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#!/usr/bin/perl
use DB_File;
use Fcntl;
use Sys::Syslog qw(:DEFAULT setlogsock);
#
# Usage: greylist.pl [-v]
#
# Demo delegated Postfix SMTPD policy server. This server implements
# greylisting. State is kept in a Berkeley DB database. Logging is
# sent to syslogd.
#
# How it works: each time a Postfix SMTP server process is started
# it connects to the policy service socket, and Postfix runs one
# instance of this PERL script. By default, a Postfix SMTP server
# process terminates after 100 seconds of idle time, or after serving
# 100 clients. Thus, the cost of starting this PERL script is smoothed
# out over time.
#
# To run this from /etc/postfix/master.cf:
#
# policy unix - n n - - spawn
# user=nobody argv=/usr/bin/perl /usr/libexec/postfix/greylist.pl
#
# To use this from Postfix SMTPD, use in /etc/postfix/main.cf:
#
# smtpd_recipient_restrictions =
# ...
# reject_unauth_destination
# check_policy_service unix:private/policy
# ...
#
# NOTE: specify check_policy_service AFTER reject_unauth_destination
# or else your system can become an open relay.
#
# To test this script by hand, execute:
#
# % perl greylist.pl
#
# Each query is a bunch of attributes. Order does not matter, and
# the demo script uses only a few of all the attributes shown below:
#
# request=smtpd_access_policy
# protocol_state=RCPT
# protocol_name=SMTP
# helo_name=some.domain.tld
# queue_id=8045F2AB23
# sender=foo@bar.tld
# recipient=bar@foo.tld
# client_address=1.2.3.4
# client_name=another.domain.tld
# instance=123.456.7
# sasl_method=plain
# sasl_username=you
# sasl_sender=
# size=12345
# [empty line]
#
# The policy server script will answer in the same style, with an
# attribute list followed by a empty line:
#
# action=dunno
# [empty line]
#
#
# greylist status database and greylist time interval. DO NOT create the
# greylist status database in a world-writable directory such as /tmp
# or /var/tmp. DO NOT create the greylist database in a file system
# that can run out of space.
#
# In case of database corruption, this script saves the database as
# $database_name.time(), so that the mail system does not get stuck.
#
$database_name="/var/mta/greylist.db";
$greylist_delay=60;
#
# Auto-whitelist threshold. Specify 0 to disable, or the number of
# successful "come backs" after which a client is no longer subject
# to greylisting.
#
$auto_whitelist_threshold = 10;
#
# Syslogging options for verbose mode and for fatal errors.
# NOTE: comment out the $syslog_socktype line if syslogging does not
# work on your system.
#
$syslog_socktype = 'unix'; # inet, unix, stream, console
$syslog_facility="mail";
$syslog_options="pid";
$syslog_priority="info";
#
# Demo SMTPD access policy routine. The result is an action just like
# it would be specified on the right-hand side of a Postfix access
# table. Request attributes are available via the %attr hash.
#
sub smtpd_access_policy {
my($key, $time_stamp, $now, $count);
# Open the database on the fly.
open_database() unless $database_obj;
# Search the auto-whitelist.
if ($auto_whitelist_threshold > 0) {
$count = read_database($attr{"client_address"});
if ($count > $auto_whitelist_threshold) {
return "dunno";
}
}
# Lookup the time stamp for this client/sender/recipient.
$key =
lc $attr{"client_address"}."/".$attr{"sender"}."/".$attr{"recipient"};
$time_stamp = read_database($key);
$now = time();
# If this is a new request add this client/sender/recipient to the database.
if ($time_stamp == 0) {
$time_stamp = $now;
update_database($key, $time_stamp);
}
# The result can be any action that is allowed in a Postfix access(5) map.
#
# To label mail, return ``PREPEND'' headername: headertext
#
# In case of success, return ``DUNNO'' instead of ``OK'' so that the
# check_policy_service restriction can be followed by other restrictions.
#
# In case of failure, specify ``DEFER_IF_PERMIT optional text...''
# so that mail can still be blocked by other access restrictions.
#
syslog $syslog_priority, "request age %d", $now - $time_stamp if $verbose;
if ($now - $time_stamp > $greylist_delay) {
# Update the auto-whitelist.
if ($auto_whitelist_threshold > 0) {
update_database($attr{"client_address"}, $count + 1);
}
return "dunno";
} else {
return "defer_if_permit Service is unavailable";
}
}
#
# You should not have to make changes below this point.
#
sub LOCK_SH { 1 }; # Shared lock (used for reading).
sub LOCK_EX { 2 }; # Exclusive lock (used for writing).
sub LOCK_NB { 4 }; # Don't block (for testing).
sub LOCK_UN { 8 }; # Release lock.
#
# Log an error and abort.
#
sub fatal_exit {
my($first) = shift(@_);
syslog "err", "fatal: $first", @_;
exit 1;
}
#
# Open hash database.
#
sub open_database {
my($database_fd);
# Use tied database to make complex manipulations easier to express.
$database_obj = tie(%db_hash, 'DB_File', $database_name,
O_CREAT|O_RDWR, 0644, $DB_BTREE) ||
fatal_exit "Cannot open database %s: $!", $database_name;
$database_fd = $database_obj->fd;
open DATABASE_HANDLE, "+<&=$database_fd" ||
fatal_exit "Cannot fdopen database %s: $!", $database_name;
syslog $syslog_priority, "open %s", $database_name if $verbose;
}
#
# Read database. Use a shared lock to avoid reading the database
# while it is being changed. XXX There should be a way to synchronize
# our cache from the on-file database before looking up the key.
#
sub read_database {
my($key) = @_;
my($value);
flock DATABASE_HANDLE, LOCK_SH ||
fatal_exit "Can't get shared lock on %s: $!", $database_name;
# XXX Synchronize our cache from the on-disk copy before lookup.
$value = $db_hash{$key};
syslog $syslog_priority, "lookup %s: %s", $key, $value if $verbose;
flock DATABASE_HANDLE, LOCK_UN ||
fatal_exit "Can't unlock %s: $!", $database_name;
return $value;
}
#
# Update database. Use an exclusive lock to avoid collisions with
# other updaters, and to avoid surprises in database readers. XXX
# There should be a way to synchronize our cache from the on-file
# database before updating the database.
#
sub update_database {
my($key, $value) = @_;
syslog $syslog_priority, "store %s: %s", $key, $value if $verbose;
flock DATABASE_HANDLE, LOCK_EX ||
fatal_exit "Can't exclusively lock %s: $!", $database_name;
# XXX Synchronize our cache from the on-disk copy before update.
$db_hash{$key} = $value;
$database_obj->sync() &&
fatal_exit "Can't update %s: $!", $database_name;
flock DATABASE_HANDLE, LOCK_UN ||
fatal_exit "Can't unlock %s: $!", $database_name;
}
#
# Signal 11 means that we have some kind of database corruption (yes
# Berkeley DB should handle this better). Move the corrupted database
# out of the way, and start with a new database.
#
sub sigsegv_handler {
my $backup = $database_name . "." . time();
rename $database_name, $backup ||
fatal_exit "Can't save %s as %s: $!", $database_name, $backup;
fatal_exit "Caught signal 11; the corrupted database is saved as $backup";
}
$SIG{'SEGV'} = 'sigsegv_handler';
#
# This process runs as a daemon, so it can't log to a terminal. Use
# syslog so that people can actually see our messages.
#
setlogsock $syslog_socktype;
openlog $0, $syslog_options, $syslog_facility;
#
# We don't need getopt() for now.
#
while ($option = shift(@ARGV)) {
if ($option eq "-v") {
$verbose = 1;
} else {
syslog $syslog_priority, "Invalid option: %s. Usage: %s [-v]",
$option, $0;
exit 1;
}
}
#
# Unbuffer standard output.
#
select((select(STDOUT), $| = 1)[0]);
#
# Receive a bunch of attributes, evaluate the policy, send the result.
#
while (<STDIN>) {
if (/([^=]+)=(.*)\n/) {
$attr{substr($1, 0, 512)} = substr($2, 0, 512);
} elsif ($_ eq "\n") {
if ($verbose) {
for (keys %attr) {
syslog $syslog_priority, "Attribute: %s=%s", $_, $attr{$_};
}
}
fatal_exit "unrecognized request type: '%s'", $attr{request}
unless $attr{"request"} eq "smtpd_access_policy";
$action = smtpd_access_policy();
syslog $syslog_priority, "Action: %s", $action if $verbose;
print STDOUT "action=$action\n\n";
%attr = ();
} else {
chop;
syslog $syslog_priority, "warning: ignoring garbage: %.100s", $_;
}
}
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