linux-kernel - Re: [CFT][PATCH 3/8] userns: Don't allow unprivileged creation of gid mappings

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Message-ID: <CALCETrU+xU3N+kPW1Mf2MV6QF2_cJFmatR2x_Mq7RTDJLcM68A@mail.gmail.com>
Date:	Tue, 9 Dec 2014 15:00:24 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Richard Weinberger <richard@....at>,
	Kenton Varda <kenton@...dstorm.io>,
	stable <stable@...r.kernel.org>
Subject: Re: [CFT][PATCH 3/8] userns: Don't allow unprivileged creation of gid mappings

On Tue, Dec 9, 2014 at 12:39 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> As any gid mapping will allow and must allow for backwards
> compatibility dropping groups don't allow any gid mappings to be
> established without CAP_SETGID in the parent user namespace.
>
> For a small class of applications this change breaks userspace
> and removes useful functionality.  This small class of applications
> includes tools/testing/selftests/mount/unprivilged-remount-test.c
>
> Most of the removed functionality will be added back with the addition
> of a one way knob to disable setgroups.  Once setgroups is disabled
> setting the gid_map becomes as safe as setting the uid_map.
>
> For more common applications that set the uid_map and the gid_map
> with privilege this change will have no affect.
>

Reviewed-by: Andy Lutomirski <luto@...capital.net>

> This is part of a fix for CVE-2014-8989.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  kernel/user_namespace.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 27c8dab48c07..1ce6d67c07b7 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -821,10 +821,6 @@ static bool new_idmap_permitted(const struct file *file,
>                         kuid_t uid = make_kuid(ns->parent, id);
>                         if (uid_eq(uid, file->f_cred->fsuid))
>                                 return true;
> -               } else if (cap_setid == CAP_SETGID) {
> -                       kgid_t gid = make_kgid(ns->parent, id);
> -                       if (gid_eq(gid, file->f_cred->fsgid))
> -                               return true;
>                 }
>         }
>
> --
> 1.9.1
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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