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-- Shooting Shark
Contributing Editor
Note: For now you can contact Phrack Inc. at:
Lunatic Labs: 415-278-7421 300/1200 (Sir Francis Drake or Elric of Imrryr)
Free World: 301-668-7657 300/1200/2400/9600 (Disk Jockey)
Phrack XV Table of Contents
===========================
15-1. Phrack XV Intro by Shooting Shark (2K)
15-2. More Stupid Unix Tricks by Shooting Shark (10K)
15-3. Making Free Local Payfone Calls by Killer Smurf (7K)
15-4. Advanced Carding XIV by The Disk Jockey (12K)
15-5. Gelled Flame Fuels by Elric of Imrryr (12K)
15-6. PWN I: The Scoop on Dan The Operator by KL (19K)
15-7. PWN II: The July Busts by Knight Lightning (21K)
15-8. PWN III: The Affidavit by SFD (6K)
===== Phrack Magazine presents Phrack 15 =====
===== File 2 of 8 =====
I thought I had written everything there is to write about the Unix operating
system until I was recently asked to put out yet another file... so I said
"I'll try, but don't publish my file along with an article by The Radical
Rocker this time!" These demands having been met, I booted up the PC and
threw together...
--- ---- ---- ------ ------ -- -- ---- -----
% Yet Even More Stupid Things to Do With Unix! $
--- ---- ---- ------ ------ -- -- ---- -----
By Shooting Shark.
Submitted August 26, 1987
These two topics are methods of annoying other users of the system and
generally being a pest. But would you want to see a file on *constructive*
things to do with Unix? Didn't think so...
-- ------- ----- --- --- ------
1. Keeping Users Off The System
-- ------- ----- --- --- ------
Now, we all know by now how to log users off (one way is to redirect an 'stty
0' command to their tty) but unless you have root privs, this will not work
when a user has set 'mesg n' and prevented other users from writing to their
terminal. But even users who have a 'mesg n' command in their .login (or
.profile or .cshrc) file still have a window of vulnerability, the time
between login and the locking of their terminal. I designed the following
program, block.c, to take advantage of this fact.
To get this source running on your favorite Unix system, upload it, call it
'block.c', and type the following at the % or $ prompt:
cc -o block block.c
once you've compiled it successfully, it is invoked like so:
block username [&]
The & is optional and recommended - it runs the program in the background,
thus letting you do other things while it's at work.
If the user specified is logged in at present, it immediately logs them out
(if possible) and waits for them to log in. If they aren't logged in, it
starts waiting for them. If the user is presently logged in but has their
messages off, you'll have to wait until they've logged out to start the thing
going.
Block is essentially an endless loop : it keeps checking for the occurrence of
the username in /etc/utmp. When it finds it, it immediately logs them out and
continues. If for some reason the logout attempt fails, the program aborts.
Normally this won't happen - the program is very quick when run unmodified.
However, to get such performance, it runs in a very tight loop and will eat up
a lot of CPU time. Notice that near the end of the program there is the line:
/*sleep(SLEEP) */
the /* and */ are comment delimiters - right now the line is commented out.
If you remove the comments and re-compile the program, it will then 'go to
sleep' for the number of seconds defined in SLEEP (default is 5) at the end of
every loop. This will save the system load but will slightly decrease the
odds of catching the user during their 'window of vulnerability.'
If you have a chance to run this program at a computer lab at a school or
somewhere similar, run this program on a friend (or an enemy) and watch the
reaction on their face when they repeatedly try to log in and are logged out
before they can do *anything*. It is quite humorous. This program is also
quite nasty and can make you a lot of enemies!
caveat #1: note that if you run the program on yourself, you will be logged
out, the program will continue to run (depending on the shell you're under)
and you'll have locked yourself out of the system - so don't do this!
caveat #2: I wrote this under OSx version 4.0, which is a licensed version of
Unix which implements 4.3bsd and AT&T sysV. No guarantees that it will work