Initial commit

README.md

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+An ansible role to set up an ssh tunnel and port forwardings from the remote machine to local machines
+
+# Caution
+Since the current debian version of sshd does not yet support dynamic configuration files (as in `/etc/ssh/sshd_config.d/*`), this role will **overwrite** your current sshd configuration! Normal ssh access on port 22 is still possible, but custom modifications will be lost on the remote machine.
+
+# Variables you need to set
+... e.g. in `group_vars`
+- `ssh_tunnel_pubkey`: The complete line to be used in `authorized_keys`, e.g. "ssh-ed25519 AAAA[...]aU root@mylocalmachine"
+- `ssh_tunnel_privkey`: The content of the corresponding private key file, including the BEGIN and END tags. It is highly recommended to put this inside an encrypted ansible vault.
+- `tunneled_ports`: A list of port forwardings. Example:
+  ```
+  tunneled_ports:
+  - exposed_port: 80 # public port at the remote machine
+    ephemeral_port: 10080 # internal port at remote machine's localhost address. The ssh tunnel will fetch traffic from there
+    dest_host: my-internal-http-server.local.domain.tld # domain or IP address of the destination machine. Must be reachable form the local machine.
+    dest_port: 80 # open port at the destination machine
+    protocols: ["tcp"] # list of protocols for this forwarding. "tcp" and "udp" are supported.
+  ```

defaults/main.yml

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+---
+ssh_tunnel_os_supported: False
+
+ssh_tunnel_autossh_system_user: autossh
+ssh_tunnel_sshd_unprivileged_user: ssh-tunnel

example_playbook.yml

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+---
+- hosts: my-remote-vps.domain.tld
+  roles:
+    - ssh_tunnel
+  vars:
+    location: "remote"
+
+- hosts: my-local-machine.domain.tld
+  roles:
+    - ssh_tunnel
+  vars:
+    location: "local"

handlers/main.yml

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+---
+- name: restart autossh
+  service:
+    name: autossh
+    state: restarted
+
+- name: restart sshd
+  service:
+    name: sshd
+    state: restarted
+
+- name: save iptables v4 rules
+  shell: iptables-save > /etc/iptables/rules.v4
+  listen: persist iptables
+
+- name: save iptables v6 rules
+  shell: ip6tables-save > /etc/iptables/rules.v6
+  listen: persist iptables

tasks/local.yml

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+---
+- name: Install autossh
+  apt:
+    name: autossh
+    state: present
+    update_cache: yes
+
+- name: Ensure unprivileged ssh user exists
+  user:
+    name: "{{ ssh_tunnel_autossh_system_user }}"
+    system: true
+    state: present
+
+- name: Set user's ssh config
+  template:
+    src: local/ssh_config.j2
+    dest: "{{ ssh_tunnel_local_sshdir }}config"
+    owner: "{{ ssh_tunnel_autossh_system_user }}"
+    mode: 0644
+
+- name: Set private key
+  copy:
+    dest: "{{ ssh_tunnel_local_sshdir }}tunnel-key"
+    content: "{{ ssh_tunnel_privkey }}"
+    owner: "{{ ssh_tunnel_autossh_system_user }}"
+    mode: 0600
+
+- name: Set public key
+  copy:
+    dest: "{{ ssh_tunnel_local_sshdir }}tunnel-key.pub"
+    content: "{{ ssh_tunnel_pubkey }}"
+    owner: "{{ ssh_tunnel_autossh_system_user }}"
+    mode: 0644
+
+- name: Set systemd service file
+  become: yes
+  template:
+    src: local/autossh.service.j2
+    dest: "{{ ssh_tunnel_autossh_service_file }}"
+
+- name: Enable service and run it
+  service:
+    name: autossh
+    state: restarted
+    enabled: yes

tasks/main.yml

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+---
+- name: Set OS dependent variables
+  ansible.builtin.include_vars: "{{ lookup('first_found', params) }}"
+  vars:
+    params:
+      files:
+        - "{{ ansible_distribution | lower }}_{{ ansible_distribution_version | lower }}.yml"
+        - "{{ ansible_distribution | lower }}_{{ ansible_distribution_major_version | lower }}.yml"
+        - "{{ ansible_distribution | lower }}.yml"
+        - "{{ ansible_os_family | lower }}.yml"
+        - "{{ ansible_system | lower }}.yml"
+      paths:
+        - '{{ role_path }}/vars'
+  ignore_errors: True
+
+- name: OS is supported
+  ansible.builtin.assert:
+    that: __os_supported
+    quiet: True
+  vars:
+    __os_supported: "{{ lookup('vars', '{}_os_supported'.format(role_name)) | bool }}"
+
+
+- include_tasks: local.yml
+  when: location == "local"
+
+- include_tasks: remote.yml
+  when: location == "remote"

tasks/remote.yml

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+---
+- name: Ensure unprivileged ssh user exists
+  user:
+    name: "{{ ssh_tunnel_sshd_unprivileged_user }}"
+    system: true
+    state: present
+
+- name: Set authorized_keys for unprivileged user
+  template:
+    src: remote/authorized_keys.j2
+    dest: "{{ ssh_tunnel_remote_sshdir }}authorized_keys"
+    owner: "{{ ssh_tunnel_sshd_unprivileged_user }}"
+    mode: 0600
+
+- name: Set sshd_config
+  become: yes
+  template:
+    src: remote/sshd_config.j2
+    dest: "{{ ssh_tunnel_sshd_conf_dir }}tunnel.conf"
+    mode: 0644
+    owner: root
+
+- name: Enable IPv4 forwarding
+  sysctl:
+    name: net.ipv4.ip_forward
+    value: '1'
+    sysctl_set: yes
+    state: present
+    reload: yes
+
+- name: Enable IPv6 forwarding
+  sysctl:
+    name: net.ipv6.conf.all.forwarding
+    value: '1'
+    sysctl_set: yes
+    state: present
+    reload: yes
+
+- name: Enable IPv4 local network forwarding
+  sysctl:
+    name: net.ipv4.conf.all.route_localnet
+    value: '1'
+    sysctl_set: yes
+    state: present
+    reload: yes
+
+- name: Install iptables-persistent
+  apt:
+    name: iptables-persistent
+    update_cache: yes
+    state: present
+
+- name: Flush existing iptables entries (IPv4)
+  become: yes
+  iptables:
+    ip_version: ipv4
+    table: nat
+    flush: yes
+
+- name: Flush existing iptables entries (IPv6)
+  become: yes
+  iptables:
+    ip_version: ipv6
+    table: nat
+    flush: yes
+
+- name: Forward privileged ports to ephemeral localhost ports (IPv4, TCP)
+  become: yes
+  iptables:
+    ip_version: ipv4
+    table: nat
+    chain: PREROUTING
+    in_interface: eth0
+    protocol: tcp
+    destination_port: "{{ item.exposed_port }}"
+    jump: DNAT
+    to_destination: "127.0.0.1:{{ item.ephemeral_port }}"
+  loop: "{{ tunneled_ports }}"
+  when: "'tcp' in item.protocols"
+  notify: persist iptables
+
+- name: Forward privileged ports to ephemeral localhost ports (IPv4, UDP)
+  become: yes
+  iptables:
+    ip_version: ipv4
+    table: nat
+    chain: PREROUTING
+    in_interface: eth0
+    protocol: udp
+    destination_port: "{{ item.exposed_port }}"
+    jump: DNAT
+    to_destination: "127.0.0.1:{{ item.ephemeral_port }}"
+  loop: "{{ tunneled_ports }}"
+  when: "'udp' in item.protocols"
+  notify: persist iptables
+
+- name: Forward privileged ports to ephemeral localhost ports (IPv6, TCP)
+  become: yes
+  iptables:
+    ip_version: ipv6
+    table: nat
+    chain: PREROUTING
+    in_interface: eth0
+    protocol: tcp
+    destination_port: "{{ item.exposed_port }}"
+    jump: DNAT
+    to_destination: "[::1]:{{ item.ephemeral_port }}"
+  loop: "{{ tunneled_ports }}"
+  when: "'tcp' in item.protocols"
+  notify: persist iptables
+
+- name: Forward privileged ports to ephemeral localhost ports (IPv6, UDP)
+  become: yes
+  iptables:
+    ip_version: ipv6
+    table: nat
+    chain: PREROUTING
+    in_interface: eth0
+    protocol: udp
+    destination_port: "{{ item.exposed_port }}"
+    jump: DNAT
+    to_destination: "[::1]:{{ item.ephemeral_port }}"
+  loop: "{{ tunneled_ports }}"
+  when: "'udp' in item.protocols"
+  notify: persist iptables

templates/local/autossh.service.j2

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+[Unit]
+Description=AutoSSH tunnel service
+After=network-online.target
+
+[Service]
+Type=simple
+User=autossh
+Environment="AUTOSSH_GATETIME=0"
+ExecStart=/usr/bin/autossh -M 0 gateway -N
+
+[Install]
+WantedBy=multi-user.target

templates/local/ssh_config.j2

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+Host gateway
+        HostName tunnel-end.a-0.me
+        User ssh-tunnel
+        Port 22
+        IdentityFile /home/autossh/.ssh/tunnel-key
+        IdentitiesOnly yes
+        ExitOnForwardFailure yes
+        ServerAliveInterval 5
+        ServerAliveCountMax 3
+{% for forwarding in tunneled_ports %}
+        RemoteForward localhost:{{ forwarding.ephemeral_port }} {{ forwarding.dest_host }}:{{ forwarding.dest_port }}
+{% endfor %}

templates/remote/authorized_keys.j2

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+{{ ssh_tunnel_pubkey }}

templates/remote/sshd_config.j2

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+ClientAliveInterval 30
+ClientAliveCountMax 3
+
+Match User ssh-tunnel
+        AllowTcpForwarding yes
+        X11Forwarding no
+        PermitTunnel no
+        GatewayPorts clientspecified
+        ForceCommand echo "Only forwarding"

vars/debian.yml

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+---
+ssh_tunnel_os_supported: True
+
+ssh_tunnel_local_sshdir: "/home/{{ ssh_tunnel_autossh_system_user }}/.ssh/"
+ssh_tunnel_remote_sshdir: "/home/{{ ssh_tunnel_sshd_unprivileged_user }}/.ssh/"
+ssh_tunnel_autossh_service_file: "/etc/systemd/system/autossh.service"
+ssh_tunnel_sshd_conf_dir: "/etc/ssh/sshd_config/"