Getting started

Security considerations

The debops.authorized_keys role is designed to manage files in /etc/ssh/authorized_keys/ directory which contain SSH public keys for user accounts.

By default, role modifies the ownership and permissions of these files after the Ansible authorized_key changes them, so that the owner of these files is root account, and the file group, either named after the specified username, set as an item.group parameter or root if the previous entries don't result in an existing group present on a given system. This assumes that each user account has a primary group of the same name as their account, and they are the only members of that group.

The file attributes will be set as 640 to allow read only access to the SSH public key files. This should ensure that user accounts can be logged into the specific SSH public keys, but they cannot be modified by their respective users.

Unfortunately, it seems that the Ansible authorized_key module enforces the "600" file permissions on any file change, therefore there exists a window of opportunity between the given user file being updated by the authorized_key module and permissions being enforced again by the file Ansible module. At the moment there's no good solution to this issue, perhaps in the future the authorized_key module will be updated to allow for setting custom file ownership and permissions similarly to the file module. However, if there are no updates to the user files, the permissions are not changed.

SSH service configuration

The debops.authorized_keys role does not manage the sshd service configuration by itself. Instead, you are expected to configure the sshd daemon to use the authorized keys from its directory, either by hand or by an Ansible role.

Note

The debops.sshd role enables use of the SSH public keys managed by the debops.authorized_keys automatically.

To enable the sshd service to use the configured public keys, you should change the configuration in the /etc/ssh/sshd_config file to something like this:

# /etc/ssh/sshd_config
AuthorizedKeysFile /etc/ssh/authorized_keys/%u %h/.ssh/authorized_keys

The above configuration will enable use of the configured keys by all subsequent SSH connections.

You can use the Match keyword to restrict the use of the authorized keys to a particular hosts, users, groups or IP addresses/subnets as needed. For example, if you want to check these authorized keys only for users in a specific subnet, you can do it like this:

# /etc/ssh/sshd_config
Match Address 192.0.2.0/24
      AuthorizedKeysFile /etc/ssh/authorized_keys/%u %h/.ssh/authorized_keys

Alternatively, you can use different conditions to restrict the SSH public keys checked by the sshd daemon to only the authorized keys maintained by this role. For example, to restrict a particular system group to only use these authorized keys for authentication, you can do it like this:

# /etc/ssh/sshd_config
Match Group sftponly
      AuthorizedKeysFile /etc/ssh/authorized_keys/%u

Example inventory

This role is included by default in the common.yml DebOps playbook, so you don't need to do anything to enable it.

Example playbook

If you are using this role without DebOps, here's an example Ansible playbook that uses the debops.authorized_keys role:

---

- name: Manage SSH public keys
  hosts: [ 'debops_all_hosts', 'debops_service_authorized_keys' ]
  become: True

  roles:

    - role: debops.authorized_keys
      tags: [ 'role::authorized_keys' ]