linux-kernel - Re: [PATCH v2 00/10] userns: sysctl limits for namespaces

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Date:	Tue, 26 Jul 2016 13:44:21 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Michael Kerrisk-manpages <mtk.manpages@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Jann Horn <jann@...jh.net>, Nikolay Borisov <kernel@...p.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 00/10] userns: sysctl limits for namespaces

On Tue, Jul 26, 2016 at 10:29 AM, Michael Kerrisk (man-pages)
<mtk.manpages@...il.com> wrote:
> On 26 July 2016 at 18:52, Kees Cook <keescook@...omium.org> wrote:
>> On Tue, Jul 26, 2016 at 8:06 AM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>>>
>>>> Hello Eric,
>>>>
>>>> I realized I had a question after the last mail.
>>>>
>>>> On 07/21/2016 06:39 PM, Eric W. Biederman wrote:
>>>>>
>>>>> This patchset addresses two use cases:
>>>>> - Implement a sane upper bound on the number of namespaces.
>>>>> - Provide a way for sandboxes to limit the attack surface from
>>>>>   namespaces.
>>>>
>>>> Can you say more about the second point? What exactly is the
>>>> problem that is being addressed, and how does the patch series
>>>> address it? (It would be good to have those details in the
>>>> revised commit message...)
>>>
>>> At some point it was reported that seccomp was not sufficient to disable
>>> namespace creation.  I need to go back and look at that claim to see
>>> which set of circumstances that was referring to.  Seccomp doesn't stack
>>> so I can see why it is an issue.
>>
>> seccomp does stack. The trouble usually comes from a perception that
>> seccomp overhead is not trivial, so setting a system-wide policy is a
>> bit of a large hammer for such a limitiation. Also, at the time,
>> seccomp could be bypasses with ptrace, but this (as of v4.8) is no
>> longer true.
>
> Sounds like someone needs to send me a patch for the seccomp.2 man page?

It's on my TODO list, no worries. :) I'm waiting for it to land in
Linus's tree first. It's only been in -next so far.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security