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Message-ID: <CAGXu5j+kkzmnrvfOhcDfsK81bxwrgnywKQKCof+Pqjv-oVB+Kw@mail.gmail.com>
Date: Tue, 26 Jan 2016 15:13:29 -0800
From: Kees Cook <keescook@...omium.org>
To: Serge Hallyn <serge.hallyn@...ntu.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>, Andy Lutomirski <luto@...capital.net>,
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>,
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>
Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to
be disabled
On Tue, Jan 26, 2016 at 9:15 AM, Serge Hallyn <serge.hallyn@...ntu.com> wrote:
> Quoting Josh Boyer (jwboyer@...oraproject.org):
>> What you're saying is true for the "oh crap" case of a new userns
>> related CVE being found. However, there is the case where sysadmins
>> know for a fact that a set of machines should not allow user
>> namespaces to be enabled. Currently they have 2 choices, 1) use their
>
> Hi - can you give a specific example of this? (Where users really should
> not be able to use them - not where they might not need them) I think
> it'll help the discussion tremendously. Because so far the only good
> arguments I've seen have been about actual bugs in the user namespaces,
> which would not warrant a designed-in permanent disable switch. If
> there are good use cases where such a disable switch will always be
> needed (and compiling out can't satisfy) that'd be helpful.
My example is a machine in a colo rack serving web pages. A site gets
attacked, and www-data uses user namespaces to continue their attack
to gain root privileges.
The admin of such a machine could have disabled userns months earlier
and limited the scope of the attack.
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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