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Date: Tue, 26 Jan 2016 15:13:29 -0800
From: Kees Cook <>
To: Serge Hallyn <>
Cc: "" <>, 
	"Eric W. Biederman" <>, Andy Lutomirski <>, 
	Andrew Morton <>, Al Viro <>, 
	Richard Weinberger <>, Robert Święcki <>, 
	Dmitry Vyukov <>, David Howells <>, 
	Kostya Serebryany <>, Alexander Potapenko <>, Eric Dumazet <>, 
	Sasha Levin <>, 
	"" <>, 
	"" <>
Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to
 be disabled

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.


Kees Cook
Chrome OS & Brillo Security

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