【Writeup】Pwnable.kr 0x01 fd

0x01 fd

题目描述：

Mommy! what is a file descriptor in Linux?

* try to play the wargame your self but if you are ABSOLUTE beginner, follow this tutorial link: https://www.youtube.com/watch?v=blAxTfcW9VU

ssh [email protected] -p2222 (pw:guest)

解题思路：

ssh连接上去后ls发现有fd fd.c flag三个文件
cat fd.c得到源代码

#include 
#include 
#include 
char buf[32];
int main(int argc, char* argv[], char* envp[]){
        if(argc<2){
                printf("pass argv[1] a number\n");
                return 0;
        }
        int fd = atoi( argv[1] ) - 0x1234;
        int len = 0;
        len = read(fd, buf, 32);
        if(!strcmp("LETMEWIN\n", buf)){
                printf("good job :)\n");
                system("/bin/cat flag");
                exit(0);
        }
        printf("learn about Linux file IO\n");
        return 0;
}

这道题的题目说的是fd，fd是文件描述符，查阅资料发现fd为0，1，2分别代表stdin,stdout,stderr,所以本题需要让fd为0，然后输入LETMEWIN就可以通过if判断，得到flag了，atoi函数是将字符串转换为整数的，0x1234的十进制为4660，那么参数为4660，运行./fd 4660然后输入LETMEWIN，即可得到flag。