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The following story was posted in news.sysadmin recently.

The more things change, the more they stay the same...

Back in the mid-1970s, several of the system support staff at Motorola (I believe it was) discovered a relatively simple way to crack system security on the Xerox CP-V timesharing system (or it may have been CP-V's predecessor UTS). Through a simple programming strategy, it was possible for a user program to trick the system into running a portion of the program in "master mode" (supervisor state), in which memory protection does not apply. The program could then poke a large value into its "privilege level" byte (normally write-protected) and could then proceed to bypass all levels of security within the file-management system, patch the system monitor, and do numerous other interesting things. In short, the barn door was wide open.

Motorola quite properly reported this problem to XEROX via an official "level 1 SIDR" (a bug report with a perceived urgency of "needs to be fixed yesterday"). Because the text of each SIDR was entered into a database that could be viewed by quite a number of people, Motorola followed the approved procedure: they simply reported the problem as "Security SIDR," and attached all of the necessary documentation, ways-to-reproduce, etc. separately.

Xerox apparently sat on the problem... they either didn't acknowledge the severity of the problem, or didn't assign the necessary operating-system-staff resources to develop and distribute an official patch.

Time passed (months, as I recall). The Motorola guys pestered their Xerox field-support rep, to no avail. Finally they decided to take Direct Action, to demonstrate to Xerox management just how easily the system could be cracked, and just how thoroughly the system security systems could be subverted.

They dug around through the operating-system listings, and devised a thoroughly devilish set of patches. These patches were then incorporated into a pair of programs called Robin Hood and Friar Tuck. Robin Hood and Friar Tuck were designed to run as "ghost jobs" (daemons, in Unix terminology); they would use the existing loophole to subvert system security, install the necessary patches, and then keep an eye on one another's statuses in order to keep the system operator (in effect, the superuser) from aborting them.

So... one day, the system operator on the main CP-V software-development system in El Segundo was surprised by a number of unusual phenomena. These included the following (as I recall... it's been a while since I heard the story):

• Tape drives would rewind and dismount their tapes in the middle of a job.
• Disk drives would seek back&forth so rapidly that they'd attempt to walk across the floor.
• The card-punch output device would occasionally start up of itself and punch a "lace card" (every hole punched). These would usually jam in the punch.
• The console would print snide and insulting messages from Robin Hood to Friar Tuck, or vice versa.
• The Xerox card reader had two output stackers; it could be instructed to stack into A, stack into B, or stack into A unless a card was unreadable, in which case the bad card was placed into stacker B. One of the patches installed by the ghosts added some code to the card-reader driver... after reading a card, it would flip over to the opposite stacker. As a result, card decks would divide themselves in half when they were read, leaving the operator to recollate them manually.

I believe that there were some other effects produced, as well.

Naturally, the operator called in the operating-system developers. They found the bandit ghost jobs running, and X'ed them... and were once again surprised. When Robin Hood was X'ed, the following sequence of events took place:

  !X id1 

  id1:   Friar Tuck... I am under attack!  Pray save me!  (Robin Hood) 
  id1: Off (aborted) 

  id2: Fear not, friend Robin!  I shall rout the Sheriff of Nottingham's men! 

  id3: Thank you, my good fellow! (Robin) 

Each ghost-job would detect the fact that the other had been killed, and would start a new copy of the recently-slain program within a few milliseconds. The only way to kill both ghosts was to kill them simultaneously (very difficult) or to deliberately crash the system.

Finally, the system programmers did the latter... only to find that the bandits appeared once again when the system rebooted! It turned out that these two programs had patched the boot-time image (the /vmunix file, in Unix terms) and had added themselves to the list of programs that were to be started at boot time...

The Robin Hood and Friar Tuck ghosts were finally eradicated when the system staff rebooted the system from a clean boot-tape and reinstalled the monitor. Not long thereafter, Xerox released a patch for this problem.

I believe that Xerox filed a complaint with Motorola's management about the merry-prankster actions of the two employees in question. To the best of my knowledge, no serious disciplinary action was taken against either of these guys.

Several years later, both of the perpetrators were hired by Honeywell, which had purchased the rights to CP-V after Xerox pulled out of the mainframe business. Both of them made serious and substantial contributions to the Honeywell CP-6 operating system development effort. Robin Hood (Dan Holle) did much of the development of the PL-6 system-programming language compiler; Friar Tuck (John Gabler) was one of the chief communications-software gurus for several years. They're both alive and well, and living in LA (Dan) and Orange County (John). Both are among the more brilliant people I've had the pleasure of working with.

Disclaimers: it has been quite a while since I heard the details of how this all went down, so some of the details above are almost certainly wrong. I shared an apartment with John Gabler for several years, and he was my Best Man when I married back in '86... so I'm somewhat predisposed to believe his version of the events that occurred.

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