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

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Message-ID: <CAGXu5j+3==XC2jtHt1_N1hMVbRaUE4cVBQ_DWZo+82rQoXcgMA@mail.gmail.com>
Date:	Sun, 24 Jan 2016 12:59:13 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Cc:	Robert Święcki <robert@...ecki.net>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	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, Jan 22, 2016 at 4:59 PM, Ben Hutchings <ben@...adent.org.uk> wrote:
> 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.

Okay, cool. We'll keep my patch as-is then. Thanks!

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security