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Message-ID: <CALCETrXNZhJdjbxYH8x3wr3EyQVJzp2fhNyXwzgmuiKzoKO24A@mail.gmail.com>
Date: Mon, 25 Jan 2016 10:53:00 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Kees Cook <keescook@...omium.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, 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 Mon, Jan 25, 2016 at 10:51 AM, Kees Cook <keescook@...omium.org> wrote:
> On Sun, Jan 24, 2016 at 2:22 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> 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.)
>
> Should I consider this an Ack for the patch? :)
Only if you explain why you need the CAP_SYS_ADMIN check. :)
IOW, I think you could change that one line of code and have a less
weird version of the patch that would work just fine.
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
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