Class: Rex::Proto::DNS::Server

Inherits:
Object
  • Object
show all
Includes:
IO::GramServer
Defined in:
lib/rex/proto/dns/server.rb

Direct Known Subclasses

MDNS::Server

Defined Under Namespace

Classes: MockDnsClient

Constant Summary collapse

Packet = 
Rex::Proto::DNS::Packet

Instance Attribute Summary collapse

Attributes included from IO::GramServer

#dispatch_request_proc, #listener_thread, #send_response_proc

Class Method Summary collapse

Instance Method Summary collapse

Methods included from IO::GramServer

#send_response, #wait

Constructor Details

#initialize(lhost = '0.0.0.0', lport = 53, udp = true, tcp = false, start_cache = true, res = nil, comm = nil, ctx = {}, dblock = nil, sblock = nil) ⇒ Rex::Proto::DNS::Server

Create DNS Server

Parameters:

  • lhost (String) (defaults to: '0.0.0.0') —

    Listener address

  • lport (Fixnum) (defaults to: 53) —

    Listener port

  • udp (TrueClass, FalseClass) (defaults to: true) —

    Listen on UDP socket

  • tcp (TrueClass, FalseClass) (defaults to: false) —

    Listen on TCP socket

  • start_cache (TrueClass, FalseClass) (defaults to: true) —

    Start the cache on initialization

  • res (Rex::Proto::DNS::Resolver) (defaults to: nil) —

    Resolver to use, nil to create a fresh one

  • comm (Object) (defaults to: nil) —

    Communication object for sockets

  • ctx (Hash) (defaults to: {}) —

    Framework context for sockets

  • dblock (Proc) (defaults to: nil) —

    Handler for :dispatch_request flow control interception

  • sblock (Proc) (defaults to: nil) —

    Handler for :send_response flow control interception



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# File 'lib/rex/proto/dns/server.rb', line 61

def initialize(lhost = '0.0.0.0', lport = 53, udp = true, tcp = false, start_cache = true, res = nil, comm = nil, ctx = {}, dblock = nil, sblock = nil)

  @serve_udp = udp
  @serve_tcp = tcp
  @sock_options = {
    'LocalHost' => lhost,
    'LocalPort' => lport,
    'Context'   => ctx,
    'Comm'      => comm
  }
  self.fwd_res = res.nil? ? Rex::Proto::DNS::Resolver.new(:comm => comm, :context => ctx) : res
  self.listener_thread = nil
  self.dispatch_request_proc = dblock
  self.send_response_proc = sblock
  self.start_cache = start_cache
  self.cache = Rex::Proto::DNS::Cache.new
  @lock = Mutex.new
end

Instance Attribute Details

#cache ⇒ Object

Returns the value of attribute cache.



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# File 'lib/rex/proto/dns/server.rb', line 43

def cache
  @cache
end

#fwd_res ⇒ Object

Returns the value of attribute fwd_res.



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# File 'lib/rex/proto/dns/server.rb', line 43

def fwd_res
  @fwd_res
end

#lock ⇒ Object (readonly)

Returns the value of attribute lock.



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

def lock
  @lock
end

#serve_tcp ⇒ Object

Returns the value of attribute serve_tcp.



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# File 'lib/rex/proto/dns/server.rb', line 43

def serve_tcp
  @serve_tcp
end

#serve_udp ⇒ Object

Returns the value of attribute serve_udp.



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# File 'lib/rex/proto/dns/server.rb', line 43

def serve_udp
  @serve_udp
end

#sock_options ⇒ Object (readonly)

Returns the value of attribute sock_options.



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

def sock_options
  @sock_options
end

#start_cache ⇒ Object

Returns the value of attribute start_cache.



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# File 'lib/rex/proto/dns/server.rb', line 43

def start_cache
  @start_cache
end

#tcp_sock ⇒ Object (readonly)

Returns the value of attribute tcp_sock.



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

def tcp_sock
  @tcp_sock
end

#udp_sock ⇒ Object (readonly)

Returns the value of attribute udp_sock.



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

def udp_sock
  @udp_sock
end

Class Method Details

.hardcore_alias(*args) ⇒ Object

Returns the hardcore alias for the DNS service



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# File 'lib/rex/proto/dns/server.rb', line 201

def self.hardcore_alias(*args)
  "#{(args[0] || '')}-#{(args[1] || '')}-#{args[5] || ''}"
end

Instance Method Details

#alias ⇒ Object

DNS server.



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# File 'lib/rex/proto/dns/server.rb', line 208

def alias
  "DNS Server"
end

#default_dispatch_request(cli, data) ⇒ Object

Default DNS request dispatcher, attempts to find response records in cache or forwards request upstream

Parameters:

  • cli (Rex::Socket::Tcp, Rex::Socket::Udp) —

    Client sending the request

  • data (String) —

    raw DNS request data



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# File 'lib/rex/proto/dns/server.rb', line 162

def default_dispatch_request(cli,data)
  return if data.strip.empty?
  req = Packet.encode_drb(data)
  forward = req.dup
  # Dnsruby#dup is shallow - req and forward share the same @question Array.
  # Give forward its own copy so deleting forwarded questions doesn't also
  # empty req.question, which we need intact when echoing it in the response.
  forward.instance_variable_set(:@question, req.question.dup)
  answers = []
  # Find cached items, remove question from forwarded packet
  req.question.each do |ques|
    cached = self.cache.find(ques.qname, ques.qtype)
    unless cached.empty?
      answers.concat(cached)
      forward.question.delete(ques)
    end
  end
  # Forward remaining requests, cache responses
  if forward.question.count > 0 && @fwd_res
    forwarded = self.fwd_res.send(forward)
    answers.concat(forwarded.answer)
    forwarded.answer.each { |ans| self.cache.cache_record(ans) }
  end
  # Build a fresh response message to avoid a Dnsruby stale-state encoding bug
  # where instance_variable_set(:@answer) on a decoded request appends answer
  # bytes after the packet end rather than inside the answer section.
  resp = Dnsruby::Message.new
  resp.header.id = req.header.id
  resp.header.qr = true
  resp.header.rd = req.header.rd      # echo Recursion Desired back to the client
  resp.header.ra = !self.fwd_res.nil? # Recursion Available when we can forward upstream
  req.question.each { |q| resp.add_question(q.qname, q.qtype, q.qclass) }
  answers.uniq.each { |a| resp.add_answer(a) }
  send_response(cli, resp.encode)
end

#dispatch_request(cli, data) ⇒ Object

Process client request, handled with dispatch_request_proc if set

Parameters:

  • cli (Rex::Socket::Tcp, Rex::Socket::Udp) —

    Client sending the request

  • data (String) —

    raw DNS request data



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# File 'lib/rex/proto/dns/server.rb', line 148

def dispatch_request(cli, data)
  if self.dispatch_request_proc
    self.dispatch_request_proc.call(cli,data)
  else
    default_dispatch_request(cli,data)
  end
end

#monitor_listener ⇒ Object (protected)

This method monitors the listener socket for new connections and calls the on_client_connect callback routine.



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# File 'lib/rex/proto/dns/server.rb', line 218

def monitor_listener
  while true
    rds = [self.udp_sock]
    wds = []
    eds = [self.udp_sock]

    r,_,_ = ::IO.select(rds,wds,eds,1)

    if (r != nil and r[0] == self.udp_sock)
      buf, addr, source_port = self.udp_sock.recvfrom(65535)
      if source_port
        host, port = addr, source_port
      else
        host, port = addr[3], addr[1]
      end
      # Mock up a client object for sending back data
      cli = MockDnsClient.new(host, port, r[0])
      dispatch_request(cli, buf)
    end
  end
end

#on_client_data(cli) ⇒ Object (protected)

Processes request coming from client

Parameters:

  • cli (Rex::Socket::Tcp) —

    Client sending request



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# File 'lib/rex/proto/dns/server.rb', line 244

def on_client_data(cli)
  begin
    data = cli.read(65535)

    raise ::EOFError if not data
    raise ::EOFError if data.empty?
    dispatch_request(cli, data)
  rescue EOFError => e
    self.tcp_socket.close_client(cli) if cli
    raise e
  end
end

#running? ⇒ Boolean

Check if server is running

Returns:

  • (Boolean) 


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# File 'lib/rex/proto/dns/server.rb', line 96

def running?
  self.listener_thread and self.listener_thread.alive?
end

#start ⇒ Object

Start the DNS server and cache



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# File 'lib/rex/proto/dns/server.rb', line 102

def start

  if self.serve_udp
    @udp_sock = Rex::Socket::Udp.create(self.sock_options)
    self.listener_thread = Rex::ThreadFactory.spawn("UDPDNSServerListener", false) {
      monitor_listener
    }
  end

  if self.serve_tcp
    @tcp_sock = Rex::Socket::TcpServer.create(self.sock_options)
    self.tcp_sock.on_client_data_proc = Proc.new { |cli|
      on_client_data(cli)
    }
    self.tcp_sock.start
    if !self.serve_udp
      self.listener_thread = tcp_sock.listener_thread
    end
  end

  self.cache.start if self.start_cache
end

#stop(flush_cache = false) ⇒ Object

Stop the DNS server and cache

Parameters:

  • flush_cache (TrueClass, FalseClass) (defaults to: false) —

    Flush eDNS cache on stop



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# File 'lib/rex/proto/dns/server.rb', line 129

def stop(flush_cache = false)
  ensure_close = [self.udp_sock, self.tcp_sock].compact
  begin
    self.listener_thread.kill if self.listener_thread.respond_to?(:kill)
    self.listener_thread = nil
  ensure
    while csock = ensure_close.shift
      csock.stop if csock.respond_to?(:stop)
      csock.close unless csock.respond_to?(:close) and csock.closed?
    end
  end
  self.cache.stop(flush_cache)
end

#switchns(ns = []) ⇒ Object

Switch DNS forwarders in resolver with thread safety

Parameters:

  • ns (Array, String) (defaults to: []) —

    List of (or single) nameservers to use



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# File 'lib/rex/proto/dns/server.rb', line 84

def switchns(ns = [])
  if ns.respond_to?(:split)
    ns = [ns]
  end
  self.lock.synchronize do
    self.fwd_res.nameserver = ns
  end
end