Fixes #36759 - only call allowed transpilers

CVE-2022-3874: OS command injection via ct_command and fcct_command

Instead of allowing to call *any* command by changing a setting, only
allow specific paths to ct/fcct. If the user needs a different path,
they can set it via settings.yaml.

app/registries/foreman/settings/provisioning.rb

@@ -2,6 +2,9 @@
 
 Foreman::SettingManager.define(:foreman) do
   category(:provisioning, N_('Provisioning')) do
+    CT_LOCATIONS = %w(/usr/bin/ct /usr/local/bin/ct)
+    FCCT_LOCATIONS = %w(/usr/bin/fcct /usr/local/bin/fcct)
+
     owner_select = proc do
       [{:name => _("Users"), :class => 'user', :scope => 'visible', :value_method => 'id_and_type', :text_method => 'login'},
        {:name => _("Usergroups"), :class => 'usergroup', :scope => 'visible', :value_method => 'id_and_type', :text_method => 'name'}]
@@ -119,16 +122,28 @@
       description: N_("Default 'Host initial configuration' template, automatically assigned when a new operating system is created"),
       default: 'Linux host_init_config default',
       full_name: N_("Default 'Host initial configuration' template"))
-    setting('ct_command',
+    setting('ct_location',
+      type: :string,
+      description: N_("Full path to CoreOS transpiler (ct)"),
+      default: CT_LOCATIONS.first
+      full_name: N_("CoreOS Transpiler Command"),
+      collection: proc { CT_LOCATIONS.zip(CT_LOCATIONS).to_h })
+    setting('ct_arguments',
       type: :array,
-      description: N_("Full path to CoreOS transpiler (ct) with arguments as an comma-separated array"),
-      default: [which('ct'), '--pretty', '--files-dir', Rails.root.join('config', 'ct').to_s],
-      full_name: N_("CoreOS Transpiler Command"))
-    setting('fcct_command',
+      description: N_("CoreOS transpiler (ct) arguments as an comma-separated array"),
+      default: ['--pretty', '--files-dir', Rails.root.join('config', 'ct').to_s],
+      full_name: N_("CoreOS Transpiler Command Arguments"))
+    setting('fcct_location',
+      type: :string,
+      description: N_("Full path to Fedora CoreOS transpiler (fcct)"),
+      default: FCCT_LOCATIONS.first,
+      full_name: N_("Fedora CoreOS Transpiler Command"),
+      collection: proc { FCCT_LOCATIONS.zip(FCCT_LOCATIONS).to_h })
+    setting('fcct_arguments',
       type: :array,
-      description: N_("Full path to Fedora CoreOS transpiler (fcct) with arguments as an comma-separated array"),
-      default: [which('fcct'), '--pretty', '--files-dir', Rails.root.join('config', 'ct').to_s],
-      full_name: N_("Fedora CoreOS Transpiler Command"))
+      description: N_("Fedora CoreOS transpiler (fcct) arguments as an comma-separated array"),
+      default: ['--pretty', '--files-dir', Rails.root.join('config', 'ct').to_s],
+      full_name: N_("Fedora CoreOS Transpiler Command Arguments"))
 
     # We have following loop twice to keep the historical order.
     # TODO: First resolve the correct order and then optimize this loop.

app/services/foreman/renderer/scope/macros/transpilers.rb

@@ -15,7 +15,8 @@ module Transpilers
           end
           def transpile_coreos_linux_config(input, validate_input = true, validate_output = false)
             YAML.safe_load(input) if validate_input
-            result = Foreman::CommandRunner.new(Setting[:ct_command], input).run!
+            ct_command = [Setting[:ct_location]] + Setting[:ct_arguments]
+            result = Foreman::CommandRunner.new(ct_command, input).run!
             JSON.parse(result) if validate_output
             result
           end
@@ -29,7 +30,8 @@ def transpile_coreos_linux_config(input, validate_input = true, validate_output
             example "transpile_coreos_linux_config(\"---\\nyaml: blah\") #=> JSON"
           end
           def transpile_fedora_coreos_config(input)
-            Foreman::CommandRunner.new(Setting[:fcct_command], input).run!
+            fcct_command = [Setting[:fcct_location]] + Setting[:fcct_arguments]
+            Foreman::CommandRunner.new(fcct_command, input).run!
           end
         end
       end

db/migrate/20230920093000_move_ct_command_into_own_setting.rb

@@ -0,0 +1,24 @@
+class MoveCtCommandIntoOwnSetting < ActiveRecord::Migration[6.1]
+  def up
+    ['ct', 'fcct'].each do |setting_prefix|
+      setting = Setting.where(name: "#{setting_prefix}_command")
+      if setting
+        setting.value = setting.value[1..]
+        setting.name = "#{setting_prefix}_arguments"
+        setting.save
+      end
+    end
+  end
+
+  def down
+    ['ct', 'fcct'].each do |setting_prefix|
+      setting = Setting.where(name: "#{setting_prefix}_arguments")
+      if setting
+        setting.value = ["/usr/bin/#{setting_prefix}"] + setting.value
+        setting.name = "#{setting_prefix}_command"
+        setting.save
+      end
+    end
+  end
+end
+