From cfc4303326d6ad4cd382e46f23ee7b141e5d7501 Mon Sep 17 00:00:00 2001
From: short <>
Date: Thu, 14 Oct 2004 08:14:48 +0000
Subject: [PATCH 1/1] Initial version.

---
 netdnsspoof | 174 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 174 insertions(+)
 create mode 100755 netdnsspoof

diff --git a/netdnsspoof b/netdnsspoof
new file mode 100755
index 0000000..65b3b83
--- /dev/null
+++ b/netdnsspoof
@@ -0,0 +1,174 @@
+#! /usr/bin/perl
+#
+#	$Id$
+
+use strict;
+use warnings;
+use Getopt::Long;
+require IO::Socket::INET;
+require Net::DNS::Packet;
+use Fcntl;
+use Carp qw(cluck confess);
+use Socket;
+
+
+my $D;
+my $opt_addr;
+my $opt_port=5353;
+my $opt_forward_addr="localhost";
+my $opt_forward_port=53;
+my $opt_spoof_ip="192.196.60.1";
+die if !GetOptions(
+		"a|addr=s",\$opt_addr,
+		"p|port=s",\$opt_port,
+		  "forward-addr=s",\$opt_forward_addr,
+		  "forward-port=s",\$opt_forward_port,
+		"i|spoof-ip=s",\$opt_spoof_ip,
+		"d|debug+",\$D,
+		);
+my $forward_host=gethostbyname($opt_forward_addr) or die "resolving $opt_forward_addr: $!";
+my $forward_addr=sockaddr_in($opt_forward_port,$forward_host) or die "assembling $opt_forward_addr:$opt_forward_port";
+
+my $sock_udp=IO::Socket::INET->new(
+		LocalAddr=>$opt_addr,
+		LocalPort=>$opt_port,
+		Proto=>"udp",
+		) or die "socket(): $!";
+my $sock_udp_priv=IO::Socket::INET->new(
+		Proto=>"udp",
+		) or die "socket(): $!";
+###fcntl($sock_udp,F_SETFL,O_NONBLOCK) or die "fnctl(sock_udp,F_SETFL,O_NONBLOCK)";
+
+sub id_next()
+{
+	our $id;
+	$id=int(rand(0x10000)) if !defined $id;
+	$id++;
+	$id&=0xFFFF;
+	return $id;
+}
+
+my %sent;
+
+sub got_query($$)
+{
+my($msg,$from_addr)=@_;
+
+	my $query=Net::DNS::Packet->new(\$msg);
+	my $query_id_orig=$query->header()->id();
+	my $query_id=id_next();
+	$query->header()->id($query_id);
+	my $msg_forward=$query->data();
+	$query->header()->id($query_id_orig);	# fix-up back
+	$sent{$query_id}={
+		"msg"=>$msg,
+		"from_addr"=>$from_addr,
+		"query"=>$query,
+		};
+	warn "registered pending query id $query_id..." if $D;
+	warn "sending forwarded DNS query (mapped id $query_id_orig -> $query_id)..." if $D;
+	send $sock_udp_priv,$msg_forward,0,$forward_addr or cluck "send(): $!";
+}
+
+sub check_spoofable($$)
+{
+my($reply,$query)=@_;
+
+	warn "checking packet spoofability from the reply... (non-spoofable if silent)" if $D;
+	my @questions=$query->question();
+	return 0 if 1!=@questions;
+	my $question=$questions[0];
+	return 0 if $question->qtype() ne "A"
+	         && $question->qtype() ne "ANY";
+	return 0 if $reply->header()->rcode() ne "NXDOMAIN";
+	warn "packet considered as spoofable." if $D;
+	return 1;
+}
+
+sub reply_spoof($$)
+{
+my($query_from_addr,$query)=@_;
+
+	warn "assembling spoof reply..." if $D;
+	my $question=($query->question())[0];
+	my $spoof=Net::DNS::Packet->new($question->qname(),$question->qclass(),$question->qtype());
+	$spoof->push("answer",Net::DNS::RR->new(join(" ",
+			$question->qname(),
+			3600,	# ttl
+			$question->qclass(),
+			"A",	# qtype
+			$opt_spoof_ip,	# rdata
+			)));
+	$spoof->header()->rcode("NOERROR");
+	$spoof->header()->aa(0);
+	$spoof->header()->qr(1);
+	$spoof->header()->ra(1);
+	$spoof->header()->rd($query->header()->rd());
+	$spoof->header()->id($query->header()->id());
+	my $msg_spoof=$spoof->data();
+	warn "sending spoof reply..." if $D;
+	send $sock_udp,$msg_spoof,0,$query_from_addr or cluck "send(): $!";
+}
+
+sub got_forward_reply($)
+{
+my($msg)=@_;
+
+	warn "parsing reply from our forwarded DNS..." if $D;
+	my $reply=Net::DNS::Packet->new(\$msg);
+	my $reply_id=$reply->header()->id();
+	my($query_msg,$query_from_addr,$query);
+	if (my $hash=$sent{$reply_id}) {
+		delete $sent{$reply_id};
+		$query_msg      =$hash->{"msg"};
+		$query_from_addr=$hash->{"from_addr"};
+		$query          =$hash->{"query"};
+		warn "deleted pending record with id $reply_id." if $D;
+		}
+	else {
+		warn "Got DNS reply for unknown packet id $reply_id";
+		return;
+		}
+	if (check_spoofable($reply,$query)) {
+		reply_spoof $query_from_addr,$query;
+		return;
+		}
+	$reply->header()->id($query->header()->id());
+	my $reply_back=$reply->data();
+	warn "parsing reply back to the original query host..." if $D;
+	send $sock_udp,$reply_back,0,$query_from_addr or cluck "send(): $!";
+}
+
+for (;;) {
+	my $rfds="";
+	vec($rfds,fileno($sock_udp),1)=1;
+	vec($rfds,fileno($sock_udp_priv),1)=1;
+	warn "select(2)..." if $D;
+	my $got=select $rfds,undef(),undef(),undef();
+	warn "got from select." if $D;
+	die "Invalid select(2): ".Dumper($got) if !defined $got || $got<0;
+
+	for my $sock ($sock_udp,$sock_udp_priv) {
+		my $msg;
+		defined(my $from_addr=recv $sock,$msg,0x1000,0) or do { cluck "recv(): $!"; next; };
+		warn "got packet." if $D;
+		my($from_addr_port,$from_addr_host)=sockaddr_in($from_addr);
+
+		if ($from_addr_host eq $forward_host && $from_addr_port eq $opt_forward_port) {
+			warn "packet returned from forwarding DNS..." if $D;
+			if ($sock eq $sock_udp) {
+				warn "packet returned from forwarding DNS forbidden from the main listening socket";
+				next;
+				}
+			got_forward_reply $msg;
+			}
+		else {
+			warn "original query..." if $D;
+			if ($sock eq $sock_udp_priv) {
+				warn "original query forbidden from the private forwarding socket";
+				next;
+				}
+			got_query $msg,$from_addr;
+			}
+		}
+	}
-- 
1.8.3.1