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-   -   Update shadow for -current please? (

chris.willing 06-03-2014 05:38 AM

Update shadow for -current please?
The shadow in -current is The most recent upstream is 4.2.1 (see: Why upgrade? Version 4.2 introduced support for subuid & subgid which are important (mandatory) for running LXC (Linux Containers) as normal user.

Is this important? Well, on my own boxes I can always sudo but in the lab that I run I don't want all users to have sudo privileges. Like, say, VirtualBox, LXC should be able to be run as a normal user. An upgraded shadow package would enable this.


WhiteWolf1776 06-03-2014 08:10 AM

Odd... I've run VirtualBox as a normal user for years before switching to KVM... maybe your users just need to be in proper groups?

chris.willing 06-03-2014 08:21 AM

What I mean is that, just as you say, VirtualBox can be run as normal user. On the other hand LXC (lxc-start etc.) needs to be run as root or via sudo. A shadow package with subuid & subgid support would enable LXC to be run by normal user, just like VirtualBox.


Drakeo 06-03-2014 10:02 AM

do you have a Slackware question. ?

moisespedro 06-03-2014 10:08 AM

Couldn't you upgrade it yourself?
Or does a shadow upgrade breaks a lot of packages?

mancha 06-03-2014 12:55 PM


Originally Posted by Drakeo (Post 5181591)
do you have a Slackware question. ?

Isn't his question about Slackware?


The OP makes a good case why the new Shadow version should be considered for the next Slackware release. Being able to use
user namespaces with LXC containers is a very important feature. Without that, LXC containment is rather unsafe: uid 0 inside
the container is uid 0 outside meaning an escape from isolation can have catastrophic consequences. It doesn't end there; To
improve the security of your LXC container you need to also be concerned with issues like resource sharing, etc.

Also, if the new Shadow is going to end up in the next Slackware, inclusion in Slackware-current is better sooner than later to
increase the probability bugs/issues/etc. are found and reported before the stable release.


Pat visits LQ but I am not sure how regularly. You might want to also send a similar request directly to him via email. In addition
to the Shadow bump you would need to request that Pat: a) upgrade to LXC 1.0+ (as of 20140602, 1.0.3 is the latest), and
b) add user namespace support to the kernel (CONFIG_USER_NS). When doing that I recommend adding memory resource


ponce 06-03-2014 01:58 PM

and, if you like, you can also add to the recipe the new two deps libnih/cgmanager, and also patch slackpkg accordingly (just two small patches I'm testing since some years, one to respect the $ROOT enviroment variable like installpkg does and another that let you specify a custom CONF directory) to use with it a template I've created and have a debootstrap-like tools to create containers. :)

thanks Chris for your work with lxc ;)

dederon 06-04-2014 02:52 AM


Originally Posted by chris.willing (Post 5181443)
Version 4.2 introduced support for subuid & subgid which are important (mandatory) for running LXC (Linux Containers) as normal user.

That's interesting. LXC 1.0 needed PAM to run as a normal user. Did that change in the mean time?

chris.willing 06-29-2014 05:26 AM

I guess the question about PAM arose because its listed as a prerequisite at Stephane Graber's page. I posted a question there about it but received no reply. Anyway, after lots of testing I can say that the answer is no, PAM is not needed.

For those interested, I set up a VM with slack64-current, modified the config & rebuilt kernel and installed the latest shadow (that includes subuid & subgid support) and lxc-1.0.4, then followed the steps outlined on Stephane's web page. At first I had very limited success until I realized that lxc wasn't able to manipulate /sys/fs/cgroup entries on my behalf. It turned out that I needed the cgmanager daemon/application as well to provide that cgroup access in a neat way. After that I was able download and run Stephane's premade containers as a normal user (its quite strange watching latest Ubuntu run inside Slackware without vbox or kvm). I also made a new Slackware template that I can create and run a container from, although this was initially a bit trickier to do. As explained on Stephane's page, there is a problem with ordinary users running a creation template since it will need to do things like run mknod - thats a no go. Thats the reason Stephane is providing a bunch of premade containers. I therefore first created a "normal" container using sudo, then ran a small application called "uidmapshift" to convert the new container's uids & gids into the range allocated to the ordinary user. Then after moving the container into the ordinary user's designated space ($HOME/.local/share/lxc/), I was able to run the new container as a regular user. Success!

I'll make a web page sometime documenting it all. In the meantime, it works enough that I now feel I can approach Pat about updating the shadow package and adding CONFIG_USER_NS to the kernel config (CONFIG_MEMCG & CONFIG_MEMCG_KMEM are already enabled in the -current kernel). I'm not sure how he'll feel about adding cgmanager and dependent libnih packages to Slackware proper but I already have SlackBuilds which could be submitted to


dederon 06-29-2014 05:51 AM

thanks a lot, please keep us updated about your documentation efforts. using a normal user as container root is something i really would like to try. usage of CONFIG_USER_NS was discouraged when i tinkered with lxc, maybe that changed. i had to recompile my kernel just because of this, which is annoying.

chris.willing 06-29-2014 08:36 PM

Yes, I see that Arch doesn't enable CONFIG_USER_NS yet after concerns about elevating normal user to root privileges. They were going to reconsider "later" but its still unset in the current version I just checked. I also checked the latest Debian (7.5), Ubuntu (14.04) and Fedora (20) and CONFIG_USER_NS is enabled in all of those. Not to say we should be strictly following the pack; just that CONFIG_USER_NS=yes has been out there in the wild for a while now and I haven't seen any reports of problems attributable to it.

The big thing about CONFIG_USER_NS is "user namespace" - the granting of any (including root) privilege is confined to a restricted environment (the user's name space) not system wide. Any such privilege has to be specifically granted - its not there by default (just able to be given). Of course we should be cautious about the possibility of escaping the restricted environment but, as above, its been around for a while now and so far looking pretty safe.


mancha 06-30-2014 01:06 AM


Originally Posted by chris.willing (Post 5196042)
Not to say we should be strictly following the pack; just that CONFIG_USER_NS=yes has been out there in the wild for a while now and I
haven't seen any reports of problems attributable to it.

Hi Chris.

Many thanks for your ongoing testing of the new Shadow, LXC, etc. Regarding your above comment, a flaw was recently found in user
namespaces that can be exploited under certain conditions to escalate privileges (CVE-2014-4014). This obviously is relevant within the
context of secure containment.

Fixes were introduced in: 3.10.44, 3.12.23, 3.14.8, and 3.16rc1.


chris.willing 06-30-2014 01:51 AM

Thanks for finding that mancha - its good to have all such problems (and fixes) out in the open so that any new features can be introduced with confidence. Hopefully the next -current updates will have kernel >= 3.14.8 then, its not much of a bump.


mancha 06-30-2014 02:15 AM

Agreed. I wanted to let you know because it seems you're preparing a set of requests for Pat to consider. This way you can let him
know about the issue and which 3.14.x introduced a fix.

Also, I wanted to let other slackers know in case they decide to use user namespaces with their LXC containers on their own kernels
(say 14.1 users sticking to 3.10.x).


ml4711 06-30-2014 02:25 AM

About CONFIG_USER_NS enabled per default


When user namespaces are enabled in the kernel it is
recommended that the MEMCG and MEMCG_KMEM options also be
enabled and that user-space use the memory control groups to
limit the amount of memory a memory unprivileged users can
Since this recommendation in the kernel config,
it may be an issue in a system with several concurrent users

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