3 files changed, 51 insertions, 17 deletions

diff --git a/lib/pleroma/web/activity_pub/activity_pub.ex b/lib/pleroma/web/activity_pub/activity_pub.ex
index 51b787272..ed579e336 100644
--- a/lib/pleroma/web/activity_pub/activity_pub.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub.ex
@@ -628,9 +628,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
   end
 
   def fetch_and_prepare_user_from_ap_id(ap_id) do
-    with {:ok, %{status_code: 200, body: body}} <-
-           @httpoison.get(ap_id, [Accept: "application/activity+json"], follow_redirect: true),
-         {:ok, data} <- Jason.decode(body) do
+    with {:ok, data} <- fetch_and_contain_remote_object_from_id(ap_id) do
       user_data_from_user_object(data)
     else
       e -> Logger.error("Could not decode user at fetch #{ap_id}, #{inspect(e)}")
@@ -732,16 +730,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     else
       Logger.info("Fetching #{id} via AP")
 
-      with true <- String.starts_with?(id, "http"),
-           {:ok, %{body: body, status_code: code}} when code in 200..299 <-
-             @httpoison.get(
-               id,
-               [Accept: "application/activity+json"],
-               follow_redirect: true,
-               timeout: 10000,
-               recv_timeout: 20000
-             ),
-           {:ok, data} <- Jason.decode(body),
+      with {:ok, data} <- fetch_and_contain_remote_object_from_id(id),
            nil <- Object.normalize(data),
            params <- %{
              "type" => "Create",
@@ -771,6 +760,27 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
+  def fetch_and_contain_remote_object_from_id(id) do
+    Logger.info("Fetching #{id} via AP")
+
+    with true <- String.starts_with?(id, "http"),
+         {:ok, %{body: body, status_code: code}} when code in 200..299 <-
+           @httpoison.get(
+             id,
+             [Accept: "application/activity+json"],
+             follow_redirect: true,
+             timeout: 10000,
+             recv_timeout: 20000
+           ),
+         {:ok, data} <- Jason.decode(body),
+         :ok <- Transmogrifier.contain_origin_from_id(id, data) do
+      {:ok, data}
+    else
+      e ->
+        {:error, e}
+    end
+  end
+
   def is_public?(activity) do
     "https://www.w3.org/ns/activitystreams#Public" in (activity.data["to"] ++
                                                          (activity.data["cc"] || []))
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index d51d8626b..5864855b0 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -50,6 +50,19 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
+  def contain_origin_from_id(id, %{"id" => nil}), do: :error
+
+  def contain_origin_from_id(id, %{"id" => other_id} = params) do
+    id_uri = URI.parse(id)
+    other_uri = URI.parse(other_id)
+
+    if id_uri.host == other_uri.host do
+      :ok
+    else
+      :error
+    end
+  end
+
   @doc """
   Modifies an incoming AP object (mastodon format) to our internal format.
   """
@@ -454,15 +467,20 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
-  # TODO: Make secure.
+  # TODO: We presently assume that any actor on the same origin domain as the object being
+  # deleted has the rights to delete that object.  A better way to validate whether or not
+  # the object should be deleted is to refetch the object URI, which should return either
+  # an error or a tombstone.  This would allow us to verify that a deletion actually took
+  # place.
   def handle_incoming(
-        %{"type" => "Delete", "object" => object_id, "actor" => actor, "id" => _id} = data
+        %{"type" => "Delete", "object" => object_id, "actor" => _actor, "id" => _id} = data
       ) do
     object_id = Utils.get_ap_id(object_id)
 
     with actor <- get_actor(data),
-         %User{} = _actor <- User.get_or_fetch_by_ap_id(actor),
+         %User{} = actor <- User.get_or_fetch_by_ap_id(actor),
          {:ok, object} <- get_obj_helper(object_id) || fetch_obj_helper(object_id),
+         :ok <- contain_origin(actor.ap_id, object.data),
          {:ok, activity} <- ActivityPub.delete(object, false) do
       {:ok, activity}
     else
diff --git a/lib/pleroma/web/federator/federator.ex b/lib/pleroma/web/federator/federator.ex
index 962cacfa3..6554fd2ef 100644
--- a/lib/pleroma/web/federator/federator.ex
+++ b/lib/pleroma/web/federator/federator.ex
@@ -101,17 +101,23 @@ defmodule Pleroma.Web.Federator do
 
     params = Utils.normalize_params(params)
 
+    # NOTE: we use the actor ID to do the containment, this is fine because an
+    # actor shouldn't be acting on objects outside their own AP server.
     with {:ok, _user} <- ap_enabled_actor(params["actor"]),
          nil <- Activity.normalize(params["id"]),
-         {:ok, _activity} <- Transmogrifier.handle_incoming(params) do
+         :ok <- Transmogrifier.contain_origin_from_id(params["actor"], params),
+         {:ok, activity} <- Transmogrifier.handle_incoming(params) do
+      {:ok, activity}
     else
       %Activity{} ->
         Logger.info("Already had #{params["id"]}")
+        :error
 
       _e ->
         # Just drop those for now
         Logger.info("Unhandled activity")
         Logger.info(Poison.encode!(params, pretty: 2))
+        :error
     end
   end