linux-kernel - Re: [CFT][PATCH 5/7] userns: Only allow the creator of the userns unprivileged mappings

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrVJ1Ld00TQOUjOT3n=G8PRpY=FG8Py+t1H9_mw93AO-aQ@mail.gmail.com>
Date:	Mon, 8 Dec 2014 14:15:59 -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 5/7] userns: Only allow the creator of the userns
 unprivileged mappings

On Mon, Dec 8, 2014 at 2:10 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> If you did not create the user namespace and are allowed
> to write to uid_map or gid_map you should already have the necessary
> privilege in the parent user namespace to establish any mapping
> you want so this will not affect userspace in practice.
>
> Limiting unprivileged uid mapping establishment to the creator of the
> user namespace reduces the set of credentials that must be verified
> can be obtained without privielge, making code verification simpler.
>

s/privielge/privilege/

But I still can't parse that sentence.

The code itself is:

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

> Limiting unprivileged gid mapping establishment (which is temporarily
> absent) to the creator of the user namespace also ensures that the
> combination of uid and gid can already be obtained without privilege.
>
> This is part of the fix for CVE-2014-8989.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  kernel/user_namespace.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index da1eeb927b21..413f60fd5983 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -812,14 +812,16 @@ static bool new_idmap_permitted(const struct file *file,
>                                 struct user_namespace *ns, int cap_setid,
>                                 struct uid_gid_map *new_map)
>  {
> +       const struct cred *cred = file->f_cred;
>         /* Don't allow mappings that would allow anything that wouldn't
>          * be allowed without the establishment of unprivileged mappings.
>          */
> -       if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1)) {
> +       if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1) &&
> +           uid_eq(ns->owner, cred->euid)) {
>                 u32 id = new_map->extent[0].lower_first;
>                 if (cap_setid == CAP_SETUID) {
>                         kuid_t uid = make_kuid(ns->parent, id);
> -                       if (uid_eq(uid, file->f_cred->euid))
> +                       if (uid_eq(uid, cred->euid))
>                                 return true;
>                 }
>         }
> --
> 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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/