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SubjectRe: inheritable set [was Re: caps in elf headers: use the sticky bit!]
   Date: 	Sat, 17 Apr 1999 15:11:45 +0200
From: Pavel Machek <pavel@bug.ucw.cz>

Which only means that "more" should have inheritable set equal to
zero. I _still_ do not see why setting inheritable set should be
privileged operation.

If it's not a privileged operation, then the attacker can change the
inheritable set of "more" first....
Ok, given example with "more"... I do not think inheritable set of
"more" set to NULL would help: even if it was that way, shell executed
from more would have uid == 0 and no privileges. But what user owns
/etc/passwd? uid == 0. And I've got a shell with... uid == 0. So I do
not need any privilege (it is owned by same uid!) to edit /etc/passwd
and you are screwed; anyway. I could this be solved in "pure
capabilities" system, but I do not see how you want to fit protection
against "more" attack and still be unix.

You can do full POSIX capabilities and still be Unix; and the way you
solve this problem using model outlined by the POSIX capabilities draft
is that /usr/ucb/Mail would no longer be setuid root, so "more" would not
be running with uid 0, and neither would the shell executing from more.
/usr/ucb/Mail would instead have a capability which allowed it to
override filesystem discretionary access controls, or whatever other
capabilities/privileges it needed. But it would not need to be setuid
root.

- Ted

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