From 940792f8ba8eae33a2cb48b313986b3674aa3a20 Mon Sep 17 00:00:00 2001 From: Oneric Date: Sat, 13 Jul 2024 06:54:37 +0200 Subject: [PATCH] Refetch on AP ID mismatch MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit As hinted at in the commit message when strict checking was added in 8684964c5d03f6c70f73730b3f1ad26784ffb004, refetching is more robust than display URL comparison but in exchange is harder to implement correctly. A similar refetch approach is also employed by e.g. Mastodon, IceShrimp and FireFish. To make sure no checks can be bypassed by forcing a refetch, id checking is placed at the very end. This will fix: - Peertube display URL arrays our transmogrifier fails to normalise - non-canonical display URLs from alternative frontends (theoretical; we didnt’t get any actual reports about this) It will also be helpful in the planned key handling overhaul. The modified user collision test was introduced in https://git.pleroma.social/pleroma/pleroma/-/merge_requests/461 and unfortunately the issues this fixes aren’t public. Afaict it was just meant to guard against someone serving faked data belonging to an unrelated domain. Since we now refetch and the id actually is mocked, lookup now succeeds but will use the real data from the authorative server making it unproblematic. Instead modify the fake data further and make sure we don’t end up using the spoofed version. --- lib/pleroma/object/containment.ex | 57 +++++++++++++++--------- lib/pleroma/object/fetcher.ex | 42 +++++++++++------ test/pleroma/object/containment_test.exs | 35 +++++++-------- test/pleroma/object/fetcher_test.exs | 2 +- test/support/http_request_mock.ex | 7 ++- 5 files changed, 87 insertions(+), 56 deletions(-) diff --git a/lib/pleroma/object/containment.ex b/lib/pleroma/object/containment.ex index 37bc20e4d..7b1cc37bd 100644 --- a/lib/pleroma/object/containment.ex +++ b/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), - do: compare_uris_exact(URI.to_string(id), URI.to_string(other)) + defp uri_strip_slash(uri), do: uri - defp compare_uris_exact(id_uri, other_uri) - when is_binary(id_uri) and is_binary(other_uri) do - norm_id = String.replace_suffix(id_uri, "/", "") - norm_other = String.replace_suffix(other_uri, "/", "") - if norm_id == norm_other, do: :ok, else: :error + # domain names are case-insensitive per spec (other parts of URIs aren’t necessarily) + defp uri_normalise_host(%URI{host: host} = uri) when is_binary(host), + do: %{uri | host: String.downcase(host, :ascii)} + + 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 - the canonical ActivityPub id or the objects url field (for display URLs from *key and Mastodon) + Check whether the fetch URL (after redirects) is the + 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 - with {:id, :error} <- {:id, compare_uris_exact(id, url)}, - # "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 + def contain_id_to_fetch(url, %{"id" => id}) when is_binary(id) do + compare_uri_identities(url, id) end def contain_id_to_fetch(_url, _data), do: :error diff --git a/lib/pleroma/object/fetcher.ex b/lib/pleroma/object/fetcher.ex index 937026e04..7f9a922aa 100644 --- a/lib/pleroma/object/fetcher.ex +++ b/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" - def fetch_and_contain_remote_object_from_id(id) + @doc """ + 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}), - do: fetch_and_contain_remote_object_from_id(id) + def fetch_and_contain_remote_object_from_id(%{"id" => id}, is_ap_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 - Logger.debug("Fetching object #{id} via AP") + def fetch_and_contain_remote_object_from_id(id, is_ap_id) when is_binary(id) do + 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)} do + {_, :ok} <- {:containment, Containment.contain_origin(final_id, data)}, + {_, _, :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 -> - log_fetch_error(id, e) - {:error, :id_mismatch} + # E.g. Mastodon and *key serve the AP object directly under their display URLs without + # redirecting to their canonical location first, thus ids will expectedly differ. + # 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) @@ -311,7 +327,7 @@ 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) diff --git a/test/pleroma/object/containment_test.exs b/test/pleroma/object/containment_test.exs index f8f40a3ac..1a1d01473 100644 --- a/test/pleroma/object/containment_test.exs +++ b/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", - "url" => "http://example.com/@alyssa/status/1234" + "id" => "http://example.com/users/capybara", + "url" => "http://example.com/@capybara" } - :ok = - Containment.contain_id_to_fetch( - "http://example.com/@alyssa/status/1234", - data - ) - - :ok = - Containment.contain_id_to_fetch( - "http://example.com/@alyssa/status/1234/", - data - ) + assert :ok == + Containment.contain_id_to_fetch( + "http://EXAMPLE.com/users/capybara#key", + 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 -> - {:error, _} = User.get_or_fetch_by_ap_id("https://n1u.moe/users/rye") - end) =~ - "[error] Could not decode user at fetch https://n1u.moe/users/rye" + # Fetch from an attempted spoof id will suceed, but automatically retrieve + # the real data from the homeserver instead of naïvely using the spoof + {:ok, fetched_user} = User.get_or_fetch_by_ap_id("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 diff --git a/test/pleroma/object/fetcher_test.exs b/test/pleroma/object/fetcher_test.exs index 12154cb05..d2de0ccc5 100644 --- a/test/pleroma/object/fetcher_test.exs +++ b/test/pleroma/object/fetcher_test.exs @@ -252,7 +252,7 @@ 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" ) diff --git a/test/support/http_request_mock.ex b/test/support/http_request_mock.ex index 6a01393e3..ea06c4966 100644 --- a/test/support/http_request_mock.ex +++ b/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