[ovs-discuss] Somebody making --user and dpdk compatible again?

Christian Ehrhardt christian.ehrhardt at canonical.com
Tue Jan 26 19:07:52 UTC 2016

Hi Ansis,
the links I referred were older and yes some had apparmor/selinux issues.
I didn't refer so much to the issues they had, but more to the fact that
they usually ended up running vswitchd as different user.
But most of that is fixed in the respective distributions already.
I did a quick test a few days ago disabling all of the which didn't change
the situation, so I reenabled them again.

I already checked the processes and sockets with ps/ls and such.
Vswitchd ran as root - so was the ownership of the sockets (root:root with
kvm/libvirt/qemu in my case is running as user libvirt-qemu and that
mismatch to the socket is what caused the permission denied, just basic
file permissions/ownership.

This is what got me to --user, which was working nice in general but as
mentioned is mutually exclusive to dpdk as of now.

I found the following to be a simplification of the Test with kvm:
  socat - UNIX-CONNECT:/var/run/openvswitch/vhost-user-1
You can run that from various users as you need.

I'm happy if we at some point want to do more fine grained apparmor/selinux
profiles to confine things more.
But IMHO they won't overcome the basic access issue as long as qemu just
isn't allowed to access the unix socket.

The sockets themselves are created from dpdk code
Unfortunately that DPDK interface has no API piece regarding socket
But eventually OVS is "owning" the socket.
We are passing that path to DPDK, we own it afterwards (since it is
user:group of the runnign process) and we could change the ownership.
I'm currently experimenting with a patch adding an OVS parameter to allow
the specification of the user:group of the created vhost_user sockets.
That would allow to "let" ovs-dpdk run as root:root in general but permit
access to these sockets to other users/groups as the admin specifies.

Here a little example messin' around with a running ovs-dpdk that just
created the socket:
srwxr-xr-x  1 root root    0 Jan 26 10:47 vhost-user-1=
$ sudo -u libvirt-qemu socat -
2016/01/26 19:00:19 socat[5006] E connect(5, AF=1
"/var/run/openvswitch/vhost-user-1", 35): Permission denied
$ sudo chown root:kvm /var/run/openvswitch/vhost-user-1
$ sudo chmod g+w /var/run/openvswitch/vhost-user-1
srwxrwxr-x  1 root kvm     0 Jan 26 10:47 vhost-user-1=
$ sudo -u libvirt-qemu socat -

Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd

On Tue, Jan 26, 2016 at 7:33 PM, Ansis Atteka <aatteka at vmware.com> wrote:

> Hi,
> In fact I think we should remove any Discretionary Access Control
> (--user) and ​implement proper Mandatory Access Control (SELinux and
> Apparmor) support. Unless anyone can bring up a good case to keep and/or
> extend DAC feature in OVS.
> The link you posted seems to mention Apparmor as the root cause for
> Permission Denied issue and not File Access bits - however this contradicts
> wit the fact that chown helped you to get rid of the error.
> To verify this can you do:
> 1. ps -Af for both processes that create and connect to the sokcet.
> 2. ls -la for the socket that is getting permission denied?
> Thanks,
> Ansis
> ------------------------------
> *From:* discuss <discuss-bounces at openvswitch.org> on behalf of Christian
> Ehrhardt <christian.ehrhardt at canonical.com>
> *Sent:* Monday, January 25, 2016 10:32 PM
> *To:* dev at openvswitch.org; discuss at openvswitch.org
> *Subject:* [ovs-discuss] Somebody making --user and dpdk compatible again?
> Hi,
> to avoid missing another work already been done (and google didn't find me
> anything).
> Is there already work going on to get --user and dpdk working together?
> (see http://openvswitch.org/pipermail/dev/2015-September/060382.html)
> Background:
> While setting up a vhost_user based ovs-dpdk setup I'm struggling to get
> access to the vhost user sockets from qemu/kvm  due to permission issues.
> Various mailing list posts like (
> http://openvswitch.org/pipermail/discuss/2015-August/018553.html)
> indicate to change the user running OVS, since the sockets are defaulting
> to process user/group.
> To run OVS as different user --user seems to be the preferred way.
> But as linked above, --user has other issues with DPDK and therefore is
> mutually exclusive for now.
> I was able to fix the permission issue with some chown/chmod, but I wonder
> if there would be cleaner way to do so at some point. Maybe eventually the
> approach is totally different anyway (like only specifying :group for the
> sockets to be created). But I wondered if that old mail thread is still
> worked on by somebody atm.
> Christian Ehrhardt
> Software Engineer, Ubuntu Server
> Canonical Ltd
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