Synnefo » snf-ganeti

Security in Ganeti

==================

Ganeti was developed to run on internal, trusted systems. As such, the

security model is all-or-nothing.

All the Ganeti code runs as root, because all the operations that Ganeti

is doing require privileges: creating logical volumes, drbd devices,

starting instances, etc. Running as root does not mean setuid, but that

you need to be root to run the cluster commands.

Host issues

-----------

For a host on which the Ganeti software has been installed, but not

joined to a cluster, there are no changes to the system.

For a host that has been joined to the cluster, there are very important

changes:

- The host will have its SSH host key replaced with the one of the

  cluster (which is the one the initial node had at the cluster

  creation)

- A new public key will be added to root's authorized_keys file,

  granting root access to all nodes of the cluster. The private part of

  the key is also distributed to all nodes. Old files are renamed.

- Communication between nodes is encrypted using SSL/TLS. A common key

  and certificate combo is shared between all nodes of the cluster.  At

  this time, no CA is used.

- The Ganeti node daemon will accept RPC requests from any host within

  the cluster with the correct certificate, and the operations it will

  do as a result of these requests are:

  - running commands under the /etc/ganeti/hooks directory

  - creating DRBD disks between it and the IP it has been told

  - overwrite a defined list of files on the host

As you can see, as soon as a node is joined, it becomes equal to all

other nodes in the cluster, and the security of the cluster is

determined by the weakest node.

Note that only the SSH key will allow other machines to run random

commands on this node; the RPC method will run only:

- well defined commands to create, remove, activate logical volumes,

  drbd devices, start/stop instances, etc;

- run SSH commands on other nodes in the cluster, again well-defined

- scripts under the /etc/ganeti/hooks directory

It is therefore important to make sure that the contents of the

/etc/ganeti/hooks directory is supervised and only trusted sources can

populate it.

Cluster issues

--------------

As told above, there are multiple ways of communication between cluster

nodes:

- SSH-based, for high-volume traffic like image dumps or for low-level

  command, e.g. restarting the Ganeti node daemon

- RPC communication between master and nodes

- DRBD real-time disk replication traffic

The SSH traffic is protected (after the initial login to a new node) by

the cluster-wide shared SSH key.

RPC communication between the master and nodes is protected using

SSL/TLS encryption. Both the client and the server must have the

cluster-wide shared SSL/TLS certificate and verify it when establishing

the connection by comparing fingerprints. We decided not to use a CA to

simplify the key handling.

The DRBD traffic is not protected by encryption, as DRBD does not

support this. It's therefore recommended to implement host-level

firewalling or to use a separate range of IP addresses for the DRBD

traffic (this is supported in Ganeti) which is not routed outside the

cluster. DRBD connections are protected from connecting due to bugs to

other machines, and from accepting connections from other machines, by

using a shared secret, exchanged via RPC requests from the master to the

nodes when configuring the device.

Master daemon

-------------

The command-line tools to master daemon communication is done via an

UNIX socket, whose permissions are reset to ``0600`` after listening but

before serving requests. This permission-based protection is documented

and works on Linux, but is not-portable; however, Ganeti doesn't work on

non-Linux system at the moment.

Remote API

----------

Starting with Ganeti 2.0, Remote API traffic is encrypted using SSL/TLS

by default. It supports Basic authentication as per :rfc:`2617`.

Paths for certificate, private key and CA files required for SSL/TLS

will be set at source configure time. Symlinks or command line

parameters may be used to use different files.

Inter-cluster instance moves

----------------------------

To move instances between clusters, different clusters must be able to

communicate with each other over a secure channel. Up to and including

Ganeti 2.1, clusters were self-contained entities and had no knowledge

of other clusters. With Ganeti 2.2, clusters can exchange data if tokens

(an encryption certificate) was exchanged by a trusted third party

before.

KVM Security

------------

When running KVM instances under Ganeti three security models ara

available: 'none', 'user' and 'pool'.

Under security model 'none' instances run by default as root. This means

that, if an instance gets jail broken, it will be able to own the host

node, and thus the ganeti cluster. This is the default model, and the

only one available before Ganeti 2.1.2.

Under security model 'user' an instance is run as the user specified by

the hypervisor parameter 'security_domain'. This makes it easy to run

all instances as non privileged users, and allows to manually allocate

specific users to specific instances or sets of instances. If the

specified user doesn't have permissions a jail broken instance will need

some local privilege escalation before being able to take over the node

and the cluster. It's possible though for a jail broken instance to

affect other ones running under the same user.

Under security model 'pool' a global cluster-level uid pool is used to

start each instance on the same node under a different user. The uids in

the cluster pool can be set with ``gnt-cluster init`` and ``gnt-cluster

modify``, and must correspond to existing users on all nodes. Ganeti

will then allocate one to each instance, as needed. This way a jail

broken instance won't be able to affect any other. Since the users are

handed out by ganeti in a per-node randomized way, in this mode there is

no way to make sure a particular instance is always run as a certain

user. Use mode 'user' for that.

In addition to these precautions, if you want to avoid instances sending

traffic on your node network, you can use an iptables rule such as::

  iptables -A OUTPUT -m owner --uid-owner <uid>[-<uid>] -j LOG \

    --log-prefix "ganeti uid pool user network traffic"

  iptables -A OUTPUT -m owner --uid-owner <uid>[-<uid>] -j DROP

This won't affect regular instance traffic (that comes out of the tapX

allocated to the instance, and can be filtered or subject to appropriate

policy routes) but will stop any user generated traffic that might come

from a jailbroken instance.

.. vim: set textwidth=72 :

.. Local Variables:

.. mode: rst

.. fill-column: 72

.. End: