changing user id's

[utzoo!decvax!ucbvax!menlo70!sri-unix!lauren at UCLA-Security]

From: lauren at UCLA-Security (Lauren Weinstein)
Given a process whose real uid != 0 and
whose effective uid == 0 ...

What would be the CLEANEST manner to allow that process to TEMPORARILY
act as if its effective uid were set to equal its real uid?

To put it another way, what would be the cleanest change to the kernel
(such as a new system call or mods to setuid) that would allow a 
process to temporarily act as if it had lower privs than it really
does, but still get its full privs back later if it needs to?

Any suggestions would be welcomed.  Thanks .

--Lauren--