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Date: Wed, 27 Jan 2016 04:27:19 -0600
From: (Eric W. Biederman)
To: Kees Cook <>
Cc: Serge Hallyn <>,
 <>,  Andy Lutomirski
 <>,  Andrew Morton <>,  Al
 Viro <>,  Richard Weinberger <>,
  Robert Święcki <>,  Dmitry Vyukov
 <>,  David Howells <>,  Kostya
 Serebryany <>,  Alexander Potapenko <>,
  Eric Dumazet <>,  Sasha Levin
 <>,  "linux-doc\"
 <>,  "linux-kernel\"
Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled

Kees Cook <> writes:

> On Tue, Jan 26, 2016 at 9:15 AM, Serge Hallyn <> wrote:
>> Quoting Josh Boyer (
>>> 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.

Of course for the paranoid there is already a mechanism to do this.

No new user namespaces are allowed to be created inside of a chroot.


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