Re: [kernel-hardening] Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled

From: Kees Cook
Date: Tue Jan 26 2016 - 18:13:35 EST

On Tue, Jan 26, 2016 at 9:15 AM, Serge Hallyn <serge.hallyn@xxxxxxxxxx> wrote:
> Quoting Josh Boyer (jwboyer@xxxxxxxxxxxxxxxxx):
>> 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 Cook
Chrome OS & Brillo Security