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

From: Kees Cook
Date: Tue Jul 26 2016 - 16:44:30 EST

On Tue, Jul 26, 2016 at 10:29 AM, Michael Kerrisk (man-pages)
<mtk.manpages@xxxxxxxxx> wrote:
> On 26 July 2016 at 18:52, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> On Tue, Jul 26, 2016 at 8:06 AM, Eric W. Biederman
>> <ebiederm@xxxxxxxxxxxx> wrote:
>>> "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> 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 Cook
Chrome OS & Brillo Security