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SubjectRe: pid ns feature request
On Fri, Apr 25, 2014 at 2:17 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Andy Lutomirski <luto@amacapital.net> writes:
>
>> On Fri, Apr 25, 2014 at 1:25 PM, Eric W. Biederman
>> <ebiederm@xmission.com> wrote:
>>> Andy Lutomirski <luto@amacapital.net> writes:
>>>
>>>> On Fri, Apr 25, 2014 at 12:37 PM, Eric W. Biederman
>>>> <ebiederm@xmission.com> wrote:
>>>>> Andy Lutomirski <luto@amacapital.net> writes:
>>>>>
>>>>>> Unless I'm missing some trick, it's currently rather painful to mount
>>>>>> a namespace /proc. You have to actually be in the pid namespace to
>>>>>> mount the correct /proc instance, and you can't unmount the old /proc
>>>>>> until you've mounted the new /proc. This means that you have to fork
>>>>>> into the new pid namespace before you can finish setting it up.
>>>>>
>>>>> Yes. You have to be inside just about all namespaces before you can
>>>>> finish setting them up.
>>>>>
>>>>> I don't know the context in which needed to be inside the pid namespace
>>>>> is a burden.
>>>>
>>>> I'm trying to sandbox myself. I unshare everything, setup up new
>>>> mounts, pivot_root, umount the old stuff, fork, and wait around for
>>>> the child to finish.
>>>>
>>>> This doesn't work: the parent can't mount the new /proc, and the child
>>>> can't either because it's too late.
>>>>
>>>> The only solution I can think of without kernel changes is to fork the
>>>> child (pid 1) before pivot_root, which makes everything more
>>>> complicated. I suppose I can unshare, fork immediately, have the
>>>> child set up all the mounts, and then wake the parent, but this is an
>>>> annoying bit of extra complexity for no obvious gain.
>>>
>>> Or perhaps just use clone and clone flags.
>>>
>>> What are you doing with the parent process? What value does it serve?
>>
>> I'm not entirely sure. I'm hacking on this thing:
>>
>> https://github.com/amluto/sandstorm/tree/userns
>>
>> which isn't really my code. But there's an inner sandbox and an outer
>> sandbox, and only the inner sandbox is in a pid namespace.
>>
>> I suppose what what I'm doing is a bit strange.
>
> A bit. But doing strange things is good.
>
> Right now most of my energy is focused on closely the last of the design
> issues. So I don't have much energy for new namespace related features
> right now.

No problem. I may write up the patch, although I'll have to support
current kernels anyway.

--Andy


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