linux-kernel - Re: [PATCH] userns/capability: Add user namespace capability

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Date:	Sun, 18 Oct 2015 22:21:10 +0200
From:	Richard Weinberger <richard@....at>
To:	Tobias Markus <tobias@...lix.eu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andrew Morton <akpm@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Christoph Lameter <cl@...ux.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	LSM <linux-security-module@...r.kernel.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH] userns/capability: Add user namespace capability

Am 18.10.2015 um 22:13 schrieb Tobias Markus:
> On 17.10.2015 22:17, Richard Weinberger wrote:
>> On Sat, Oct 17, 2015 at 5:58 PM, Tobias Markus <tobias@...lix.eu> wrote:
>>> One question remains though: Does this break userspace executables that
>>> expect being able to create user namespaces without priviledge? Since
>>> creating user namespaces without CAP_SYS_ADMIN was not possible before
>>> Linux 3.8, programs should already expect a potential EPERM upon calling
>>> clone. Since creating a user namespace without CAP_SYS_USER_NS would
>>> also cause EPERM, we should be on the safe side.
>>
>> In case of doubt, yes it will break existing software.
>> Hiding user namespaces behind CAP_SYS_USER_NS will not magically
>> make them secure.
>>
> The goal is not to make user namespaces secure, but to limit access to
> them somewhat in order to reduce the potential attack surface.

We have already a framework to reduce the attack surface, seccomp.
There is no need to invent new capabilities for every non-trivial
kernel feature.

I can understand the user namespaces seems scary and had bugs.
But which software didn't?

Are there any unfixed exploitable bugs in user namespaces in recent kerenls?

Thanks,
//richard

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