[libvirt] [RFC PATCH 2/2] LXC: Create ro overlay mounts only if we're not within a user namespace

[Richard Weinberger]

Am 01.07.2013 12:33, schrieb Daniel P. Berrange:
> On Mon, Jul 01, 2013 at 08:29:14AM +0200, Richard Weinberger wrote:
>> Am 01.07.2013 04:26, schrieb Gao feng:
>>>> Well, given that we're at rc2 now & I'm still unclear about how some
>>>> aspects of the userns setup is working, I'm afraid we'll have to wait
>>>> until 1.1.1 for the userns LXC code to merge.  I'll aim todo it next
>>>> week, so that we have plenty of time for further testing before the
>>>> 1.1.1 release.
>>>>
>>>
>>> Ok, I think Richard had tested the userns support.
>>> Hi Richard, can you give me your ack or tested-by?
>>
>> I'm still facing one userns related issue.
> 
> [snip]
> 
>> After creating it attach to it's console, you'll find bash as pid 1.
>> And you'll find that /proc/1/ is not fully uid/gid-mapped:
>> ---cut---
>> # ls -la /proc/1/
>> total 0
>> dr-xr-xr-x  8 root   root    0 Jul  1 06:06 .
>> dr-xr-xr-x 74 nobody nogroup 0 Jul  1 06:06 ..
>> dr-xr-xr-x  2 root   root    0 Jul  1 06:06 attr
> 
> [snip]
> 
>> Any ideas what's going on here?
> 
> No, it is very odd. It smells like a kernel issue to me. What
> version are you running ?

I see this issue on all kernels.
Currently I'm using vanilla v3.9.x and v3.10.

> I've also tried running the demo programs shown on the LWN.net
> article
> 
>    https://lwn.net/Articles/532593/
> 
> and they don't operate in the way described by the article - the demo
> programs continue to ru as 'nfsnobody' even after the mappings are
> setup.
> 
> I'm just using the Fedora 3.9.4-303 kernel, rebuilt with userns enabled
> in KConfig.  I'm wondering if there is still stuff missing in 3.9.x
> that prevents this from working properly, or if the kernel behaviour
> changed after those LWN articles were written.

To me it looks like the capability system behaves odd.
The mappings in /proc are fine as long I do not call capng_updatev().
Also calling capng_updatev() with parameters that do not change the current cap set
triggers the odd behavior too.

So we see two (related?) issues:
1. If we try updating the capabilities of pid1 /proc/1/ has unmapped files till we exec().
2. Dropping  capabilities does not work we always gain a fresh and full capability set.

BTW: I'm sure the issues are not caused by Gau Feng's userns patches.
Feel free to add:
Acked-by: Richard Weinberger <richard at nod.at>
Tested-by: Richard Weinberger <richard at nod.at>

Thanks,
//richard