142 lines
4.3 KiB
Perl
142 lines
4.3 KiB
Perl
#!perl -w
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=head1 NAME
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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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=item check-at [string: connect, data]
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Defines when to check for early talkers, either at connect time (pre-greet pause)
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or at DATA time (pause before sending "354 go ahead").
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The default is I<connect>.
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Note that defer-reject has no meaning if check-at is I<data>.
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=back
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=cut
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my $MSG = 'Connecting host started transmitting before SMTP greeting';
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sub register {
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my ($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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'check-at' => 'connect',
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@args,
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};
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print STDERR "Check at: ", $self->{_args}{'check-at'}, "\n";
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$self->register_hook($self->{_args}->{'check-at'}, 'check_talker_poll');
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$self->register_hook($self->{_args}->{'check-at'}, 'check_talker_post');
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if ($self->{_args}{'check-at'} eq 'connect') {
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$self->register_hook('mail', 'hook_mail')
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if $self->{_args}->{'defer-reject'};
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}
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1;
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}
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sub check_talker_poll {
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my ($self, $transaction) = @_;
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my $qp = $self->qp;
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my $conn = $qp->connection;
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my $check_until = time + $self->{_args}{'wait'};
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$qp->AddTimer(
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1,
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sub {
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read_now($qp, $conn, $check_until, $self->{_args}{'check-at'});
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}
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);
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return YIELD;
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}
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sub read_now {
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my ($qp, $conn, $until, $phase) = @_;
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if ($qp->has_data) {
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$qp->log(LOGNOTICE,
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'remote host started talking after $phase before we responded');
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$qp->clear_data if $phase eq 'data';
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$conn->notes('earlytalker', 1);
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$qp->run_continuation;
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}
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elsif (time >= $until) {
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# no early talking
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$qp->run_continuation;
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}
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else {
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$qp->AddTimer(1, sub { read_now($qp, $conn, $until, $phase) });
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}
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}
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sub check_talker_post {
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my ($self, $transaction) = @_;
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return DECLINED unless $self->connection->notes('earlytalker');
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return DECLINED if $self->{'defer-reject'};
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return (DENY, $MSG) if $self->{_args}->{'action'} eq 'deny';
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return (DENYSOFT, $MSG) if $self->{_args}->{'action'} eq 'denysoft';
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return DECLINED; # assume action eq 'log'
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}
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sub hook_mail {
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my ($self, $transaction) = @_;
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return DECLINED unless $self->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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