From: Kees Cook <keescook@chromium.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Djalal Harouni <tixxdz@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
LSM List <linux-security-module@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Dongsu Park <dpark@posteo.net>,
Casey Schaufler <casey@schaufler-ca.com>,
James Morris <james.l.morris@oracle.com>,
Paul Moore <paul@paul-moore.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jonathan Corbet <corbet@lwn.net>, Jessica Yu <jeyu@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
belakhdar abdeldjalil <zendyani@gmail.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction
Date: Sat, 22 Apr 2017 12:29:37 -0700 [thread overview]
Message-ID: <CAGXu5jLV+WZyj+xnxVFkFEgEthNt6eXdcSgHT-=85mJ1ECZ1Rw@mail.gmail.com> (raw)
In-Reply-To: <CALCETrUT73CcPQx2T=1zWbOUhw9r-c_YqXw5-KTwxgWPgXuTwA@mail.gmail.com>
On Fri, Apr 21, 2017 at 11:51 PM, Andy Lutomirski <luto@kernel.org> wrote:
> On Fri, Apr 21, 2017 at 5:12 PM, Djalal Harouni <tixxdz@gmail.com> wrote:
>> On Sat, Apr 22, 2017 at 1:51 AM, Andy Lutomirski <luto@kernel.org> wrote:
>> [...]
>>>>> I personally like my implicit_rights idea, and it might be interesting
>>>>> to prototype it.
>>>>
>>>> I don't like blocking a needed feature behind a large super-feature
>>>> that doesn't exist yet. We'd be able to refactor this code into using
>>>> such a thing in the future, so I'd prefer to move ahead with this
>>>> since it would stop actual exploits.
>>>
>>> I don't think the super-feature is so hard, and I think we should not
>>> add the per-task thing the way it's done in this patch. Let's not add
>>> per-task things where the best argument for their security is "not
>>> sure how it would be exploited".
>>
>> Actually the XFRM framework CVE-2017-7184 [1] is one real example, of
>> course there are others. The exploit was used on a generic distro
>> during a security contest that distro is Ubuntu. That distro will
>> never provide a module autoloading restriction by default to not harm
>> it's users. Consumers or containers/sandboxes then can run their
>> confined apps using such facilities.
>>
>> These bugs will stay in embedded devices that use these generic
>> distros for ever.
>>
>>> Anyway, I think the sysctl is really the important bit. The per-task
>>> setting is icing on the cake IMO. One upon a time autoload was more
>>> important, but these days modaliases are supposed to do most of the
>>> work. I bet that modern distros don't need unprivileged autoload at
>>> all.
>>
>> Actually I think they do and we can't just change that. Users may
>> depend on it, it is a well established facility.
>>
>> Now the other problem is CAP_NET_ADMIN which does lot of things, it is
>> more like the CAP_SYS_ADMIN.
>>
>> This is a quick list that I got from only the past months, I'm pretty
>> sure there are more:
>>
>> * 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
>
> 3. A per-user-ns sysctl.
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2017-04-22 19:29 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 22:20 [PATCH v3 0/2] modules:capabilities: automatic module loading restrictions Djalal Harouni
2017-04-19 22:20 ` [PATCH v3 1/2] modules:capabilities: automatic module loading restriction Djalal Harouni
2017-04-19 23:16 ` Andy Lutomirski
2017-04-20 2:22 ` Ben Hutchings
2017-04-20 12:44 ` [kernel-hardening] " Djalal Harouni
2017-04-20 15:02 ` Ben Hutchings
2017-04-20 20:39 ` Djalal Harouni
2017-04-20 21:28 ` Kees Cook
2017-04-19 22:20 ` [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction Djalal Harouni
2017-04-19 22:38 ` Djalal Harouni
2017-04-19 23:15 ` Andy Lutomirski
2017-04-19 23:43 ` Kees Cook
2017-04-20 2:41 ` Andy Lutomirski
2017-04-21 23:19 ` Kees Cook
2017-04-21 23:28 ` Andy Lutomirski
2017-04-21 23:40 ` Kees Cook
2017-04-21 23:51 ` Andy Lutomirski
2017-04-22 0:12 ` Djalal Harouni
2017-04-22 1:19 ` Djalal Harouni
2017-04-22 6:51 ` Andy Lutomirski
2017-04-22 19:29 ` Kees Cook [this message]
2017-04-24 14:25 ` Djalal Harouni
2017-04-24 18:02 ` Kees Cook
2017-04-24 18:35 ` Djalal Harouni
2017-04-21 23:52 ` Casey Schaufler
2017-04-22 0:00 ` Andy Lutomirski
2017-04-22 0:13 ` Casey Schaufler
2017-04-22 6:45 ` Andy Lutomirski
2017-04-22 12:17 ` Djalal Harouni
2017-05-04 13:07 ` Djalal Harouni
2017-05-04 14:58 ` Serge E. Hallyn
2017-05-05 13:06 ` Djalal Harouni
2017-05-05 16:18 ` Andy Lutomirski
2017-04-20 1:57 ` kbuild test robot
2017-04-24 4:29 ` Rusty Russell
2017-04-26 9:06 ` Djalal Harouni
2017-04-27 2:07 ` Rusty Russell
2017-04-27 13:16 ` Djalal Harouni
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