Guard against outdated Updates

It is possible for an earlier Update to be received by us later.
For this, we now
(1) only allows Updates to poll counts if there is no updated field,
    or the updated field is the same as the last updated date or
    creation date;
(2) does not allow updating anything if the updated field
    is older than the last updated date or creation date;
(3) allows updating updatable fields otherwise (normal updates);
(4) if only the updated field is changed, it does not create
    a new history item on its own.

1 files changed, 52 insertions, 13 deletions

diff --git a/lib/pleroma/object/updater.ex b/lib/pleroma/object/updater.ex
index 0b21f6c99..3d34c3f27 100644
--- a/lib/pleroma/object/updater.ex
+++ b/lib/pleroma/object/updater.ex
@@ -10,7 +10,10 @@ defmodule Pleroma.Object.Updater do
     |> Enum.reduce(
       %{data: orig_object_data, updated: false},
       fn field, %{data: data, updated: updated} ->
-        updated = updated or Map.get(updated_object, field) != Map.get(orig_object_data, field)
+        updated =
+          updated or
+            (field != "updated" and
+               Map.get(updated_object, field) != Map.get(orig_object_data, field))
 
         data =
           if Map.has_key?(updated_object, field) do
@@ -136,21 +139,57 @@ defmodule Pleroma.Object.Updater do
   # This calculates the data of the new Object from an Update.
   # new_data's formerRepresentations is considered.
   def make_new_object_data_from_update_object(original_data, new_data) do
-    %{data: updated_data, updated: updated} =
-      original_data
-      |> update_content_fields(new_data)
+    update_is_reasonable =
+      with {_, updated} when not is_nil(updated) <- {:cur_updated, new_data["updated"]},
+           {_, {:ok, updated_time, _}} <- {:cur_updated, DateTime.from_iso8601(updated)},
+           {_, last_updated} when not is_nil(last_updated) <-
+             {:last_updated, original_data["updated"] || original_data["published"]},
+           {_, {:ok, last_updated_time, _}} <-
+             {:last_updated, DateTime.from_iso8601(last_updated)},
+           :gt <- DateTime.compare(updated_time, last_updated_time) do
+        :update_everything
+      else
+        # only allow poll updates
+        {:cur_updated, _} -> :no_content_update
+        :eq -> :no_content_update
+        # allow all updates
+        {:last_updated, _} -> :update_everything
+        # allow no updates
+        _ -> false
+      end
 
-    %{updated_object: updated_data, used_history_in_new_object?: used_history_in_new_object?} =
-      updated_data
-      |> maybe_update_history(original_data,
-        updated: updated,
-        use_history_in_new_object?: true,
-        new_data: new_data
-      )
+    %{
+      updated_object: updated_data,
+      used_history_in_new_object?: used_history_in_new_object?,
+      updated: updated
+    } =
+      if update_is_reasonable == :update_everything do
+        %{data: updated_data, updated: updated} =
+          original_data
+          |> update_content_fields(new_data)
+
+        updated_data
+        |> maybe_update_history(original_data,
+          updated: updated,
+          use_history_in_new_object?: true,
+          new_data: new_data
+        )
+        |> Map.put(:updated, updated)
+      else
+        %{
+          updated_object: original_data,
+          used_history_in_new_object?: false,
+          updated: false
+        }
+      end
 
     updated_data =
-      updated_data
-      |> maybe_update_poll(new_data)
+      if update_is_reasonable != false do
+        updated_data
+        |> maybe_update_poll(new_data)
+      else
+        updated_data
+      end
 
     %{
       updated_data: updated_data,