Class: Rex::Proto::DNS::Resolver

Inherits:
Net::DNS::Resolver
  • Object
show all
Defined in:
lib/rex/proto/dns/resolver.rb

Overview

Provides Rex::Sockets compatible version of Net::DNS::Resolver Modified to work with Dnsruby::Messages, their resolvers are too heavy

Direct Known Subclasses

CachedResolver

Constant Summary collapse

Defaults = 
{
  :config_file => "/dev/null", # default can lead to info leaks
  :log_file => "/dev/null", # formerly $stdout, should be tied in with our loggers
  :port => 53,
  :searchlist => [],
  :nameservers => [IPAddr.new("127.0.0.1")],
  :domain => "",
  :source_port => 0,
  :source_address => IPAddr.new("0.0.0.0"),
  :retry_interval => 5,
  :retry_number => 4,
  :recursive => true,
  :defname => true,
  :dns_search => true,
  :use_tcp => false,
  :ignore_truncated => false,
  :packet_size => 512,
  :tcp_timeout => TcpTimeout.new(30),
  :udp_timeout => UdpTimeout.new(30),
  :context => {},
  :comm => nil
}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config = {}) ⇒ Resolver

Provide override for initializer to use local Defaults constant

Parameters:

  • config (Hash) (defaults to: {}) —

    Configuration options as conusumed by parent class

Raises:

  • (ResolverArgumentError) 


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# File 'lib/rex/proto/dns/resolver.rb', line 44

def initialize(config = {})
  raise ResolverArgumentError, "Argument has to be Hash" unless config.kind_of? Hash
  # config.key_downcase!
  @config = Defaults.merge config
  @raw = false

  # New logger facility
  @logger = Logger.new(@config[:log_file])
  @logger.level = $DEBUG ? Logger::DEBUG : Logger::WARN

  #------------------------------------------------------------
  # Resolver configuration will be set in order from:
  # 1) initialize arguments
  # 2) ENV variables
  # 3) config file
  # 4) defaults (and /etc/resolv.conf for config)
  #------------------------------------------------------------



  #------------------------------------------------------------
  # Parsing config file
  #------------------------------------------------------------
  parse_config_file

  #------------------------------------------------------------
  # Parsing ENV variables
  #------------------------------------------------------------
  parse_environment_variables

  #------------------------------------------------------------
  # Parsing arguments
  #------------------------------------------------------------
  comm = config.delete(:comm)
  context = context = config.delete(:context)
  config.each do |key,val|
    next if key == :log_file or key == :config_file
    begin
      eval "self.#{key.to_s} = val"
    rescue NoMethodError
      raise ResolverArgumentError, "Option #{key} not valid"
    end
  end
end

Instance Attribute Details

#comm ⇒ Object

Returns the value of attribute comm.



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# File 'lib/rex/proto/dns/resolver.rb', line 39

def comm
  @comm
end

#context ⇒ Object

Returns the value of attribute context.



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# File 'lib/rex/proto/dns/resolver.rb', line 39

def context
  @context
end

Instance Method Details

#proxies ⇒ String

Provides current proxy setting if configured

Returns:

  • (String) —

    Current proxy configuration



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# File 'lib/rex/proto/dns/resolver.rb', line 92

def proxies
  @config[:proxies].inspect if @config[:proxies]
end

#proxies=(prox, timeout_added = 250) ⇒ Object

Configure proxy setting and additional timeout

Parameters:

  • prox (String) —

    SOCKS proxy connection string

  • timeout_added (Fixnum) (defaults to: 250) —

    Added TCP timeout to account for proxy



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# File 'lib/rex/proto/dns/resolver.rb', line 101

def proxies=(prox, timeout_added = 250)
  return if prox.nil?
  if prox.is_a?(String) and prox.strip =~ /^socks/i
    @config[:proxies] = prox.strip
    @config[:use_tcp] = true
    self.tcp_timeout = self.tcp_timeout.to_s.to_i + timeout_added
    @logger.info "SOCKS proxy set, using TCP, increasing timeout"
  else
    raise ResolverError, "Only socks proxies supported"
  end
end

#query(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN) ⇒ Object

Perform query with default domain validation

Parameters:

  • name
  • type (Fixnum) (defaults to: Dnsruby::Types::A) —

    Type of record to look up

  • cls (Fixnum) (defaults to: Dnsruby::Classes::IN) —

    Class of question to look up



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# File 'lib/rex/proto/dns/resolver.rb', line 366

def query(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)

  return send(name,type,cls) if name.class == IPAddr

  # If the name doesn't contain any dots then append the default domain.
  if name !~ /\./ and name !~ /:/ and @config[:defname]
    name += "." + @config[:domain]
  end

  @logger.debug "Query(#{name},#{Dnsruby::Types.new(type)},#{Dnsruby::Classes.new(cls)})"

  return send(name,type,cls)

end

#search(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN) ⇒ Object

Perform search using the configured searchlist and resolvers

Parameters:

  • name
  • type (Fixnum) (defaults to: Dnsruby::Types::A) —

    Type of record to look up

  • cls (Fixnum) (defaults to: Dnsruby::Classes::IN) —

    Class of question to look up



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# File 'lib/rex/proto/dns/resolver.rb', line 336

def search(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)
  return query(name,type,cls) if name.class == IPAddr
  # If the name contains at least one dot then try it as is first.
  if name.include? "."
    @logger.debug "Search(#{name},#{Dnsruby::Types.new(type)},#{Dnsruby::Classes.new(cls)})"
    ans = query(name,type,cls)
    return ans if ans.header.ancount > 0
  end
  # If the name doesn't end in a dot then apply the search list.
  if name !~ /\.$/ and @config[:dns_search]
    @config[:searchlist].each do |domain|
      newname = name + "." + domain
      @logger.debug "Search(#{newname},#{Dnsruby::Types.new(type)},#{Dnsruby::Classes.new(cls)})"
      ans = query(newname,type,cls)
      return ans if ans.header.ancount > 0
    end
  end
  # Finally, if the name has no dots then try it as is.
  @logger.debug "Search(#{name},#{Dnsruby::Types.new(type)},#{Dnsruby::Classes.new(cls)})"
  return query(name+".",type,cls)
end

#send(argument, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN) ⇒ Dnsruby::Message

Send DNS request over appropriate transport and process response

Parameters:

  • argument (Object) —

    An object holding the DNS message to be processed.

  • type (Fixnum) (defaults to: Dnsruby::Types::A) —

    Type of record to look up

  • cls (Fixnum) (defaults to: Dnsruby::Classes::IN) —

    Class of question to look up

Returns:

  • (Dnsruby::Message) —

    DNS response



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# File 'lib/rex/proto/dns/resolver.rb', line 121

def send(argument, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)
  if @config[:nameservers].size == 0
    raise ResolverError, "No nameservers specified!"
  end

  method = self.use_tcp? ? :send_tcp : :send_udp

  case argument
  when Dnsruby::Message
    packet = argument
  when Net::DNS::Packet, Resolv::DNS::Message
    packet = Rex::Proto::DNS::Packet.encode_drb(argument)
  else
    net_packet = make_query_packet(argument,type,cls)
    # This returns a Net::DNS::Packet. Convert to Dnsruby::Message for consistency
    packet = Rex::Proto::DNS::Packet.encode_drb(net_packet)
  end

  # Store packet_data for performance improvements,
  # so methods don't keep on calling Packet#encode
  packet_data = packet.encode
  packet_size = packet_data.size

  # Choose whether use TCP, UDP
  if packet_size > @config[:packet_size] # Must use TCP
    @logger.info "Sending #{packet_size} bytes using TCP due to size"
    method = :send_tcp
  else # Packet size is inside the boundaries
    if use_tcp? or !(proxies.nil? or proxies.empty?) # User requested TCP
      @logger.info "Sending #{packet_size} bytes using TCP due to tcp flag"
      method = :send_tcp
    else # Finally use UDP
      @logger.info "Sending #{packet_size} bytes using UDP"
      method = :send_udp unless method == :send_tcp
    end
  end

  if type == Dnsruby::Types::AXFR
    @logger.warn "AXFR query, switching to TCP" unless method == :send_tcp
    method = :send_tcp
  end

  ans = self.__send__(method, packet, packet_data)

  unless (ans and ans[0].length > 0)
    @logger.fatal "No response from nameservers list: aborting"
    raise NoResponseError
  end

  @logger.info "Received #{ans[0].size} bytes from #{ans[1][2]+":"+ans[1][1].to_s}"
  # response = Net::DNS::Packet.parse(ans[0],ans[1])
  response = Dnsruby::Message.decode(ans[0])

  if response.header.tc and not ignore_truncated?
    @logger.warn "Packet truncated, retrying using TCP"
    self.use_tcp = true
    begin
      return send(argument,type,cls)
    ensure
      self.use_tcp = false
    end
  end

  response
end

#send_tcp(packet, packet_data, prox = ) ⇒ Object

Send request over TCP

Parameters:

  • packet (Net::DNS::Packet) —

    Packet associated with packet_data

  • packet_data (String) —

    Data segment of DNS request packet

  • prox (String) (defaults to: ) —

    Proxy configuration for TCP socket



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# File 'lib/rex/proto/dns/resolver.rb', line 195

def send_tcp(packet,packet_data,prox = @config[:proxies])
  ans = nil
  length = [packet_data.size].pack("n")
  @config[:nameservers].each do |ns|
    begin
      socket = nil
      @config[:tcp_timeout].timeout do
        catch(:next_ns) do
          begin
            config = {
              'PeerHost' => ns.to_s,
              'PeerPort' => @config[:port].to_i,
              'Proxies' => prox,
              'Context' => @config[:context],
              'Comm' => @config[:comm]
            }
            if @config[:source_port] > 0
              config['LocalPort'] = @config[:source_port]
            end
            if @config[:source_host].to_s != '0.0.0.0'
              config['LocalHost'] = @config[:source_host] unless @config[:source_host].nil?
            end
            socket = Rex::Socket::Tcp.create(config)
          rescue
            @logger.warn "TCP Socket could not be established to #{ns}:#{@config[:port]} #{@config[:proxies]}"
            throw :next_ns
          end
          next unless socket #
          @logger.info "Contacting nameserver #{ns} port #{@config[:port]}"
          socket.write(length+packet_data)
          got_something = false
          loop do
            buffer = ""
            attempts = 3
            begin
              ans = socket.recv(2)
            rescue Errno::ECONNRESET
              @logger.warn "TCP Socket got Errno::ECONNRESET from #{ns}:#{@config[:port]} #{@config[:proxies]}"
              attempts -= 1
              retry if attempts > 0
            end
            if ans.size == 0
              if got_something
                break #Proper exit from loop
              else
                @logger.warn "Connection reset to nameserver #{ns}, trying next."
                throw :next_ns
              end
            end
            got_something = true
            len = ans.unpack("n")[0]

            @logger.info "Receiving #{len} bytes..."

            if len.nil? or len == 0
              @logger.warn "Receiving 0 length packet from nameserver #{ns}, trying next."
              throw :next_ns
            end

            while (buffer.size < len)
              left = len - buffer.size
              temp,from = socket.recvfrom(left)
              buffer += temp
            end

            unless buffer.size == len
              @logger.warn "Malformed packet from nameserver #{ns}, trying next."
              throw :next_ns
            end
            if block_given?
              yield [buffer,["",@config[:port],ns.to_s,ns.to_s]]
            else
              return [buffer,["",@config[:port],ns.to_s,ns.to_s]]
            end
          end
        end
      end
    rescue Timeout::Error
      @logger.warn "Nameserver #{ns} not responding within TCP timeout, trying next one"
      next
    ensure
      socket.close if socket
    end
  end
  return nil
end

#send_udp(packet, packet_data) ⇒ Object

Send request over UDP

Parameters:

  • packet (Net::DNS::Packet) —

    Packet associated with packet_data

  • packet_data (String) —

    Data segment of DNS request packet



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# File 'lib/rex/proto/dns/resolver.rb', line 289

def send_udp(packet,packet_data)
  ans = nil
  response = ""
  @config[:nameservers].each do |ns|
    begin
      @config[:udp_timeout].timeout do
        begin
          config = {
            'PeerHost' => ns.to_s,
            'PeerPort' => @config[:port].to_i,
            'Context' => @config[:context],
            'Comm' => @config[:comm]
          }
          if @config[:source_port] > 0
            config['LocalPort'] = @config[:source_port]
          end
          if @config[:source_host] != IPAddr.new('0.0.0.0')
            config['LocalHost'] = @config[:source_host] unless @config[:source_host].nil?
          end
          socket = Rex::Socket::Udp.create(config)
        rescue
          @logger.warn "UDP Socket could not be established to #{ns}:#{@config[:port]}"
          return nil
        end
        @logger.info "Contacting nameserver #{ns} port #{@config[:port]}"
        #socket.sendto(packet_data, ns.to_s, @config[:port].to_i, 0)
        socket.write(packet_data)
        ans = socket.recvfrom(@config[:packet_size])
      end
      break if ans
    rescue Timeout::Error
      @logger.warn "Nameserver #{ns} not responding within UDP timeout, trying next one"
      next
    end
  end
  return ans
end