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Message-ID: <CALCETrWYRvqhyCwx5RX6L3TEYCfW0j6ThFUc+ASL7BpxgO5dEQ@mail.gmail.com>
Date: Sun, 24 Jan 2016 14:22:19 -0800
From: Andy Lutomirski <luto@...capital.net>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>, Richard Weinberger <richard@....at>,
Robert Święcki <robert@...ecki.net>,
Dmitry Vyukov <dvyukov@...gle.com>, David Howells <dhowells@...hat.com>,
Miklos Szeredi <mszeredi@...e.cz>, Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>, Eric Dumazet <edumazet@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled
On Fri, Jan 22, 2016 at 7:02 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> There continues to be unexpected side-effects and security exposures
>> via CLONE_NEWUSER. For many end-users running distro kernels with
>> CONFIG_USER_NS enabled, there is no way to disable this feature when
>> desired. As such, this creates a sysctl to restrict CLONE_NEWUSER so
>> admins not running containers or Chrome can avoid the risks of this
>> feature.
>
> I don't actually think there do continue to be unexpected side-effects
> and security exposures with CLONE_NEWUSER. It takes a while for all of
> the fixes to trickle out to distros. At most what I have seen recently
> are problems with other kernel interfaces being amplified with user
> namespaces. AKA the current mess with devpts, and the unexpected
> issues with bind mounts in mount namespaces.
>
>
> So to keep this productive. Please tell me about the threat model
> you envision, and how you envision knobs in the kernel being used to
> counter those threats.
I consider the ability to use CLONE_NEWUSER to acquire CAP_NET_ADMIN
over /any/ network namespace and to thus access the network
configuration API to be a huge risk. For example, unprivileged users
can program iptables. I'll eat my hat if there are no privilege
escalations in there. (They can't request module loading, but still.)
--Andy
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