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From: Andy Lutomirski <luto@amacapital.net>
To: Kees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Richard Weinberger" <richard@nod.at>,
	"Robert Święcki" <robert@swiecki.net>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	"David Howells" <dhowells@redhat.com>,
	"Miklos Szeredi" <mszeredi@suse.cz>,
	"Kostya Serebryany" <kcc@google.com>,
	"Alexander Potapenko" <glider@google.com>,
	"Eric Dumazet" <edumazet@google.com>,
	"Sasha Levin" <sasha.levin@oracle.com>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled
Date: Mon, 25 Jan 2016 10:53:00 -0800	[thread overview]
Message-ID: <CALCETrXNZhJdjbxYH8x3wr3EyQVJzp2fhNyXwzgmuiKzoKO24A@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5j+mx+6BOKb42yfyKnL7VTCUBNC0Nk9aCOd0D5tSD6DbCg@mail.gmail.com>

On Mon, Jan 25, 2016 at 10:51 AM, Kees Cook <keescook@chromium.org> wrote:
> On Sun, Jan 24, 2016 at 2:22 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Fri, Jan 22, 2016 at 7:02 PM, Eric W. Biederman
>> <ebiederm@xmission.com> wrote:
>>> Kees Cook <keescook@chromium.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

  reply	other threads:[~2016-01-25 18:53 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-22 22:39 [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled Kees Cook
2016-01-22 22:39 ` [PATCH 1/2] sysctl: expand use of proc_dointvec_minmax_sysadmin Kees Cook
2016-01-23  3:10   ` Eric W. Biederman
2016-01-23 22:25     ` [kernel-hardening] " Jann Horn
2016-01-24  1:20       ` Eric W. Biederman
2016-01-24  1:43         ` Al Viro
2016-01-24  1:56           ` Jann Horn
2016-01-24  6:02             ` Eric W. Biederman
2016-01-24  6:32               ` Jann Horn
2016-01-24  6:44                 ` Eric W. Biederman
2016-01-22 22:39 ` [PATCH 2/2] sysctl: allow CLONE_NEWUSER to be disabled Kees Cook
2016-01-22 22:47   ` Robert Święcki
2016-01-22 22:50     ` Kees Cook
2016-01-22 22:55       ` Robert Święcki
2016-01-22 23:00         ` Kees Cook
2016-01-23  0:44           ` Serge Hallyn
2016-01-23  0:44           ` Serge Hallyn
2016-01-23  0:59           ` [kernel-hardening] " Ben Hutchings
2016-01-24 20:59             ` Kees Cook
2016-01-24 22:20               ` Andy Lutomirski
2016-01-25 18:51                 ` Kees Cook
2016-01-22 22:49 ` [PATCH 0/2] " Richard Weinberger
2016-01-23  3:02 ` Eric W. Biederman
2016-01-24 20:57   ` Kees Cook
2016-01-26  7:38     ` [kernel-hardening] " Serge Hallyn
2016-01-24 22:22   ` Andy Lutomirski
2016-01-25 18:51     ` Kees Cook
2016-01-25 18:53       ` Andy Lutomirski [this message]
2016-01-25 18:56         ` Kees Cook
2016-01-25 19:33           ` Eric W. Biederman
2016-01-25 22:34             ` Kees Cook
2016-01-25 23:33               ` Andy Lutomirski
2016-01-26  2:27               ` [kernel-hardening] " Daniel Micay
2016-01-26  4:57               ` Eric W. Biederman
2016-01-26 14:38                 ` Josh Boyer
2016-01-26 14:46                   ` Austin S. Hemmelgarn
2016-01-26 14:56                     ` Josh Boyer
2016-01-26 17:20                       ` [kernel-hardening] " Serge Hallyn
2016-01-26 19:56                         ` Josh Boyer
2016-01-26 20:11                           ` Austin S. Hemmelgarn
2016-01-26 17:15                   ` Serge Hallyn
2016-01-26 18:09                     ` Austin S. Hemmelgarn
2016-01-26 18:27                       ` Andy Lutomirski
2016-01-26 18:45                         ` Austin S. Hemmelgarn
2016-01-26 23:15                         ` Kees Cook
2016-01-26 23:13                     ` Kees Cook
2016-01-27 10:27                       ` Eric W. Biederman
2016-01-27 12:32                         ` Austin S. Hemmelgarn
2016-01-28 14:41                         ` Robert Święcki
2016-01-26 16:37                 ` Kees Cook
2016-01-28  8:56                 ` [kernel-hardening] " Serge E. Hallyn
2016-01-28 12:53                   ` Austin S. Hemmelgarn

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