discourse/lib/upload_security.rb

# frozen_string_literal: true

##
# A note on determining whether an upload should be marked as secure:
#
# Some of these flags checked (e.g. all of the for_X flags and the opts[:type])
# are only set when _initially uploading_ via UploadCreator and are not present
# when an upload already exists.
#
# If the upload already exists the best way to figure out whether it should be
# secure alongside the site settings is the access_control_post_id, because the
# original post the upload is linked to has far more bearing on its security context
# post-upload. If the access_control_post_id does not exist then we just rely
# on the current secure? status, otherwise there would be a lot of additional
# complex queries and joins to perform.
class UploadSecurity
  def initialize(upload, opts = {})
    @upload = upload
    @opts = opts
    @upload_type = @opts[:type]
  end

  def should_be_secure?
    return false if uploading_in_public_context?
    secure_attachment? || secure_media?
  end

  private

  def uploading_in_public_context?
    @upload.for_theme || @upload.for_site_setting || @upload.for_gravatar || public_type?
  end

  def supported_media?
    FileHelper.is_supported_media?(@upload.original_filename)
  end

  def secure_attachment?
    !supported_media? && SiteSetting.prevent_anons_from_downloading_files
  end

  def secure_media?
    SiteSetting.secure_media? && supported_media? && uploading_in_secure_context?
  end

  def uploading_in_secure_context?
    return true if SiteSetting.login_required?
    if @upload.access_control_post_id.present?
      return access_control_post_has_secure_media?
    end
    uploading_in_composer? || @upload.for_private_message || @upload.for_group_message || @upload.secure?
  end

  # whether the upload should remain secure or not after posting depends on its context,
  # which is based on the post it is linked to via access_control_post_id.
  # if that post is with_secure_media? then the upload should also be secure.
  # this may change to false if the upload was set to secure on upload e.g. in
  # a post composer then it turned out that the post itself was not in a secure context
  #
  # if there is no access control post id and the upload is currently secure, we
  # do not want to make it un-secure to avoid unintentionally exposing it
  def access_control_post_has_secure_media?
    Post.find_by(id: @upload.access_control_post_id).with_secure_media?
  end

  def public_type?
    %w[avatar custom_emoji profile_background card_background].include?(@upload_type)
  end

  def uploading_in_composer?
    @upload_type == "composer"
  end
end