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On Debian saved rulesets may be found in /var/lib/iptables.

# The LearningOnline Network with CAPA
# Firewall configuration to allow internal LON-CAPA communication between servers   
#
# $Id: Firewall.pm,v 1.5 2009/07/17 00:15:49 raeburn Exp $
#
# The LearningOnline Network with CAPA
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#
# Startup script for the LON-CAPA network processes
#

package LONCAPA::Firewall;

use strict;
use lib '/home/httpd/perl/lib';
use LONCAPA::Configuration;

# Firewall code is based on the code in FC2 /etc/init.d/ntpd

sub firewall_open_port {
    my ($iptables,$fw_chain,$lond_port,$iphost,$ports) = @_;
    return 'inactive firewall' if (!&firewall_is_active());
    return 'port number unknown' if !$lond_port;
    my @opened;
    if (! `$iptables -L -n 2>/dev/null | grep $fw_chain | wc -l`) {
        return 'Expected chain "'.$fw_chain.'" missing from iptables'."\n";
    }
    #
    # iptables is running with expected chain
    #
    if ($fw_chain =~ /^([\w\-]+)$/) {
        $fw_chain = $1;
    } else {
        return 'Chain name has unexpected format'."\n";
    }
    if (ref($ports) ne 'ARRAY') {
        return 'List of ports to open needed.';
    }
    foreach my $portnum (@{$ports}) {
        my $port = '';
        if ($portnum =~ /^(\d+)$/) {
            $port = $1;
        } else {
            print "Skipped non-numeric port: $portnum\n";
            next;
        }
        print "Opening firewall access on port $port.\n";
        my $result;
        if ($port eq $lond_port) {
            # For lond port, restrict the servers allowed to attempt to communicate
            # to include only source IPs in the LON-CAPA cluster.
            my (@port_error,@command_error,@lond_port_open);
            if (ref($iphost) eq 'HASH') {
                if (keys(%{$iphost}) > 0) { 
                    &firewall_close_anywhere($iptables,$fw_chain,$port);
                    foreach my $key (keys(%{$iphost})) {
                        my $ip = '';
                        if ($key =~ /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/) {
                            if (($1<=255) && ($2<=255) && ($3<=255) && ($4<=255)) {
                                $ip = "$1.$2.$3.$4";
                            } else {
                                next;
                            }
                        } else {
                            next;
                        }
                        my $firewall_command =
                            "$iptables -I $fw_chain -p tcp -s $ip -d 0/0 --dport $port -j ACCEPT";
                        system($firewall_command);
                        my $return_status = $?>>8;
                        if ($return_status == 1) {
                            push (@port_error,$ip);
                        } elsif ($return_status == 2) {
                            push(@command_error,$ip);
                        } elsif ($return_status == 0) {
                            push(@lond_port_open,$ip);
                        }
                    }
                }
            }
            if (@lond_port_open) {
                push(@opened,$port);
                print "Port $port opened for ".scalar(@lond_port_open)." IP addresses\n";
            }
            if (@port_error) {
                print "Error opening port $port for following IP addresses: ".join(', ',@port_error)."\n";
            }
            if (@command_error) {
                print "Bad command error opening port for following IP addresses: ".
                      join(', ',@command_error)."\n".
                      'Command was: "'."$iptables -I $fw_chain -p tcp -s ".'$ip'." -d 0/0 --dport $port -j ACCEPT".'", where $ip is IP address'."\n";
            }
        } else {
            my $firewall_command =
               "$iptables -I $fw_chain -p tcp -d 0/0 --dport $port -j ACCEPT";
            system($firewall_command);
            my $return_status = $?>>8;
            if ($return_status == 1) {
                # Error
                print "Error opening port.\n";
            } elsif ($return_status == 2) {
                # Bad command
                print "Bad command error opening port.  Command was\n".
                      "  ".$firewall_command."\n";
            } elsif ($return_status == 0) {
                push(@opened,$port);
            }
        }
    }
    foreach my $port (@{$ports}) {
        if (!grep(/^\Q$port\E$/,@opened)) {
            return 'Required port not open: '.$port."\n";
        }
    }
    return 'ok';
}

sub firewall_is_port_open {
    my ($iptables,$fw_chain,$port,$lond_port,$iphost) = @_;
    # for lond port returns number of source IPs for which firewall port is open
    # for other ports returns 1 if the firewall port is open, 0 if not.
    #
    # check if firewall is active or installed
    return if (! &firewall_is_active());
    if ($port eq $lond_port) {
        my $count ++;
        if (ref($iphost) eq 'HASH') {
            if (keys(%{$iphost}) > 0) {
                foreach my $ip (keys(%{$iphost})) {
                    open(PIPE,"$iptables -L $fw_chain -n 2>/dev/null");
                    while(<PIPE>) {
                        $count++ if (/^ACCEPT\s+tcp\s+\-{2}\s+\Q$ip\E\s+/);
                    }
                    close(PIPE);
                }
            }
        }
        return $count;
    } else {
        if (`$iptables -L -n 2>/dev/null | grep "tcp dpt:$port"`) {
            return 1;
        } else {
            return 0;
        }
    }
}

sub firewall_is_active {
    if (-e '/proc/net/ip_tables_names') {
        return 1;
    } else {
        return 0;
    }
}

sub firewall_close_port {
    my ($iptables,$fw_chain,$lond_port,$ports) = @_;
    return 'inactive firewall' if (!&firewall_is_active());
    return 'port number unknown' if !$lond_port;
    if (! `$iptables -L -n 2>/dev/null | grep $fw_chain | wc -l`) {
        return 'Expected chain "'.$fw_chain.'" missing from iptables'."\n";
    }
    if (ref($ports) ne 'ARRAY') {
        return 'List of ports to close needed.';
    }
    if ($fw_chain =~ /^([\w\-]+)$/) {
        $fw_chain = $1;
    } else {
        return 'Chain name has unexpected format'."\n";
    }
    foreach my $portnum (@{$ports}) {
        my $port = '';
        if ($portnum =~ /^(\d+)$/) {
            $port = $1;
        } else {
            print "Skipped non-numeric port: $portnum\n"; 
            next;
        }
        print "Closing firewall access on port $port\n";
        if (($port ne '') && ($port eq $lond_port)) {
            my (@port_error,@command_error,@lond_port_close);
            my %to_close;
            open(PIPE, "$iptables -n -L $fw_chain |");
            while (<PIPE>) {
                chomp();
                next unless (/dpt:\Q$port\E\s*$/);
                if (/^ACCEPT\s+tcp\s+\-{2}\s+(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+/) {
                    $to_close{$1} = $port;
                }
            }
            close(PIPE);
            if (keys(%to_close) > 0) {
                foreach my $ip (keys(%to_close)) {
                    my $firewall_command =
                        "$iptables -D $fw_chain -p tcp -s $ip -d 0/0 --dport $port -j ACCEPT";
                    system($firewall_command);
                    my $return_status = $?>>8;
                    if ($return_status == 1) {
                        push (@port_error,$ip);
                    } elsif ($return_status == 2) {
                        push(@command_error,$ip);
                    } elsif ($return_status == 0) {
                        push(@lond_port_close,$ip);
                    }
                }
            }
            if (@lond_port_close) {
                print "Port $port closed for ".scalar(@lond_port_close)." IP addresses\n";
            }
            if (@port_error) {
                print "Error closing port $port for following IP addresses: ".join(', ',@port_error)."\n";
            }
            if (@command_error) {
                print "Bad command error opening port for following IP addresses: ".
                      join(', ',@command_error)."\n".
                      'Command was: "'."$iptables -D $fw_chain -p tcp -s ".'$ip'." -d 0/0 --dport $port -j ACCEPT".'", where $ip is IP address'."\n";
            }
        } else {
            my $firewall_command =
                "$iptables -D $fw_chain -p tcp -d 0/0 --dport $port -j ACCEPT";
            system($firewall_command);
            my $return_status = $?>>8;
            if ($return_status == 1) {
                # Error
                print "Error closing port.\n";
            } elsif ($return_status == 2) {
                # Bad command
                print "Bad command error closing port.  Command was\n".
                      "  ".$firewall_command."\n";
            } else {
                print "Port closed.\n";
            }
        }
    }
    return;
}

sub firewall_close_anywhere {
    my ($iptables,$fw_chain,$port) = @_;
    open(PIPE, "$iptables --line-numbers -n -L $fw_chain |");
    while (<PIPE>) {
        next unless (/dpt:\Q$port\E/);
        chomp();
        if (/^(\d+)\s+ACCEPT\s+tcp\s+\-{2}\s+0\.0\.0\.0\/0\s+0\.0\.0\.0\/0/) {
            my $firewall_command = "$iptables -D $fw_chain $1";
            system($firewall_command);
            my $return_status = $?>>8;
            if ($return_status == 1) {
                print 'Error closing port '.$port.' for source "anywhere"'."\n";
            } elsif ($return_status == 2) {
                print 'Bad command error closing port '.$port.' for source "anywhere".  Command was'."\n".
                      ' '.$firewall_command."\n";
            } else {
                print 'Port '.$port.' closed for source "anywhere"'."\n";
            }
        }
    }
    close(PIPE);
}

sub get_lond_port {
    my $perlvarref=&LONCAPA::Configuration::read_conf();
    my $lond_port;
    if (ref($perlvarref) eq 'HASH') {
        if (defined($perlvarref->{'londPort'})) {
            $lond_port = $perlvarref->{'londPort'};
        }
    }
    if (!$lond_port) {
        print("Unable to determine lond port number from LON-CAPA configuration.\n");
    }
    return $lond_port;
}

sub get_fw_chain {
    my ($iptables) = @_;
    my $fw_chain = 'RH-Firewall-1-INPUT';
    my $suse_config = "/etc/sysconfig/SuSEfirewall2";
    if (-e $suse_config) {
        $fw_chain = 'input_ext';
    } else {
        if (!-e '/etc/sysconfig/iptables') {
            if (!-e '/var/lib/iptables') {
                print("Unable to find iptables file containing static definitions\n");
            }
        }
        if ($iptables eq '') {
            $iptables = &get_pathto_iptables();
        }
        my $count = `$iptables -L -n 2>/dev/null |grep $fw_chain |wc -l`;
        chomp($count);
        if (!$count) {
            $fw_chain ='INPUT';
        }
    }
    return $fw_chain;
}

sub get_pathto_iptables {
    my $iptables;
    if (-e '/sbin/iptables') {
        $iptables = '/sbin/iptables';
    } elsif (-e '/usr/sbin/iptables') {
        $iptables = '/usr/sbin/iptables';
    } else {
        print("Unable to find iptables command\n");
    }
    return $iptables;
}

1;
__END__

=pod

=head1 NAME

B<LONCAPA::Firewall> - dynamic opening/closing of firewall ports

=head1 SYNOPSIS

 use lib '/home/httpd/lib/perl/';
 use LONCAPA::Firewall;

 LONCAPA::Firewall::firewall_open_port();
 LONCAPA::Firewall::firewall_close_port();
 LONCAPA::Firewall::firewall_is_port_open();
 LONCAPA::Firewall::firewall_is_active();
 LONCAPA::Firewall::firewall_close_anywhere();

=head1 DESCRIPTION

The scripts: /etc/init.d/loncontrol, used to stop or start LON-CAPA services, 
as well as the setuid script /home/httpd/perl/lciptables, called by loncron 
for housekeeping tasks, make use of the methods provided by this module to 
open and close firewall ports (currently the default port: 5663), used
for socket-based communication between LON-CAPA servers in the cluster
of networked servers to which the server belongs. 

The following methods are available:

=over 4

=item LONCAPA::Firewall::firewall_open_port( $iptables,$fw_chain,$lond_port,$iphost,$port );

=back

=over 4

=item LONCAPA::Firewall::firewall_close_port( $iptables,$fw_chain,$lond_port,$ports );

=back

=over 4

=item LONCAPA::Firewall::firewall_is_port_open( $iptables,$fw_chain,$port,$lond_port,$iphost );

=back

=over 4

=item LONCAPA::Firewall::firewall_is_active();

=back

=over 4

=item LONCAPA::Firewall::firewall_close_anywhere( $iptables,$fw_chain,$port );

=back

=over 4

=item LONCAPA::Firewall::get_lond_port();

=back

=over 4

=item LONCAPA::Firewall::get_fw_chain();

=back

=over 4

=item LONCAPA::Firewall::get_pathto_iptables();


=head1 AUTHORS

This library is free software; you can redistribute it and/or
modify it under the same terms as LON-CAPA itself.

=cut