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 => nil,
  :log_file => File::NULL, # formerly $stdout, should be tied in with our loggers
  :port => 53,
  :searchlist => [],
  :nameservers => [],
  :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(5),
  :udp_timeout => UdpTimeout.new(5),
  :context => {},
  :comm => nil,
  :static_hosts => {}
}

Instance Attribute Summary collapse

Class Method 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 consumed by parent class

Raises:

  • (ResolverArgumentError) 


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# File 'lib/rex/proto/dns/resolver.rb', line 45

def initialize(config = {})
  raise ResolverArgumentError, "Argument has to be Hash" unless config.kind_of? Hash
  # config.key_downcase!
  @config = Defaults.merge config
  @config[:config_file] ||= self.class.default_config_file
  @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 = config.delete(:context)
  static_hosts = config.delete(:static_hosts)
  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

  self.static_hostnames = StaticHostnames.new(hostnames: static_hosts)
  begin
    self.static_hostnames.parse_hosts_file
  rescue StandardError => e
    @logger.error 'Failed to parse the hosts file, ignoring it'
    # if the hosts file is corrupted, just use a default instance with any specified hostnames
    self.static_hostnames = StaticHostnames.new(hostnames: static_hosts)
  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 40

def comm
  @comm
end

#context ⇒ Object

Returns the value of attribute context.



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# File 'lib/rex/proto/dns/resolver.rb', line 40

def context
  @context
end

#static_hostnames ⇒ Object

Returns the value of attribute static_hostnames.



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# File 'lib/rex/proto/dns/resolver.rb', line 40

def static_hostnames
  @static_hostnames
end

Class Method Details

.default_config_file ⇒ Object 



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# File 'lib/rex/proto/dns/resolver.rb', line 399

def self.default_config_file
  %w[
    /etc/resolv.conf
    /data/data/com.termux/files/usr/etc/resolv.conf
  ].find do |path|
    File.file?(path) && File.readable?(path)
  end
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 101

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 110

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 393

def query(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)
  name, type, cls = preprocess_query_arguments(name, type, cls)
  @logger.debug "Query(#{name},#{Dnsruby::Types.new(type)},#{Dnsruby::Classes.new(cls)})"
  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 363

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 150

def send(argument, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)
  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


  upstream_resolvers = upstream_resolvers_for_packet(packet)
  if upstream_resolvers.empty?
    raise ResolverError, "No upstream resolvers specified!"
  end

  ans = nil
  upstream_resolvers.each do |upstream_resolver|
    case upstream_resolver.type
    when UpstreamResolver::Type::BLACK_HOLE
      ans = resolve_via_black_hole(upstream_resolver, packet, type, cls)
    when UpstreamResolver::Type::DNS_SERVER
      ans = resolve_via_dns_server(upstream_resolver, packet, type, cls)
    when UpstreamResolver::Type::STATIC
      ans = resolve_via_static(upstream_resolver, packet, type, cls)
    when UpstreamResolver::Type::SYSTEM
      ans = resolve_via_system(upstream_resolver, packet, type, cls)
    end

    break if (ans and ans[0].length > 0)
  end

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

  # 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, nameservers, 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

  • nameservers (Array<[String,Hash]>) —

    List of nameservers to use for this request, and their associated socket options

  • prox (String) (defaults to: ) —

    Proxy configuration for TCP socket



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# File 'lib/rex/proto/dns/resolver.rb', line 214

def send_tcp(packet, packet_data, nameservers, prox = @config[:proxies])
  ans = nil
  length = [packet_data.size].pack("n")
  nameservers.each do |ns, socket_options|
    socket = nil
    config = {
      'PeerHost' => ns.to_s,
      'PeerPort' => @config[:port].to_i,
      'Proxies' => prox,
      'Context' => @config[:context],
      'Comm' => @config[:comm],
      'Timeout' => @config[:tcp_timeout]
    }
    config.update(socket_options)
    unless config['Comm'].nil? || config['Comm'].alive?
      @logger.warn("Session #{config['Comm'].sid} not active, and cannot be used to resolve DNS")
      next
    end

    suffix = " over session #{@config['Comm'].sid}" unless @config['Comm'].nil?
    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
    begin
      suffix = ''
      begin
        socket = Rex::Socket::Tcp.create(config)
      rescue
        @logger.warn "TCP Socket could not be established to #{ns}:#{@config[:port]} #{@config[:proxies]}#{suffix}"
        next
      end
      next unless socket #
      @logger.info "Contacting nameserver #{ns} port #{@config[:port]}#{suffix}"
      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]}#{suffix}"
          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}#{suffix}, 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}#{suffix}, 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}#{suffix}, 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
    rescue Timeout::Error
      @logger.warn "Nameserver #{ns}#{suffix} not responding within TCP timeout, trying next one"
      next
    ensure
      socket.close if socket
    end
  end
  return nil
end

#send_udp(packet, packet_data, nameservers) ⇒ Object

Send request over UDP

Parameters:

  • packet (Net::DNS::Packet) —

    Packet associated with packet_data

  • packet_data (String) —

    Data segment of DNS request packet

  • nameservers (Array<[String,Hash]>) —

    List of nameservers to use for this request, and their associated socket options



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# File 'lib/rex/proto/dns/resolver.rb', line 314

def send_udp(packet,packet_data, nameservers)
  ans = nil
  nameservers.each do |ns, socket_options|
    begin
      config = {
        'PeerHost' => ns.to_s,
        'PeerPort' => @config[:port].to_i,
        'Context' => @config[:context],
        'Comm' => @config[:comm],
        'Timeout' => @config[:udp_timeout]
      }
      config.update(socket_options)
      unless config['Comm'].nil? || config['Comm'].alive?
        @logger.warn("Session #{config['Comm'].sid} not active, and cannot be used to resolve DNS")
        next
      end

      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]}"
      next
    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])
    break if ans
  rescue Timeout::Error
    @logger.warn "Nameserver #{ns} not responding within UDP timeout, trying next one"
    next
  end
  ans
end

#upstream_resolvers_for_packet(_dns_message) ⇒ Array<Array>

Find the nameservers to use for a given DNS request

Parameters:

  • _dns_message (Dnsruby::Message) —

    The DNS message to be sent

Returns:

  • (Array<Array>) —

    A list of nameservers, each with Rex::Socket options



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# File 'lib/rex/proto/dns/resolver.rb', line 128

def upstream_resolvers_for_packet(_dns_message)
  @config[:nameservers].map do |ns|
    UpstreamResolver.create_dns_server(ns.to_s)
  end
end

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



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# File 'lib/rex/proto/dns/resolver.rb', line 134

def upstream_resolvers_for_query(name, type = Dnsruby::Types::A, cls = Dnsruby::Classes::IN)
  name, type, cls = preprocess_query_arguments(name, type, cls)
  net_packet = make_query_packet(name, type, cls)
  # This returns a Net::DNS::Packet. Convert to Dnsruby::Message for consistency
  packet = Rex::Proto::DNS::Packet.encode_drb(net_packet)
  upstream_resolvers_for_packet(packet)
end