Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753828AbaLIWt3 (ORCPT ); Tue, 9 Dec 2014 17:49:29 -0500 Received: from mail-la0-f54.google.com ([209.85.215.54]:59785 "EHLO mail-la0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753728AbaLIWtY (ORCPT ); Tue, 9 Dec 2014 17:49:24 -0500 MIME-Version: 1.0 In-Reply-To: <87d27slfsw.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> <87mw6xpzb0.fsf_-_@x220.int.ebiederm.org> <87ppbtn4mv.fsf@x220.int.ebiederm.org> <87a92xn2io.fsf@x220.int.ebiederm.org> <87r3w8liw4.fsf@x220.int.ebiederm.org> <87iohklfvj.fsf_-_@x220.int.ebiederm.org> <87d27slfsw.fsf_-_@x220.int.ebiederm.org> From: Andy Lutomirski Date: Tue, 9 Dec 2014 14:49:02 -0800 Message-ID: Subject: Re: [CFT][PATCH 2/8] userns: Don't allow setgroups until a gid mapping has been setablished To: "Eric W. Biederman" 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" , Richard Weinberger , Kenton Varda , stable Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 9, 2014 at 12:38 PM, Eric W. Biederman wrote: > > 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. Reviewed-by: Andy Lutomirski > > Cc: stable@vger.kernel.org > Signed-off-by: "Eric W. Biederman" > --- > include/linux/user_namespace.h | 5 +++++ > kernel/groups.c | 4 +++- > kernel/user_namespace.c | 14 ++++++++++++++ > 3 files changed, 22 insertions(+), 1 deletion(-) > > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > index e95372654f09..8d493083486a 100644 > --- a/include/linux/user_namespace.h > +++ b/include/linux/user_namespace.h > @@ -63,6 +63,7 @@ extern const struct seq_operations proc_projid_seq_operations; > extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *); > extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *); > extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *); > +extern bool userns_may_setgroups(const struct user_namespace *ns); > #else > > static inline struct user_namespace *get_user_ns(struct user_namespace *ns) > @@ -87,6 +88,10 @@ static inline void put_user_ns(struct user_namespace *ns) > { > } > > +static inline bool userns_may_setgroups(const struct user_namespace *ns) > +{ > + return true; > +} > #endif > > #endif /* _LINUX_USER_H */ > diff --git a/kernel/groups.c b/kernel/groups.c > index 02d8a251c476..664411f171b5 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 +218,8 @@ bool may_setgroups(void) > { > struct user_namespace *user_ns = current_user_ns(); > > - return ns_capable(user_ns, CAP_SETGID); > + return ns_capable(user_ns, CAP_SETGID) && > + userns_may_setgroups(user_ns); > } > > /* > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index b99c862a2e3f..27c8dab48c07 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file, > return false; > } > > +bool userns_may_setgroups(const struct user_namespace *ns) > +{ > + bool allowed; > + > + mutex_lock(&id_map_mutex); > + /* It is not safe to use setgroups until a gid mapping in > + * the user namespace has been established. > + */ > + allowed = ns->gid_map.nr_extents != 0; > + mutex_unlock(&id_map_mutex); > + > + return allowed; > +} > + > static void *userns_get(struct task_struct *task) > { > struct user_namespace *user_ns; > -- > 1.9.1 > -- Andy Lutomirski AMA Capital Management, LLC -- 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/