#!/usr/bin/perl
###################################################################
# identd.perl5 : An implementation of RFC 1413 Ident Server
# using Vic Abell's lsof.
#
# - Started from inetd with 'nowait' option. This entry in
# /etc/inetd.conf will suffice :
#
# ident stream tcp nowait root /usr/local/bin/identd.perl5 -t200
#
# - Multiple instances of the server are not a performance penalty
# since they shall use lsof's cacheing mechanism. (compare with
# Peter Eriksson's pidentd)
# - assumes 'lsof' binary in $PATH
# - Command line arguments :
# -t TIMEOUT Number of seconds to wait for a query before aborting.
# Default is 120.
#
# Kapil Chowksey <[email protected]>
###################################################################

use Socket;
use Getopt::Std;

# Set path to lsof.

if (($LSOF = &isexec("../lsof")) eq "") { # Try .. first
if (($LSOF = &isexec("lsof")) eq "") { # Then try . and $PATH
print "can't execute $LSOF\n"; exit 1
}
}

# redirect lsof's warnings/errors to /dev/null
close(STDERR);
open(STDERR, ">/dev/null");

$Timeout = "120";

&getopts('t:');
if ($opt_t) {
$Timeout = $opt_t;
}

($port, $iaddr) = sockaddr_in(getpeername(STDIN));
$peer_addr = inet_ntoa($iaddr);

# read ident-query from socket (STDIN) with a timeout.
$timeout = int($Timeout);
eval {
local $SIG{ALRM} = sub { die "alarm\n" };
alarm $timeout;
$query = <STDIN>;
alarm 0;
};
die if $@ && $@ ne "alarm\n";
if ($@) {
# timed out
exit;
}

# remove all white-spaces from query
$query =~ s/\s//g;

$serv_port = "";
$cli_port = "";
($serv_port,$cli_port) = split(/,/,$query);

if ($serv_port =~ /^[0-9]+$/) {
if (int($serv_port) < 1 || int($serv_port) > 65535) {
print $query." : ERROR : INVALID-PORT"."\n";
exit;
}
} else {
print $query." : ERROR : INVALID-PORT"."\n";
exit;
}

if ($cli_port =~ /^[0-9]+$/) {
if (int($cli_port) < 1 || int($cli_port) > 65535) {
print $query." : ERROR : INVALID-PORT"."\n";
exit;
}
} else {
print $query." : ERROR : INVALID-PORT"."\n";
exit;
}

open(LSOFP,"$LSOF -nPDi -T -FLn -iTCP@".$peer_addr.":".$cli_port."|");

$user = "UNKNOWN";
while ($a_line = <LSOFP>) {
# extract user name.
if ($a_line =~ /^L.*/) {
($user) = ($a_line =~ /^L(.*)/);
}

# make sure local port matches.
if ($a_line =~ /^n.*:\Q$serv_port->/) {
print $serv_port.", ".$cli_port." : USERID : UNIX :".$user."\n";
exit;
}
}

print $serv_port.", ".$cli_port." : ERROR : NO-USER"."\n";


## isexec($path) -- is $path executable
#
# $path = absolute or relative path to file to test for executabiity.
# Paths that begin with neither '/' nor '.' that arent't found as
# simple references are also tested with the path prefixes of the
# PATH environment variable.

sub
isexec {
my ($path) = @_;
my ($i, @P, $PATH);

$path =~ s/^\s+|\s+$//g;
if ($path eq "") { return(""); }
if (($path =~ m#^[\/\.]#)) {
if (-x $path) { return($path); }
return("");
}
$PATH = $ENV{PATH};
@P = split(":", $PATH);
for ($i = 0; $i <= $#P; $i++) {
if (-x "$P[$i]/$path") { return("$P[$i]/$path"); }
}
return("");
}