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#!/usr/bin/env perl
# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
#
# SPDX-License-Identifier: MPL-2.0
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, you can obtain one at https://mozilla.org/MPL/2.0/.
#
# See the COPYRIGHT file distributed with this work for additional
# information regarding copyright ownership.
use strict;
use warnings;
use IO::File;
use IO::Socket;
use Net::DNS;
my $localaddr = "10.53.0.2";
my $limit = getlimit();
my $no_more_waiting = 0;
my @delayed_response;
my $timeout;
my $localport = int($ENV{'PORT'});
if (!$localport) { $localport = 5300; }
my $udpsock = IO::Socket::INET->new(LocalAddr => "$localaddr",
LocalPort => $localport, Proto => "udp", Reuse => 1) or die "$!";
my $pidf = new IO::File "ans.pid", "w" or die "cannot open pid file: $!";
print $pidf "$$\n" or die "cannot write pid file: $!";
$pidf->close or die "cannot close pid file: $!";
sub rmpid { unlink "ans.pid"; exit 1; };
$SIG{INT} = \&rmpid;
$SIG{TERM} = \&rmpid;
my $count = 0;
my $send_response = 0;
sub getlimit {
if ( -e "ans.limit") {
open(FH, "<", "ans.limit");
my $line = <FH>;
chomp $line;
close FH;
if ($line =~ /^\d+$/) {
return $line;
}
}
return 0;
}
# If $wait == 0 is returned, returned reply will be sent immediately.
# If $wait == 1 is returned, sending the returned reply might be delayed; see
# comments inside handle_UDP() for details.
sub reply_handler {
my ($qname, $qclass, $qtype) = @_;
my ($rcode, @ans, @auth, @add, $wait);
print ("request: $qname/$qtype\n");
STDOUT->flush();
$wait = 0;
$count += 1;
if ($qname eq "count" ) {
if ($qtype eq "TXT") {
my ($ttl, $rdata) = (0, "$count");
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
push @ans, $rr;
print ("\tcount: $count\n");
}
$rcode = "NOERROR";
} elsif ($qname eq "reset" ) {
$count = 0;
$send_response = 0;
$limit = getlimit();
$rcode = "NOERROR";
print ("\tlimit: $limit\n");
} elsif ($qname eq "direct.example.org" ) {
if ($qtype eq "A") {
my ($ttl, $rdata) = (3600, $localaddr);
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
push @ans, $rr;
}
$rcode = "NOERROR";
} elsif ($qname eq "indirect1.example.org" ||
$qname eq "indirect2.example.org" ||
$qname eq "indirect3.example.org" ||
$qname eq "indirect4.example.org" ||
$qname eq "indirect5.example.org" ||
$qname eq "indirect6.example.org" ||
$qname eq "indirect7.example.org" ||
$qname eq "indirect8.example.org") {
if (! $send_response) {
my $rr = new Net::DNS::RR("$qname 86400 $qclass NS ns1.1.example.org");
push @auth, $rr;
} elsif ($qtype eq "A") {
my ($ttl, $rdata) = (3600, $localaddr);
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
push @ans, $rr;
}
$rcode = "NOERROR";
} elsif ($qname =~ /^ns1\.(\d+)\.example\.org$/) {
my $next = $1 + 1;
$wait = 1;
if ($limit == 0 || (! $send_response && $next <= $limit)) {
my $rr = new Net::DNS::RR("$1.example.org 86400 $qclass NS ns1.$next.example.org");
push @auth, $rr;
} else {
$send_response = 1;
if ($qtype eq "A") {
my ($ttl, $rdata) = (3600, "10.53.0.4");
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
print("\tresponse: $qname $ttl $qclass $qtype $rdata\n");
push @ans, $rr;
}
}
$rcode = "NOERROR";
} elsif ($qname eq "direct.example.net" ) {
if ($qtype eq "A") {
my ($ttl, $rdata) = (3600, $localaddr);
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
push @ans, $rr;
}
$rcode = "NOERROR";
} elsif( $qname =~ /^ns1\.(\d+)\.example\.net$/ ) {
my $next = ($1 + 1) * 16;
for (my $i = 1; $i < 16; $i++) {
my $s = $next + $i;
my $rr = new Net::DNS::RR("$1.example.net 86400 $qclass NS ns1.$s.example.net");
push @auth, $rr;
$rr = new Net::DNS::RR("ns1.$s.example.net 86400 $qclass A 10.53.0.7");
push @add, $rr;
}
$rcode = "NOERROR";
} else {
$rcode = "NXDOMAIN";
}
return ($rcode, \@ans, \@auth, \@add, $wait);
}
sub handleUDP {
my ($buf, $peer) = @_;
my ($request, $rcode, $ans, $auth, $add, $wait);
$request = new Net::DNS::Packet(\$buf, 0);
$@ and die $@;
my ($question) = $request->question;
my $qname = $question->qname;
my $qclass = $question->qclass;
my $qtype = $question->qtype;
($rcode, $ans, $auth, $add, $wait) = reply_handler($qname, $qclass, $qtype);
my $reply = $request->reply();
$reply->header->rcode($rcode);
$reply->header->aa(@$ans ? 1 : 0);
$reply->header->id($request->header->id);
$reply->{answer} = $ans if $ans;
$reply->{authority} = $auth if $auth;
$reply->{additional} = $add if $add;
if ($wait) {
# reply_handler() asked us to delay sending this reply until
# another reply with $wait == 1 is generated or a timeout
# occurs.
if (@delayed_response) {
# A delayed reply is already queued, so we can now send
# both the delayed reply and the current reply.
send_delayed_response();
return $reply;
} elsif ($no_more_waiting) {
# It was determined before that there is no point in
# waiting for "accompanying" queries. Thus, send the
# current reply immediately.
return $reply;
} else {
# No delayed reply is queued and the client is expected
# to send an "accompanying" query shortly. Do not send
# the current reply right now, just save it for later
# and wait for an "accompanying" query to be received.
@delayed_response = ($reply, $peer);
$timeout = 0.5;
return;
}
} else {
# Send reply immediately.
return $reply;
}
}
sub send_delayed_response {
my ($reply, $peer) = @delayed_response;
# Truncation to 512 bytes is required for triggering "NS explosion" on
# builds without IPv6 support
$udpsock->send($reply->data(512), 0, $peer);
undef @delayed_response;
undef $timeout;
}
# Main
my $rin;
my $rout;
for (;;) {
$rin = '';
vec($rin, fileno($udpsock), 1) = 1;
select($rout = $rin, undef, undef, $timeout);
if (vec($rout, fileno($udpsock), 1)) {
my ($buf, $peer, $reply);
$udpsock->recv($buf, 512);
$peer = $udpsock->peername();
$reply = handleUDP($buf, $peer);
# Truncation to 512 bytes is required for triggering "NS
# explosion" on builds without IPv6 support
$udpsock->send($reply->data(512), 0, $peer) if $reply;
} else {
# An "accompanying" query was expected to come in, but did not.
# Assume the client never sends "accompanying" queries to
# prevent pointlessly waiting for them ever again.
$no_more_waiting = 1;
# Send the delayed reply to the query which caused us to wait.
send_delayed_response();
}
}
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