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From: msw@unix.cis.pittsburgh.edu (Matt S Wartell)
Newsgroups: comp.unix.questions
Subject: SUID usage accounting under 4.2BSD
Summary: does real or effective user id get charged for cpu usage on SUID prog.
Keywords: SUID accounting 4.2BSD
Message-ID: <18663@unix.cis.pittsburgh.edu>
Date: 7 Jul 89 14:42:45 GMT
Reply-To: msw@unix.cis.pittsburgh.edu (Matt S Wartell)
Distribution: na
Organization: University of Pittsburgh
Lines: 29

Under 4.2BSD, who gets charged for the running of an SUID program?

I have a program that needs to write to a log-file which should not
be world writable.  Therefore I am using a 4755 mode on the program
which is owned by me. 

If another user runs my program, will he be charged for the cpu
usage or will I?  If I am charged for time spent while another user
is executing my program, can I `reverse the charges' with:

	write_logfile();
	seteuid(getuid());
	/* program now runs under user's real ID and get charged to him */

Finally, if I can use the above code, can I do the following:

	euid = geteuid();
	seteuid(getuid());
	/* do unprivileged processing */
	seteuid(euid);
	/* do privileged writes */

I don't think so.  Is there perhaps another way of doing this without,
say, forking a child which resets its euid and piping info back to a
privileged parent?

Please respond via mail, I will summarize.
-- 
matt wartell, university of pittsburgh             msw@unix.cis.pittsburgh.edu