linux-kernel - Re: [kernel-hardening] Re: [PATCH 2/2] sysctl: allow CLONE

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Date:	Sat, 23 Jan 2016 00:59:59 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	kernel-hardening@...ts.openwall.com,
	Robert Święcki <robert@...ecki.net>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Richard Weinberger <richard@....at>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...capital.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>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH 2/2] sysctl: allow CLONE_NEWUSER
 to be disabled

On Fri, 2016-01-22 at 15:00 -0800, Kees Cook wrote:
> On Fri, Jan 22, 2016 at 2:55 PM, Robert Święcki <robert@...ecki.net> wrote:
> > 2016-01-22 23:50 GMT+01:00 Kees Cook <keescook@...omium.org>:
> > 
> > > > Seems that Debian and some older Ubuntu versions are already using
> > > > 
> > > > $ sysctl -a | grep usern
> > > > kernel.unprivileged_userns_clone = 0
> > > > 
> > > > Shall we be consistent wit it?
> > > 
> > > Oh! I didn't see that on systems I checked. On which version did you find that?
> > 
> > $ uname -a
> > Linux bc1 4.3.0-0.bpo.1-amd64 #1 SMP Debian 4.3.3-5~bpo8+1
> > (2016-01-07) x86_64 GNU/Linux
> > $ cat /etc/debian_version
> > 8.2
> 
> Ah-ha, Debian only, though it looks like this was just committed to
> the Ubuntu kernel tree too:
> 
> 
> > IIRC some older kernels delivered with Ubuntu Precise were also using
> > it (but maybe I'm mistaken)
> 
> I don't see it there.
> 
> I think my patch is more complete, but I'm happy to change the name if
> this sysctl has already started to enter the global consciousness. ;)
> 
> Serge, Ben, what do you think?

I agree that using the '_restrict' suffix for new restrictions makes
sense.  I also don't think that a third possible value for
kernel.unprivileged_userns_clone would would be understandable.

I would probably make kernel.unprivileged_userns_clone a wrapper for
kernel.userns_restrict in Debian, then deprecate and eventually remove
it.

Ben.

-- 
Ben Hutchings
Life is what happens to you while you're busy making other plans.
                                                               - John Lennon
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