firstboot: Prompt for secret during firstboot welcome

- A freshly installed FreedomBox can be hijacked by a third party and an admin
  account can be created which can be used to inject malware or simply take over
  the instance. Password protecting the firstboot step is a good way to avoid
  this. A secret will be displayed to the user as soon as the Plinth package
  is installed, which they have to enter during firstboot welcome step. Also,
  writing this to a file in plinth's home in case the user loses it.
- This protection is not applicable for images built by freedom-maker and for
  Amazon Machine Images.

Signed-off-by: Joseph Nuthalapati <njoseph@thoughtworks.com>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

debian/control

@@ -51,6 +51,7 @@ Depends: ${python3:Depends}
  , ${misc:Depends}
  , ${plinth:Depends}
  , adduser
+ , debconf
  , augeas-tools
  , e2fsprogs
  , fonts-lato

debian/postinst

@@ -2,6 +2,9 @@
 
 set -e
 
+# Source debconf library.
+. /usr/share/debconf/confmodule
+
 daemonuser=plinth
 daemongroup=plinth
 
@@ -12,11 +15,20 @@ daemongroup=plinth
 sed -ie 's+-:ALL EXCEPT root fbx (admin) (sudo):ALL+-:ALL EXCEPT root fbx plinth (admin) (sudo):ALL+' /etc/security/access.conf
 
 case "$1" in
-configure)
-	addgroup --system --quiet plinth
-	adduser --system --quiet --ingroup plinth --no-create-home --home /var/lib/plinth plinth
-	chown -R plinth: /var/lib/plinth /var/log/plinth
-	;;
+    configure)
+	      addgroup --system --quiet plinth
+	      adduser --system --quiet --ingroup plinth --no-create-home --home /var/lib/plinth plinth
+	      chown -R plinth: /var/lib/plinth /var/log/plinth
+
+        if [ ! -e '/var/lib/freedombox/is-freedombox-disk-image' ]; then
+            umask 377
+            cat /dev/urandom | base64 | head -c16 > /var/lib/plinth/firstboot-wizard-secret
+            chown plinth:plinth /var/lib/plinth/firstboot-wizard-secret
+            db_subst plinth/firstboot_wizard_secret secret $(cat /var/lib/plinth/firstboot-wizard-secret)
+            db_input high plinth/firstboot_wizard_secret || true
+            db_go
+        fi
+	      ;;
 esac
 
 #DEBHELPER#

debian/templates

@@ -0,0 +1,8 @@
+Template: plinth/firstboot_wizard_secret
+Type: note
+Description: FreedomBox first wizard secret - ${secret}
+ Please save this string. You will be asked to enter this in the first screen
+ after you launch the FreedomBox interface. In case you lose it, you can find
+ it in the file /var/lib/plinth/firstboot-wizard-secret.
+ .
+ ${secret}

plinth/modules/first_boot/__init__.py

@@ -19,10 +19,11 @@ FreedomBox app for first boot wizard.
 """
 
 import operator
+import os
 
 from django.urls import reverse
 
-from plinth import module_loader
+from plinth import cfg, module_loader
 from plinth.signals import post_setup
 
 version = 1
@@ -140,3 +141,14 @@ def set_completed():
     global _is_completed
     _is_completed = True
     kvstore.set('firstboot_completed', 1)
+
+
+def get_secret_file_path():
+    """Returns the path to the first boot wizard secret file."""
+    return os.path.join(cfg.data_dir, 'firstboot-wizard-secret')
+
+
+def firstboot_wizard_secret_exists():
+    """Return whether a firstboot wizard secret exists."""
+    secret_file = get_secret_file_path()
+    return os.path.exists(secret_file) and os.path.getsize(secret_file) > 0

plinth/modules/first_boot/forms.py

@@ -0,0 +1,47 @@
+#
+# 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/>.
+#
+
+from django import forms
+from django.utils.translation import ugettext_lazy as _
+
+from plinth.modules import first_boot
+
+
+class FirstbootWizardSecretForm(forms.Form):
+    """Form to collect and validate the first boot wizard secret."""
+    secret = forms.CharField(
+        label='', help_text=_(
+            'Enter the secret generated during FreedomBox installation. '
+            'This secret can also be obtained from the file '
+            '/var/lib/plinth/firstboot-wizard-secret'), required=False,
+        widget=forms.PasswordInput(attrs={'placeholder': _('Secret')}))
+
+    def validate_secret(self, secret):
+        """Match the secret provided by the user with the one
+        generated during installation.
+        """
+        secret_file_path = first_boot.get_secret_file_path()
+        with open(secret_file_path) as secret_file:
+            if secret != secret_file.read().strip():
+                self.add_error('secret', 'Invalid secret')
+
+    def clean(self):
+        """Override clean to add form validation logic."""
+        cleaned_data = super().clean()
+        if first_boot.firstboot_wizard_secret_exists():
+            self.validate_secret(cleaned_data.get("secret"))
+        return cleaned_data

plinth/modules/first_boot/templates/firstboot_welcome.html

@@ -27,28 +27,29 @@
    .navbar-brand {
        display: none;
    }
+   img.firstboot {
+       display: block;
+       max-width: 100%;
+   }
   </style>
 {% endblock %}
 
 {% block content %}
-  <p class="text-center">
-    <img src="{% static 'theme/img/FreedomBox-logo-standard.png' %}"
-         alt="{{ box_name }}" width="640"/>
-  </p>
+  <div class="logo">
+    <img class="firstboot" src="{% static 'theme/img/FreedomBox-logo-standard.png' %}"
+         alt="{{ box_name }}" />
+  </div>
 
   <form class="form text-center" method="post">
     {% csrf_token %}
 
+    {% if show_wizard_password_prompt %}
+      {{ form|bootstrap }}
+    {% endif %}
+
     <p>
       <input type="submit" class="btn btn-lg btn-primary"
              value="{% trans "Start Setup" %}"/>
     </p>
   </form>
-
-  <p class="text-center" style="font-size: larger">
-    {% blocktrans trimmed %}
-      To complete the setup of your {{ box_name }}, please provide
-      some basic information.
-    {% endblocktrans %}
-  </p>
 {% endblock %}

plinth/modules/first_boot/templatetags/firstboot_extras.py

@@ -14,7 +14,6 @@
 # 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/>.
 #
-
 """
 Template tags for first boot module.
 """

plinth/modules/first_boot/urls.py

@@ -14,7 +14,6 @@
 # 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/>.
 #
-
 """
 URLs for the First Boot module
 """
@@ -22,8 +21,7 @@ URLs for the First Boot module
 from django.conf.urls import url
 from stronghold.decorators import public
 
-from .views import WelcomeView, CompleteView
-
+from .views import CompleteView, WelcomeView
 
 urlpatterns = [
     # Take care of the firstboot middleware when changing URLs

plinth/modules/first_boot/views.py

@@ -19,21 +19,31 @@ from django import http
 from django.urls import reverse
 from django.utils.translation import ugettext as _
 from django.views.generic import TemplateView
+from django.views.generic.edit import FormView
 
 from plinth import network
 from plinth.modules import first_boot
 
+from .forms import FirstbootWizardSecretForm
 
-class WelcomeView(TemplateView):
+
+class WelcomeView(FormView):
     """Show the welcome screen."""
-
+    form_class = FirstbootWizardSecretForm
     template_name = 'firstboot_welcome.html'
 
-    def post(self, request, *args, **kwargs):
-        """On POST, mark this step as done and move to next step."""
+    def form_valid(self, form):
+        """If form is valid, mark this step as done and move to next step."""
         first_boot.mark_step_done('firstboot_welcome')
         return http.HttpResponseRedirect(reverse(first_boot.next_step()))
 
+    def get_context_data(self, **kwargs):
+        """Add network connections to context list."""
+        context = super().get_context_data(**kwargs)
+        show_prompt = first_boot.firstboot_wizard_secret_exists()
+        context['show_wizard_password_prompt'] = show_prompt
+        return context
+
 
 class CompleteView(TemplateView):
     """Show summary after all firstboot setup is done.