test9_8.txt

Linux下的C语言编程

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <stdarg.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>

void enhancedperms(void);
void normalperms(void);
void tryopen(void);

int ruid, euid;

int main(void)
{
    	ruid=getuid();
    	euid=geteuid();
    	normalperms();

    	if(ruid==euid)
    	{
        	printf("euid%4d: Warning:this program wasn;t marked setuid in the filesystem \n", euid);
        	printf("euid%4d: or you running the program ar root.\n", euid);
    	}

    	tryopen();
    	enhancedperms();
    	tryopen();
    	normalperms();

    	printf("euid%4d: Exiting now. \n", euid);
    	return 0;
}


void enhancedperms(void)
{
    	if(seteuid(euid)==-1)
    	{
        	printf("euid%4d: Railed to switch to enhanced permissions:%s.\n", euid, sys_errlist[errno]);
        	exit(255);
    	}
    	else
    	{
        	printf("euid%4d: Switched to enhanced permissions. \n");
    	}
}


void normalperms(void)
{
    	if(seteuid(ruid)==-1)
    	{
        	printf("euid%4d: Failed to switch to normal permissions: %s. \n", euid, sys_errlist[errno]);
        	exit(255);
    	}
    	else
    	{
        	printf("euid%4d: Switched to enhanced permissions. \n");
    	}
}


void tryopen(void)
{
    	char *filename="/etc/shadow";
    	int result;

	if(result=open(filename, O_RDONLY)==-1)
	{
    		printf("euid%4d: Open failed: %s.\n", euid, sys_errlist[errno]);
	}
	else
	{
    		printf("euid%4d: Open was successful.\n", euid);
    		close(result);
	}
}