On 09/30/2015 10:03 PM, Barak Azulay wrote:
Barak
On Sep 30, 2015, at 10:04, Michal Skrivanek
<michal.skriva...@redhat.com <mailto:michal.skriva...@redhat.com>> wrote:
On Sep 25, 2015, at 19:40 , David Mansfield <ov...@dm.cobite.com
<mailto:ov...@dm.cobite.com>> wrote:
[cross-posted to de...@ovirt.org <mailto:de...@ovirt.org> and
spice-devel@lists.freedesktop.org
<mailto:spice-devel@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.
Actually not completely correct, currently we only lock the first, we
don't try to match the user, the current assumption is that we only
allow one user per VM therefore there can't be more than one active session.
That said, that's how it is currently implemented. Not that this is the
best way.
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
The only configuration you can do as of ovirt/RHEV 3.6 is that you are
now able to say to perform one of the following actions on console
disconnect:
- Lock the screen
- Logout the current user
- Reboot the VM
- Shutdown the VM
- Do nothing
Does the agent lock linux consoles (VC1, VC2) "sessions" (e.g. with
vlock?)
AFAIU no, Vinzenz ?
No, currently we don't however I guess we should consider that in case
of 'Lock screen'
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 lock�we receive multiple disconnecst(per channel) and
don't really know what's going on�having 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
This is why I have reported this issue:
https://bugs.freedesktop.org/show_bug.cgi?id=91085
Having session based events would make it easier to avoid starting the
handling on migrations, where in some conditions there's a race which
can cause the screen lock mechanism to kick in just in the moment the
transfer of the VM goes over to the destination hypervisor.
Thanks,
michal
Enough questions for now, sorry for the battering.
Feel free to ask ;-)
--
Thanks,
David Mansfield
Cobite, INC.
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--
Regards,
Vinzenz Feenstra | Senior Software Engineer
RedHat Engineering Virtualization R & D
Phone: +420 532 294 625
IRC: vfeenstr or evilissimo
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