146 lines
4.5 KiB
Plaintext
146 lines
4.5 KiB
Plaintext
=head1 NAME
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check_earlytalker - Check that the client doesn't talk before we send the SMTP banner
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=head1 DESCRIPTION
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Checks to see if the remote host starts talking before we've issued a 2xx
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greeting. If so, we're likely looking at a direct-to-MX spam agent which
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pipelines its entire SMTP conversation, and will happily dump an entire spam
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into our mail log even if later tests deny acceptance.
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Depending on configuration, clients which behave in this way are either
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immediately disconnected with a deny or denysoft code, or else are issued this
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on all mail/rcpt commands in the transaction.
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=head1 CONFIGURATION
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=over 4
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=item wait [integer]
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The number of seconds to delay the initial greeting to see if the connecting
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host speaks first. The default is 1. Do not select a value that is too high,
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or you may be unable to receive mail from MTAs with short SMTP connect or
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greeting timeouts -- these are known to range as low as 30 seconds, and may
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in some cases be configured lower by mailserver admins. Network transit time
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must also be allowed for.
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=item action [string: deny, denysoft, log]
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What to do when matching an early-talker -- the options are I<deny>,
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I<denysoft> or I<log>.
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If I<log> is specified, the connection will be allowed to proceed as normal,
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and only a warning will be logged.
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The default is I<denysoft>.
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=item defer-reject [boolean]
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When an early-talker is detected, if this option is set to a true value, the
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SMTP greeting will be issued as usual, but all RCPT/MAIL commands will be
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issued a deny or denysoft (depending on the value of I<action>). The default
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is to react at the SMTP greeting stage by issuing the apropriate response code
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and terminating the SMTP connection.
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=back
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=cut
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use IO::Select;
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use warnings;
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use strict;
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sub register {
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my ($self, $qp, @args) = @_;
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if (@args % 2) {
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$self->log(LOGERROR, "Unrecognized/mismatched arguments");
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return undef;
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}
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$self->{_args} = {
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'wait' => 1,
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'action' => 'denysoft',
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'defer-reject' => 0,
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@args,
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};
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if ( $qp->{conn} && $qp->{conn}->isa('Apache2::Connection')) {
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require APR::Const;
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APR::Const->import(qw(POLLIN SUCCESS));
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$self->register_hook('connect', 'apr_connect_handler');
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}
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else {
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$self->register_hook('connect', 'connect_handler');
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}
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$self->register_hook('mail', 'mail_handler')
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if $self->{_args}->{'defer-reject'};
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1;
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}
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sub apr_connect_handler {
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my ($self, $transaction) = @_;
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return DECLINED if ($self->qp->connection->notes('whitelistclient'));
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my $ip = $self->qp->connection->remote_ip;
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my $c = $self->qp->{conn};
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my $socket = $c->client_socket;
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my $timeout = $self->{_args}->{'wait'} * 1_000_000;
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my $rc = $socket->poll($c->pool, $timeout, APR::Const::POLLIN());
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if ($rc == APR::Const::SUCCESS()) {
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$self->log(LOGNOTICE, "remote host started talking before we said hello [$ip]");
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if ($self->{_args}->{'defer-reject'}) {
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$self->qp->connection->notes('earlytalker', 1);
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}
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else {
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my $msg = 'Connecting host started transmitting before SMTP greeting';
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return (DENY,$msg) if $self->{_args}->{'action'} eq 'deny';
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return (DENYSOFT,$msg) if $self->{_args}->{'action'} eq 'denysoft';
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}
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}
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else {
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$self->log(LOGINFO, "remote host said nothing spontaneous, proceeding");
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}
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}
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sub connect_handler {
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my ($self, $transaction) = @_;
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my $in = new IO::Select;
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my $ip = $self->qp->connection->remote_ip;
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return DECLINED
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if ($self->qp->connection->notes('whitelistclient'));
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$in->add(\*STDIN) || return DECLINED;
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if ($in->can_read($self->{_args}->{'wait'})) {
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$self->log(LOGNOTICE, "remote host started talking before we said hello [$ip]");
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if ($self->{_args}->{'defer-reject'}) {
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$self->qp->connection->notes('earlytalker', 1);
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} else {
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my $msg = 'Connecting host started transmitting before SMTP greeting';
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return (DENY,$msg) if $self->{_args}->{'action'} eq 'deny';
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return (DENYSOFT,$msg) if $self->{_args}->{'action'} eq 'denysoft';
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}
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} else {
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$self->log(LOGINFO, 'remote host said nothing spontaneous, proceeding');
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}
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return DECLINED;
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}
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sub mail_handler {
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my ($self, $txn) = @_;
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my $msg = 'Connecting host started transmitting before SMTP greeting';
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return DECLINED unless $self->qp->connection->notes('earlytalker');
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return (DENY,$msg) if $self->{_args}->{'action'} eq 'deny';
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return (DENYSOFT,$msg) if $self->{_args}->{'action'} eq 'denysoft';
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return DECLINED;
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}
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1;
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