SFTP-Server

An Ansible role which configures an OpenSSH server for chrooted SFTP access. The role is built in such a way that it will not unnecessarily alter a user's OpenSSH customisations. Instead, it simply changes the crucial bits that it needs to, and adds the rest of its configuration in the form of a custom config block (OpenSSH's lack of some form of conf.d/ support forces this behaviour).

Requirements

It is advisable that scp_if_ssh be set to true in the ssh_connection section of your ansible.cfg file, seeing as how Ansible uses SFTP for file transfers by default, and you can easily lock yourself out of your server's SFTP by using this role. The SCP fallback will continue to work. Example config:

; ansible.cfg
...
[ssh_connection]
scp_if_ssh=True

Other than that, only Ansible itself is required. Tested using Ansible 2.0.2.0, 2.2.2.0 and 2.3.0.0, and 2.8.2.x Works on Ubuntu 14.04, 16.04 and 18.04. Untested on other versions. Some work has been done on supporting RHEL, though this is not currently officially supported by the original author (further contributions are obviously welcome ;-)

Role Variables

The following role variables are relevant:

• sftp_home_partition: The partition where SFTP users' home directories will be located. Defaults to "/home".
• sftp_group_name: The name of the Unix group to which all SFTP users must belong. Defaults to "sftpusers".
• sftp_directories: A list of directories that need to be created automatically by default for all SFTP user. Defaults to a blank list (i.e. "[]").
  • Values can be plain strings, or dictionaries containing name, group and mode key/value pairs. (an ansible bug force us to accept only 3 digits for mode, not 4)
• sftp_allow_passwords: Whether or not to allow password authentication for SFTP users. Defaults to False. NOTE: if global SSH configuration does not allow to use passwords, setting this to True will not work (see and adapt PasswordAuthentication from SSH configuration).
• sftp_enable_logging: Enable logging. Auth logs will be written to /var/log/sftp/auth.log, and SFTP activity logs will be written to /var/log/sftp/verbose.log. Defaults to False.
• sftp_enable_login_directory: Enable user to log in to a specific subdirectory from its home. When True, can specify a login_directory in some or all sftp_users. Defaults to False.
• sftp_groups: A list of groups, in map form, containing the following elements:
  • name: The Unix name of the group that requires SFTP access.
  • gid: The group identifier.
  • readonly: Whether or not to enable readonly SFTP session for the current group. Defaults to False.
• sftp_users: A list of users, in map form, containing the following elements:
  • name: The Unix name of the user that requires SFTP access.
  • password: A password hash for the user to login with. Blank passwords can be set with password: "". See 'Notes' section above to checkout out how generate hashed password from plain-text password. NOTE: It appears that UsePAM yes and PermitEmptyPassword yes need to be set in sshd_config in order for blank passwords to work properly. Making those changes currently falls outside the scope of this role and will need to be done externally. NOTE2: when updating this value, please check update_password property.
  • update_password: Set it to true when you need to force the password to be changed.
  • uid : Specify the user identifier on the system
  • group : Define the main group the user belongs to (default to sftp_group_name).
  • groups : Define at which groups the user belongs to (i.e. "[]").
  • shell: Boolean indicating if the user should have a shell access (default to True).
  • authorized: An optional list of files placed in files/ which contain valid public keys for the SFTP user.
  • sftp_directories: A list of directories that need to be individually created for an SFTP user. Defaults to a blank list (i.e. "[]").
  • append: Boolean to add sftp_group_name to the user groups (if any) instead of setting it (default to False).
  • login_directory: An optional path for the user to connect to at login when sftp_enable_login_directory is set to True.
• sftp_nologin_shell: The "nologin" user shell. (defaults to /sbin/nologin.)
• sftp_host_keys: Dictionnary of ssh host keys. Useful when you want to use custom ssh host keys. For example when you need to share the same ssh host keys on several hosts.

Notes

• The sftp_nologin_shell setting defines the shell assigned to sftp_users when the sftp user's shell is set to False. (The nologin shell ensures the user may only use SFTP and have no other login permissions.) This value may vary depending on the operating system version.
• Here is the way to generate a hashed password for sftp_users. The associated hash must be set into the password attribute.

pass='mypa$$w*rd' && ansible all -i localhost, -m debug -a "msg={{ '${pass}' | password_hash('sha512', 'mysecretsalt') }}"
localhost | SUCCESS => {
    "msg": "$6$mysecretsalt$CwBxxKCk8CiFIRrIW6pduZ5U0b8pcEaaSMTfDFrkxjwnFjCLP4Uv.5QGwnnKxfQpbi4nHcTPW1CY1iBpVQRcE/"
}

Every '\' char in the plain-text password must be backslashed :

pass='mypa\\word' && ansible all -i localhost, -m debug -a "msg={{ '${pass}' | password_hash('sha512', 'mysecretsalt') }}"
localhost | SUCCESS => {
    "msg": "$6$mysecretsalt$WVhiKVoovyRrQ8AY9Q.l6BV797wWSkmnhgAMPvtXwO5HVNRD1r0bArRYvLnh9Uu0gh0urkeeybdJhoaXpYi270"
}

In the last example, the real password is 'mypa\word'

Example Playbook

---
- name: test-playbook | Test sftp-server role
  hosts: all
  become: yes
  become_user: root

  roles:
    - role: ansible-role-sftp
      sftp_allow_passwords: true
      sftp_enable_logging: true
      sftp_groups:
        - name: sftpusers
          gid: 1337
      sftp_directories:
        - imports
        - exports
        - { name: public, mode: 755, group: 'sftpusers' }
      sftp_users:
        - name: peter
          password: "$1$salty$li5TXAa2G6oxHTDkqx3Dz/" # passpass
          shell: False
          append: True
          groups:
            - sftpusers
          sftp_directories:
            - directory_only_for_peter1
            - directory_only_for_peter2
        - name: sally
          password: ""
          authorized: [sally.pub]
          append: True
      sftp_host_keys:
        rsa: "ssh-rsa 8mKWxzxGTBQpwVAYVm8mKWxzxGTBQpwVAYVm8mKWxzxGTBQpwVAYVm root@ip-172-31-6-3"
        dsa: "ssh-dss qF+nlhDHHGw4yb3M+yvkxPO6HTbJTK4FKHCNc9e8ThgL5oQwDSOA== root@ip-172-31-6-32"

License

This Ansible role is distributed under the MIT License. See the LICENSE file for more details.

Thanks

• johanmeiring for the hard work
• Scalair