Normalise public adressing to fix federation

Due to JSON-LD compaction the full address of public scope
may also occur in shorter forms and the spec requires us to treat them
all equivalently. To save us the pain of repeatedly checking for all
variants internally, normalise inbound data to just one form.
See note at: https://www.w3.org/TR/activitypub/#public-addressing

This needs to happen very early, even before the other addressing fixes
else an earlier validator will reject the object. This in turn required
to move the list-tpye normalisation earlier as well, but since I was
unsure about putting empty lists into the data when no such field
existed before, I excluded this case and thus the later fixing had to be
kept as well.

Fixes: https://akkoma.dev/AkkomaGang/akkoma/issues/670

CHANGELOG.md

@@ -18,6 +18,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## Fixed
 - Issue preventing fetching anything from IPv6-only instances
 - Issue allowing post content to leak via opengraph tags despite :estrict\_unauthenticated being set
+- Scope misdetection of remote posts resulting from not recognising
+  JSON-LD-compacted forms of public scope; affected e.g. federation with bovine
 
 ## 2024.03
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -58,21 +58,48 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
 
   def fix_summary(object), do: Map.put(object, "summary", "")
 
-  def fix_addressing_list(map, field) do
+  defp fix_addressing_list(addrs) do
-    addrs = map[field]
-
     cond do
-      is_list(addrs) ->
+      is_list(addrs) -> Enum.filter(addrs, &is_binary/1)
-        Map.put(map, field, Enum.filter(addrs, &is_binary/1))
+      is_binary(addrs) -> [addrs]
-
+      true -> []
-      is_binary(addrs) ->
-        Map.put(map, field, [addrs])
-
-      true ->
-        Map.put(map, field, [])
     end
   end
 
+  # Due to JSON-LD simply "Public" and "as:Public" are equivalent to the full URI
+  # but to simplify later checks we only want to deal with one reperesentation internally
+  defp normalise_addressing_public_list(map, all_fields)
+
+  defp normalise_addressing_public_list(%{} = map, [field | fields]) do
+    full_uri = Pleroma.Constants.as_public()
+
+    map =
+      if map[field] != nil do
+        new_fval =
+          map[field]
+          |> fix_addressing_list()
+          |> Enum.map(fn
+            "Public" -> full_uri
+            "as:Public" -> full_uri
+            x -> x
+          end)
+
+        Map.put(map, field, new_fval)
+      else
+        map
+      end
+
+    normalise_addressing_public_list(map, fields)
+  end
+
+  defp normalise_addressing_public_list(map, _) do
+    map
+  end
+
+  defp normalise_addressing_public(map) do
+    normalise_addressing_public_list(map, ["to", "cc", "bto", "bcc"])
+  end
+
   # if directMessage flag is set to true, leave the addressing alone
   def fix_explicit_addressing(%{"directMessage" => true} = object, _follower_collection),
     do: object
@@ -96,6 +123,10 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     |> Map.put("cc", final_cc)
   end
 
+  def fix_addressing_list_key(map, field) do
+    Map.put(map, field, fix_addressing_list(map[field]))
+  end
+
   def fix_addressing(object) do
     {:ok, %User{follower_address: follower_collection}} =
       object
@@ -103,10 +134,10 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       |> User.get_or_fetch_by_ap_id()
 
     object
-    |> fix_addressing_list("to")
+    |> fix_addressing_list_key("to")
-    |> fix_addressing_list("cc")
+    |> fix_addressing_list_key("cc")
-    |> fix_addressing_list("bto")
+    |> fix_addressing_list_key("bto")
-    |> fix_addressing_list("bcc")
+    |> fix_addressing_list_key("bcc")
     |> fix_explicit_addressing(follower_collection)
     |> CommonFixes.fix_implicit_addressing(follower_collection)
   end
@@ -383,11 +414,28 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end)
   end
 
-  def handle_incoming(data, options \\ [])
+  def handle_incoming(data, options \\ []) do
+    data = normalise_addressing_public(data)
+
+    data =
+      if data["object"] != nil do
+        object = normalise_addressing_public(data["object"])
+        Map.put(data, "object", object)
+      else
+        data
+      end
+
+    handle_incoming_normalised(data, options)
+  end
+
+  defp handle_incoming_normalised(data, options)
 
   # Flag objects are placed ahead of the ID check because Mastodon 2.8 and earlier send them
   # with nil ID.
-  def handle_incoming(%{"type" => "Flag", "object" => objects, "actor" => actor} = data, _options) do
+  defp handle_incoming_normalised(
+         %{"type" => "Flag", "object" => objects, "actor" => actor} = data,
+         _options
+       ) do
     with context <- data["context"] || Utils.generate_context_id(),
          content <- data["content"] || "",
          %User{} = actor <- User.get_cached_by_ap_id(actor),
@@ -408,14 +456,15 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   end
 
   # disallow objects with bogus IDs
-  def handle_incoming(%{"id" => nil}, _options), do: :error
+  defp handle_incoming_normalised(%{"id" => nil}, _options), do: :error
-  def handle_incoming(%{"id" => ""}, _options), do: :error
+  defp handle_incoming_normalised(%{"id" => ""}, _options), do: :error
   # length of https:// = 8, should validate better, but good enough for now.
-  def handle_incoming(%{"id" => id}, _options) when is_binary(id) and byte_size(id) < 8,
+  defp handle_incoming_normalised(%{"id" => id}, _options)
+       when is_binary(id) and byte_size(id) < 8,
        do: :error
 
-  @doc "Rewrite misskey likes into EmojiReacts"
+  # Rewrite misskey likes into EmojiReacts
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{
            "type" => "Like",
            "content" => reaction
@@ -433,7 +482,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{"type" => "Create", "object" => %{"type" => objtype, "id" => obj_id}} = data,
          options
        )
@@ -469,7 +518,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(%{"type" => type} = data, _options)
+  defp handle_incoming_normalised(%{"type" => type} = data, _options)
        when type in ~w{Like EmojiReact Announce Add Remove} do
     with :ok <- ObjectValidator.fetch_actor_and_object(data),
          {:ok, activity, _meta} <- Pipeline.common_pipeline(data, local: false) do
@@ -480,7 +529,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{"type" => type} = data,
          _options
        )
@@ -492,7 +541,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{"type" => "Delete"} = data,
          _options
        ) do
@@ -515,7 +564,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{
            "type" => "Undo",
            "object" => %{"type" => "Follow", "object" => followed},
@@ -534,7 +583,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{
            "type" => "Undo",
            "object" => %{"type" => type}
@@ -548,7 +597,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   end
 
   # For Undos that don't have the complete object attached, try to find it in our database.
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{
            "type" => "Undo",
            "object" => object
@@ -565,7 +614,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(
+  defp handle_incoming_normalised(
          %{
            "type" => "Move",
            "actor" => origin_actor,
@@ -588,7 +637,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  def handle_incoming(_, _), do: :error
+  defp handle_incoming_normalised(_, _), do: :error
 
   @spec get_obj_helper(String.t(), Keyword.t()) :: {:ok, Object.t()} | nil
   def get_obj_helper(id, options \\ []) do

test/pleroma/web/federator_test.exs

@@ -137,6 +137,37 @@ defmodule Pleroma.Web.FederatorTest do
       assert {:error, :already_present} = ObanHelpers.perform(job)
     end
 
+    test "successfully normalises public scope descriptors" do
+      params = %{
+        "@context" => "https://www.w3.org/ns/activitystreams",
+        "actor" => "http://mastodon.example.org/users/admin",
+        "type" => "Create",
+        "id" => "http://mastodon.example.org/users/admin/activities/1",
+        "object" => %{
+          "type" => "Note",
+          "content" => "hi world!",
+          "id" => "http://mastodon.example.org/users/admin/objects/1",
+          "attributedTo" => "http://mastodon.example.org/users/admin",
+          "to" => ["Public"]
+        },
+        "to" => ["as:Public"]
+      }
+
+      assert {:ok, job} = Federator.incoming_ap_doc(params)
+      assert {:ok, activity} = ObanHelpers.perform(job)
+      assert activity.data["to"] == ["https://www.w3.org/ns/activitystreams#Public"]
+
+      object =
+        from(
+          object in Pleroma.Object,
+          where: fragment("(?)->>'id' = ?", object.data, ^activity.data["object"]),
+          limit: 1
+        )
+        |> Repo.one()
+
+      assert object.data["to"] == ["https://www.w3.org/ns/activitystreams#Public"]
+    end
+
     test "rejects incoming AP docs with incorrect origin" do
       params = %{
         "@context" => "https://www.w3.org/ns/activitystreams",