#!/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 = "10.53.0.4"; 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 = 1; sub getlimit { if ( -e "ans.limit") { open(FH, "<", "ans.limit"); my $line = ; 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 = 1; $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, $rr; print ("\twait=$wait ans: $qname $ttl $qclass $qtype $rdata\n"); } $rcode = "NOERROR"; } elsif ($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" || $qname eq "indirect8.example.org") { if ($qtype eq "A") { my ($ttl, $rdata) = (3600, $localaddr); my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata"); push @ans, $rr; print ("\twait=$wait ans: $qname $ttl $qclass $qtype $rdata\n"); } $rcode = "NOERROR"; } elsif ($qname =~ /^ns1\.(\d+)\.example\.org$/) { my $next = $1 + 1; $wait = 1; if ($limit == 0) { my $rr = new Net::DNS::RR("$1.example.org 86400 $qclass NS ns1.$next.example.org"); push @auth, $rr; print ("\twait=$wait auth: $1.example.org 86400 $qclass NS ns1.$next.example.org\n"); } else { $send_response = 1; if ($qtype eq "A") { my ($ttl, $rdata) = (3600, $localaddr); 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, $rr; print ("\twait=$wait ans: $qname $ttl $qclass $qtype $rdata\n"); } $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, $rr; print ("\twait=$wait auth: $1.example.net 86400 $qclass NS ns1.$s.example.net\n"); $rr = new Net::DNS::RR("ns1.$s.example.net 86400 $qclass A 10.53.0.7"); print ("\twait=$wait add: ns1.$s.example.net 86400 $qclass A 10.53.0.7\n"); push @add, $rr; } $rcode = "NOERROR"; } else { $rcode = "NXDOMAIN"; print ("\twait=$wait NXDOMAIN\n"); } 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; print ("send_delayed_response\n"); } # 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(); } }