ssh: Show server fingerprints in SSH page

- Add a function to the ssh module that returns information about the SSH host
  keys as dict.

- Move SSHAppView to a new ssh/views.py.

- Add the ssh host key information to the SSHAppView context.

- Create a template for the SSH module.

- Display the sshkeys context information in the template below the status area.

Closes: #1650

Signed-off-by: Birger Schacht <birger@rantanplan.org>
[sunil@medhas.org Minor styling updates for variable names, isort, yapf]
[sunil@medhas.org Styling updates on the HTML output for consistency]
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/ssh/__init__.py

@@ -18,6 +18,10 @@
 FreedomBox app for OpenSSH server.
 """
 
+import pathlib
+import re
+import subprocess
+
 from django.utils.translation import ugettext_lazy as _
 
 from plinth import actions
@@ -25,9 +29,8 @@ from plinth import app as app_module
 from plinth import menu
 from plinth.daemon import Daemon
 from plinth.modules.firewall.components import Firewall
-from plinth.views import AppView
 
-from .manifest import backup # noqa, pylint: disable=unused-import
+from .manifest import backup  # noqa, pylint: disable=unused-import
 
 version = 1
 
@@ -84,8 +87,21 @@ def setup(helper, old_version=None):
     actions.superuser_run('ssh', ['setup'])
 
 
-class SshAppView(AppView):
-    app_id = 'ssh'
-    name = name
-    description = description
-    port_forwarding_info = port_forwarding_info
+def get_host_keys():
+    """Return Host keys of the system."""
+    etc_ssh = pathlib.Path('/etc/ssh/')
+    host_keys = []
+    pattern = re.compile(r'^(?P<bit_size>\d+) (?P<fingerprint>[\S]+) '
+                         r'.+ \((?P<algorithm>\w+)\)$')
+
+    for public_key in etc_ssh.glob('*.pub'):
+        process = subprocess.run(['ssh-keygen', '-l', '-f',
+                                  str(public_key)], stdout=subprocess.PIPE,
+                                 check=True)
+        output = process.stdout.decode().strip()
+        if output:
+            match = re.match(pattern, output)
+            if match:
+                host_keys.append(match.groupdict())
+
+    return host_keys

plinth/modules/ssh/templates/ssh.html

@@ -0,0 +1,51 @@
+{% extends "app.html" %}
+{% comment %}
+#
+# This file is part of FreedomBox.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+{% endcomment %}
+{% load bootstrap %}
+{% load i18n %}
+
+{% block status %}
+  {{ block.super }}
+
+  <h3>{% trans "Server Fingerprints" %}</h3>
+
+  <p>
+    {% blocktrans trimmed %}
+      When connecting to the server, ensure that the fingerprint shown by the
+      SSH client matches one of these fingerprints.
+    {% endblocktrans %}
+  </p>
+
+  <table class="table table-bordered table-condensed table-striped">
+    <thead>
+      <tr>
+        <th>{% trans "Algorithm" %}</th>
+        <th>{% trans "Fingerprint" %}</th>
+      </tr>
+    </thead>
+    <tbody>
+      {% for host_key in host_keys %}
+        <tr>
+          <td>{{ host_key.algorithm }}</td>
+          <td><samp>{{ host_key.fingerprint }}</samp></td>
+        </tr>
+      {% endfor %}
+    </tbody>
+  </table>
+{% endblock %}

plinth/modules/ssh/urls.py

@@ -20,7 +20,7 @@ URLs for the Secure Shell Server module.
 
 from django.conf.urls import url
 
-from plinth.modules.ssh import SshAppView
+from plinth.modules.ssh.views import SshAppView
 
 urlpatterns = [
     url(r'^sys/ssh/$', SshAppView.as_view(), name='index'),

plinth/modules/ssh/views.py

@@ -0,0 +1,36 @@
+#
+# This file is part of FreedomBox.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+"""
+Views for the SSH module
+"""
+
+from plinth.modules import ssh
+from plinth.views import AppView
+
+
+class SshAppView(AppView):
+    app_id = 'ssh'
+    name = ssh.name
+    description = ssh.description
+    port_forwarding_info = ssh.port_forwarding_info
+    template_name = 'ssh.html'
+
+    def get_context_data(self, *args, **kwargs):
+        context = super().get_context_data(**kwargs)
+        context['host_keys'] = ssh.get_host_keys()
+
+        return context