dns_whitelist_soft

#!perl -w

=head1 NAME

dns_whitelist_soft - dns-based whitelist override for other qpsmtpd plugins

=head1 DESCRIPTION

The dns_whitelist_soft plugin allows selected host to be whitelisted as
exceptions to later plugin processing.  It is strongly based on the original
dnsbl plugin as well as Gavin Carr's original whitelist_soft plugin.  It is
most suitable for multisite installations, so that the whitelist is stored
in one location and available from all.

=head1 CONFIGURATION

To enable the plugin, add it to the ~qpsmtpd/config/plugins file as usual.
It should precede any plugins whose rejections you wish to override.  You may
have to alter those plugins to check the appropriate notes field.

Several configuration files are supported, corresponding to different
parts of the SMTP conversation:

=over 4

=item whitelist_zones

Any IP address listed in the whitelist_zones file is queried using
the connecting MTA's IP address.  Any A or TXT answer means that the
remote HOST address can be selectively exempted at other stages by plugins
testing for a 'whitelisthost' connection note.

=back

NOTE: other 'connect' hooks will continue to fire (e.g. dnsbl), since the DNS
queries happen in the background.  This plugin's 'rcpt_handler' retrieves
the results of the query and sets the connection note if found.

=head1 AUTHOR

John Peacock <jpeacock@rowman.com>

Based on the 'whitelist_soft' plugin by Gavin Carr <gavin@openfusion.com.au>,
based on the 'whitelist' plugin by Devin Carraway <qpsmtpd@devin.com>.

=cut

use strict;
use warnings;

use Qpsmtpd::Constants;

sub register {
    my ($self, $qp) = (shift, shift);
    $self->log(LOGERROR, "Bad arguments") if @_ % 2;
    $self->{_args} = {@_};
}

sub hook_connect {
    my ($self, $transaction) = @_;

    my $remote_ip = $self->qp->connection->remote_ip;

    my %whitelist_zones =
      map { (split /\s+/, $_, 2)[0, 1] } $self->qp->config('whitelist_zones');

    return DECLINED unless %whitelist_zones;

    my $reversed_ip = join('.', reverse(split(/\./, $remote_ip)));

    # queue lookups in the background and fetch the
    # results in the first rcpt handler

    my $res = $self->get_resolver();
    my $sel = IO::Select->new();

    for my $dnsbl (keys %whitelist_zones) {
        $self->log(LOGDEBUG, "Checking $reversed_ip.$dnsbl in the background");
        $sel->add($res->bgsend("$reversed_ip.$dnsbl", 'TXT'));
    }

    $self->connection->notes('whitelist_sockets', $sel);
    return DECLINED;
}

sub process_sockets {
    my ($self) = @_;

    my $conn = $self->connection;

    return $conn->notes('whitelisthost') if $conn->notes('whitelisthost');

    my $res = $self->get_resolver();
    my $sel = $conn->notes('whitelist_sockets') or return '';

    $self->log(LOGDEBUG, "waiting for whitelist dns");

    # don't wait more than 4 seconds here
    my @ready = $sel->can_read(4);

    $self->log(LOGDEBUG,
               "done waiting for whitelist dns, got ",
               scalar @ready,
               " answers ...");
    return '' unless @ready;

    my $result;

    for my $socket (@ready) {
        my $query = $res->bgread($socket);
        $sel->remove($socket);
        undef $socket;

        my $whitelist;

        if ($query) {
            my $a_record = 0;
            foreach my $rr ($query->answer) {
                $a_record = 1 if $rr->type eq 'A';
                my $name = $rr->name;
                ($whitelist) = ($name =~ m/(?:\d+\.){4}(.*)/) unless $whitelist;
                $whitelist = $name unless $whitelist;
                $self->log(LOGDEBUG, 'name ', $rr->name);
                next unless $rr->type eq 'TXT';
                $self->log(LOGDEBUG, "got txt record");
                $result = $rr->txtdata and last;
            }
            $a_record and $result = "Blocked by $whitelist";
        }
        else {
            $self->log(LOGERROR, "$whitelist query failed: ", $res->errorstring)
              if $res->errorstring ne "NXDOMAIN";
        }

        if ($result) {

            # kill any other pending I/O
            $conn->notes('whitelist_sockets', undef);
            return $conn->notes('whitelisthost', $result);
        }
    }

    if ($sel->count) {

        # loop around if we have dns blacklists left to see results from
        return $self->process_sockets();
    }

    # er, the following code doesn't make much sense anymore...

    # if there was more to read; then forget it
    $conn->notes('whitelist_sockets', undef);

    return $conn->notes('whitelisthost', $result);
}

sub hook_rcpt {
    my ($self, $transaction, $rcpt, %param) = @_;
    my $ip = $self->qp->connection->remote_ip or return DECLINED;
    my $note = $self->process_sockets;
    if ($note) {
        $self->log(LOGNOTICE, "Host $ip is whitelisted: $note");
    }
    return DECLINED;
}