DeleteValidator: Only allow deletion of certain types.

lib/pleroma/web/activity_pub/object_validators/common_validations.ex

@@ -28,7 +28,9 @@ def validate_recipients_presence(cng, fields \\ [:to, :cc]) do
     end
   end
 
-  def validate_actor_presence(cng, field_name \\ :actor) do
+  def validate_actor_presence(cng, options \\ []) do
+    field_name = Keyword.get(options, :field_name, :actor)
+
     cng
     |> validate_change(field_name, fn field_name, actor ->
       if User.get_cached_by_ap_id(actor) do
@@ -39,25 +41,39 @@ def validate_actor_presence(cng, field_name \\ :actor) do
     end)
   end
 
-  def validate_object_presence(cng, field_name \\ :object) do
+  def validate_object_presence(cng, options \\ []) do
+    field_name = Keyword.get(options, :field_name, :object)
+    allowed_types = Keyword.get(options, :allowed_types, false)
+
     cng
-    |> validate_change(field_name, fn field_name, object ->
-      if Object.get_cached_by_ap_id(object) do
-        []
-      else
-        [{field_name, "can't find object"}]
+    |> validate_change(field_name, fn field_name, object_id ->
+      object = Object.get_cached_by_ap_id(object_id)
+
+      cond do
+        !object ->
+          [{field_name, "can't find object"}]
+
+        object && allowed_types && object.data["type"] not in allowed_types ->
+          [{field_name, "object not in allowed types"}]
+
+        true ->
+          []
       end
     end)
   end
 
-  def validate_object_or_user_presence(cng, field_name \\ :object) do
-    cng
-    |> validate_change(field_name, fn field_name, object ->
-      if Object.get_cached_by_ap_id(object) || User.get_cached_by_ap_id(object) do
-        []
-      else
-        [{field_name, "can't find object"}]
-      end
-    end)
+  def validate_object_or_user_presence(cng, options \\ []) do
+    field_name = Keyword.get(options, :field_name, :object)
+    options = Keyword.put(options, :field_name, field_name)
+
+    actor_cng =
+      cng
+      |> validate_actor_presence(options)
+
+    object_cng =
+      cng
+      |> validate_object_presence(options)
+
+    if actor_cng.valid?, do: actor_cng, else: object_cng
   end
 end

lib/pleroma/web/activity_pub/object_validators/delete_validator.ex

@@ -42,13 +42,23 @@ def add_deleted_activity_id(cng) do
     end
   end
 
+  @deletable_types ~w{
+    Answer
+    Article
+    Audio
+    Event
+    Note
+    Page
+    Question
+    Video
+  }
   def validate_data(cng) do
     cng
     |> validate_required([:id, :type, :actor, :to, :cc, :object])
     |> validate_inclusion(:type, ["Delete"])
     |> validate_actor_presence()
     |> validate_deletion_rights()
-    |> validate_object_or_user_presence()
+    |> validate_object_or_user_presence(allowed_types: @deletable_types)
     |> add_deleted_activity_id()
   end
 

lib/pleroma/web/activity_pub/side_effects.ex

@@ -36,6 +36,7 @@ def handle(%{data: %{"type" => "Like"}} = object, meta) do
   # - Set up notification
   # - Reduce the user note count
   # - Reduce the reply count
+  # - Stream out the activity
   def handle(%{data: %{"type" => "Delete", "object" => deleted_object}} = object, meta) do
     deleted_object =
       Object.normalize(deleted_object, false) || User.get_cached_by_ap_id(deleted_object)

test/web/activity_pub/object_validator_test.exs

@@ -1,6 +1,7 @@
 defmodule Pleroma.Web.ActivityPub.ObjectValidatorTest do
   use Pleroma.DataCase
 
+  alias Pleroma.Object
   alias Pleroma.Web.ActivityPub.Builder
   alias Pleroma.Web.ActivityPub.ObjectValidator
   alias Pleroma.Web.ActivityPub.ObjectValidators.LikeValidator
@@ -26,6 +27,24 @@ test "it is valid for a post deletion", %{valid_post_delete: valid_post_delete}
       assert valid_post_delete["deleted_activity_id"]
     end
 
+    test "it is invalid if the object isn't in a list of certain types", %{
+      valid_post_delete: valid_post_delete
+    } do
+      object = Object.get_by_ap_id(valid_post_delete["object"])
+
+      data =
+        object.data
+        |> Map.put("type", "Like")
+
+      {:ok, _object} =
+        object
+        |> Ecto.Changeset.change(%{data: data})
+        |> Object.update_and_set_cache()
+
+      {:error, cng} = ObjectValidator.validate(valid_post_delete, [])
+      assert {:object, {"object not in allowed types", []}} in cng.errors
+    end
+
     test "it is valid for a user deletion", %{valid_user_delete: valid_user_delete} do
       assert match?({:ok, _, _}, ObjectValidator.validate(valid_user_delete, []))
     end