Commit 28cc354f authored by Iustin Pop's avatar Iustin Pop
Browse files

Add small security considerations file.

Reviewed-by: imsnah
parent 137161c9
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, md arrays,
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 which has
not been joined in 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)
- root will have added to its authorized_keys file a public key which
grants access to all other nodes in the cluster, and furthermore it
will also get the private part of this key, which will allow it to
login to the other nodes in the cluster (its previous private key
will be backed up)
- the Ganeti node daemon will accept RPC requests from any host which
has the cluster shared secret, 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 disks, md arrays, 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 (image dumps) or for low-level
command (restart the Ganeti node daemon)
- python-twisted based, for the usual operation
- DRBD traffic, for 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.
The python-twisted traffic is secured by SSL and two pre-conditions: the
client will refuse to connect to servers which don't have the
cluster-wide shared SSL certificate, and server will not allow clients
which don't have the cluster-wide shared secret.
The DRBD traffic is not protected by anything, as the version of DRBD we
require (0.7) does not have any protections. 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.
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