[fix] Disallow changing configuration backend from UI #789

Make the backend read-only on Django admin change forms for
device configuration, template, and VPN server, while keeping
it selectable on create forms.

Also add recover-view regression coverage and ensure device
inline backend changes are ignored on change-form submissions.

Fixes #789

Author: hypnoastic

openwisp_controller/config/admin.py

@@ -66,6 +66,15 @@
     from django.contrib.admin import ModelAdmin
 
 
+def is_recover_view(request):
+    resolver_match = getattr(request, "resolver_match", None)
+    return getattr(request, "_recover_view", False) or bool(
+        resolver_match
+        and resolver_match.url_name
+        and resolver_match.url_name.endswith("_recover")
+    )
+
+
 class SystemDefinedVariableMixin(object):
     def system_context(self, obj):
         system_context = obj.get_system_context()
@@ -349,6 +358,12 @@ class Meta:
 
 class ConfigForm(AlwaysHasChangedMixin, BaseForm):
     _old_templates = None
+    readonly_backend = False
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        if self.readonly_backend and "backend" in self.fields:
+            self.fields["backend"].disabled = True
 
     def get_temp_model_instance(self, **options):
         config_model = self.Meta.model
@@ -457,6 +472,17 @@ class ConfigInline(
     verbose_name_plural = verbose_name
     multitenant_shared_relations = ("templates",)
 
+    def get_formset(self, request, obj=None, **kwargs):
+        readonly_backend = bool(
+            obj and obj._has_config() and not is_recover_view(request)
+        )
+        kwargs["form"] = type(
+            "ConfigInlineForm",
+            (self.form,),
+            {"readonly_backend": readonly_backend},
+        )
+        return super().get_formset(request, obj, **kwargs)
+
     def get_queryset(self, request):
         qs = super().get_queryset(request)
         return qs.select_related(*self.change_select_related)
@@ -468,7 +494,14 @@ def _error_reason_field_conditional(self, obj, fields):
         return fields
 
     def get_readonly_fields(self, request, obj):
-        fields = super().get_readonly_fields(request, obj)
+        fields = list(super().get_readonly_fields(request, obj))
+        if (
+            obj
+            and obj._has_config()
+            and not is_recover_view(request)
+            and "backend" not in fields
+        ):
+            fields.append("backend")
         return self._error_reason_field_conditional(obj, fields)
 
     def get_fields(self, request, obj):
@@ -1082,6 +1115,12 @@ class TemplateAdmin(MultitenantAdminMixin, BaseConfigAdmin, SystemDefinedVariabl
     readonly_fields = ["system_context"]
     autocomplete_fields = ["vpn"]
 
+    def get_readonly_fields(self, request, obj=None):
+        fields = list(super().get_readonly_fields(request, obj))
+        if obj and not is_recover_view(request) and "backend" not in fields:
+            fields.append("backend")
+        return fields
+
     @admin.action(permissions=["add"])
     def clone_selected_templates(self, request, queryset):
         selectable_orgs = None
@@ -1261,6 +1300,12 @@ class VpnAdmin(
         "modified",
     ]
 
+    def get_readonly_fields(self, request, obj=None):
+        fields = list(super().get_readonly_fields(request, obj))
+        if obj and not is_recover_view(request) and "backend" not in fields:
+            fields.append("backend")
+        return fields
+
     class Media(BaseConfigAdmin):
         js = list(BaseConfigAdmin.Media.js) + [f"{prefix}js/vpn.js"]
 

openwisp_controller/config/static/config/js/relevant_templates.js

@@ -10,9 +10,11 @@ django.jQuery(function ($) {
       return isDeviceGroup() ? "templates" : "config-0-templates";
     },
     isAddingNewObject = function () {
-      return isDeviceGroup()
-        ? !$(".add-form").length
-        : $('input[name="config-0-id"]').val().length === 0;
+      if (isDeviceGroup()) {
+        return $(".add-form").length > 0;
+      }
+      var configIdField = $('input[name="config-0-id"]');
+      return !configIdField.length || configIdField.val().length === 0;
     },
     getTemplateOptionElement = function (
       index,
@@ -123,11 +125,12 @@ django.jQuery(function ($) {
     },
     showRelevantTemplates = function () {
       var orgID = $(orgFieldSelector).val(),
-        backend = isDeviceGroup() ? "" : $(backendFieldSelector).val(),
+        backend = isDeviceGroup() ? "" : $(backendFieldSelector).val() || "",
+        configID = $('input[name="config-0-id"]').val(),
         currentSelection = getSelectedTemplates();
 
       // Hide templates if no organization or backend is selected
-      if (!orgID || (!isDeviceGroup() && backend.length === 0)) {
+      if (!orgID || (!isDeviceGroup() && backend.length === 0 && !configID)) {
         resetTemplateOptions();
         updateTemplateHelpText();
         return;
@@ -193,14 +196,23 @@ django.jQuery(function ($) {
       initTemplateField();
       var backendField = $(backendFieldSelector);
       $(orgFieldSelector).change(function () {
-        // Only fetch templates when backend field is present
-        if ($(backendFieldSelector).length > 0 || isDeviceGroup()) {
+        // Fetch templates when backend can be determined either from
+        // an editable backend field or from an existing config object.
+        if (
+          $(backendFieldSelector).length > 0 ||
+          isDeviceGroup() ||
+          !isAddingNewObject()
+        ) {
           showRelevantTemplates();
         }
       });
       // Change view: backendField is rendered on page load
       if (backendField.length > 0) {
         addChangeEventHandlerToBackendField();
+      } else if (!isDeviceGroup() && !isAddingNewObject()) {
+        // Change view for device config has readonly backend with no input element.
+        // In this case the backend is inferred server-side from config_id.
+        showRelevantTemplates();
       } else if (isDeviceGroup()) {
         // Initially request data to get templates
         initTemplateField();

openwisp_controller/config/static/config/js/vpn.js

@@ -33,12 +33,29 @@ django.jQuery(function ($) {
     return el.parents(".form-row").eq(0);
   };
 
+  var getBackendValue = function () {
+    var backendInput = $("#id_backend");
+    if (backendInput.length && backendInput.val() !== undefined) {
+      return String(backendInput.val()).toLocaleLowerCase();
+    }
+    var readonlyBackendEl = $(".field-backend .readonly").first();
+    if (!readonlyBackendEl.length) {
+      return "";
+    }
+    var readonlyBackend = readonlyBackendEl.data("backend");
+    if (
+      readonlyBackend === undefined ||
+      readonlyBackend === null ||
+      String(readonlyBackend).trim() === ""
+    ) {
+      readonlyBackend = readonlyBackendEl.text().trim();
+    }
+    return String(readonlyBackend).toLocaleLowerCase();
+  };
+
   var toggleRelatedFields = function () {
     // Show IP and Subnet field only for WireGuard backend
-    var backendValue =
-        $("#id_backend").val() === undefined
-          ? ""
-          : $("#id_backend").val().toLocaleLowerCase().toLocaleLowerCase(),
+    var backendValue = getBackendValue(),
       op;
     if (backendValue.includes("wireguard") || backendValue.includes("vxlan")) {
       op = "show";
@@ -62,10 +79,12 @@ django.jQuery(function ($) {
   };
 
   // clean config when VPN backend is changed
-  $("#id_backend").change(function () {
-    $("#id_config").val("{}");
-    toggleRelatedFields();
-  });
+  if ($("#id_backend").length) {
+    $("#id_backend").change(function () {
+      $("#id_config").val("{}");
+      toggleRelatedFields();
+    });
+  }
 
   toggleRelatedFields();
 });