qpsmtpd/plugins/ident/p0f

#!perl -w

=head1 NAME

p0f - A TCP Fingerprinting Identification Plugin

=head1 SYNOPSIS

Use TCP fingerprint info (remote computer OS, network distance, etc) to
implement more sophisticated anti-spam policies.

=head1 DESCRIPTION

This p0f module inserts a 'p0f' note that other qpsmtpd plugins can inspect.
It includes the following information about the TCP fingerprint (link,
detail, distance, uptime, genre). Here's an example connection note:

 genre    => FreeBSD
 detail   => 6.x (1)
 uptime   => 1390
 link     => ethernet/modem
 distance => 17

Which was parsed from this p0f fingerprint:

  24.18.227.2:39435 - FreeBSD 6.x (1) (up: 1390 hrs)
    -> 208.75.177.101:25 (distance 17, link: ethernet/modem)

=head1 MOTIVATION

This p0f plugin provides a way to make sophisticated policies for email
messages. For example, the vast majority of email connections to my server
from Windows computers are spam (>99%). But, I have a few clients that use
Exchange servers so I can't just block email from all Windows computers.

Same goes for greylisting. Finance companies (AmEx, BoA, etc) just love to
send notices that they won't queue and retry. Either they deliver at that
instant or never. When I enable greylisting, I lose valid messages. Grrr.

So, while I'm not willing to use greylisting, and I'm not willing to block
connections from Windows computers, I am quite willing to greylist all email
from Windows computers.

=head1 CONFIGURATION

Configuration consists of two steps: starting p0f and configuring this plugin.

=head2 start p0f

Create a startup script for PF that creates a communication socket when your
server starts up.

p0f v2 example:

 p0f -u qpsmtpd -d -q -Q /tmp/.p0f_socket2 'dst port 25' -o /dev/null
 chown qpsmtpd /tmp/.p0f_socket2

p0f v3 example:

 p0f -u qpsmtpd -d -s /tmp/.p0f_socket3 'dst port 25'
 chown qpsmtpd /tmp/.p0f_socket3

=head2 configure p0f plugin

add an entry to config/plugins to enable p0f:

 ident/p0f /tmp/.p0f_socket3

It's even possible to run both versions of p0f simultaneously:

 ident/p0f:2 /tmp/.p0f_socket2 version 2
 ident/p0f:3 /tmp/.p0f_socket3

=head2 local_ip

Use the local_ip option to override the IP address of your mail server. This
is useful if your mail server has a private IP because it is running behind
a firewall. For example, my mail server has the IP 127.0.0.6, but the world
knows my mail server as 208.75.177.101.

Example config/plugins entry with local_ip override:

  ident/p0f /tmp/.p0f_socket local_ip 208.75.177.101


=head2 version

The version settings specifies the version of p0f you are running. This plugin supports p0f versions 2 and 3. If version is not defined, version 3 is assumed.

Example entry specifying p0f version 2

  ident/p0f /tmp/.p0f_socket version 2

=head1 Environment requirements

p0f v3 requires only the remote IP.

p0f v2 requires four pieces of information to look up the p0f fingerprint:
local_ip, local_port, remote_ip, and remote_port. TcpServer.pm has been
has been updated to provide that information when running under djb's
tcpserver. The async, forkserver, and prefork models will likely require
some additional changes to make sure these fields are populated.

=head1 ACKNOWLEDGEMENTS

Version 2 code heavily based upon the p0fq.pl included with the p0f distribution.

=head1 AUTHORS

Robert Spier ( original author )

Matt Simerson

=head1 CHANGES

Added local_ip option - Matt Simerson (5/2010)

Refactored and added p0f v3 support - Matt Simerson (4/2012)

=cut

use strict;
use warnings;

use Qpsmtpd::Constants;
use IO::Socket;
use Net::IP;

my $QUERY_MAGIC_V2 = 0x0defaced;
my $QUERY_MAGIC_V3 = 0x50304601;
my  $RESP_MAGIC_V3 = 0x50304602;

my $P0F_STATUS_BADQUERY = 0x00;
my $P0F_STATUS_OK       = 0x10;
my $P0F_STATUS_NOMATCH  = 0x20;

sub register {
    my ($self, $qp, $p0f_socket, %args) = @_;

    $p0f_socket =~ /(.*)/; # untaint
    $self->{_args}->{p0f_socket} = $1;
    foreach (keys %args) {
        $self->{_args}->{$_} = $args{$_};
    }
}

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

    my $p0f_version = $self->{_args}->{version} || 3;
    if ( $p0f_version == 3 ) {
        my $response = $self->query_p0f_v3() or return DECLINED;
        $self->test_v3_response( $response ) or return DECLINED;
        $self->store_v3_results( $response );
    }
    else {
        my $response = $self->query_p0f_v2() or return DECLINED;
        $self->test_v2_response( $response ) or return DECLINED;
        $self->store_v2_results( $response );
    }

    return DECLINED;
}

sub get_v2_query {
    my $self = shift;

    my $local_ip = $self->{_args}{local_ip} || $self->qp->connection->local_ip;

    my $src = new Net::IP ($self->qp->connection->remote_ip) 
        or $self->log(LOGERROR, "p0f: ".Net::IP::Error()), return;

    my $dst = new Net::IP($local_ip)
        or $self->log(LOGERROR, "p0f: ".NET::IP::Error()), return;

    return pack("L L L N N S S",
                   $QUERY_MAGIC_V2, 
                   1, 
                   rand ^ 42 ^ time,
                   $src->intip(), 
                   $dst->intip(), 
                   $self->qp->connection->remote_port,
                   $self->qp->connection->local_port);
};

sub get_v3_query {
    my $self = shift;

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

    if ( $src_ip =~ /:/ ) {   # IPv6
        my @bits = split(/\:/, $src_ip );
        return pack( "L C C C C C C C C C C C C C C C C C", $QUERY_MAGIC_V3, 0x06, @bits );
    };

    my @octets = split(/\./, $src_ip);
    return pack( "L C C16", $QUERY_MAGIC_V3, 0x04, @octets );
};

sub query_p0f_v3 {
    my $self = shift;

    my $p0f_socket = $self->{_args}->{p0f_socket} or return;
    my $query = $self->get_v3_query();

# Open the connection to p0f
    my $sock;
    eval {
        $sock = IO::Socket::UNIX->new(Peer => $p0f_socket, Type => SOCK_STREAM );
    };
    if ( ! $sock ) {
        $self->log(LOGERROR, "p0f: could not open socket: $@");
        return;
    };

    $sock->autoflush(1);  # paranoid redundancy
    $sock->connected or do {
            $self->log(LOGERROR, "p0f: socket not connected: $!");
            return;
        };

    my $sent = $sock->send($query, 0) or do {
            $self->log(LOGERROR, "p0f: send failed: $!");
            return;
        };

    print $sock $query;  # yes, this is redundant, but I get no response from p0f otherwise

    $self->log(LOGDEBUG, "p0f: send $sent byte request");

    my $response;
    $sock->recv( $response, 232 );
    my $length = length $response;
    $self->log(LOGDEBUG, "p0f: received $length byte response");
    close $sock;
    return $response;
};

sub query_p0f_v2 {
    my $self = shift;

    my $p0f_socket = $self->{_args}->{p0f_socket};
    my $query = $self->get_v2_query() or return;

    # Open the connection to p0f
    socket(SOCK, PF_UNIX, SOCK_STREAM, 0) 
        or $self->log(LOGERROR, "p0f: socket: $!"), return;
    connect(SOCK, sockaddr_un($p0f_socket)) 
        or $self->log(LOGERROR, "p0f: connect: $!"), return;
    defined syswrite SOCK, $query 
        or $self->log(LOGERROR, "p0f: write: $!"), close SOCK, return;

    my $response;
    defined sysread SOCK, $response, 1024 
        or $self->log(LOGERROR, "p0f: read: $!"), close SOCK, return;
    close SOCK;
    return $response;
};

sub test_v2_response {
    my ($self, $response ) = @_;

    # Extract part of the p0f response
    my ($magic, $id, $type) = unpack ("L L C", $response);

    # $self->log(LOGERROR, $response);
    if ($magic != $QUERY_MAGIC_V2) {
        $self->log(LOGERROR, "p0f: Bad response magic.");
        return;
    }

    if ($type == 1) {
        $self->log(LOGERROR, "p0f: p0f did not honor our query");
        return;
    }
    elsif ($type == 2) {
        $self->log(LOGWARN, "p0f: This connection is no longer in the cache");
        return;
    }
    return 1;
};

sub test_v3_response {
    my ($self, $response ) = @_;

    my ($magic,$status) = unpack ("L L", $response);

    # check the magic response value (a p0f constant)
    if ($magic != $RESP_MAGIC_V3 ) {
        $self->log(LOGERROR, "p0f: Bad response magic.");
        return;
    }

    # check the response status
    if ($status == $P0F_STATUS_BADQUERY ) {
        $self->log(LOGERROR, "p0f: bad query");
        return;
    }
    elsif ($status == $P0F_STATUS_NOMATCH ) {
        $self->log(LOGINFO, "p0f: no match");
        return;
    }
    if ($status == $P0F_STATUS_OK ) {
        $self->log(LOGDEBUG, "p0f: query ok");
        return 1;
    }
    return;
};

sub store_v2_results {
    my ($self, $response ) = @_;

    my ($magic, $id, $type, $genre, $detail, $dist, $link, $tos, $fw,
        $nat, $real, $score, $mflags, $uptime) =
            unpack ("L L C Z20 Z40 c Z30 Z30 C C C s S N", $response);

    my $p0f = { 
        genre    => $genre,
        detail   => $detail,
        distance => $dist,
        link     => $link,
        uptime   => $uptime,
    };

    $self->qp->connection->notes('p0f', $p0f);
    $self->log(LOGINFO, $genre." (".$detail.")");
    $self->log(LOGERROR,"error: $@") if $@;
};

sub store_v3_results {
    my ($self, $response ) = @_;

    my @labels = qw/ magic status first_seen last_seen total_conn uptime_min
        up_mod_days last_nat last_chg distance bad_sw os_match_q os_name os_flavor
        http_name http_flavor link_type language /;
    my @values = unpack ("L L L L L L L L L s C C A32 A32 A32 A32 A32 A32 A32", $response);

    my %r;
    foreach my $i ( 0 .. ( scalar @labels -1 ) ) {
        next if ! defined $values[$i];
        next if ! defined $values[$i];
        $r{ $labels[$i] } = $values[$i];
    };

    $self->qp->connection->notes('p0f', \%r);
    $self->log(LOGINFO, "$values[12] $values[13]");
    $self->log(LOGDEBUG, join(' ', @values ));
    $self->log(LOGERROR,"error: $@") if $@;
};