SECURITY: Filter unread bookmark reminders the user cannot see

There is an edge case where the following occurs:

1. The user sets a bookmark reminder on a post/topic
2. The post/topic is changed to a PM before or after the reminder
   fires, and the notification remains unread by the user
3. The user opens their bookmark reminder notification list
   and they can still see the notification even though they cannot
   access the topic anymore

There is a very low chance for information leaking here, since
the only thing that could be exposed is the topic title if it
changes to something sensitive.

This commit filters the bookmark unread notifications by using
the bookmarkable can_see? methods and also prevents sending
reminder notifications for bookmarks the user can no longer see.

plugins/chat/lib/chat/message_bookmarkable.rb

@@ -11,7 +11,7 @@ module Chat
     end
 
     def self.preload_associations
-      [:chat_channel]
+      [{ chat_channel: :chatable }]
     end
 
     def self.list_query(user, guardian)
@@ -58,7 +58,8 @@ module Chat
     end
 
     def self.reminder_conditions(bookmark)
-      bookmark.bookmarkable.present? && bookmark.bookmarkable.chat_channel.present?
+      bookmark.bookmarkable.present? && bookmark.bookmarkable.chat_channel.present? &&
+        self.can_see?(bookmark.user.guardian, bookmark)
     end
 
     def self.can_see?(guardian, bookmark)

plugins/chat/spec/lib/chat/message_bookmarkable_spec.rb

@@ -119,6 +119,13 @@ describe Chat::MessageBookmarkable do
       bookmark1.reload
       expect(registered_bookmarkable.can_send_reminder?(bookmark1)).to eq(false)
     end
+
+    it "cannot send reminder if the user cannot access the channel" do
+      expect(registered_bookmarkable.can_send_reminder?(bookmark1)).to eq(true)
+      bookmark1.bookmarkable.update!(chat_channel: Fabricate(:private_category_channel))
+      bookmark1.reload
+      expect(registered_bookmarkable.can_send_reminder?(bookmark1)).to eq(false)
+    end
   end
 
   describe "#reminder_handler" do

plugins/chat/spec/requests/core_ext/users_controller_spec.rb

@@ -22,4 +22,33 @@ describe UsersController do
       expect(membership.following).to eq(true)
     end
   end
+
+  describe "#user_menu_bookmarks" do
+    fab!(:chatters) { Fabricate(:group) }
+    let(:current_user) { Fabricate(:user, group_ids: [chatters.id]) }
+    let(:bookmark_message) { Fabricate(:chat_message) }
+    let(:bookmark_user) { current_user }
+
+    before do
+      register_test_bookmarkable(Chat::MessageBookmarkable)
+      SiteSetting.chat_allowed_groups = [chatters]
+      sign_in(current_user)
+    end
+
+    it "does not return any unread notifications for chat bookmarks that the user no longer has access to" do
+      bookmark_with_reminder =
+        Fabricate(:bookmark, user: current_user, bookmarkable: bookmark_message)
+      BookmarkReminderNotificationHandler.new(bookmark_with_reminder).send_notification
+
+      bookmark_with_reminder.bookmarkable.update!(
+        chat_channel: Fabricate(:private_category_channel),
+      )
+
+      get "/u/#{current_user.username}/user-menu-bookmarks"
+      expect(response.status).to eq(200)
+
+      notifications = response.parsed_body["notifications"]
+      expect(notifications.size).to eq(0)
+    end
+  end
 end