OpenSSH Server

This role configures the OpenSSH daemon. It:

WARNING Misconfiguration of this role can lock you out of your server! Please test your configuration and its interaction with your users configuration before using in production!

WARNING Digital Ocean allows root with passwords via SSH on Debian and Ubuntu. This is not the default assigned by this module - it will set PermitRootLogin without-password which will allow access via SSH key but not via simple password. If you need this functionality, be sure to set sshd_PermitRootLogin yes for those hosts.

Requirements

Tested on:

It will likely work on other flavours and more direct support via suitable vars/ files is welcome.

Optional requirements

If you want to use advanced functionality of this role that can configure firewall and selinux for you, which is mostly useful when custom port is used, the role requires additional collections which are specified in meta/collection-requirements.yml. These are not automatically installed. You must install them like this:

ansible-galaxy install -vv -r meta/collection-requirements.yml

For more information, see sshd_manage_firewall and sshd_manage_selinux options below. These roles are supported only on Red Hat based Linux.

Role variables

Primary role variables

Unconfigured, this role will provide a sshd_config that matches the OS default, minus the comments and in a different order.

sshd_enable

If set to false, the role will be completely disabled. Defaults to true.

sshd_skip_defaults

If set to true, don't apply default values. This means that you must have a complete set of configuration defaults via either the sshd dict, or sshd_Key variables. Defaults to false unless sshd_config_namespace is set or sshd_config_file points to a drop-in directory to avoid recursive include.

sshd_manage_service

If set to false, the service/daemon won't be managed at all, i.e. will not try to enable on boot or start or reload the service. Defaults to true unless: Running inside a docker container (it is assumed ansible is used during build phase) or AIX (Ansible service module does not currently support enabled for AIX)

sshd_allow_reload

If set to false, a reload of sshd wont happen on change. This can help with troubleshooting. You'll need to manually reload sshd if you want to apply the changed configuration. Defaults to the same value as sshd_manage_service. (Except on AIX, where sshd_manage_service is default false, but sshd_allow_reload is default true)

sshd_install_service

If set to true, the role will install service files for the ssh service. Defaults to false.

The templates for the service files to be used are pointed to by the variables

Using these variables, you can use your own custom templates. With the above default templates, the name of the installed ssh service will be provided by the sshd_service variable.

sshd_manage_firewall

If set to true, the the SSH port(s) will be opened in firewall. Note, this works only on Red Hat based OS. The default is false.

NOTE: sshd_manage_firewall is limited to adding ports. It cannot be used for removing ports. If you want to remove ports, you will need to use the firewall system role directly.

sshd_manage_selinux

If set to true, the the selinux will be configured to allow sshd listening on the given SSH port(s). Note, this works only on Red Hat based OS. The default is false.

NOTE: sshd_manage_selinux is limited to adding policy. It cannot be used for removing policy. If you want to remove ports, you will need to use the selinux system role directly.

sshd

A dict containing configuration. e.g.

sshd:
  Compression: delayed
  ListenAddress:
    - 0.0.0.0

sshd_<OptionName>

Simple variables can be used rather than a dict. Simple values override dict values. e.g.:

sshd_Compression: off

In all cases, booleans are correctly rendered as yes and no in sshd configuration. Lists can be used for multiline configuration items. e.g.

sshd_ListenAddress:
  - 0.0.0.0
  - '::'

Renders as:

ListenAddress 0.0.0.0
ListenAddress ::

sshd_match, sshd_match_1 through sshd_match_9

A list of dicts or just a dict for a Match section. Note, that these variables do not override match blocks as defined in the sshd dict. All of the sources will be reflected in the resulting configuration file. The use of sshd_match_* variant is deprecated and no longer recommended.

sshd_backup

When set to false, the original sshd_config file is not backed up. Default is true.

sshd_sysconfig

On RHEL-based systems, sysconfig is used for configuring more details of sshd service. If set to true, this role will manage also the /etc/sysconfig/sshd configuration file based on the following configurations. Default is false.

sshd_sysconfig_override_crypto_policy

In RHEL8-based systems, this can be used to override system-wide crypto policy by setting to true. Without this option, changes to ciphers, MACs, public key algorithms will have no effect on the resulting service in RHEL8. Defaults to false.

sshd_sysconfig_use_strong_rng

In RHEL-based systems (before RHEL9), this can be used to force sshd to reseed openssl random number generator with the given amount of bytes as an argument. The default is 0, which disables this functionality. It is not recommended to turn this on if the system does not have hardware random number generator.

sshd_config_file

The path where the openssh configuration produced by this role should be saved. This is useful mostly when generating configuration snippets to Include from drop-in directory (default in Fedora and RHEL9).

When this path points to a drop-in directory (like /etc/ssh/sshd_confg.d/00-custom.conf), the main configuration file (defined with the variable sshd_main_config_file) is checked to contain a proper Include directive.

sshd_config_namespace

By default (null), the role defines whole content of the configuration file including system defaults. You can use this variable to invoke this role from other roles or from multiple places in a single playbook as an alternative to using a drop-in directory. The sshd_skip_defaults is ignored and no system defaults are used in this case.

When this variable is set, the role places the configuration that you specify to configuration snippets in a existing configuration file under the given namespace. You need to select different namespaces when invoking the role several times.

Note that limitations of the openssh configuration file still apply. For example, only the first option specified in a configuration file is effective for most of the variables.

Technically, the role places snippets in Match all blocks, unless they contain other match blocks, to ensure they are applied regardless of the previous match blocks in the existing configuration file. This allows configuring any non-conflicting options from different roles invocations.

sshd_config_owner, sshd_config_group, sshd_config_mode

Use these variables to set the ownership and permissions for the openssh config file that this role produces.

sshd_verify_hostkeys

By default (auto), this list contains all the host keys that are present in the produced configuration file. If there are none, the OpenSSH default list will be used after excluding non-FIPS approved keys in FIPS mode. The paths are checked for presence and new keys are generated if they are missing. Additionally, permissions and file owners are set to sane defaults. This is useful if the role is used in deployment stage to make sure the service is able to start on the first attempt.

To disable this check, set this to empty list.

sshd_hostkey_owner, sshd_hostkey_group, sshd_hostkey_mode

Use these variables to set the ownership and permissions for the host keys from the above list.

Secondary role variables

These variables are used by the role internals and can be used to override the defaults that correspond to each supported platform. They are not tested and generally are not needed as the role will determine them from the OS type.

sshd_packages

Use this variable to override the default list of packages to install.

sshd_binary

The path to the openssh executable

sshd_service

The name of the openssh service. By default, this variable contains the name of the ssh service that the target platform uses. But it can also be used to set the name of the custom ssh service when the sshd_install_service variable is used.

sshd_sftp_server

Default path to the sftp server binary.

Variables Exported by the Role

sshd_has_run

This variable is set to true after the role was successfully executed.

Configure SSH certificate authentication

To configure SSH certificate authentication on your SSH server, you need to provide at least the trusted user CA key, which will be used to validate client certificates against. This is done with the sshd_trusted_user_ca_keys_list variable.

If you need to map some of the authorized principals to system users, you can do that using the sshd_principals variable.

Additional variables

sshd_trusted_user_ca_keys_list

List of the trusted user CA public keys in OpenSSH (one-line) format (mandatory).

sshd_trustedusercakeys_directory_owner, shsd_trustedusercakeys_directory_group, sshd_trustedusercakeys_directory_mode

Use these variables to set the ownership and permissions for the Trusted User CA Keys directory. Defaults are respectively root, root and 0755.

sshd_trustedusercakeys_file_owner, shsd_trustedusercakeys_file_group, sshd_trustedusercakeys_file_mode

Use these variables to set the ownership and permissions for the Trusted User CA Keys file. Defaults are respectively root, root and 0640.

sshd_principals

A dict containing principals for users in the os (optional). e.g.

sshd_principals:
  admin:
    - frontend-admin
    - backend-admin
  somelinuxuser:
    - some-principal-defined-in-certificate

sshd_authorizedprincipals_directory_owner, shsd_authorizedprincipals_directory_group, sshd_authorizedprincipals_directory_mode

Use these variables to set the ownership and permissions for the Authorized Principals directory. Defaults are respectively root, root and 0755.

sshd_authorizedprincipals_file_owner, shsd_authorizedprincipals_file_group, sshd_authorizedprincipals_file_mode

Use these variables to set the ownership and permissions for the Authorized Principals file. Defaults are respectively root, root and 0644.

Additional configuration

The SSH server needs this information stored in files so in addition to the above variables, respective configuration options TrustedUserCAKeys (mandatory) and AuthorizedPrincipalsFile (optional) need to be present the sshd dictionary when invoking the role. For example:

sshd:
  TrustedUserCAKeys: /etc/ssh/path-to-trusted-user-ca-keys/trusted-user-ca-keys.pub
  AuthorizedPrincipalsFile: "/etc/ssh/path-to-auth-principals/auth_principals/%u"

To learn more about SSH Certificates, here is a nice tutorial to pure SSH certificates, from wikibooks.

To understand principals and to set up SSH certificates with Vault, this is a well-explained tutorial from Hashicorp.

Dependencies

None

For tests, the ansible.posix collection is required for the mount role to emulate FIPS mode.

Example Playbook

DANGER! This example is to show the range of configuration this role provides. Running it will likely break your SSH access to the server!

---
- hosts: all
  vars:
    sshd_skip_defaults: true
    sshd:
      Compression: true
      ListenAddress:
        - "0.0.0.0"
        - "::"
      GSSAPIAuthentication: false
      Match:
        - Condition: "Group user"
          GSSAPIAuthentication: true
    sshd_UsePrivilegeSeparation: false
    sshd_match:
        - Condition: "Group xusers"
          X11Forwarding: true
  roles:
    - role: willshersystems.sshd

Results in:

# Ansible managed: ...
Compression yes
GSSAPIAuthentication no
UsePrivilegeSeparation no
Match Group user
  GSSAPIAuthentication yes
Match Group xusers
  X11Forwarding yes

Since Ansible 2.4, the role can be invoked using include_role keyword, for example:

---
- hosts: all
  become: true
  tasks:
  - name: "Configure sshd"
    include_role:
      name: willshersystems.sshd
    vars:
      sshd_skip_defaults: true
      sshd:
        Compression: true
        ListenAddress:
          - "0.0.0.0"
          - "::"
        GSSAPIAuthentication: false
        Match:
          - Condition: "Group user"
            GSSAPIAuthentication: true
      sshd_UsePrivilegeSeparation: false
      sshd_match:
          - Condition: "Group xusers"
            X11Forwarding: true

You can just add a configuration snippet with the sshd_config_namespace option:

---
- hosts: all
  tasks:
  - name: Configure sshd to accept some useful environment variables
    include_role:
      name: ansible-sshd
    vars:
      sshd_config_namespace: accept-env
      sshd:
        # there are some handy environment variables to accept
        AcceptEnv:
          LANG
          LS_COLORS
          EDITOR

The following snippet will be added to the default configuration file (if not yet present):

# BEGIN sshd system role managed block: namespace accept-env
Match all
  AcceptEnv LANG LS_COLORS EDITOR
# END sshd system role managed block: namespace accept-env

More example playbooks can be found in examples/ directory.

Template Generation

The sshd_config.j2 and sshd_config_snippet.j2 templates are programatically generated by the scripts in meta. New options should be added to the options_body and/or options_match.

To regenerate the templates, from within the meta/ directory run: ./make_option_lists

License

LGPLv3

Authors

Matt Willsher matt@willsher.systems

© 2014,2015 Willsher Systems Ltd.

Jakub Jelen jjelen@redhat.com

© 2020 - 2022 Red Hat, Inc.