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#!/usr/bin/perl

#
# spfd: Simple forking daemon to provide SPF query services
# 
# (C) 2003-2004 Meng Weng Wong <mengwong+spf@pobox.com>
#     2005-2006 Julian Mehnle <julian@mehnle.net>
# 
# If you're reading source code, you should probably be on
# spf-devel@v2.listbox.com.
#
# $Id: spfd 141 2006-02-07 00:04:51Z julian $
#
##############################################################################

=head1 NAME

spfd - simple forking daemon to provide SPF query services

=head1 VERSION

2006-02-07

=head1 SYNOPSIS

B<spfd> B<--port> I<port> [B<--set-user> I<uid>|I<username>] [B<--set-group>
I<gid>|I<groupname>]

B<spfd> B<--socket> I<filename> [B<--socket-user> I<uid>|I<username>]
[B<--socket-group> I<gid>|I<groupname>] [B<--socket-perms> I<octal-perms>]
[B<--set-user> I<uid>|I<username>] [B<--set-group> I<gid>|I<groupname>]

B<spfd> B<--help>

=head1 DESCRIPTION

B<spfd> is a simple forking Sender Policy Framework (SPF) query proxy server.
spfd receives and answers SPF query requests on a TCP/IP or UNIX domain
socket.

The B<--port> form listens on a TCP/IP socket on the specified I<port>.  The
default port is B<5970>.

The B<--socket> form listens on a UNIX domain socket that is created with the
specified I<filename>.  The socket can be assigned specific user and group
ownership with the B<--socket-user> and B<--socket-group> options, and specific
filesystem permissions with the B<--socket-perms> option.

Generally, spfd can be instructed with the B<--set-user> and B<--set-group>
options to drop root privileges and change to another user and group before it
starts listening for requests.

The B<--help> form prints usage information for B<spfd>.

=head1 REQUEST

A request consists of a series of lines delimited by \x0A (LF) characters (or
whatever your system considers a newline).  Each line must be of the form
I<key>B<=>I<value>, where the following keys are required:

=over

=item B<ip>

The sender IP address.

=item B<sender>

The envelope sender address (from the SMTP C<MAIL FROM> command).

=item B<helo>

The envelope sender hostname (from the SMTP C<HELO> command).

=back

=head1 RESPONSE

spfd responds to query requests with similar series of lines of the form
I<key>B<=>I<value>.  The most important response keys are:

=over

=item B<result>

The result of the SPF query:

=over 10

=item I<pass>

The specified IP address is an authorized mailer for the sender domain/address.

=item I<fail>

The specified IP address is not an authorized mailer for the sender
domain/address.

=item I<softfail>

The specified IP address is not an authorized mailer for the sender
domain/address, however the domain is still in the process of transitioning to
SPF.

=item I<neutral>

The sender domain makes no assertion about the status of the IP address.

=item I<unknown>

The sender domain has a syntax error in its SPF record.

=item I<error>

A temporary DNS error occurred while resolving the sender policy.  Try again
later.

=item I<none>

There is no SPF record for the sender domain.

=back

=item B<smtp_comment>

The text that should be included in the receiver's SMTP response.

=item B<header_comment>

The text that should be included as a comment in the message's C<Received-SPF:>
header.

=item B<spf_record>

The SPF record of the envelope sender domain.

=back

For the description of other response keys see L<Mail::SPF::Query>.

For more information on SPF see L<http://www.openspf.org>.

=head1 EXAMPLE

A running spfd could be tested using the C<netcat> utility like this:

    $ echo -e "ip=11.22.33.44\nsender=user@pobox.com\nhelo=spammer.example.net\n" | nc localhost 5970
    result=neutral
    smtp_comment=Please see http://spf.pobox.com/why.html?sender=user%40pobox.com&ip=11.22.33.44&receiver=localhost
    header_comment=localhost: 11.22.33.44 is neither permitted nor denied by domain of user@pobox.com
    guess=neutral
    smtp_guess=
    header_guess=
    guess_tf=neutral
    smtp_tf=
    header_tf=
    spf_record=v=spf1 ?all

=head1 SEE ALSO

L<Mail::SPF::Query>, L<http://www.openspf.org>

=head1 AUTHORS

This version of B<spfd> was written by Meng Weng Wong <mengwong+spf@pobox.com>.
Improved argument parsing was added by Julian Mehnle <julian@mehnle.net>.

This man-page was written by Julian Mehnle <julian@mehnle.net>.

=cut

use warnings;
use strict;

use Mail::SPF::Query;
use Getopt::Long qw(:config gnu_compat);
use Socket;

use constant DEBUG => $ENV{DEBUG};

sub usage () {
  print STDERR <<'EOT';
Usage:
    spfd --port <port>
        [--set-user <uid>|<username>] [--set-group <gid>|<groupname>]
    spfd --socket <filename> [--socket-user <uid>|<username>]
        [--socket-group <gid>|<groupname>] [--socket-perms <octal-perms>]
        [--set-user <uid>|<username>] [--set-group <gid>|<groupname>]
EOT
}

my %opt;

my $getopt_result = GetOptions(
  \%opt,
  'port=i',
  'socket|path=s',
  'socket-user|pathuser=s',
  'socket-group|pathgroup=s',
  'socket-perms|pathmode=s',
  'set-user|setuser=s',
  'set-group|setgroup=s',
  'help!'
);

if ($opt{help}) {
  usage;
  exit 0;
}

if ($opt{port} and $opt{socket}) {
  usage;
  exit 1;
}

if (not $opt{port} and not $opt{socket}) {
  print STDERR "Using default TCP/IP port.  Run `spfd --help` for possible options.\n";
  $opt{port} = 5970;
}

$| = 1;

my @args;
my $sock_type;

if ($opt{port}) {
  $sock_type = 'inet';
  @args = (Listen    => 1,
           LocalAddr => '127.0.0.1',
           LocalPort => $opt{port},
           ReuseAddr => 1
           );
  print "$$: will listen on TCP port $opt{port}\n";
  $0 = "spfd listening on TCP port $opt{port}";
} elsif ($opt{socket}) {
  $sock_type = 'unix';
  unlink $opt{socket} if -S $opt{socket};
  @args = (Listen => 1,
           Local => $opt{socket},
           );
  print "$$: will listen at UNIX socket $opt{socket}\n";
  $0 = "spfd listening at UNIX socket $opt{socket}";
}

print "$$: creating server with args @args\n";

my $server = $sock_type eq 'inet' ? IO::Socket::INET->new(@args) : IO::Socket::UNIX->new(@args);

if ($opt{socket}) {
  if (defined $opt{'socket-user'} or defined $opt{'socket-group'}) {
    $opt{'socket-user'}  = -1 if not defined($opt{'socket-user'});
    $opt{'socket-group'} = -1 if not defined($opt{'socket-group'});

    if ($opt{'socket-user'} =~ /\D/) {
      $opt{'socket-user'} = getpwnam($opt{'socket-user'}) || die "User: $opt{'socket-user'} not found\n";
    }

    if ($opt{'socket-group'} =~ /\D/) {
      $opt{'socket-group'} = getgrnam($opt{'socket-group'}) || die "Group: $opt{'socket-group'} not found\n";
    }

    chown $opt{'socket-user'}, $opt{'socket-group'}, $opt{socket} or die "chown call failed on $opt{socket}: $!\n";
  }
  if (defined $opt{'socket-perms'}) {
    chmod oct($opt{'socket-perms'}), $opt{socket} or die "Cannot fixup perms on $opt{socket}: $!\n";
  }
}

DEBUG and print "$$: server is $server\n";

if ($opt{'set-group'}) {
  if ($opt{'set-group'} =~ /\D/) {
    $opt{'set-group'} = getgrnam($opt{'set-group'}) || die "Group: $opt{'set-group'} not found\n";
  }
  $( = $opt{'set-group'};
  $) = $opt{'set-group'};
  unless ($( == $opt{'set-group'} and $) == $opt{'set-group'}) {
    die( "setgid($opt{'set-group'}) call failed: $!\n" );
  }
}

if ($opt{'set-user'}) {
  if ($opt{'set-user'} =~ /\D/) {
    $opt{'set-user'} = getpwnam($opt{'set-user'}) || die "User: $opt{'set-user'} not found\n"; 
  }
  $< = $opt{'set-user'};
  $> = $opt{'set-user'};
  unless ($< == $opt{'set-user'} and $> == $opt{'set-user'}) {
    die( "setuid($opt{'set-user'}) call failed: $!\n" );
  }
}

while (my $sock = $server->accept()) {
  if    (fork) { close $sock; wait; next; } # this is the grandfather trick.
  elsif (fork) {                    exit; } # the child exits immediately, so no zombies.

  my $oldfh = select($sock); $| = 1; select($oldfh);

  my %in;

  while (<$sock>) {
    chomp; chomp;
    last if (/^$/);
    my ($lhs, $rhs) = split /=/, $_, 2;
    $in{lc $lhs} = $rhs;
  }

  my $peerinfo = $sock_type eq "inet" ? ($sock->peerhost . "/" . gethostbyaddr($sock->peeraddr, AF_INET)) : "";

  my $time = localtime;
  
  DEBUG and print "$time $peerinfo\n";
  foreach my $key (sort keys %in) { DEBUG and print "learned $key = $in{$key}\n" };

  my %q = map { exists $in{$_} ? ($_ => $in{$_}) : () } qw ( ip ipv4 ipv6 sender helo guess_mechs trusted local );

  my %a;

  my $query = eval { Mail::SPF::Query->new(%q); };

  my $error = $@; for ($error) { s/\n/ /; s/\s+$//; }

  if ($@) { @a{qw(result smtp_comment header_comment)} = ("unknown", $error, "SPF error: $error"); }
  else {
    @a{qw(result    smtp_comment header_comment spf_record)} = $query->result();
    @a{qw(guess     smtp_guess   header_guess  )} = $query->best_guess();
    @a{qw(guess_tf  smtp_tf      header_tf     )} = $query->trusted_forwarder();
  }

  if (DEBUG) {
    for (qw(result    smtp_comment header_comment
            guess     smtp_guess   header_guess
            guess_tf  smtp_tf      header_tf
            spf_record
            )) {
      print "moo!  $_=$a{$_}\n";
    }
  }

  for (qw(result    smtp_comment header_comment
          guess     smtp_guess   header_guess
          guess_tf  smtp_tf      header_tf
          spf_record
          )) {
    no warnings 'uninitialized';
    print $sock "$_=$a{$_}\n";
  }

  DEBUG and print "moo!  output all done.\n";
  print $sock "\n";
  DEBUG and print "\n";

  close $sock;

  exit;
}