From 9b765652649f8b6110bd70aa90b148a90057ff6a Mon Sep 17 00:00:00 2001
From: Ivan Tashkinov <ivantashkinov@gmail.com>
Date: Mon, 18 May 2020 09:51:53 +0300
Subject: [PATCH] MediaController: enforced owner-only access in :show action.
 Improved error response on denied access (now 403). Adjusted tests.

---
 lib/pleroma/object.ex                         | 15 +++++++++-----
 .../controllers/fallback_controller.ex        |  4 ++++
 .../controllers/media_controller.ex           |  8 ++++----
 .../controllers/media_controller_test.exs     | 20 ++++++++++++++-----
 4 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/lib/pleroma/object.ex b/lib/pleroma/object.ex
index e678fd415..ab16bf2db 100644
--- a/lib/pleroma/object.ex
+++ b/lib/pleroma/object.ex
@@ -138,12 +138,17 @@ defmodule Pleroma.Object do
 
   def normalize(_, _, _), do: nil
 
-  # Owned objects can only be mutated by their owner
-  def authorize_mutation(%Object{data: %{"actor" => actor}}, %User{ap_id: ap_id}),
-    do: actor == ap_id
+  # Owned objects can only be accessed by their owner
+  def authorize_access(%Object{data: %{"actor" => actor}}, %User{ap_id: ap_id}) do
+    if actor == ap_id do
+      :ok
+    else
+      {:error, :forbidden}
+    end
+  end
 
-  # Legacy objects can be mutated by anybody
-  def authorize_mutation(%Object{}, %User{}), do: true
+  # Legacy objects can be accessed by anybody
+  def authorize_access(%Object{}, %User{}), do: :ok
 
   @spec get_cached_by_ap_id(String.t()) :: Object.t() | nil
   def get_cached_by_ap_id(ap_id) do
diff --git a/lib/pleroma/web/mastodon_api/controllers/fallback_controller.ex b/lib/pleroma/web/mastodon_api/controllers/fallback_controller.ex
index 0a257f604..8af557b61 100644
--- a/lib/pleroma/web/mastodon_api/controllers/fallback_controller.ex
+++ b/lib/pleroma/web/mastodon_api/controllers/fallback_controller.ex
@@ -20,6 +20,10 @@ defmodule Pleroma.Web.MastodonAPI.FallbackController do
     render_error(conn, :not_found, "Record not found")
   end
 
+  def call(conn, {:error, :forbidden}) do
+    render_error(conn, :forbidden, "Access denied")
+  end
+
   def call(conn, {:error, error_message}) do
     conn
     |> put_status(:bad_request)
diff --git a/lib/pleroma/web/mastodon_api/controllers/media_controller.ex b/lib/pleroma/web/mastodon_api/controllers/media_controller.ex
index afa8b2ea2..513de279f 100644
--- a/lib/pleroma/web/mastodon_api/controllers/media_controller.ex
+++ b/lib/pleroma/web/mastodon_api/controllers/media_controller.ex
@@ -56,7 +56,7 @@ defmodule Pleroma.Web.MastodonAPI.MediaController do
   @doc "PUT /api/v1/media/:id"
   def update(%{assigns: %{user: user}, body_params: %{description: description}} = conn, %{id: id}) do
     with %Object{} = object <- Object.get_by_id(id),
-         true <- Object.authorize_mutation(object, user),
+         :ok <- Object.authorize_access(object, user),
          {:ok, %Object{data: data}} <- Object.update_data(object, %{"name" => description}) do
       attachment_data = Map.put(data, "id", object.id)
 
@@ -66,10 +66,10 @@ defmodule Pleroma.Web.MastodonAPI.MediaController do
 
   def update(conn, data), do: show(conn, data)
 
-  # TODO: clarify: is the access to non-owned objects granted intentionally?
   @doc "GET /api/v1/media/:id"
-  def show(conn, %{id: id}) do
-    with %Object{data: data, id: object_id} <- Object.get_by_id(id) do
+  def show(%{assigns: %{user: user}} = conn, %{id: id}) do
+    with %Object{data: data, id: object_id} = object <- Object.get_by_id(id),
+         :ok <- Object.authorize_access(object, user) do
       attachment_data = Map.put(data, "id", object_id)
 
       render(conn, "attachment.json", %{attachment: attachment_data})
diff --git a/test/web/mastodon_api/controllers/media_controller_test.exs b/test/web/mastodon_api/controllers/media_controller_test.exs
index 98ec239b1..906fd940f 100644
--- a/test/web/mastodon_api/controllers/media_controller_test.exs
+++ b/test/web/mastodon_api/controllers/media_controller_test.exs
@@ -63,10 +63,9 @@ defmodule Pleroma.Web.MastodonAPI.MediaControllerTest do
       assert media["type"] == "image"
       assert media["description"] == desc
       assert media["id"]
-      object = Object.get_by_id(media["id"])
 
-      # TODO: clarify: if this EP allows access to non-owned objects, the following may be false:
-      assert object.data["actor"] == User.ap_id(conn.assigns[:user])
+      object = Object.get_by_id(media["id"])
+      assert object.data["actor"] == user.ap_id
     end
   end
 
@@ -102,7 +101,7 @@ defmodule Pleroma.Web.MastodonAPI.MediaControllerTest do
     end
   end
 
-  describe "Get media by id" do
+  describe "Get media by id (/api/v1/media/:id)" do
     setup do: oauth_access(["read:media"])
 
     setup %{user: actor} do
@@ -122,7 +121,7 @@ defmodule Pleroma.Web.MastodonAPI.MediaControllerTest do
       [object: object]
     end
 
-    test "/api/v1/media/:id", %{conn: conn, object: object} do
+    test "it returns media object when requested by owner", %{conn: conn, object: object} do
       media =
         conn
         |> get("/api/v1/media/#{object.id}")
@@ -132,5 +131,16 @@ defmodule Pleroma.Web.MastodonAPI.MediaControllerTest do
       assert media["type"] == "image"
       assert media["id"]
     end
+
+    test "it returns 403 if media object requested by non-owner", %{object: object, user: user} do
+      %{conn: conn, user: other_user} = oauth_access(["read:media"])
+
+      assert object.data["actor"] == user.ap_id
+      refute user.id == other_user.id
+
+      conn
+      |> get("/api/v1/media/#{object.id}")
+      |> json_response(403)
+    end
   end
 end