Schaufler , Andrew Morton List-Id: linux-man@vger.kernel.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.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; +} + #ifdef CONFIG_USER_NS static inline struct user_namespace *get_user_ns(struct user_namespace *ns) diff --git a/kernel/groups.c b/kernel/groups.c index 02d8a251c476..e0335e44f76a 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -6,6 +6,7 @@ #include #include #include +#include #include /* init to 2 - one for init_task, one to ensure it is never freed */ @@ -217,7 +218,11 @@ bool may_setgroups(void) { struct user_namespace *user_ns = current_user_ns(); - return ns_capable(user_ns, CAP_SETGID); + /* It is not safe to use setgroups until a gid mapping in + * the user namespace has been established. + */ + return userns_gid_mappings_established(user_ns) && + ns_capable(user_ns, CAP_SETGID); } /* -- 1.9.1