Real and effective userids.

[Piercarlo Grandi]

In article <PCG.89Oct3145353 at thor.cs.aber.ac.uk> pcg at thor.cs.aber.ac.uk (Piercarlo Grandi) writes:
    
    An obvious generalization is to have real (accounting) and
    effective (protection) owners for files as well. This would solve
    some problems with file ownership and accounting for closed
    subsystems (notably ingres and the spoolers) that implement their
    own protection policies, and thus need to give access to files
    only to their own setuid programs, but do not want the space
    taken up to be debited to them.

It would also solve the famous chown problem. Currently either chown is
allowed anybody, and then anybody may cheat filespace accounting (by
chowning their files to somebody's else account), or only root (and then
you must write a chown utility that asks for passwords).

If we had "chown -[er]" and user A wanted to let user B acquire
ownership of a file, the following sequence would do the trick with
perfect safety:

	user A: chown -e B file
	user B: chown -r B file

with a rule that the [er]owner may change the other owner id to itself.

User A has no qualms in making B the eowner, after all it wants to transfer
the actual ownership; user B then may actually acquire the rownership. If
user B does not, user A can always revert the eownership to itself.
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk at nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg at cs.aber.ac.uk