t_setuid.c

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/*
**  This program checks to see if your version of setuid works.
**  Compile it, make it setuid root, and run it as yourself (NOT as
**  root).
**
**	NOTE:  This should work everywhere, but Linux has the ability
**	to use the undocumented setcap() call to make this break.
**
**  Compilation is trivial -- just "cc t_setuid.c".  Make it setuid,
**  root and then execute it as a non-root user.
*/

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>

#ifndef lint
static char id[] = "@(#)$Id: t_setuid.c,v 8.2.2.1 2000/05/31 00:29:47 gshapiro Exp $";
#endif /* ! lint */

static void
printuids(str, r, e)
	char *str;
	int r, e;
{
	printf("%s (should be %d/%d): r/euid=%d/%d\n", str, r, e,
		getuid(), geteuid());
}

int
main(argc, argv)
	int argc;
	char **argv;
{
	int fail = 0;
	uid_t realuid = getuid();

	printuids("initial uids", realuid, 0);

	if (geteuid() != 0)
	{
		printf("SETUP ERROR: re-run setuid root\n");
		exit(1);
	}

	if (getuid() == 0)
	{
		printf("SETUP ERROR: must be run by a non-root user\n");
		exit(1);
	}

	if (setuid(1) < 0)
		printf("setuid(1) failure\n");
	printuids("after setuid(1)", 1, 1);

	if (geteuid() != 1)
	{
		fail++;
		printf("MAYDAY!  Wrong effective uid\n");
	}

	if (getuid() != 1)
	{
		fail++;
		printf("MAYDAY!  Wrong real uid\n");
	}


	/* do activity here */
	if (setuid(0) == 0)
	{
		fail++;
		printf("MAYDAY!  setuid(0) succeeded (should have failed)\n");
	}
	else
	{
		printf("setuid(0) failed (this is correct)\n");
	}
	printuids("after setuid(0)", 1, 1);

	if (geteuid() != 1)
	{
		fail++;
		printf("MAYDAY!  Wrong effective uid\n");
	}
	if (getuid() != 1)
	{
		fail++;
		printf("MAYDAY!  Wrong real uid\n");
	}
	printf("\n");

	if (fail)
	{
		printf("\nThis system cannot use setuid (maybe use setreuid)\n");
		exit(1);
	}

	printf("\nIt is safe to use setuid on this system\n");
	exit(0);
}