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Date: Mon, 24 Apr 2017 11:02:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Djalal Harouni <tixxdz@...il.com>
Cc: Andy Lutomirski <luto@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
LSM List <linux-security-module@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>, Dongsu Park <dpark@...teo.net>,
Casey Schaufler <casey@...aufler-ca.com>, James Morris <james.l.morris@...cle.com>,
Paul Moore <paul@...l-moore.com>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jonathan Corbet <corbet@....net>,
Jessica Yu <jeyu@...hat.com>, Rusty Russell <rusty@...tcorp.com.au>,
Arnaldo Carvalho de Melo <acme@...hat.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Ingo Molnar <mingo@...nel.org>,
belakhdar abdeldjalil <zendyani@...il.com>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules
autoload restriction
On Mon, Apr 24, 2017 at 7:25 AM, Djalal Harouni <tixxdz@...il.com> wrote:
> On Sat, Apr 22, 2017 at 9:29 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Fri, Apr 21, 2017 at 11:51 PM, Andy Lutomirski <luto@...nel.org> wrote:
>>> On Fri, Apr 21, 2017 at 5:12 PM, Djalal Harouni <tixxdz@...il.com> wrote:
>>>> On Sat, Apr 22, 2017 at 1:51 AM, Andy Lutomirski <luto@...nel.org> wrote:
>>>>
> [...]
>>>> * DCCP use after free CVE-2017-6074
>>>> * n_hldc CVE-2017-2636
>>>> * XFRM framework CVE-2017-7184
>>>> * L2TPv3 CVE-2016-10200
>>>>
>>>> Most of these need CAP_NET_ADMIN to be autoloaded, however we also
>>>> need CAP_NET_ADMIN for other things... therefore it is better to have
>>>> an extra facility that could coexist with CAP_NET_ADMIN and other
>>>> sandbox features.
>>>>
>>>
>>> I agree that the feature is important, but I think your implementation
>>> is needlessly dangerous. I imagine that the main uses that you care
>>> about involve containers. How about doing it in a safer way that
>>> works for containers? I can think of a few. For example:
>>>
>>> 1. A sysctl that, if set, prevents autoloading outside the root
>>> userns. This isn't very flexible at all, but it might work.
>>>
>>> 2. Your patch, but require privilege within the calling namespace to
>>> set the prctl.
>>
>> How about CAP_SYS_ADMIN || no_new_privs?
>>
>> -Kees
>>
>
> Yes I can update as per Andy suggestion to require privileges inside
> the calling namespace to set prctl. Other options that are not prctl
> based have more variants, that make them hard to use.
>
> So I would got with CAP_SYS_ADMIN in the calling userns ||
> no_new_privs , I would have said CAP_SYS_MODULE in the userns but it
> seems better to standardize on CAP_SYS_ADMIN to set the prctl.
Andy's concern is that it would provide an escalation from SYS_MODULE
to SYS_ADMIN through some privileged process being tricked through a
missing API provided by modules, so we have to use either SYS_ADMIN ||
nnp.
-Kees
--
Kees Cook
Pixel Security
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