#!/usr/bin/perl
# block - maintain firewall block rules for specified hosts based on specific events
# vi: set sw=4 ts=4 tw=0:

use strict;
use warnings;

use Sys::Syslog;
use Getopt::Long;
use File::Tail;

our @patterns = ('pam_unix\(sshd:auth\): authentication failure; logname=\S* uid=\d* euid=\d* tty=\S* ruser=\S* rhost=(\S*)');
our $maxhits = 3;
our $keeptime = 1;
our $chain = "BLOCK";
our %hits;
our $phone = "0415439838";

openlog "block", "ndelay,pid", "user"
	or die "Cannot open connection to log server\n";

# modes
#my $clean;		# unblock all IP addresses not seen in last $keeptime minutes
my $block;		# block specified IP address
my $daemon;		# fork and continue running in the background as a daemon
my $unblock;	# unblock specified IP address
my $monitor;	# read from the specified file, taking action on lines matching @patterns
my $simulate;	# simulation only, no blocking is done
my $list;		# list blocked addresses
my $help;		# show a brief usage message

our $verbose;	# print debugging messages to STDERR

sub sendsms
{
	system('smssend "' . $phone . '" "' . "@_" . '"');
}

sub notice
{
	syslog("notice", @_);
	sendsms(@_);
}

sub error
{
	syslog("err", @_);
	sendsms(@_);
}

sub debug
{
	syslog("debug", @_);
}

sub usage
{
	print STDERR "Block:    block -b <host>\n";
	print STDERR "Unblock:  block -u <host>\n";
	print STDERR "List:     block -l\n";
	print STDERR "Monitor:  block -m <file>\n";
	print STDERR "Simulate: block -n [other options]\n";
	print STDERR "Daemon:   block -d [other options]\n";
	print STDERR "Verbose:  block -v [other options]\n";
}

GetOptions('add|block|a|b=s' => \$block,
		   'daemon|d' => \$daemon,
		   'monitor|m=s' => \$monitor,
		   'remove|unblock|r|u=s' => \$unblock,
		   'list|l' => \$list,
		   'help|h' => \$help,
		   'test|simulate|t|s|n' => \$simulate,
		   'verbose|v' => \$verbose)
	or print STDERR "Error reading options\n", usage(), exit(2);

if (defined($block)) {
	block($block);
}
if (defined($unblock)) {
	unblock($unblock);
}
if (defined($list)) {
	list();
}
if (defined($daemon)) {
	daemonize();
}
if (defined($monitor)) {
	monitor($monitor);
}
if (defined($help)) {
	usage();
}

exit(0);

# get the iptables rule for the given address
# this must be the same for block and unblock, so we generalize it here
sub rule
{
	my $host = shift @_;

	return "-s $host -j REJECT";
}

sub block
{
	my $host = shift @_;

	my $rule = rule($host);
	if ($host =~ /^(0|127|172|192)\./) {
		notice("Not blocking special network address $host");
	}
	else {
		if (defined($simulate)) {
			notice("Would block $host");
		}
		else {
			if (system("/sbin/iptables -A $chain $rule") == 0) {
				notice("Blocked $host");
			}
			else {
				error("Error blocking $host");
			}
		}
	}
}

sub unblock
{
	my $host = shift @_;

	my $rule = rule($host);
	if (defined($simulate)) {
		notice("Would unblock $host");
	}
	else {
		if (system("/sbin/iptables -D $chain $rule") == 0) {
			notice("Unblocked $host");
		}
		else {
			error("Error unblocking $host");
		}
	}
}

sub daemonize
{
	my $pid = fork();
	if (!defined($pid)) {
		error("Fork failed, cannot daemonize");
		exit(1);
	}
	if ($pid == 0) {
		debug("FORKED");
		# child, continue
		close(STDERR);
		close(STDOUT);
		close(STDIN);
	}
	else {
		debug("PARENT EXITING (CHILD IS $pid)");
		exit(0);
	}
}

# Watch a file and block a host if it matches more than $maxhits times
sub monitor
{
	my $filename = shift @_;

	my @files;
	push(@files, File::Tail->new($filename));
	while (1) {
		debug("READING");
		my $timeout = 10;	# this must be > 0
		my ($nfound, $timeleft, @pending) = File::Tail::select(undef, undef, undef, $timeout, @files);
		if (!$nfound) {
			debug("TIMED OUT");
		}
		elsif (@pending) {
			debug("PENDING INPUT");
			foreach my $file (@pending) {
				my $line = $file->read();
				chomp $line;
				debug("LINE IS $line");

				foreach my $pattern (@patterns) {
					if ($line =~ /$pattern/) {
						my $host = $1;
						push @{$hits{$host}}, time();
						debug("$host");

						my $nhits = @{$hits{$host}};
						if ($nhits > $maxhits) {
							debug("BLOCK $host");
							block($host);
						}
						else {
							debug("HIT $nhits for $host");
						}
					}
				}
			}
		}
		cleanup();
	}
}

# Delete and unblock entries older than $keeptime minutes
sub cleanup
{
	my $time = time();
	my $expirytime = $time - $keeptime * 60;

	foreach my $host (keys %hits) {
		my @hits = @{$hits{$host}};
		foreach my $i (0..scalar(@hits)-1) {
			my $hit = $hits[$i];
			if ($hit < $expirytime) {
				debug("Deleting old entry for $host");
				debug("OLD @{$hits{$host}}");
				delete ${$hits{$host}}[$i];
				debug("NEW @{$hits{$host}}");
			}
		}
		if (@{$hits{$host}} < $maxhits) {
			notice("Unblocking $host after $keeptime minutes");
			unblock($host);
		}
	}
}

# Show the list of hosts currently blocked
sub list
{
	debug("LISTING");
	system("/sbin/iptables -L $chain -n");
}