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Date: Thu, 28 Jan 2016 02:56:55 -0600
From: "Serge E. Hallyn" <>
Cc: Kees Cook <>,
	Andy Lutomirski <>,
	Andrew Morton <>,
	Al Viro <>,
	Richard Weinberger <>,
	Robert Święcki <>,
	Dmitry Vyukov <>,
	David Howells <>,
	Miklos Szeredi <>,
	Kostya Serebryany <>,
	Alexander Potapenko <>,
	Eric Dumazet <>,
	Sasha Levin <>,
	"" <>,
	"" <>
Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER
 to be disabled

On Mon, Jan 25, 2016 at 10:57:32PM -0600, Eric W. Biederman wrote:
> What sounds like a generally useful feature that would cover your use
> case and many others is a per user limit on the number of user
> namespaces users may create.

Ok, I'm sorry, but after thinking about this quite awhile, I think this
is a bad idea.  If I'm allowed to create exactly one, then (a) I won't
be able to run two instances of chrome (does chrome use one userns per
tab or per application?), yet (b) i can easily just not use chrome and
use my allocation to run a vulnerability.

IMO, having a (hopefully temporary, so cleanly separated out) sysctl,
which perhaps goes so far as to kill all non-init user namespaces when
set to -1, makes the most sense.  I still think the harm due to having
userspace not being able to rely on user namespaces will, long term, be
worse than the security implications of having user namespaces always

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