Re: One process with multiple user ids.

[Bill Davidsen <davidsen@tmr.com>]

Giuliano Gagliardi wrote:
> Hello,
> 
> I have a server that has to switch to different user ids, but because it does 
> other complex things, I would rather not have it run as root. I only need the 
> server to be able to switch to certain pre-defined user ids.
> 
> I have seen that two possible solutions have already been suggested here on 
> the LKML, but it was some years ago, and nothing like it has been 
> implemented.
> 
> (1) Having supplementary user ids like there are supplementary group ids and 
> system calls getuids() and setuids() that work like getgroups() and 
> setgroups()
> 
> (2) Allowing processes to pass user and group ids via sockets.
> 
> Both (1) and (2) would solve my problem. Now my question is whether there are 
> any fundamental flaws with (1) or (2), or whether the right way to solve my 
> problem is another one.
> 
Changing to a limited set of IDs is interesting, I have never looked at 
what happens when a thread does setuid, and neither the man page or a 
very quick look at the code tells me. But the portable way is to do the 
things needed for init, then fork into three processes and give each a 
UID as needed. I would really evaluate the design which made this 
necessary, to see if some IPC could be used. Certainly that's more 
likely to be portable.

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot