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 $V=1;
  16 $|=1;
  17
  18 my $D;
  19 my $opt_addr;
  20 my $opt_port=5353;
  21 my $opt_forward_addr="localhost";
  22 my $opt_forward_port=53;
  23 my $opt_spoof_ip="192.168.1.1";
  24 die if !GetOptions(
  25                 "a|addr=s",\$opt_addr,
  26                 "p|port=s",\$opt_port,
  27                   "forward-addr=s",\$opt_forward_addr,
  28                   "forward-port=s",\$opt_forward_port,
  29                 "i|spoof-ip=s",\$opt_spoof_ip,
  30                 "d|debug+",\$D,
  31                 );
  32 my $forward_host=gethostbyname($opt_forward_addr) or die "resolving $opt_forward_addr: $!";
  33 my $forward_addr=sockaddr_in($opt_forward_port,$forward_host) or die "assembling $opt_forward_addr:$opt_forward_port";
  34
  35 my $sock_udp=IO::Socket::INET->new(
  36                 LocalAddr=>$opt_addr,
  37                 LocalPort=>$opt_port,
  38                 Proto=>"udp",
  39                 ) or die "socket(): $!";
  40 my $sock_udp_priv=IO::Socket::INET->new(
  41                 Proto=>"udp",
  42                 ) or die "socket(): $!";
  43 ###fcntl($sock_udp,F_SETFL,O_NONBLOCK) or die "fnctl(sock_udp,F_SETFL,O_NONBLOCK)";
  44
  45 sub id_next()
  46 {
  47         our $id;
  48         $id=int(rand(0x10000)) if !defined $id;
  49         $id++;
  50         $id&=0xFFFF;
  51         return $id;
  52 }
  53
  54 my %sent;
  55
  56 sub got_query($$)
  57 {
  58 my($msg,$from_addr)=@_;
  59
  60         my $query=Net::DNS::Packet->new(\$msg);
  61         my $query_id_orig=$query->header()->id();
  62         my $query_id=id_next();
  63         $query->header()->id($query_id);
  64         my $msg_forward=$query->data();
  65         $query->header()->id($query_id_orig);   # fix-up back
  66         $sent{$query_id}={
  67                 "msg"=>$msg,
  68                 "from_addr"=>$from_addr,
  69                 "query"=>$query,
  70                 };
  71         warn "registered pending query id $query_id..." if $D;
  72         warn "sending forwarded DNS query (mapped id $query_id_orig -> $query_id)..." if $D;
  73         send $sock_udp_priv,$msg_forward,0,$forward_addr or cluck "send(): $!";
  74 }
  75
  76 sub check_spoofable($$)
  77 {
  78 my($reply,$query)=@_;
  79
  80         warn "checking packet spoofability from the reply... (non-spoofable if silent)" if $D;
  81         my @questions=$query->question();
  82         return 0 if 1!=@questions;
  83         my $question=$questions[0];
  84         return 0 if $question->qtype() ne "A"
  85                  && $question->qtype() ne "ANY";
  86         return 0 if $reply->header()->rcode() ne "NXDOMAIN";
  87         warn "packet considered as spoofable." if $D;
  88         return 1;
  89 }
  90
  91 sub reply_spoof($$)
  92 {
  93 my($query_from_addr,$query)=@_;
  94
  95         warn "assembling spoof reply..." if $D;
  96         my $question=($query->question())[0];
  97         my $spoof=Net::DNS::Packet->new($question->qname(),$question->qclass(),$question->qtype());
  98         $spoof->push("answer",Net::DNS::RR->new(join(" ",
  99                         $question->qname(),
 100                         3600,   # ttl
 101                         $question->qclass(),
 102                         "A",    # qtype
 103                         $opt_spoof_ip,  # rdata
 104                         )));
 105         $spoof->header()->rcode("NOERROR");
 106         $spoof->header()->aa(0);
 107         $spoof->header()->qr(1);
 108         $spoof->header()->ra(1);
 109         $spoof->header()->rd($query->header()->rd());
 110         $spoof->header()->id($query->header()->id());
 111         my $msg_spoof=$spoof->data();
 112         warn "sending spoof reply..." if $D;
 113         send $sock_udp,$msg_spoof,0,$query_from_addr or cluck "send(): $!";
 114         if ($V) {
 115                 my($query_from_addr_port,$query_from_addr_host)=sockaddr_in($query_from_addr);
 116                 my $query_from_addr_name=inet_ntoa $query_from_addr_host;
 117                 print localtime()." spoof:"
 118                                 ." from=$query_from_addr_name:$query_from_addr_port"
 119                                 ." qname=".$question->qname()
 120                                 ." ip=".$opt_spoof_ip
 121                                 ."\n";
 122                 }
 123 }
 124
 125 sub got_forward_reply($)
 126 {
 127 my($msg)=@_;
 128
 129         warn "parsing reply from our forwarded DNS..." if $D;
 130         my $reply=Net::DNS::Packet->new(\$msg);
 131         my $reply_id=$reply->header()->id();
 132         my($query_msg,$query_from_addr,$query);
 133         if (my $hash=$sent{$reply_id}) {
 134                 delete $sent{$reply_id};
 135                 $query_msg      =$hash->{"msg"};
 136                 $query_from_addr=$hash->{"from_addr"};
 137                 $query          =$hash->{"query"};
 138                 warn "deleted pending record with id $reply_id." if $D;
 139                 }
 140         else {
 141                 warn "Got DNS reply for unknown packet id $reply_id";
 142                 return;
 143                 }
 144         if (check_spoofable($reply,$query)) {
 145                 reply_spoof $query_from_addr,$query;
 146                 return;
 147                 }
 148         $reply->header()->id($query->header()->id());
 149         my $reply_back=$reply->data();
 150         warn "passing reply back to the original query host..." if $D;
 151         send $sock_udp,$reply_back,0,$query_from_addr or cluck "send(): $!";
 152 }
 153
 154 $V and print localtime()." START\n";
 155 for (;;) {
 156         my $rfds="";
 157         vec($rfds,fileno($sock_udp),1)=1;
 158         vec($rfds,fileno($sock_udp_priv),1)=1;
 159         warn "select(2)..." if $D;
 160         my $got=select $rfds,undef(),undef(),undef();
 161         warn "got from select." if $D;
 162         die "Invalid select(2): ".Dumper($got) if !defined $got || $got<0;
 163
 164         for my $sock ($sock_udp,$sock_udp_priv) {
 165                 next if !vec($rfds,fileno($sock),1);
 166                 my $msg;
 167                 defined(my $from_addr=recv $sock,$msg,0x1000,0) or do { cluck "recv(): $!"; next; };
 168                 warn "got packet." if $D;
 169                 my($from_addr_port,$from_addr_host)=sockaddr_in($from_addr);
 170
 171                 if ($from_addr_host eq $forward_host && $from_addr_port eq $opt_forward_port) {
 172                         warn "packet returned from forwarding DNS..." if $D;
 173                         if ($sock eq $sock_udp) {
 174                                 warn "packet returned from forwarding DNS forbidden from the main listening socket";
 175                                 next;
 176                                 }
 177                         got_forward_reply $msg;
 178                         }
 179                 else {
 180                         warn "original query..." if $D;
 181                         if ($sock eq $sock_udp_priv) {
 182                                 warn "original query forbidden from the private forwarding socket";
 183                                 next;
 184                                 }
 185                         got_query $msg,$from_addr;
 186                         }
 187                 }
 188         }