[ovirt-devel] ovirt-guest-agent behavior on disconnect

Wed Sep 30 20:03:33 UTC 2015

Barak

On Sep 30, 2015, at 10:04, Michal Skrivanek <michal.skrivanek at redhat.com>
wrote:

On Sep 25, 2015, at 19:40 , David Mansfield <ovirt at dm.cobite.com> wrote:

[cross-posted to devel at ovirt.org and spice-devel at lists.freedesktop.org]

Hi oVirt Devs,

I'm here from the spice-devel list where we were discussing some changes to
the behavior of the spice guest agent reacting to a user disconnect (of the
spice console).

Hi David,
great, any enhancement is good! Vinzenz, please add more details to my
guesses below:)

Some information about how the ovirt-guest-agent works would be informative
if you can spare a minute.

The functionality being discussed is locking the user session in the VM
when the user disconnects from spice (either intentionally or
unintentionally).

What OSs are we talking about (the behavior is significantly different and
each pose different challenges.

Also, peripherally, how does oVirt ensure secure access by authorized users
of a VM and prevent "over-the-shoulder" snooping (spice graphics session
stealing) or other forms of information leak from a VM shared by multiple
users.

We have several mechanisms to ensure that:
1 - ticketing system managed by the engine, so permissions are checked on
the ovirt-engine, if a user has permissions to connect to the vm than the
engines sends vdsm the ticket (and it sets the ticket to the spice server
... Through libvirt), and than the client receives this ticket to present
to the spice server on connect (of course this ticket has time expiration)
2 - every time the client disconnects we receive an event and immediately
send lock desktop command to the guest (through the ovirt-guest-agent).
This is implemented both for win and Linux but for a Linux guest for that
to work one must work on run level 5.
3 - anyway since this is racy , in order to avoid session theft we do not
allow a second user to connect to a vm when the first user disconnected,
the second user will be able to login only after the cm was rebooted.

So here are some questions:

Can a VM be "shared" by multiple users in oVirt at all? Are there known
security issues that would make this a non-recommended or fundamentally
un-securable setup?

normally no, there is a semi-supported hook to allow that with VNC (and
even that is slightly broken IIRC at the moment), but in general we do want
so support that for specific usecases

The question is not clear enough,

In case you mean simultaneously (2 users) than the above answer is relevant.
In case you mean sequential ... Than the answer is explained above , and
yes we allow a vm to be shared among several users or groups.

Does the oVirt agent lock the session on disconnect? Always /
unconditionally?

IIRC It will always try to lock, but we can not guarantee that the
operation actually succeeded (long story ...)

If it's configurable, where does the configuration reside - in the vm
guest, on the vm host (/engine) or on the client?

it's oVirt management UI configuration, it changes the host's behavior on
spice disconnect per VM

Does the oVirt agent lock all sessions or the current active session?

just the active AFAIK

On windows its implemented only for desktop OSs (... Xp ...win7 ...) we
lock only the interactive session, for win server this is not supported ,
in fact we do not install the SSO mechanism at all because it works
differently for those OSs (w2k3 , 2008, 2010)

On Linux it's a bit more complicated , but we find the session of the user
we know connected to the vm ... And send the lock command.

As explained above since there is no guarantee for that to succeed than we
do not allow other users to connect till the cm is rebooted.

How does it lock the sessions?  I've looked at the code and it appears
'/usr/bin/loginctl lock-sessions' is being used on machines it's provided
on and something more complicated on older boxes.  Does the user have a way
to customize this behavior? and if so, is it VM guest, VM host or client
configuration?

AFAIR this is not configurable ... But Vinzenz should be able to give an
accurate answer

Does the agent lock linux consoles (VC1, VC2) "sessions" (e.g. with vlock?)

AFAIU no, Vinzenz ?

As I understand it, console access in ovirt is managed by setting a
temporary graphics password and then generating an .ini file which is
launched by remote-viewer. This password expires after a short period of
time.  So is there a mechanism where access is denied if a user is already
connected or is this allowed?

The  mechanism is explained above , it's the ticketing system (or temporary
password as you referee to it above) t. The second user will not get a
ticket from the ovirt-engine

connection is not allowed unless "strict user checking" disabled in UI
if it is disable or you use the same pwd then the previous session is
terminated and replaced (unless using that hook I mentioned).
But we try to treat the .vv file as a one time thing, there's
delete_this_file=1 which instructs virt-viewer to remove the file upon
startup, so even when browser place them on a shared drive they shouldn't
be there for too long

What kind of changes do you have in mind on the SPICE side?
It would certainly make it easier for us as currently we kind of guess when
to lockï¿½we receive multiple disconnecst(per channel) and don't really
know what's going onï¿½having a direct support for this inside the spice
server would be better. But it needs to allow the flexibility of different
actions except desktop lock (we have "nothing", "shutdown", "logoff" I
think). Perhaps a way how to signal relevant information to vdsm is enough

Thanks,
michal

Enough questions for now, sorry for the battering.

Feel free to ask ;-)

-- 

Thanks,

David Mansfield

Cobite, INC.

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