(general point, could we please try not top-posting ? It makes a little
harder to follow the conversation)
Replies inline.
Le 24/06/2015 08:15, Wei, Gang a écrit :
Only if all the hosts managed by OpenStack are capable for measured boot
process, then let 3rd-party tool call nova fencing API might be better than
using TrustedFilter.
But if not all the hosts support measured boot, then with TrustedFilter we can
schedule VM to only measured and trusted host, but in 3rd-party tool case, only
untrusted/compromised hosts will be fenced, the host with unknown
trustworthiness will still be able to run VM but the owner is not willing to do
it that way.
You don't need a specific filter for fencing one host from being
scheduled. Just calling the Nova os-services API to explicitly disable
the service (and providing a reason) just makes the hosts belonging to
the service not able to be elected (thanks to the ComputeFilter)
To be clear, I would love to see the logic inverted, ie. something which
would call the OAT service for a specific host would then fire a service
disable.
So I would suggest using the 3rd-party tools as enhancing way to supplement our
TCP/trustedfilter feature. And the 3rd party tools can also call attestation
API for host attestation.
I don't see much benefits of keeping such filter for the reasons I
mentioned below. Again, if you want to fence one host, you can just
disable its service, that's enough.
Thanks
Jimmy
-----Original Message-----
From: Bhandaru, Malini K [mailto:malini.k.bhand...@intel.com]
Sent: Wednesday, June 24, 2015 1:13 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [nova] How to properly detect and fence a
compromised host (and why I dislike TrustedFilter)
Would like to add to Shane's points below.
1) The Trust filter can be treated as an API, with different underlying implementations.
Its default could even be "Not Implemented" and always return false.
And Nova.conf could specify use the OAT trust implementation. This would
not break present day users of the functionality.
Don't get me wrong, I'm not against OAT, I'm just saying that the
TrustedFilter design is wrong. Even if another alternative would come up
to serve the TrustedComputePool model of things, it would still be bad
for the reasons I mentioned below, and wouldn't cover the usecase I quoted.
2) The issue in the original bug is a a VM waking up after a reboot on a host
that has not pre-determined whether the host is still trustable.
This is essentially begging a feature to check that all constraints
requested by a VM during launch are confirmed to hold when it re-awakens, even
if it is not
going through Nova scheduler at this point.
So I think we are in agreement that for covering that usecase, it can't
be done at the scheduler level.
Using TrustedFilter just ensures that at the instance creation time, the
host is checked but confuses people because they think it will be
enforced for the whole instance lifecyle.
This holds even for aggregates that might be specified by geo, or even reservation such as
"Coke" or "Pepsi".
What if a host, even without a reboot and certainly before a reboot was
assigned from Coke to Pepsi, there is cross contamination.
Perhaps we need Nova hooks that can be registered with functions that
check expected aggregate values.
I don't honestly see the point of an host aggregate. Given the failure
domain is an host, you only need to trust that host or not. The fact
that the host belongs to an aggregate or not is orthogonal to our
problem IMHO.
Better still have libvirt functionality that makes a call back for each
VM on a host to ensure its constraints are satisfied on start-up/boot, and
re-start when it comes out of pause.
Hum, doesn't it sound weird to have the host being the source of truth ?
Also, if an host gets compromised, why couldn't we assume that the
instances can be compromised too and need to be resurrected (ie.
evacuated) ?
Using aggregate for trust with a cron job to check for trust is
inefficient in this case, trust status gets updated only on a host reboot.
Intel TXT is a boot
time authentication.
Isn't that a specific implementation of OAT ? Couldn't we assume some
alternative implementations able to do live checks ? I mean, whatever on
how you trigger an host check (at boot time or periodically), you can
then fire an alarm which would set the necessary remediation actions :
fence the host and evacuate the instances
Regards
Malini
-----Original Message-----
From: Wang, Shane [mailto:shane.w...@intel.com]
Sent: Tuesday, June 23, 2015 9:26 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [nova] How to properly detect and fence a
compromised host (and why I dislike TrustedFilter)
AFAIK, TrustedFilter is using a sort of cache to cache the trusted state, which
is designed to solve the performance issue mentioned here.
Fair point, even if it can be a security flaw because we know that
caching can be having stale data.
My thoughts for deprecating it are:
#1. We already have customers here in China who are using that filter. How are
they going to do upgrade in the future?
I didn't said remove the filter, but rather deprecating it. It would
basically mean that users would get a LOG warning for the next 2 cycles
saying "this filter will be removed in the next future, please consider
using other ways".
Also, removing a filter from in-tree doesn't prevent you to ship it in a
distro since out-of-tree filters can easily be added using a
configuration flag.
#2. Dependency should not be a reason to deprecate a module in OpenStack, Nova
is not a stand-alone module, and it depends on various technologies and
libraries.
You made me wrong. The dependency issue is one of the reasons I have
serious concerns with that filter, but that's not the only one. From my
perspective, like I said, the main compelling reason is that the filter
makes a promise it can't sustain (make sure that Nova fences my
compromised hosts)
Intel is setting up the third party CI for TCP/OAT in Liberty, which is to
address the concerns mentioned in the thread. And also, OAT is an open source
project which is being maintained as the long-term strategy.
Again, like I said, I have strong respect for OAT. My problem is not
with OAT but with TrustedFilter. I'm perfectly fine keeping OAT for
performing host checks.
For the situation that a host gets compromised, OAT checks trusted or untrusted
from the start point of boot/reboot, it is hard for OAT to detect whether a
host gets compromised when it is running, I don't know how to detect that
without the filter?
Back to Michael's question, the process of the verification is done by software
automatically when a host boots or reboots, will that be an overhead for the
admin to have a separate job?
I think the real question is : "who will trigger the detection and
when?". Given my original thread, I said it can't be Nova because Nova
is not designed that way. Please consider the link I gave about HA to
see how I feel it can be done (using Pacemaker or not)
Thanks.
--
Shane
-----Original Message-----
From: Michael Still [mailto:mi...@stillhq.com]
Sent: Wednesday, June 24, 2015 7:49 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [nova] How to properly detect and fence a
compromised host (and why I dislike TrustedFilter)
I agree. I feel like this is another example of functionality which is
trivially implemented outside nova, and where it works much better if we don't
do it. Couldn't an admin just have a cron job which verifies hosts, and then
adds them to a compromised-hosts host aggregate if they're owned? I assume
without testing it that you can migrate instances _out_ of a host aggregate you
can't boot in?
Like I said, I see 3 steps there :
- periodically check status of the hosts (can be done using a cron
job, Nagios or whatever else even Pacemaker or HAProxy) by calling OAT
=> that would replace TrustedFilter
- if one host is marked compromised, fence the host => my proposal was
to disable the service, but yours is good too (move the host to a toxic
host aggregate, provided we're using a filter for explicitely removing
hosts belonging to that filter to be elected)
- potentially resurrect the instances that were running on that host,
and here I proposed calling the evacuate API for rebuilding the instance
HTH,
-Sylvain
Michael
On Tue, Jun 23, 2015 at 8:41 PM, Sylvain Bauza <sba...@redhat.com> wrote:
Hi team,
Some discussion occurred over IRC about a bug which was publicly open
related to TrustedFilter [1] I want to take the opportunity for
raising my concerns about that specific filter, why I dislike it and
how I think we could improve the situation - and clarify everyone's
thoughts)
The current situation is that way : Nova only checks if one host is
compromised only when the scheduler is called, ie. only when
booting/migrating/evacuating/unshelving an instance (well, not exactly
all the evacuate/live-migrate cases, but let's not discuss about that
now). When the request goes in the scheduler, all the hosts are
checked against all the enabled filters and the TrustedFilter is
making an external HTTP(S) call to the Attestation API service (not
handled by Nova) for *each host* to see if the host is valid (not compromised)
or not.
To be clear, that's the only in-tree scheduler filter which explicitly
does an external call to a separate service that Nova is not managing.
I can see at least 3 reasons for thinking about why it's bad :
#1 : that's a terrible bottleneck for performance, because we're
IO-blocking N times given N hosts (we're even not multiplexing the
HTTP requests)
#2 : all the filters are checking an internal Nova state for the host
(called HostState) but that the TrustedFilter, which means that
conceptually we defer the decision to a 3rd-party engine
#3 : that Attestation API services becomes a de facto dependency for
Nova (since it's an in-tree filter) while it's not listed as a
dependency and thus not gated.
All of these reasons could be acceptable if that would cover the
exposed usecase given in [1] (ie. I want to make sure that if my host
gets compromised, my instances will not be running on that host) but
that just doesn't work, due to the situation I mentioned above.
So, given that, here are my thoughts :
a/ if a host gets compromised, we can just disable its service to
prevent its election as a valid destination host. There is no need for
a specialised filter.
b/ if a host is compromised, we can assume that the instances have to
resurrect elsewhere, ie. we can call a nova evacuate c/ checking if an
host is compromised or not is not a Nova responsibility since it's
already perfectly done by [2]
In other words, I'm considering that "security" usecase as something
analog as the HA usecase [3] where we need a 3rd-party tool
responsible for periodically checking the state of the hosts, and if
compromised then call the Nova API for fencing the host and evacuating the
compromised instances.
Given that, I'm proposing to deprecate TrustedFilter and explictly
mention to drop it from in-tree in a later cycle
https://review.openstack.org/194592
Thoughts ?
-Sylvain
[1] https://bugs.launchpad.net/nova/+bug/1456228
[2] https://github.com/OpenAttestation/OpenAttestation
[3]
http://blog.russellbryant.net/2014/10/15/openstack-instance-ha-proposa
l/
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