ostatus: explicitly disallow protocol downgrade from activitypub

This closes embargoed bug #1135.

CHANGELOG.md

@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
+### Security
+- OStatus: eliminate the possibility of a protocol downgrade attack.
+
 ### Changed
 - **Breaking:** Configuration: A setting to explicitly disable the mailer was added, defaulting to true, if you are using a mailer add `config :pleroma, Pleroma.Emails.Mailer, enabled: true` to your config
 - **Breaking:** Configuration: `/media/` is now removed when `base_url` is configured, append `/media/` to your `base_url` config to keep the old behaviour if desired

lib/pleroma/web/ostatus/handlers/follow_handler.ex

@@ -9,7 +9,7 @@ defmodule Pleroma.Web.OStatus.FollowHandler do
   alias Pleroma.Web.XML
 
   def handle(entry, doc) do
-    with {:ok, actor} <- OStatus.find_make_or_update_user(doc),
+    with {:ok, actor} <- OStatus.find_make_or_update_actor(doc),
          id when not is_nil(id) <- XML.string_from_xpath("/entry/id", entry),
          followed_uri when not is_nil(followed_uri) <-
            XML.string_from_xpath("/entry/activity:object/id", entry),

lib/pleroma/web/ostatus/handlers/note_handler.ex

@@ -111,7 +111,7 @@ def handle_note(entry, doc \\ nil, options \\ []) do
     with id <- XML.string_from_xpath("//id", entry),
          activity when is_nil(activity) <- Activity.get_create_by_object_ap_id_with_object(id),
          [author] <- :xmerl_xpath.string('//author[1]', doc),
-         {:ok, actor} <- OStatus.find_make_or_update_user(author),
+         {:ok, actor} <- OStatus.find_make_or_update_actor(author),
          content_html <- OStatus.get_content(entry),
          cw <- OStatus.get_cw(entry),
          in_reply_to <- XML.string_from_xpath("//thr:in-reply-to[1]/@ref", entry),

lib/pleroma/web/ostatus/handlers/unfollow_handler.ex

@@ -9,7 +9,7 @@ defmodule Pleroma.Web.OStatus.UnfollowHandler do
   alias Pleroma.Web.XML
 
   def handle(entry, doc) do
-    with {:ok, actor} <- OStatus.find_make_or_update_user(doc),
+    with {:ok, actor} <- OStatus.find_make_or_update_actor(doc),
          id when not is_nil(id) <- XML.string_from_xpath("/entry/id", entry),
          followed_uri when not is_nil(followed_uri) <-
            XML.string_from_xpath("/entry/activity:object/id", entry),

lib/pleroma/web/ostatus/ostatus.ex

@@ -56,7 +56,7 @@ def remote_follow_path do
 
   def handle_incoming(xml_string, options \\ []) do
     with doc when doc != :error <- parse_document(xml_string) do
-      with {:ok, actor_user} <- find_make_or_update_user(doc),
+      with {:ok, actor_user} <- find_make_or_update_actor(doc),
            do: Pleroma.Instances.set_reachable(actor_user.ap_id)
 
       entries = :xmerl_xpath.string('//entry', doc)
@@ -120,7 +120,7 @@ def handle_incoming(xml_string, options \\ []) do
   end
 
   def make_share(entry, doc, retweeted_activity) do
-    with {:ok, actor} <- find_make_or_update_user(doc),
+    with {:ok, actor} <- find_make_or_update_actor(doc),
          %Object{} = object <- Object.normalize(retweeted_activity),
          id when not is_nil(id) <- string_from_xpath("/entry/id", entry),
          {:ok, activity, _object} = ActivityPub.announce(actor, object, id, false) do
@@ -138,7 +138,7 @@ def handle_share(entry, doc) do
   end
 
   def make_favorite(entry, doc, favorited_activity) do
-    with {:ok, actor} <- find_make_or_update_user(doc),
+    with {:ok, actor} <- find_make_or_update_actor(doc),
          %Object{} = object <- Object.normalize(favorited_activity),
          id when not is_nil(id) <- string_from_xpath("/entry/id", entry),
          {:ok, activity, _object} = ActivityPub.like(actor, object, id, false) do
@@ -264,11 +264,18 @@ def maybe_update_ostatus(doc, user) do
     end
   end
 
-  def find_make_or_update_user(doc) do
+  def find_make_or_update_actor(doc) do
     uri = string_from_xpath("//author/uri[1]", doc)
 
-    with {:ok, user} <- find_or_make_user(uri) do
+    with {:ok, %User{} = user} <- find_or_make_user(uri),
+         {:ap_enabled, false} <- {:ap_enabled, User.ap_enabled?(user)} do
       maybe_update(doc, user)
+    else
+      {:ap_enabled, true} ->
+        {:error, :invalid_protocol}
+
+      _ ->
+        {:error, :unknown_user}
     end
   end
 

test/web/ostatus/ostatus_test.exs

@@ -426,7 +426,7 @@ test "find_or_make_user sets all the nessary input fields" do
                }
     end
 
-    test "find_make_or_update_user takes an author element and returns an updated user" do
+    test "find_make_or_update_actor takes an author element and returns an updated user" do
       uri = "https://social.heldscal.la/user/23211"
 
       {:ok, user} = OStatus.find_or_make_user(uri)
@@ -439,14 +439,56 @@ test "find_make_or_update_user takes an author element and returns an updated us
 
       doc = XML.parse_document(File.read!("test/fixtures/23211.atom"))
       [author] = :xmerl_xpath.string('//author[1]', doc)
-      {:ok, user} = OStatus.find_make_or_update_user(author)
+      {:ok, user} = OStatus.find_make_or_update_actor(author)
       assert user.avatar["type"] == "Image"
       assert user.name == old_name
       assert user.bio == old_bio
 
-      {:ok, user_again} = OStatus.find_make_or_update_user(author)
+      {:ok, user_again} = OStatus.find_make_or_update_actor(author)
       assert user_again == user
     end
+
+    test "find_or_make_user disallows protocol downgrade" do
+      user = insert(:user, %{local: true})
+      {:ok, user} = OStatus.find_or_make_user(user.ap_id)
+
+      assert User.ap_enabled?(user)
+
+      user =
+        insert(:user, %{
+          ap_id: "https://social.heldscal.la/user/23211",
+          info: %{ap_enabled: true},
+          local: false
+        })
+
+      assert User.ap_enabled?(user)
+
+      {:ok, user} = OStatus.find_or_make_user(user.ap_id)
+      assert User.ap_enabled?(user)
+    end
+
+    test "find_make_or_update_actor disallows protocol downgrade" do
+      user = insert(:user, %{local: true})
+      {:ok, user} = OStatus.find_or_make_user(user.ap_id)
+
+      assert User.ap_enabled?(user)
+
+      user =
+        insert(:user, %{
+          ap_id: "https://social.heldscal.la/user/23211",
+          info: %{ap_enabled: true},
+          local: false
+        })
+
+      assert User.ap_enabled?(user)
+
+      {:ok, user} = OStatus.find_or_make_user(user.ap_id)
+      assert User.ap_enabled?(user)
+
+      doc = XML.parse_document(File.read!("test/fixtures/23211.atom"))
+      [author] = :xmerl_xpath.string('//author[1]', doc)
+      {:error, :invalid_protocol} = OStatus.find_make_or_update_actor(author)
+    end
   end
 
   describe "gathering user info from a user id" do