[libvirt] [PATCH] lxc: Cleaning up mount setup

Richard Weinberger richard at nod.at
Thu Jan 8 14:10:38 UTC 2015

Am 08.01.2015 um 15:06 schrieb Daniel P. Berrange:
> On Thu, Jan 08, 2015 at 03:02:59PM +0100, Richard Weinberger wrote:
>> Am 08.01.2015 um 14:45 schrieb Daniel P. Berrange:
>>> On Thu, Jan 08, 2015 at 02:36:36PM +0100, Richard Weinberger wrote:
>>>> Am 08.01.2015 um 14:02 schrieb Daniel P. Berrange:
>>>>> We have historically done a number of things with LXC that are
>>>>> somewhat questionable in retrospect
>>>>>  1. Mounted /proc/sys read-only, but then mounted
>>>>>     /proc/sys/net/ipv* read-write again
>>>>>  2. Mounted /sys read only
>>>>>  3. Mount /sys/fs/cgroup/NNN/the/guest/dir to /sys/fs/cgroup/NNN
>>>>>  4. FUSE mount on /proc/meminfo
>>>>> Items 1 & 2 are pointless as they offer no security benefit either
>>>>> with or without user namespaces. Without userns it is always insecure,
>>>>> with userns it is always secure, no matter what the mount state is.
>>>> I agree. Thanks a lot for addressing this, Daniel!
>>>>> Item 3 is some what dubious, since /proc/self/cgroup paths for
>>>>> processes are now not visible at /sys/fs/cgroup. This really
>>>>> confuses systemd inside the container making it create a broken
>>>>> layout
>>>> The question is, how to support systemd in containers?
>>>> As of now I'm not aware of a working concept.
>>>> With current libvirt it kind of works but recently I found a very nasty issue:
>>>> See: https://www.redhat.com/archives/libvir-list/2014-November/msg01090.html
>>> That reply from Lennart suggests systemd should pretty much work,
>>> albeit in a hacky way.
>> What hack to you mean?
> Lennarts reply detailing their workaround hacks:

Oh yes. But these do not work as I've stated in the mail.
My containers show thousands of orphaned login sessions
and render the container unusable after some time.

>> My use case is different. I need most of the time at least an init.
>> And if the distro is systemd based....
>> Yeah but we have to warn the user that she is doing something insecure
>> if no mappings are set up.
> Ultimately I think that's a docs problem, or something that a higher level
> app needs to deal with. eg OpenStack should setup LXC such that user
> namespaces are unconditionally enabled all the time, even if that's not
> the case in libvirt itself. OpenStack manages the whole machine, so it
> has enough context to do the setup that libvirt cannot do.

I don't run OpenStack but i tend to agree. :-)


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