netdnsspoof

   1 #! /usr/bin/perl
   2 #
   3 #       $Id$
   4
   5 use strict;
   6 use warnings;
   7 use Getopt::Long;
   8 require IO::Socket::INET;
   9 require Net::DNS::Packet;
  10 use Fcntl;
  11 use Carp qw(cluck confess);
  12 use Socket;
  13
  14
  15 my $D;
  16 my $opt_addr;
  17 my $opt_port=5353;
  18 my $opt_forward_addr="localhost";
  19 my $opt_forward_port=53;
  20 my $opt_spoof_ip="192.196.60.1";
  21 die if !GetOptions(
  22                 "a|addr=s",\$opt_addr,
  23                 "p|port=s",\$opt_port,
  24                   "forward-addr=s",\$opt_forward_addr,
  25                   "forward-port=s",\$opt_forward_port,
  26                 "i|spoof-ip=s",\$opt_spoof_ip,
  27                 "d|debug+",\$D,
  28                 );
  29 my $forward_host=gethostbyname($opt_forward_addr) or die "resolving $opt_forward_addr: $!";
  30 my $forward_addr=sockaddr_in($opt_forward_port,$forward_host) or die "assembling $opt_forward_addr:$opt_forward_port";
  31
  32 my $sock_udp=IO::Socket::INET->new(
  33                 LocalAddr=>$opt_addr,
  34                 LocalPort=>$opt_port,
  35                 Proto=>"udp",
  36                 ) or die "socket(): $!";
  37 my $sock_udp_priv=IO::Socket::INET->new(
  38                 Proto=>"udp",
  39                 ) or die "socket(): $!";
  40 ###fcntl($sock_udp,F_SETFL,O_NONBLOCK) or die "fnctl(sock_udp,F_SETFL,O_NONBLOCK)";
  41
  42 sub id_next()
  43 {
  44         our $id;
  45         $id=int(rand(0x10000)) if !defined $id;
  46         $id++;
  47         $id&=0xFFFF;
  48         return $id;
  49 }
  50
  51 my %sent;
  52
  53 sub got_query($$)
  54 {
  55 my($msg,$from_addr)=@_;
  56
  57         my $query=Net::DNS::Packet->new(\$msg);
  58         my $query_id_orig=$query->header()->id();
  59         my $query_id=id_next();
  60         $query->header()->id($query_id);
  61         my $msg_forward=$query->data();
  62         $query->header()->id($query_id_orig);   # fix-up back
  63         $sent{$query_id}={
  64                 "msg"=>$msg,
  65                 "from_addr"=>$from_addr,
  66                 "query"=>$query,
  67                 };
  68         warn "registered pending query id $query_id..." if $D;
  69         warn "sending forwarded DNS query (mapped id $query_id_orig -> $query_id)..." if $D;
  70         send $sock_udp_priv,$msg_forward,0,$forward_addr or cluck "send(): $!";
  71 }
  72
  73 sub check_spoofable($$)
  74 {
  75 my($reply,$query)=@_;
  76
  77         warn "checking packet spoofability from the reply... (non-spoofable if silent)" if $D;
  78         my @questions=$query->question();
  79         return 0 if 1!=@questions;
  80         my $question=$questions[0];
  81         return 0 if $question->qtype() ne "A"
  82                  && $question->qtype() ne "ANY";
  83         return 0 if $reply->header()->rcode() ne "NXDOMAIN";
  84         warn "packet considered as spoofable." if $D;
  85         return 1;
  86 }
  87
  88 sub reply_spoof($$)
  89 {
  90 my($query_from_addr,$query)=@_;
  91
  92         warn "assembling spoof reply..." if $D;
  93         my $question=($query->question())[0];
  94         my $spoof=Net::DNS::Packet->new($question->qname(),$question->qclass(),$question->qtype());
  95         $spoof->push("answer",Net::DNS::RR->new(join(" ",
  96                         $question->qname(),
  97                         3600,   # ttl
  98                         $question->qclass(),
  99                         "A",    # qtype
 100                         $opt_spoof_ip,  # rdata
 101                         )));
 102         $spoof->header()->rcode("NOERROR");
 103         $spoof->header()->aa(0);
 104         $spoof->header()->qr(1);
 105         $spoof->header()->ra(1);
 106         $spoof->header()->rd($query->header()->rd());
 107         $spoof->header()->id($query->header()->id());
 108         my $msg_spoof=$spoof->data();
 109         warn "sending spoof reply..." if $D;
 110         send $sock_udp,$msg_spoof,0,$query_from_addr or cluck "send(): $!";
 111 }
 112
 113 sub got_forward_reply($)
 114 {
 115 my($msg)=@_;
 116
 117         warn "parsing reply from our forwarded DNS..." if $D;
 118         my $reply=Net::DNS::Packet->new(\$msg);
 119         my $reply_id=$reply->header()->id();
 120         my($query_msg,$query_from_addr,$query);
 121         if (my $hash=$sent{$reply_id}) {
 122                 delete $sent{$reply_id};
 123                 $query_msg      =$hash->{"msg"};
 124                 $query_from_addr=$hash->{"from_addr"};
 125                 $query          =$hash->{"query"};
 126                 warn "deleted pending record with id $reply_id." if $D;
 127                 }
 128         else {
 129                 warn "Got DNS reply for unknown packet id $reply_id";
 130                 return;
 131                 }
 132         if (check_spoofable($reply,$query)) {
 133                 reply_spoof $query_from_addr,$query;
 134                 return;
 135                 }
 136         $reply->header()->id($query->header()->id());
 137         my $reply_back=$reply->data();
 138         warn "parsing reply back to the original query host..." if $D;
 139         send $sock_udp,$reply_back,0,$query_from_addr or cluck "send(): $!";
 140 }
 141
 142 for (;;) {
 143         my $rfds="";
 144         vec($rfds,fileno($sock_udp),1)=1;
 145         vec($rfds,fileno($sock_udp_priv),1)=1;
 146         warn "select(2)..." if $D;
 147         my $got=select $rfds,undef(),undef(),undef();
 148         warn "got from select." if $D;
 149         die "Invalid select(2): ".Dumper($got) if !defined $got || $got<0;
 150
 151         for my $sock ($sock_udp,$sock_udp_priv) {
 152                 my $msg;
 153                 defined(my $from_addr=recv $sock,$msg,0x1000,0) or do { cluck "recv(): $!"; next; };
 154                 warn "got packet." if $D;
 155                 my($from_addr_port,$from_addr_host)=sockaddr_in($from_addr);
 156
 157                 if ($from_addr_host eq $forward_host && $from_addr_port eq $opt_forward_port) {
 158                         warn "packet returned from forwarding DNS..." if $D;
 159                         if ($sock eq $sock_udp) {
 160                                 warn "packet returned from forwarding DNS forbidden from the main listening socket";
 161                                 next;
 162                                 }
 163                         got_forward_reply $msg;
 164                         }
 165                 else {
 166                         warn "original query..." if $D;
 167                         if ($sock eq $sock_udp_priv) {
 168                                 warn "original query forbidden from the private forwarding socket";
 169                                 next;
 170                                 }
 171                         got_query $msg,$from_addr;
 172                         }
 173                 }
 174         }