discourse/lib/remote_ip_improved.rb

# https://github.com/rails/rails/pull/7234

class RemoteIpImproved
  class IpSpoofAttackError < StandardError ; end

  # IP addresses that are "trusted proxies" that can be stripped from
  # the comma-delimited list in the X-Forwarded-For header. See also:
  # http://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces
  # http://en.wikipedia.org/wiki/Private_network#Private_IPv6_addresses.
  TRUSTED_PROXIES = %r{
    ^127\.0\.0\.1$                | # localhost
    ^::1$                         |
    ^(10                          | # private IP 10.x.x.x
      172\.(1[6-9]|2[0-9]|3[0-1]) | # private IP in the range 172.16.0.0 .. 172.31.255.255
      192\.168                    | # private IP 192.168.x.x
      fc00::                        # private IP fc00
     )\.
  }x

  attr_reader :check_ip, :proxies

  def initialize(app, check_ip_spoofing = true, custom_proxies = nil)
    @app = app
    @check_ip = check_ip_spoofing
    @proxies = case custom_proxies
      when Regexp
        custom_proxies
      when nil
        TRUSTED_PROXIES
      else
        Regexp.union(TRUSTED_PROXIES, custom_proxies)
      end
  end

  def call(env)
    env["action_dispatch.remote_ip"] = GetIp.new(env, self)
    @app.call(env)
  end

  class GetIp

    # IP v4 and v6 (with compression) validation regexp
    # https://gist.github.com/1289635
    VALID_IP = %r{
      (^(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[0-9]{1,2})(\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[0-9]{1,2})){3}$)                                                        | # ip v4
      (^(
      (([0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4})                                                                                                                   | # ip v6 not abbreviated
      (([0-9A-Fa-f]{1,4}:){6}:[0-9A-Fa-f]{1,4})                                                                                                                  | # ip v6 with double colon in the end
      (([0-9A-Fa-f]{1,4}:){5}:([0-9A-Fa-f]{1,4}:)?[0-9A-Fa-f]{1,4})                                                                                              | # - ip addresses v6
      (([0-9A-Fa-f]{1,4}:){4}:([0-9A-Fa-f]{1,4}:){0,2}[0-9A-Fa-f]{1,4})                                                                                          | # - with
      (([0-9A-Fa-f]{1,4}:){3}:([0-9A-Fa-f]{1,4}:){0,3}[0-9A-Fa-f]{1,4})                                                                                          | # - double colon
      (([0-9A-Fa-f]{1,4}:){2}:([0-9A-Fa-f]{1,4}:){0,4}[0-9A-Fa-f]{1,4})                                                                                          | # - in the middle
      (([0-9A-Fa-f]{1,4}:){6} ((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3} (\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))                            | # ip v6 with compatible to v4
      (([0-9A-Fa-f]{1,4}:){1,5}:((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))                           | # ip v6 with compatible to v4
      (([0-9A-Fa-f]{1,4}:){1}:([0-9A-Fa-f]{1,4}:){0,4}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))     | # ip v6 with compatible to v4
      (([0-9A-Fa-f]{1,4}:){0,2}:([0-9A-Fa-f]{1,4}:){0,3}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))   | # ip v6 with compatible to v4
      (([0-9A-Fa-f]{1,4}:){0,3}:([0-9A-Fa-f]{1,4}:){0,2}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))   | # ip v6 with compatible to v4
      (([0-9A-Fa-f]{1,4}:){0,4}:([0-9A-Fa-f]{1,4}:){1}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))     | # ip v6 with compatible to v4
      (::([0-9A-Fa-f]{1,4}:){0,5}((\b((25[0-5])|(1\d{2})|(2[0-4]\d) |(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b))                         | # ip v6 with compatible to v4
      ([0-9A-Fa-f]{1,4}::([0-9A-Fa-f]{1,4}:){0,5}[0-9A-Fa-f]{1,4})                                                                                               | # ip v6 with compatible to v4
      (::([0-9A-Fa-f]{1,4}:){0,6}[0-9A-Fa-f]{1,4})                                                                                                               | # ip v6 with double colon at the begining
      (([0-9A-Fa-f]{1,4}:){1,7}:)                                                                                                                                  # ip v6 without ending
      )$)
    }x

    def initialize(env, middleware)
      @env           = env
      @middleware    = middleware
      @calculated_ip = false
    end

    # Determines originating IP address. REMOTE_ADDR is the standard
    # but will be wrong if the user is behind a proxy. Proxies will set
    # HTTP_CLIENT_IP and/or HTTP_X_FORWARDED_FOR, so we prioritize those.
    # HTTP_X_FORWARDED_FOR may be a comma-delimited list in the case of
    # multiple chained proxies. The first address which is in this list
    # if it's not a known proxy will be the originating IP.
    # Format of HTTP_X_FORWARDED_FOR:
    # client_ip, proxy_ip1, proxy_ip2...
    # http://en.wikipedia.org/wiki/X-Forwarded-For
    def calculate_ip
      client_ip    = @env['HTTP_CLIENT_IP']
      forwarded_ip = ips_from('HTTP_X_FORWARDED_FOR').first
      remote_addrs = ips_from('REMOTE_ADDR')

      check_ip = client_ip && @middleware.check_ip
      if check_ip && forwarded_ip != client_ip
        # We don't know which came from the proxy, and which from the user
        raise IpSpoofAttackError, "IP spoofing attack?!" \
          "HTTP_CLIENT_IP=#{@env['HTTP_CLIENT_IP'].inspect}" \
          "HTTP_X_FORWARDED_FOR=#{@env['HTTP_X_FORWARDED_FOR'].inspect}"
      end

      client_ips = remove_proxies [client_ip, forwarded_ip, remote_addrs].flatten
      if client_ips.present?
        client_ips.first
      else
        # If there is no client ip we can return first valid proxy ip from REMOTE_ADDR etc
        [remote_addrs, client_ip, forwarded_ip].flatten.find { |ip| valid_ip? ip }
      end
    end

    def to_s
      return @ip if @calculated_ip
      @calculated_ip = true
      @ip = calculate_ip
    end

    private

    def ips_from(header)
      @env[header] ? @env[header].strip.split(/[,\s]+/) : []
    end

    def valid_ip?(ip)
      ip =~ VALID_IP
    end

    def not_a_proxy?(ip)
      ip !~ @middleware.proxies
    end

    def remove_proxies(ips)
      ips.select { |ip| valid_ip?(ip) && not_a_proxy?(ip) }
    end

  end

end