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From: Andy Lutomirski <luto@amacapital.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kees Cook" <keescook@chromium.org>,
	"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: Sun, 24 Jan 2016 14:22:19 -0800	[thread overview]
Message-ID: <CALCETrWYRvqhyCwx5RX6L3TEYCfW0j6ThFUc+ASL7BpxgO5dEQ@mail.gmail.com> (raw)
In-Reply-To: <8737tp0zhr.fsf@x220.int.ebiederm.org>

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.)

--Andy

WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@amacapital.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kees Cook" <keescook@chromium.org>,
	"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: [kernel-hardening] Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled
Date: Sun, 24 Jan 2016 14:22:19 -0800	[thread overview]
Message-ID: <CALCETrWYRvqhyCwx5RX6L3TEYCfW0j6ThFUc+ASL7BpxgO5dEQ@mail.gmail.com> (raw)
In-Reply-To: <8737tp0zhr.fsf@x220.int.ebiederm.org>

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.)

--Andy

  parent reply	other threads:[~2016-01-24 22:22 UTC|newest]

Thread overview: 80+ 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 ` [kernel-hardening] " Kees Cook
2016-01-22 22:39 ` [PATCH 1/2] sysctl: expand use of proc_dointvec_minmax_sysadmin Kees Cook
2016-01-22 22:39   ` [kernel-hardening] " Kees Cook
2016-01-23  3:10   ` Eric W. Biederman
2016-01-23  3:10     ` [kernel-hardening] " Eric W. Biederman
2016-01-23 22:25     ` 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 22:39   ` [kernel-hardening] " Kees Cook
2016-01-22 22:47   ` Robert Święcki
2016-01-22 22:47     ` [kernel-hardening] " Robert Święcki
2016-01-22 22:50     ` Kees Cook
2016-01-22 22:50       ` [kernel-hardening] " Kees Cook
2016-01-22 22:55       ` Robert Święcki
2016-01-22 22:55         ` [kernel-hardening] " Robert Święcki
2016-01-22 23:00         ` Kees Cook
2016-01-22 23:00           ` [kernel-hardening] " Kees Cook
2016-01-23  0:44           ` Serge Hallyn
2016-01-23  0:44             ` [kernel-hardening] " Serge Hallyn
2016-01-23  0:44           ` Serge Hallyn
2016-01-23  0:44             ` [kernel-hardening] " Serge Hallyn
2016-01-23  0:59           ` Ben Hutchings
2016-01-24 20:59             ` Kees Cook
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
2016-01-22 22:49   ` [kernel-hardening] " Richard Weinberger
2016-01-23  3:02 ` Eric W. Biederman
2016-01-23  3:02   ` [kernel-hardening] " Eric W. Biederman
2016-01-24 20:57   ` Kees Cook
2016-01-24 20:57     ` [kernel-hardening] " Kees Cook
2016-01-26  7:38     ` Serge Hallyn
2016-01-24 22:22   ` Andy Lutomirski [this message]
2016-01-24 22:22     ` Andy Lutomirski
2016-01-25 18:51     ` Kees Cook
2016-01-25 18:51       ` [kernel-hardening] " Kees Cook
2016-01-25 18:53       ` Andy Lutomirski
2016-01-25 18:53         ` [kernel-hardening] " Andy Lutomirski
2016-01-25 18:56         ` Kees Cook
2016-01-25 18:56           ` [kernel-hardening] " Kees Cook
2016-01-25 19:33           ` Eric W. Biederman
2016-01-25 19:33             ` [kernel-hardening] " Eric W. Biederman
2016-01-25 22:34             ` Kees Cook
2016-01-25 22:34               ` [kernel-hardening] " Kees Cook
2016-01-25 23:33               ` Andy Lutomirski
2016-01-25 23:33                 ` [kernel-hardening] " Andy Lutomirski
2016-01-26  2:27               ` Daniel Micay
2016-01-26  4:57               ` Eric W. Biederman
2016-01-26  4:57                 ` [kernel-hardening] " Eric W. Biederman
2016-01-26 14:38                 ` Josh Boyer
2016-01-26 14:38                   ` [kernel-hardening] " Josh Boyer
2016-01-26 14:46                   ` Austin S. Hemmelgarn
2016-01-26 14:46                     ` [kernel-hardening] " Austin S. Hemmelgarn
2016-01-26 14:56                     ` Josh Boyer
2016-01-26 14:56                       ` [kernel-hardening] " Josh Boyer
2016-01-26 17:20                       ` 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
2016-01-28 14:41                           ` Robert Święcki
2016-01-26 23:47                     ` Josh Boyer
2016-01-26 16:37                 ` Kees Cook
2016-01-26 16:37                   ` [kernel-hardening] " Kees Cook
2016-01-28  8:56                 ` Serge E. Hallyn
2016-01-28 12:53                   ` Austin S. Hemmelgarn

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