netdev - Re: [PATCH] netns: unix: only allow to find out unix socket in same net namespace

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Date:	Wed, 21 Aug 2013 00:06:52 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	netdev@...r.kernel.org, systemd-devel@...ts.freedesktop.org,
	lxc-devel@...ts.sourceforge.net, davem@...emloft.net,
	Linux Containers <containers@...ts.linux-foundation.org>,
	"libvir-list\@redhat.com" <libvir-list@...hat.com>
Subject: Re: [PATCH] netns: unix: only allow to find out unix socket in same net namespace

Gao feng <gaofeng@...fujitsu.com> writes:

> cc libvirt-list
>
> On 08/21/2013 01:30 PM, Eric W. Biederman wrote:
>> Gao feng <gaofeng@...fujitsu.com> writes:
>> 
>>> Unix sockets are private resources of net namespace,
>>> allowing one net namespace to access to other netns's unix
>>> sockets is meaningless.
>> 
>> Allowing one net namespace to access another netns's unix socket is
>> deliberate behavior.  This is a desired and useful feature, and
>> only a misconfiguration of visible files would allow this to be a
>> problem.
>> 
>>> I'm researching a problem about shutdown from container,
>>> if the cotainer shares the same file /run/systemd/private
>>> with host, when we run shutdown -h xxx in container, the
>>> shutdown message will be send to the systemd-shutdownd
>>> through unix socket /run/systemd/private, and because
>>> systemd-shutdownd is running in host, so finally, the host
>>> will become shutdown.
>> 
>> The simple answer is don't do that then.  I can see no reason
>> to share /run outside of the container unless you want this kind of
>> behavior.
>> 
>> Quite frankly I want this behavior if I am using network namespaces
>> to support multiple routing contexts. That is if I am using scripts
>> like:
>> 
>> ip netns add other
>> ip netns exec other script
>> 
>> I don't want to have to remember to say 
>> ip netns orig exec shutdown -h now
>> 
>> There are more compelling uses and there is no cost in supporting this
>> in the kernel.
>> 
>> What kind of misconfiguration caused someone to complain about this?
>> 
>
> libvirt lxc allows user to set up a container which shares the same root
> directory with host.
>
> seems like the unix sockets whose sun_path is an abstract socket address
> are net namespace aware.
>
> Should we use "abstract" type of address instead of a file system pathname
> for systemd in this case?

I suspect libvirt should simply not share /run or any other normally
writable directory with the host.  Sharing /run /var/run or even /tmp
seems extremely dubious if you want some kind of containment, and
without strange things spilling through.

Eric

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