From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Tolpin <dvd@davidashen.net>
Message-Id: <200403170718.i2H7ICJm083368@adat.davidashen.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Novice question - run as other
In-Reply-To: <5697eeee83e079696212a62a1122c1f9@9netics.com>
Date: Wed, 17 Mar 2004 11:18:12 +0400
Topicbox-Message-UUID: 31f1a4ee-eacd-11e9-9e20-41e7f4b1d025

> > a program from a shell script and change the user it runs as.
>
> The security model doesn't allow this. Perhaps by running it as a service
> on a cpu.  Check /sys/src/cmd/auth/cron.c and cap(3).  For somethings
> you can cpu over and change to a different uid:

The following works:

cpu% cat > test.c
#include <u.h>
#include <libc.h>

void main(int argc,char **argv) {
	int fd = open("#c/user",OWRITE);

	if(argc==1) exits("argument required");
	fd>=0 && (write(fd,"none",strlen("none"))!=-1)
	|| (exits("cannot become none"),1);
	close(fd);

  	exec(argv[1], argv+1);
}
^D
cpu% 8c test.c
cpu% 8l test.8
cpu% 8.out /bin/rc -c 'while () {}'

In another window

cpu% ps -a|grep 8.out
none           4546    0:15   0:00     244K Ready    /bin/rc -c 'while () {}'

How can I do this without the code in C?

David