debian: run a separate sshd in mgmt VRF

Leave the default sshd alone. If ssh is not necessary in default VRF,
another role should disable it.

roles/debian/files/ssh.service-override.conf

@@ -1,4 +0,0 @@
-[Service]
-ExecStartPre=sleep 10
-ExecStart=
-ExecStart=/usr/bin/ip vrf exec mgmt /usr/sbin/sshd -D $SSHD_OPTS

roles/debian/files/sshd@mgmt.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=OpenBSD Secure Shell server (management VRF)
+After=network.target auditd.service
+
+[Service]
+ExecStartPre=/usr/sbin/sshd -t
+ExecStart=ip vrf exec mgmt /usr/sbin/sshd -f /etc/ssh/sshd_config.mgmt
+ExecReload=/usr/sbin/sshd -t
+ExecReload=/bin/kill -HUP $MAINPID
+KillMode=process
+Restart=on-failure
+RestartPreventExitStatus=255
+Type=notify
+
+[Install]
+WantedBy=multi-user.target

roles/debian/files/sshd_config.mgmt

@@ -0,0 +1,14 @@
+# This is for sshd in management VRF, for ansible and other not-really-OOB stuff.
+
+PidFile none
+UsePAM no
+
+# Only allow pubkey auth.
+KbdInteractiveAuthentication no
+PasswordAuthentication no
+PermitRootLogin prohibit-password
+
+# Disable what we can.
+AllowTcpForwarding no
+GatewayPorts no
+X11Forwarding no

roles/debian/tasks/mgmt.yml

@@ -16,24 +16,24 @@
   package: name=ifupdown2
   notify: reboot
 
-- name: Create override directory for ssh service
-  file:
-    path: /etc/systemd/system/ssh.service.d
-    state: directory
-
-- name: Set up ssh to run in mgmt VRF
+- name: Configure SSH instance in management VRF
   copy:
-    dest: /etc/systemd/system/ssh.service.d/override.conf
-    src: ssh.service-override.conf
+    dest: /etc/ssh/sshd_config.mgmt
+    src: sshd_config.mgmt
+    mode: 0644
   notify: reboot
 
-# With PAM enabled, login shell would run in default VRF instead of mgmt.
-- name: Disable PAM for ssh
-  lineinfile:
-    path: /etc/ssh/sshd_config
-    regexp: '^UsePAM .*yes'
-    state: absent
+- name: Set up a SSH instance in management VRF
+  copy:
+    dest: /etc/systemd/system/
+    src: sshd@mgmt.service
+    mode: 0644
+  notify: reboot
+
+- name: Enable management SSH
+  service:
+    name: sshd@mgmt
+    enabled: yes
   notify: reboot
 
 - meta: flush_handlers
-