Path: utzoo!attcan!uunet!mcsun!hp4nl!tuegate.tue.nl!rcpt
From: rcpt@tuegate.tue.nl (Piet Tutelaers)
Newsgroups: comp.lang.perl
Subject: CPWI - Strange side effects in perl program!
Keywords: system management exercise
Message-ID: <1778@tuegate.tue.nl>
Date: 9 Jun 90 16:39:59 GMT
Organization: Eindhoven University of Technology, The Netherlands
Lines: 108


Last week I tried to do my programming in Perl instead of Bourne shell.
I like the language and you NEED some practice after all :-). 

I wanted a program that could be installed as the login shell for a user
so that when he logs in he is forced to change his password immediately. 
When he does so he get's back his original shell which is derived from a
copy of the passwd file.  When I tested the perl-program, shown at the
end, I was unpleasantly surprised that the program had a NASTY SIDE
EFFECT.  For the user `rctest' I had put the `/someplace/cpwi' shell in
/etc/passwd, his originally shell saved in /etc/opasswd was the
/bin/csh.  When rctest logged in, and changed his password, he gets the
the default shell (!) AND in the opasswd file this /bin/chs changes to cpwi!

/etc/passwd (before login of rctest):
rctest:hisoldpasswd:UID:GID:Test:/his/home:/someplace/cpwi
/etc/opasswd (before login of rctest):
rctest:hisoldpasswd:UID:GID:Test:/his/home:/bin/csh
/etc/passwd (after login of rctest):
rctest:hisnewpasswd:UID:GID:Test:/his/home:
                                           ^^ Why? 
/etc/opasswd (after login of rctest):
rctest:hisoldpasswd:UID:GID:Test:/his/home:/someplace/cpwi
                                           ^^^^^^^^^^^^^^^ Why? 
The logfile showed:
 9 Jun 18:04.03 ** rctest ** password changed, shell `'.

Am I doing something stupid in my perl program? In the mean time we have
written a Bourne shell script, but I would like to know what can be the
reason for this behaviour. Which perl-expert shines his light on this?

I have to mention the fact that I used `perl -u cpwi' and `undump' to create
a compiled version op cpwi, because I need the group ID facility to
write into the logfile. The version of `chsh' we have on Ultrix3.1 does not
allow a user to change to a shell other than the default or some tolerated
shells (csh). Lastly, show is a stripped version of more(1) which does not
allow shell escapes and jumping into an editor. Perhaps this can be done
also easily in perl?

Piet Tutelaers
rcpt@urc.tue.nl

----------cpwi-----------------------------------------------------
#!/usr/bin/perl

#
# Perl script to force a user to change his password at login time. After
# changing the password the loginshell, being this command, will be
# restored to the value obtained from /etc/oldpasswd. 
#

$LOGFILE="/etc/pwlog";
$OLDPASSWD="/etc/opasswd";
$changed_pw=0;

&message; 			# give some explanation

($user, $encrypt, $UID, $GID, $quota, $comment, $gecos, $home, $shell)
   = getpwuid("$<");

system "/bin/passwd", $user;

($newuser, $newencrypt) = getpwuid("$<");

if ($encrypt ne $newencrypt) {
   $changed_pw=1;
   open(oldpasswd, $OLDPASSWD) || die "Can't open $OLDPASSWD\n";
   while (<oldpasswd>) {
      chop;
      ($USER, $ENCRYPT, $uid, $gid, $GECOS, $HOME, $SHELL) = split(/:/);
      last if ($USER eq $user);
   }
   close(oldpasswd);
   if ("$USER:$uid:$gid:$HOME" eq "$user:$UID:$GID:$home") {
      if ($SHELL eq "/bin/csh") {
         system '/usr/ucb/chsh',$user,$SHELL;
      }
      else {
         system '/usr/ucb/chsh',$user;
      }
   }
}
else {
   system '/bin/echo', '## YOU DID NOT CHANGE YOUR PASSORD! ##';
}

($user, $encrypt, $UID, $GID, $quota, $comment, $gecos, $home, $shell)
   = getpwuid("$<");

@mo = ('Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec');
($usec,$umin,$uhour,$umday,$umon) = localtime(time);

open(logfile, ">>$LOGFILE") || die "Can't open $LOGFILE\n";
printf logfile "%2d %s %02d:%02d.%02d", $umday, $mo[$umon],$uhour,$umin,$usec;

if ($changed_pw) {
   print logfile " ** $user ** password changed, shell `$shell'.\n";
}
else {
   print logfile " ** $user ** password not changed!\n";
}
close(logfile);

system '/bin/echo', '## YOU WILL NOW BE LOGGED OUT, LOGIN AGAIN. ##';

sub message {
   system 'someplace/show', '/someplace/cpwi.txt';
}