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#!/usr/bin/perl
#
# dyndns.pl - CGI-BIN script to handle Dynamic DNS updates through http
#
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# Version 1.0, latest version, documentation and bugtracker available at:
# https://gitlab.lindenaar.net/scripts/dyndns
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#
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# Copyright (c) 2013 Frederik Lindenaar
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#
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# This script is free software: you can redistribute and/or modify it under the
# terms of version 3 of the GNU General Public License as published by the Free
# Software Foundation, or (at your option) any later version of the license.
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#
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# This script is distributed in the hope that it will be useful but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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#
# You should have received a copy of the GNU General Public License along with
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# this program. If not, visit <http://www.gnu.org/licenses/> to download it.
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#
use strict;
use CGI;
use POSIX;
use Net::DNS;
use feature 'state';
##############################
# Configuration section
my $DNSServer = '192.168.1.1'; # DNS Server to communicate with (use IP!)
my $ExpandCNAMEs = 1; # CNAME levels to expand (0 to disable)
my $AllowDebugKey = 'on'; # Debuging, 'off' to disable, '' for always on
# and other values to enable with debug= param.
my $AuthMode = 'remote'; # either 'static', 'remote' or 'both'
my $StaticSigner = ''; # required for AuthMode 'static' or 'both'
my $StaticKey = ''; # required for AuthMode 'static' or 'both'
my $RequireRR = ''; # Require existing record of this type for upd.
my $ExpireAfter = '1w'; # Expire time for registrations in minutes,
# hours, weeks or seconds. format: [0-9]+[mhws]?
my @ReplaceRR = ('A', 'AAAA', 'TXT'); # Records types to replace in update
my $UpdateTXT = 'Last DynDNS update on ';
my $DeleteTXT = 'DynDNS cleared on ';
##############################
# Support functions
my %months = (Jan=> 0, Feb=> 1, Mar=> 2, Apr=> 3, May=>4, Jun=> 5, Jul=> 6,
Aug=> 7, Sep=> 8, Sep=> 8, Oct=> 9, Nov=> 10, Dec=> 11);
# Parse the date and return time for: Sun May 26 21:22:15 2013
sub parse_localtime($) {
my ($day, $month, $mday, $time, $year)=split(' ', $_[0]);
return mktime(reverse(split(':',$time)),$mday,$months{$month},$year-1900);
}
sub is_ipv4 { return $_[0]=~/^((25[0-5]|(2[0-4]|[01]?[0-9]?)[0-9])(\.|$)){4}/; }
sub is_ipv6 { return $_[0]=~/^([0-9a-fA-F]{0,4}(:|$)){3,8}/i; }
sub periodSeconds($) {
my ($number, $units) = ($_[0]=~/^(\d+)([smhdw])?$/);
if($number && $units && $units cmp 's') {
$number *= 60; # Convert to minutes
if($units cmp 'm') {
$number *= 60; # Convert to hours
if($units cmp 'h') {
$number *= 24; # Convert to days
if($units cmp 'd') {
$number *= 7; # Convert to weeks
}
}
}
}
return $number;
}
# Provide a resolver object for further use, re-using the initially created one
sub getResolver() {
state $resolver;
unless($resolver) {
$resolver = Net::DNS::Resolver->new(
nameservers => [ $DNSServer ],
recurse => 0,
);
}
return $resolver;
}
my %DNS_label = (
A => 'IPv4 Address',
AAAA => 'IPv6 Address',
CNAME => 'Alias',
TXT => 'Additional Information',
MX => 'Mail Server',
NS => 'Name Server',
HINFO => 'Host Information',
);
sub DNS_decode_rr($) {
my ($rr) = @_;
return $rr->address if($rr->type eq 'A');
return $rr->address if($rr->type eq 'AAAA');
return lc($rr->cname) if($rr->type eq 'CNAME');
return $rr->txtdata if($rr->type eq 'TXT');
return $rr->nsdname if($rr->type eq 'NS');
return $rr->exchange.' (priority '.$rr->preference.')' if($rr->type eq 'MX');
return $rr->cpu.', '.$rr->os if($rr->type eq 'HINFO');
die "No support for $rr->type in DNS_get()!, aborted!";
}
# Retrieve a single value from the DNS server of a given type or everything
sub DNS_get($;$) {
my ($host, $type) = @_;
if (my $response = getResolver()->send($host, $type || 'ANY')) {
return $response unless($type);
foreach my $rr ($response->answer) {
next unless $rr->type eq $type;
return DNS_decode_rr($rr);
}
} else {
die 'DNS query failed: ', getResolver()->errorstring, "\n";
}
}
# Check whether the hostname provided is actually a CNAME, returns the host
# it points to in case of a CNAME or the original hostname if it is not.
sub expand_CNAME($;$) {
my ($host, @found) = @_;
if(my $cname=DNS_get($host, 'CNAME')) {
push(@found, $host);
die $found[0]."has > $ExpandCNAMEs level deep CNAME chain, aborting!\n"
unless($#found < $ExpandCNAMEs);
foreach my $r (@found) {
die "found CNAME loop for $host, aborting!\n" if($cname eq $r);
}
return &expand_CNAME($cname, @found);
}
return $host;
}
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# Get signer and key CGI paramseters, abort with HTTP 400 error if not present
sub get_authinfo($$) {
my ($cgi, $host) = @_;
# Get signer and key parameters
my $signer = ($AuthMode eq 'static') ? $StaticSigner : ($cgi->param('user')
|| (($AuthMode eq 'both') ? $StaticSigner : $host));
my $key = ($AuthMode eq 'static') ? $StaticKey : ($cgi->param('secret')
|| (($AuthMode eq 'both') ? $StaticSigner : undef));
# Ensure we have a value for signer and key, otherwise abort the processing
if($signer eq '' or $key eq '') {
print $cgi->header(-status=>400, -type=>'text/plain'),
"ERROR - No/incomplete authentication information provided\n";
exit
}
# and return the values
return($signer, $key);
}
# Perform an DNS Update for a single host
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sub DNS_Update($$$$$$$) {
my ($dnsdomain, $dnshost, $ipv4, $ipv6, $signer, $key, $debug) = @_;
my $dnsupdate = Net::DNS::Update->new($dnsdomain);
# If $RequireRR is set, ensure an records of specified type exist for the name
$dnsupdate->push(pre => yxrrset("$dnshost. $RequireRR")) if($RequireRR);
# Replace any existing A, AAAA and TXT entries (update was requested)
foreach my $rrtype (@ReplaceRR) {
$dnsupdate->push(update=>rr_del("$dnshost. $rrtype"));
}
# Add new A and AAAA record based on whether ipv4 and ipv6 address provided
$dnsupdate->push(update=>rr_add("$dnshost. 3600 A $ipv4")) if($ipv4);
$dnsupdate->push(update=>rr_add("$dnshost. 3600 AAAA $ipv6")) if($ipv6);
# Always add a new TXT record with the timestamp of the last update
my $txt = ($ipv4 or $ipv6) ? $UpdateTXT : $DeleteTXT;
$dnsupdate->push(update=>rr_add($dnshost. '. 3600 TXT "' . $txt . localtime()
. '"')) if($txt);
# Sign the request with the signer and key
$dnsupdate->sign_tsig($signer, $key);
my $debugmessage = ($debug)
? "\n\n\n========================================================\n" .
$dnsupdate->string . "\n"
: "\n";
if(my $response = getResolver()->send($dnsupdate)) {
$debugmessage .= $response->string . "\n" if($debug);
if ($response->header->rcode eq 'NOERROR') {
return (200, "OK - DNS update for $dnshost succeeded: " .
$response->header->rcode . $debugmessage);
} else {
# REFUSED, FORMERR
return (400, "ERROR - DNS update for $dnshost failed: " .
$response->header->rcode . $debugmessage);
}
} else {
return (503, 'ERROR - DNS update for $dnshost failed: '.
getResolver()->errorstring. $debugmessage);
}
}
##############################
# Handlers for the different requests
sub handle_update($$$$$$) {
my ($cgi, $mode, $host, $dnshost, $dnsdomain, $debug) = @_;
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my ($signer, $key) = get_authinfo($cgi, $host);
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# perform the action
my ($statuscode, $statusmessage);
if($mode eq 'delete') {
($statuscode, $statusmessage) =
DNS_Update($dnsdomain, $dnshost, undef, undef, $signer, $key, $debug)
} else {
# Get ipv4, and ipv6 parameters
my $remote_addr = $cgi->remote_addr;
my $ipv4addr = $cgi->param('ipv4addr')
|| $cgi->param('ip')
|| (is_ipv4($remote_addr) ? $remote_addr : undef);
my $ipv6addr = $cgi->param('ipv6addr')
|| (! $ipv4addr and is_ipv6($remote_addr)) ? $remote_addr : undef;
($statuscode, $statusmessage) =
DNS_Update($dnsdomain, $dnshost, $ipv4addr, $ipv6addr, $signer, $key, $debug);
}
# And report back the status
print $cgi->header(-status=>$statuscode, -type=>'text/plain'), $statusmessage;
}
sub handle_expire($$$$$$) {
my ($cgi, $mode, $host, $dnshost, $dnsdomain, $debug) = @_;
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my ($signer, $key) = get_authinfo($cgi, $host);
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my $debugmsg = ($debug) ? "\n" : '';
# perform the action
if(my $period = periodSeconds($ExpireAfter)) {
my $validafter = time - $period;
if($debug) {
$debugmsg .= "ExpireAfter $ExpireAfter, expiring all entries older than ";
$debugmsg .= localtime($validafter) . "\n";
}
foreach my $rr (getResolver->axfr($dnsdomain)) {
next if($rr->name eq $dnsdomain);
if($rr->type eq 'TXT' &&
$rr->txtdata=~/$UpdateTXT(.*\d\d:\d\d:\d\d \d{4})$/){
if(my $lastupdate = parse_localtime($1)) {
DNS_Update($dnsdomain, $dnshost, undef, undef, $signer, $key, $debug)
unless($lastupdate > $validafter);
if($debug) {
$debugmsg .= ($lastupdate > $validafter) ? 'Keeping ' : 'Expiring ';
$debugmsg .= $rr->name . " last update ($1)\n";
}
} elsif($debug) {
$debugmsg .= 'Skipping '. $rr->name ." TXT: '". $rr->txtdata ."'\n";
}
}
}
# And report back the status
print $cgi->header(-status=>200, -type=>'text/plain'),
"OK - DNS expiry for $dnsdomain succeeded\n" . $debugmsg;
}
}
sub handle_status($$$$$$) {
my ($cgi, $mode, $host, $dnshost, $dnsdomain, $debug) = @_;
my $title = "DynDNS Updater - $host";
print $cgi->header(-status=>200),
$cgi->start_html(-title => $title),
$cgi->h1($title);
print $cgi->p("$host resolves to $dnshost") if($host cmp $dnshost);
print $cgi->p("Current DNS information for $dnshost:"),
$cgi->start_table,
$cgi->Tr({-align=>'LEFT',-valign=>'TOP'}, [
$cgi->th(['Field', 'Value'])
]);
foreach my $rr (DNS_get($dnshost)->answer) {
print $cgi->Tr([
$cgi->td([$DNS_label{$rr->type}, DNS_decode_rr($rr)])
]);
}
print $cgi->end_table();
print $cgi->end_html();
}
sub handle_view($$$$$$) {
my ($cgi, $mode, $host, $dnshost, $dnsdomain, $debug) = @_;
my $title = "DynDNS Updater - $dnsdomain";
print $cgi->header(-status=>200),
$cgi->start_html(-title => $title),
$cgi->h1($title);
print $cgi->p("Current DNS information for $dnsdomain:"),
$cgi->start_table,
$cgi->Tr({-align=>'LEFT',-valign=>'TOP'}, [
$cgi->th(['Name', 'Field', 'Value'])
]);
my $lastname = '';
foreach my $rr (getResolver->axfr($dnsdomain)) {
next if($rr->name eq $dnsdomain);
print $cgi->Tr([
$cgi->td([ ($lastname cmp $rr->name) ? $rr->name : '',
$DNS_label{$rr->type}, DNS_decode_rr($rr)])
]);
$lastname = $rr->name;
}
print $cgi->end_table();
print $cgi->end_html();
}
my $cgi = CGI->new;
##############################
# Validate Configuration
my $CE = 'Configuration Error:';
die "$CE \$AuthMode '$AuthMode' is unsupported must be remote, static or both\n"
unless $AuthMode=~/remote|static|both/;
die "$CE \$StaticSigner must be set for \$AuthMode '$AuthMode'\n"
unless ($StaticSigner or $AuthMode eq 'remote');
die "$CE \$StaticKey must be set for \$AuthMode '$AuthMode'\n"
unless ($StaticKey or $AuthMode eq 'remote');
die "$CE \$RequireRR is set to unsupported type '$RequireRR'\n"
if ($RequireRR and not $DNS_label{$RequireRR});
die "$CE \$ExpireAfter '$ExpireAfter' is not supported\n"
unless ($ExpireAfter=~/^\d+[smhw]$/);
die "$CE \$UpdateTXT must be set when \$ExpireAfter is set\n"
if($ExpireAfter and not $UpdateTXT);
foreach my $rrtype (@ReplaceRR) {
die "$CE \$ReplaceRR contains unsupported type '$rrtype'\n"
unless ($DNS_label{$rrtype});
}
##############################
# Determine what to do and fetch the input parameters
my $mode = $cgi->path_info || $cgi->param('mode') || '/status';
$mode=~s/^\/([^\/]+)(\/(.*))?/$1/;
my $host = $cgi->param('host') || $3;
my $debug = ($AllowDebugKey eq 'off') ? 0 : ($AllowDebugKey eq ($cgi->param('debug') || ''));
##############################
# Dispatch the request to the correct handler
my %handlers = (
status => \&handle_status,
update => \&handle_update,
delete => \&handle_update,
view => \&handle_view,
expire => \&handle_expire,
);
if($host eq '' and $mode cmp 'view' and $mode cmp 'expire') {
print $cgi->header(-status=>400, -type=>'text/plain'),
"ERROR - No host name to act on specified\n";
} elsif(my $handler = $handlers{$mode}) {
# Replace provided host with that of a CNAME it points to and determine domain
my $dnshost = ($host) ? expand_CNAME($host) : undef;
my $dnsdomain = $cgi->param('domain') || ($dnshost=~/\.(.*)$/)[0];
$handler->($cgi, $mode, $host, $dnshost, $dnsdomain, $debug);
} else {
print $cgi->header(-status=>($cgi->path_info) ? 404 : 400,
-type=>'text/plain'),
"ERROR - File Not Found / Invalid Mode '$mode' specified\n";
}
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