[#1505] Restricted max thread distance for fetching replies on incoming federation (in addition to reply-to depth restriction).

lib/pleroma/object/fetcher.ex

@@ -10,6 +10,7 @@ defmodule Pleroma.Object.Fetcher do
   alias Pleroma.Signature
   alias Pleroma.Web.ActivityPub.InternalFetchActor
   alias Pleroma.Web.ActivityPub.Transmogrifier
+  alias Pleroma.Web.Federator
 
   require Logger
   require Pleroma.Constants
@@ -59,20 +60,23 @@ defmodule Pleroma.Object.Fetcher do
     end
   end
 
-  # TODO:
-  # This will create a Create activity, which we need internally at the moment.
+  # Note: will create a Create activity, which we need internally at the moment.
   def fetch_object_from_id(id, options \\ []) do
-    with {:fetch_object, nil} <- {:fetch_object, Object.get_cached_by_ap_id(id)},
-         {:fetch, {:ok, data}} <- {:fetch, fetch_and_contain_remote_object_from_id(id)},
-         {:normalize, nil} <- {:normalize, Object.normalize(data, false)},
+    with {_, nil} <- {:fetch_object, Object.get_cached_by_ap_id(id)},
+         {_, true} <- {:allowed_depth, Federator.allowed_thread_distance?(options[:depth])},
+         {_, {:ok, data}} <- {:fetch, fetch_and_contain_remote_object_from_id(id)},
+         {_, nil} <- {:normalize, Object.normalize(data, false)},
          params <- prepare_activity_params(data),
-         {:containment, :ok} <- {:containment, Containment.contain_origin(id, params)},
-         {:transmogrifier, {:ok, activity}} <-
+         {_, :ok} <- {:containment, Containment.contain_origin(id, params)},
+         {_, {:ok, activity}} <-
            {:transmogrifier, Transmogrifier.handle_incoming(params, options)},
-         {:object, _data, %Object{} = object} <-
+         {_, _data, %Object{} = object} <-
            {:object, data, Object.normalize(activity, false)} do
       {:ok, object}
     else
+      {:allowed_depth, false} ->
+        {:error, "Max thread distance exceeded."}
+
       {:containment, _} ->
         {:error, "Object containment failed."}
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -156,8 +156,9 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       when not is_nil(in_reply_to) do
     in_reply_to_id = prepare_in_reply_to(in_reply_to)
     object = Map.put(object, "inReplyToAtomUri", in_reply_to_id)
+    depth = (options[:depth] || 0) + 1
 
-    if Federator.allowed_incoming_reply_depth?(options[:depth]) do
+    if Federator.allowed_thread_distance?(depth) do
       with {:ok, replied_object} <- get_obj_helper(in_reply_to_id, options),
            %Activity{} = _ <- Activity.get_create_by_object_ap_id(replied_object.data["id"]) do
         object
@@ -312,7 +313,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
 
   def fix_type(%{"inReplyTo" => reply_id, "name" => _} = object, options)
       when is_binary(reply_id) do
-    with true <- Federator.allowed_incoming_reply_depth?(options[:depth]),
+    with true <- Federator.allowed_thread_distance?(options[:depth]),
          {:ok, %{data: %{"type" => "Question"} = _} = _} <- get_obj_helper(reply_id, options) do
       Map.put(object, "type", "Answer")
     else
@@ -406,7 +407,6 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
 
     with nil <- Activity.get_create_by_object_ap_id(object["id"]),
          {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
-      options = Keyword.put(options, :depth, (options[:depth] || 0) + 1)
       object = fix_object(object, options)
 
       params = %{
@@ -425,8 +425,15 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       }
 
       with {:ok, created_activity} <- ActivityPub.create(params) do
-        for reply_id <- replies(object) do
-          Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{"id" => reply_id})
+        reply_depth = (options[:depth] || 0) + 1
+
+        if Federator.allowed_thread_distance?(reply_depth) do
+          for reply_id <- replies(object) do
+            Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{
+              "id" => reply_id,
+              "depth" => reply_depth
+            })
+          end
         end
 
         {:ok, created_activity}
@@ -448,7 +455,8 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       |> fix_addressing
 
     with {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
-      options = Keyword.put(options, :depth, (options[:depth] || 0) + 1)
+      reply_depth = (options[:depth] || 0) + 1
+      options = Keyword.put(options, :depth, reply_depth)
       object = fix_object(object, options)
 
       params = %{

lib/pleroma/web/federator/federator.ex

@@ -15,13 +15,19 @@ defmodule Pleroma.Web.Federator do
 
   require Logger
 
-  @doc "Addresses [memory leaks on recursive replies fetching](https://git.pleroma.social/pleroma/pleroma/issues/161)"
+  @doc """
+  Returns `true` if the distance to target object does not exceed max configured value.
+  Serves to prevent fetching of very long threads, especially useful on smaller instances.
+  Addresses [memory leaks on recursive replies fetching](https://git.pleroma.social/pleroma/pleroma/issues/161).
+  Applies to fetching of both ancestor (reply-to) and child (reply) objects.
+  """
   # credo:disable-for-previous-line Credo.Check.Readability.MaxLineLength
-  def allowed_incoming_reply_depth?(depth) do
-    max_replies_depth = Pleroma.Config.get([:instance, :federation_incoming_replies_max_depth])
+  def allowed_thread_distance?(distance) do
+    max_distance = Pleroma.Config.get([:instance, :federation_incoming_replies_max_depth])
 
-    if max_replies_depth do
-      (depth || 1) <= max_replies_depth
+    if max_distance && max_distance >= 0 do
+      # Default depth is 0 (an object has zero distance from itself in its thread)
+      (distance || 0) <= max_distance
     else
       true
     end

lib/pleroma/workers/remote_fetcher_worker.ex

@@ -12,9 +12,9 @@ defmodule Pleroma.Workers.RemoteFetcherWorker do
         %{
           "op" => "fetch_remote",
           "id" => id
-        },
+        } = args,
         _job
       ) do
-    {:ok, _object} = Fetcher.fetch_object_from_id(id)
+    {:ok, _object} = Fetcher.fetch_object_from_id(id, depth: args["depth"])
   end
 end