Merge pull request 'Tweak fetch security checks' (#819) from Oneric/akkoma:id-refetch into develop

Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/819

lib/pleroma/object/containment.ex

@@ -12,8 +12,6 @@ defmodule Pleroma.Object.Containment do
   spoofing, therefore removal of object containment functions is NOT recommended.
   """
 
-  alias Pleroma.Web.ActivityPub.Transmogrifier
-
   def get_actor(%{"actor" => actor}) when is_binary(actor) do
     actor
   end
@@ -50,16 +48,39 @@ defmodule Pleroma.Object.Containment do
   defp compare_uris(%URI{host: host} = _id_uri, %URI{host: host} = _other_uri), do: :ok
   defp compare_uris(_id_uri, _other_uri), do: :error
 
-  defp compare_uris_exact(uri, uri), do: :ok
+  defp uri_strip_slash(%URI{path: path} = uri) when is_binary(path),
+    do: %{uri | path: String.replace_suffix(path, "/", "")}
 
-  defp compare_uris_exact(%URI{} = id, %URI{} = other),
+  defp uri_strip_slash(uri), do: uri
-    do: compare_uris_exact(URI.to_string(id), URI.to_string(other))
 
-  defp compare_uris_exact(id_uri, other_uri)
+  # domain names are case-insensitive per spec (other parts of URIs aren’t necessarily)
-       when is_binary(id_uri) and is_binary(other_uri) do
+  defp uri_normalise_host(%URI{host: host} = uri) when is_binary(host),
-    norm_id = String.replace_suffix(id_uri, "/", "")
+    do: %{uri | host: String.downcase(host, :ascii)}
-    norm_other = String.replace_suffix(other_uri, "/", "")
+
-    if norm_id == norm_other, do: :ok, else: :error
+  defp uri_normalise_host(uri), do: uri
+
+  defp compare_uri_identities(uri, uri), do: :ok
+
+  defp compare_uri_identities(id_uri, other_uri) when is_binary(id_uri) and is_binary(other_uri),
+    do: compare_uri_identities(URI.parse(id_uri), URI.parse(other_uri))
+
+  defp compare_uri_identities(%URI{} = id, %URI{} = other) do
+    normid =
+      %{id | fragment: nil}
+      |> uri_strip_slash()
+      |> uri_normalise_host()
+
+    normother =
+      %{other | fragment: nil}
+      |> uri_strip_slash()
+      |> uri_normalise_host()
+
+    # Conversion back to binary avoids issues from non-normalised deprecated authority field
+    if URI.to_string(normid) == URI.to_string(normother) do
+      :ok
+    else
+      :error
+    end
   end
 
   @doc """
@@ -93,21 +114,13 @@ defmodule Pleroma.Object.Containment do
   def contain_origin(_id, _data), do: :ok
 
   @doc """
-  Check whether the fetch URL (after redirects) exactly (sans tralining slash) matches either
+  Check whether the fetch URL (after redirects) is the
-  the canonical ActivityPub id or the objects url field (for display URLs from *key and Mastodon)
+  same location the canonical ActivityPub id points to.
 
   Since this is meant to be used for fetches, anonymous or transient objects are not accepted here.
   """
-  def contain_id_to_fetch(url, %{"id" => id} = data) when is_binary(id) do
+  def contain_id_to_fetch(url, %{"id" => id}) when is_binary(id) do
-    with {:id, :error} <- {:id, compare_uris_exact(id, url)},
+    compare_uri_identities(url, id)
-         # "url" can be a "Link" object and this is checked before full normalisation
-         display_url <- Transmogrifier.fix_url(data)["url"],
-         true <- display_url != nil do
-      compare_uris_exact(display_url, url)
-    else
-      {:id, :ok} -> :ok
-      _ -> :error
-    end
   end
 
   def contain_id_to_fetch(_url, _data), do: :error

lib/pleroma/object/fetcher.ex

@@ -116,7 +116,7 @@ defmodule Pleroma.Object.Fetcher do
   @doc "Assumes object already is in our database and refetches from remote to update (e.g. for polls)"
   def refetch_object(%Object{data: %{"id" => id}} = object) do
     with {:local, false} <- {:local, Object.local?(object)},
-         {:ok, new_data} <- fetch_and_contain_remote_object_from_id(id),
+         {:ok, new_data} <- fetch_and_contain_remote_object_from_id(id, true),
          {:id, true} <- {:id, new_data["id"] == id},
          {:ok, object} <- reinject_object(object, new_data) do
       {:ok, object}
@@ -253,14 +253,17 @@ defmodule Pleroma.Object.Fetcher do
     end
   end
 
-  @doc "Fetches arbitrary remote object and performs basic safety and authenticity checks"
+  @doc """
-  def fetch_and_contain_remote_object_from_id(id)
+  Fetches arbitrary remote object and performs basic safety and authenticity checks.
+  When the fetch URL is known to already be a canonical AP id, checks are stricter.
+  """
+  def fetch_and_contain_remote_object_from_id(id, is_ap_id \\ false)
 
-  def fetch_and_contain_remote_object_from_id(%{"id" => id}),
+  def fetch_and_contain_remote_object_from_id(%{"id" => id}, is_ap_id),
-    do: fetch_and_contain_remote_object_from_id(id)
+    do: fetch_and_contain_remote_object_from_id(id, is_ap_id)
 
-  def fetch_and_contain_remote_object_from_id(id) when is_binary(id) do
+  def fetch_and_contain_remote_object_from_id(id, is_ap_id) when is_binary(id) do
-    Logger.debug("Fetching object #{id} via AP")
+    Logger.debug("Fetching object #{id} via AP [ap_id=#{is_ap_id}]")
 
     with {:valid_uri_scheme, true} <- {:valid_uri_scheme, String.starts_with?(id, "http")},
          %URI{} = uri <- URI.parse(id),
@@ -270,18 +273,31 @@ defmodule Pleroma.Object.Fetcher do
            {:mrf_accept_check, Pleroma.Web.ActivityPub.MRF.SimplePolicy.check_accept(uri)},
          {:local_fetch, :ok} <- {:local_fetch, Containment.contain_local_fetch(id)},
          {:ok, final_id, body} <- get_object(id),
+         # a canonical ID shouldn't be a redirect
+         true <- !is_ap_id || final_id == id,
          {:ok, data} <- safe_json_decode(body),
-         {_, :ok} <- {:strict_id, Containment.contain_id_to_fetch(final_id, data)},
+         {_, :ok} <- {:containment, Containment.contain_origin(final_id, data)},
-         {_, :ok} <- {:containment, Containment.contain_origin(final_id, data)} do
+         {_, _, :ok} <- {:strict_id, data["id"], Containment.contain_id_to_fetch(final_id, data)} do
       unless Instances.reachable?(final_id) do
         Instances.set_reachable(final_id)
       end
 
       {:ok, data}
     else
-      {:strict_id, _} = e ->
+      # E.g.  Mastodon and *key serve the AP object directly under their display URLs without
-        log_fetch_error(id, e)
+      # redirecting to their canonical location first, thus ids will expectedly differ.
-        {:error, :id_mismatch}
+      # Similarly keys, either use a fragment ID and are a subobjects or a distinct ID
+      # but for compatibility are still a subobject presenting their owning actors ID at the toplevel.
+      # Refetching _once_ from the listed id, should yield a strict match afterwards.
+      {:strict_id, ap_id, _} = e ->
+        case is_ap_id do
+          false ->
+            fetch_and_contain_remote_object_from_id(ap_id, true)
+
+          true ->
+            log_fetch_error(id, e)
+            {:error, :id_mismatch}
+        end
 
       {:mrf_reject_check, _} = e ->
         log_fetch_error(id, e)
@@ -301,7 +317,7 @@ defmodule Pleroma.Object.Fetcher do
 
       {:containment, reason} ->
         log_fetch_error(id, reason)
-        {:error, reason}
+        {:error, {:containment, reason}}
 
       {:error, e} ->
         {:error, e}
@@ -311,25 +327,13 @@ defmodule Pleroma.Object.Fetcher do
     end
   end
 
-  def fetch_and_contain_remote_object_from_id(_id),
+  def fetch_and_contain_remote_object_from_id(_id, _is_ap_id),
     do: {:error, :invalid_id}
 
-  defp check_crossdomain_redirect(final_host, original_url)
-
   # HOPEFULLY TEMPORARY
   # Basically none of our Tesla mocks in tests set the (supposed to
   # exist for Tesla proper) url parameter for their responses
   # causing almost every fetch in test to fail otherwise
-  if @mix_env == :test do
-    defp check_crossdomain_redirect(nil, _) do
-      {:cross_domain_redirect, false}
-    end
-  end
-
-  defp check_crossdomain_redirect(final_host, original_url) do
-    {:cross_domain_redirect, final_host != URI.parse(original_url).host}
-  end
-
   if @mix_env == :test do
     defp get_final_id(nil, initial_url), do: initial_url
     defp get_final_id("", initial_url), do: initial_url
@@ -355,10 +359,6 @@ defmodule Pleroma.Object.Fetcher do
     with {:ok, %{body: body, status: code, headers: headers, url: final_url}}
          when code in 200..299 <-
            HTTP.Backoff.get(id, headers),
-         remote_host <-
-           URI.parse(final_url).host,
-         {:cross_domain_redirect, false} <-
-           check_crossdomain_redirect(remote_host, id),
          {:has_content_type, {_, content_type}} <-
            {:has_content_type, List.keyfind(headers, "content-type", 0)},
          {:parse_content_type, {:ok, "application", subtype, type_params}} <-

test/pleroma/object/containment_test.exs

@@ -9,7 +9,6 @@ defmodule Pleroma.Object.ContainmentTest do
   alias Pleroma.User
 
   import Pleroma.Factory
-  import ExUnit.CaptureLog
 
   setup_all do
     Tesla.Mock.mock_global(fn env -> apply(HttpRequestMock, :request, [env]) end)
@@ -136,23 +135,17 @@ defmodule Pleroma.Object.ContainmentTest do
         )
     end
 
-    test "contain_id_to_fetch() allows display URLs" do
+    test "contain_id_to_fetch() allows fragments and normalises domain casing" do
       data = %{
-        "id" => "http://example.com/~alyssa/activities/1234.json",
+        "id" => "http://example.com/users/capybara",
-        "url" => "http://example.com/@alyssa/status/1234"
+        "url" => "http://example.com/@capybara"
       }
 
-      :ok =
+      assert :ok ==
-        Containment.contain_id_to_fetch(
+               Containment.contain_id_to_fetch(
-          "http://example.com/@alyssa/status/1234",
+                 "http://EXAMPLE.com/users/capybara#key",
-          data
+                 data
-        )
+               )
-
-      :ok =
-        Containment.contain_id_to_fetch(
-          "http://example.com/@alyssa/status/1234/",
-          data
-        )
     end
 
     test "users cannot be collided through fake direction spoofing attempts" do
@@ -164,10 +157,14 @@ defmodule Pleroma.Object.ContainmentTest do
           follower_address: User.ap_followers(%User{nickname: "rye@niu.moe"})
         })
 
-      assert capture_log(fn ->
+      # Fetch from an attempted spoof id will suceed, but automatically retrieve
-               {:error, _} = User.get_or_fetch_by_ap_id("https://n1u.moe/users/rye")
+      # the real data from the homeserver instead of naïvely using the spoof
-             end) =~
+      {:ok, fetched_user} = User.get_or_fetch_by_ap_id("https://n1u.moe/users/rye")
-               "[error] Could not decode user at fetch https://n1u.moe/users/rye"
+
+      refute fetched_user.name == "evil rye"
+      refute fetched_user.raw_bio == "boooo!"
+      assert fetched_user.name == "♡ rye ♡"
+      assert fetched_user.nickname == "rye@niu.moe"
     end
 
     test "contain_origin_from_id() gracefully handles cases where no ID is present" do

test/pleroma/object/fetcher_test.exs

@@ -22,6 +22,7 @@ defmodule Pleroma.Object.FetcherTest do
     |> Jason.decode!()
     |> Map.put("id", id)
     |> Map.put("actor", actor_id)
+    |> Map.put("attributedTo", actor_id)
     |> Jason.encode!()
   end
 
@@ -109,7 +110,7 @@ defmodule Pleroma.Object.FetcherTest do
           body: spoofed_object_with_ids("https://patch.cx/objects/spoof_media_redirect1")
         }
 
-      # Spoof: cross-domain redirect with final domain id
+      # Spoof: cross-domain redirect with final domain id, but original id actor
       %{method: :get, url: "https://patch.cx/objects/spoof_media_redirect2"} ->
         %Tesla.Env{
           status: 200,
@@ -118,6 +119,19 @@ defmodule Pleroma.Object.FetcherTest do
           body: spoofed_object_with_ids("https://media.patch.cx/objects/spoof_media_redirect2")
         }
 
+      # No-Spoof: cross-domain redirect with id and actor from final domain
+      %{method: :get, url: "https://patch.cx/objects/spoof_media_redirect3"} ->
+        %Tesla.Env{
+          status: 200,
+          url: "https://media.patch.cx/objects/spoof_media_redirect3",
+          headers: [{"content-type", "application/activity+json"}],
+          body:
+            spoofed_object_with_ids(
+              "https://media.patch.cx/objects/spoof_media_redirect3",
+              "https://media.patch.cx/users/rin"
+            )
+        }
+
       # No-Spoof: same domain redirect
       %{method: :get, url: "https://patch.cx/objects/spoof_redirect"} ->
         %Tesla.Env{
@@ -252,7 +266,7 @@ defmodule Pleroma.Object.FetcherTest do
     end
 
     test "it does not fetch a spoofed object with id different from URL" do
-      assert {:error, :id_mismatch} =
+      assert {:error, :not_found} =
                Fetcher.fetch_and_contain_remote_object_from_id(
                  "https://patch.cx/media/03ca3c8b4ac3ddd08bf0f84be7885f2f88de0f709112131a22d83650819e36c2.json"
                )
@@ -264,19 +278,29 @@ defmodule Pleroma.Object.FetcherTest do
     end
 
     test "it does not fetch an object via cross-domain redirects (initial id)" do
-      assert {:error, {:cross_domain_redirect, true}} =
+      assert {:error, {:containment, _}} =
                Fetcher.fetch_and_contain_remote_object_from_id(
                  "https://patch.cx/objects/spoof_media_redirect1"
                )
     end
 
-    test "it does not fetch an object via cross-domain redirects (final id)" do
+    test "it does not fetch an object via cross-domain redirect if the actor is from the original domain" do
-      assert {:error, {:cross_domain_redirect, true}} =
+      assert {:error, {:containment, :error}} =
                Fetcher.fetch_and_contain_remote_object_from_id(
                  "https://patch.cx/objects/spoof_media_redirect2"
                )
     end
 
+    test "it allows cross-domain redirects when id and author are from final domain" do
+      assert {:ok, %{"id" => id, "attributedTo" => author}} =
+               Fetcher.fetch_and_contain_remote_object_from_id(
+                 "https://patch.cx/objects/spoof_media_redirect3"
+               )
+
+      assert URI.parse(id).host == "media.patch.cx"
+      assert URI.parse(author).host == "media.patch.cx"
+    end
+
     test "it accepts same-domain redirects" do
       assert {:ok, %{"id" => id} = _object} =
                Fetcher.fetch_and_contain_remote_object_from_id(

test/support/http_request_mock.ex

@@ -263,7 +263,12 @@ defmodule HttpRequestMock do
     {:ok,
      %Tesla.Env{
        status: 200,
-       body: File.read!("test/fixtures/tesla_mock/rye.json"),
+       body:
+         File.read!("test/fixtures/tesla_mock/rye.json")
+         |> Jason.decode!()
+         |> Map.put("name", "evil rye")
+         |> Map.put("bio", "boooo!")
+         |> Jason.encode!(),
        headers: activitypub_object_headers()
      }}
   end