Fix: リモートからの参照を無限に受け入れる問題

app/controllers/activitypub/references_controller.rb

@@ -5,8 +5,6 @@ class ActivityPub::ReferencesController < ActivityPub::BaseController
   include Authorization
   include AccountOwnedConcern
 
-  REFERENCES_LIMIT = 5
-
   before_action :require_signature!, if: :authorized_fetch_mode?
   before_action :set_status
 
@@ -40,17 +38,21 @@ class ActivityPub::ReferencesController < ActivityPub::BaseController
     @results ||= begin
       references = @status.reference_objects.order(target_status_id: :asc)
       references = references.where('target_status_id > ?', page_params[:min_id]) if page_params[:min_id].present?
-      references = references.limit(limit_param(REFERENCES_LIMIT))
+      references = references.limit(limit_param(references_limit))
       references.pluck(:target_status_id)
     end
   end
 
+  def references_limit
+    StatusReference::REFERENCES_LIMIT
+  end
+
   def pagination_min_id
     results.last
   end
 
   def records_continue?
-    results.size == limit_param(REFERENCES_LIMIT)
+    results.size == limit_param(references_limit)
   end
 
   def references_collection_presenter

app/models/status_reference.rb

@@ -13,6 +13,8 @@
 #
 
 class StatusReference < ApplicationRecord
+  REFERENCES_LIMIT = 5
+
   belongs_to :status
   belongs_to :target_status, class_name: 'Status'
 

app/services/activitypub/fetch_references_service.rb

@@ -6,7 +6,7 @@ class ActivityPub::FetchReferencesService < BaseService
   def call(status, collection_or_uri)
     @account = status.account
 
-    collection_items(collection_or_uri)&.map { |item| value_or_id(item) }
+    collection_items(collection_or_uri)&.take(8)&.map { |item| value_or_id(item) }
   end
 
   private
@@ -20,9 +20,9 @@ class ActivityPub::FetchReferencesService < BaseService
 
     case collection['type']
     when 'Collection', 'CollectionPage'
-      collection['items']
+      as_array(collection['items'])
     when 'OrderedCollection', 'OrderedCollectionPage'
-      collection['orderedItems']
+      as_array(collection['orderedItems'])
     end
   end
 
@@ -31,6 +31,19 @@ class ActivityPub::FetchReferencesService < BaseService
     return if unsupported_uri_scheme?(collection_or_uri)
     return if ActivityPub::TagManager.instance.local_uri?(collection_or_uri)
 
-    fetch_resource_without_id_validation(collection_or_uri, nil, true)
+    # NOTE: For backward compatibility reasons, Mastodon signs outgoing
+    # queries incorrectly by default.
+    #
+    # While this is relevant for all URLs with query strings, this is
+    # the only code path where this happens in practice.
+    #
+    # Therefore, retry with correct signatures if this fails.
+    begin
+      fetch_resource_without_id_validation(collection_or_uri, nil, true)
+    rescue Mastodon::UnexpectedResponseError => e
+      raise unless e.response && e.response.code == 401 && Addressable::URI.parse(collection_or_uri).query.present?
+
+      fetch_resource_without_id_validation(collection_or_uri, nil, true, request_options: { with_query_string: true })
+    end
   end
 end

spec/services/activitypub/fetch_references_service_spec.rb

@@ -0,0 +1,128 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe ActivityPub::FetchReferencesService, type: :service do
+  subject { described_class.new.call(status, payload) }
+
+  let(:actor)          { Fabricate(:account, domain: 'example.com', uri: 'http://example.com/account') }
+  let(:status)         { Fabricate(:status, account: actor) }
+  let(:collection_uri) { 'http://example.com/references/1' }
+
+  let(:items) do
+    [
+      'http://example.com/self-references-1',
+      'http://example.com/self-references-2',
+      'http://example.com/self-references-3',
+      'http://other.com/other-references-1',
+      'http://other.com/other-references-2',
+      'http://other.com/other-references-3',
+      'http://example.com/self-references-4',
+      'http://example.com/self-references-5',
+      'http://example.com/self-references-6',
+      'http://example.com/self-references-7',
+      'http://example.com/self-references-8',
+    ]
+  end
+
+  let(:payload) do
+    {
+      '@context': 'https://www.w3.org/ns/activitystreams',
+      type: 'Collection',
+      id: collection_uri,
+      items: items,
+    }.with_indifferent_access
+  end
+
+  describe '#call' do
+    context 'when the payload is a Collection with inlined replies' do
+      context 'when there is a single reference, with the array compacted away' do
+        let(:items) { 'http://example.com/self-references-1' }
+
+        it 'a item is returned' do
+          expect(subject).to eq ['http://example.com/self-references-1']
+        end
+      end
+
+      context 'when passing the collection itself' do
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+
+      context 'when passing the URL to the collection' do
+        subject { described_class.new.call(status, collection_uri) }
+
+        before do
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        end
+
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+    end
+
+    context 'when the payload is an OrderedCollection with inlined references' do
+      let(:payload) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          type: 'OrderedCollection',
+          id: collection_uri,
+          orderedItems: items,
+        }.with_indifferent_access
+      end
+
+      context 'when passing the collection itself' do
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+
+      context 'when passing the URL to the collection' do
+        subject { described_class.new.call(status, collection_uri) }
+
+        before do
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        end
+
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+    end
+
+    context 'when the payload is a paginated Collection with inlined references' do
+      let(:payload) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          type: 'Collection',
+          id: collection_uri,
+          first: {
+            type: 'CollectionPage',
+            partOf: collection_uri,
+            items: items,
+          },
+        }.with_indifferent_access
+      end
+
+      context 'when passing the collection itself' do
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+
+      context 'when passing the URL to the collection' do
+        subject { described_class.new.call(status, collection_uri) }
+
+        before do
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        end
+
+        it 'first 8 items are returned' do
+          expect(subject).to eq items.take(8)
+        end
+      end
+    end
+  end
+end