From: harley@engrhub.ucsb.edu (Hahn)
Newsgroups: comp.unix.misc
Subject: Re: Daemons must never die
Date: 5 Nov 92 08:36:02 GMT

In article <49215@shamash.cdc.com> alf@shamash.cdc.com (Alessandro Forghieri) writes:
>
>On the subject of never-dying daemons, I remember an interesting
>discussion took place a few weeks back (maybe on comp.unix.wizards ?) on
>Robin Hood-Friar TUck programs, on of whose purposes was to ensure that
>the companion process would never die.

Here is the story from the Jargon file.

To ftp this file, connect to pit-manager.mit.edu and look
in the /pub/jargon directory.

-- Harley Hahn

----------

     Back in the mid-1970s, several of the system support staff at
     Motorola discovered a relatively simple way to crack system
     security on the Xerox CP-V timesharing system.  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 an intended 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.

     The CP-V people at Xerox sat on their thumbs; they either didn't
     realize the severity of the problem, or didn't assign the necessary
     operating-system-staff resources to develop and distribute an
     official patch.

     Months passed.  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 security
     safeguards could be subverted.

     They dug around in 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.

     One fine 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:

        * Tape drives would rewind and dismount their tapes in the
          middle of a job.
        * Disk drives would seek back and forth so rapidly that they
          would attempt to walk across the floor (see {walking drives}).
        * The card-punch output device would occasionally start up of
          itself and punch a {lace card}.  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.

     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!
          id1: Off (aborted)

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

          id1: Thank you, my good fellow!

     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 OS
     image (the kernel 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.

     It is alleged that Xerox filed a complaint with Motorola's management
     about the merry-prankster actions of the two employees in question.
     It is not recorded that any serious disciplinary action was taken
     against either of them.

--- end ---
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