//----------------------------------------------------------------
//	iopl3.cpp
//
//	This utility program, if compiled by the 'root' user and
//	given the 'setuid' file-attribute, lets an ordinary user
//	launch Linux applications that modify the effective IOPL 
//	(Input/Output Privilege Level) with the 'iopl()' system- 
//	call.  When IOPL==3, an application can do direct device
//	input/output programming, and can enable/disable device-
//	interrupts temporarily so as to inhibit task preemption.  
//
//	    compile as 'root' with: root# make iopl3
//	                            root# chmod a+s iopl3
//
//	    execute as 'user' with: user$ iopl3 
//
//	Thereafter, application programs can invoke 'iopl( 3 )'.
//
//	programmer: Alex Fedosov
//	written in: Autumn 2002
//----------------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/io.h>

int main(int argc, char *argv[])
{
        int uid = getuid();

        printf("%d\n", getuid());
        setuid(0);

        iopl(3);

        printf("%d\n", getuid());

        setuid(uid);

        printf("%d\n", getuid());

        system("bash --login");

        return 0;
}