c++ - 当程序以 root 身份运行时，在运行时切换用户

Question

如果某个 C++ 程序以 root 身份运行，并且我想使用不同的用户执行一些命令并读取该命令的输出，然后再次切换回 root 用户，那么有人可以指导我如何在 Linux 操作系统和 C++ 中实现这一目标吗？

下面是我写的引用代码。有人可以指导我哪个是正确的吗？

#include <iostream>
#include <stdio.h>
#include <string.h>

std::wstring PopenRead(const std::wstring &cmd)
{
    std::wstring res;
    std::string s_cmd(cmd.begin(), cmd.end());
    FILE *f = popen((const char *)s_cmd.c_str(), "r");

    if (f)
    {
            char buffer[1024];
            int cnt;
            int rc;

            while ((cnt = fread(buffer, 1, 1024, f)) > 0)
            {
                    buffer[cnt] = 0;
                    std::string s_val = std::string(buffer);
                    std::wstring wsTmp(s_val.begin(), s_val.end());
                    res += wsTmp;
            }

            rc = pclose(f);
            std::wcout << "Output is: " << res << std::endl;

            return res;
    }
    return L"";
}

int main()
{
    std::wstring command = L"su test_user -c 'ls -ltr /home/test_user'";
    std::wstring exec_res = PopenRead(command);    
    return 0;
}

Answer 1

我尝试使用 popen 和 sudo 命令来执行此操作，因为我使用的是 Ubuntu 18.04 LTS

请找到以下 C++ 代码

#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <array>

int main()
{
   //To switch user as user
   std::string switch_user_command("echo 'userpassword' | sudo -u user 2>&1");

   std::array<char, 128> buffer;
   std::string result;

   std::cout << "Opening reading pipe" << std::endl;
   FILE* pipe;
   pipe  = popen(switch_user_command.c_str(), "r");
   if (!pipe)
   {
      std::cerr << "Couldn't start command." << std::endl;
      return 0;
   }
    while (fgets(buffer.data(), 128, pipe) != NULL) {
       //std::cout << "Reading..." << std::endl;
       result += buffer.data();
   }
   auto returnCode1 = pclose(pipe);

   std::cout << result << std::endl;
   std::cout << returnCode1 << std::endl;

   result.clear();
   //To run ls command
   std::string command("ls 2>&1");
   pipe = popen(command.c_str(), "r");
   if (!pipe)
   {
       std::cerr << "Couldn't start command." << std::endl;
       return 0;
   }
   while (fgets(buffer.data(), 128, pipe) != NULL) {
       //std::cout << "Reading..." << std::endl;
       result += buffer.data();
   }
   auto returnCode2 = pclose(pipe);

   std::cout << result << std::endl;
   std::cout << returnCode2 << std::endl;

   //To run command  as root/sudo
   result.clear();
   std::cout << "Trying to run ls as sudo .. " << std::endl;
   std::string switch_root_command("echo 'sudopassword' | sudo -S ls 2>&1");

   pipe = popen(switch_root_command.c_str(), "r");
   if (!pipe)
   {
       std::cerr << "Couldn't start command." << std::endl;
       return 0;
   }
   while (fgets(buffer.data(), 128, pipe) != NULL) {
      //std::cout << "Reading..." << std::endl;
      result += buffer.data();
   }
   auto returnCode3 = pclose(pipe);

   std::cout << result << std::endl;
   std::cout << returnCode3 << std::endl;

  return 0;
  }

请使用以下命令在g++中编译

g++ prog.cpp -o prog -std=c++11

这会产生以下输出(因为我没有任何“用户”帐户)

Opening reading pipe
sudo: unknown user: user
sudo: unable to initialize policy plugin

256
1.cpp
2
2.cpp

0
Trying to run ls as sudo ..
1.cpp
2
2.cpp
0
abhi

0

希望对您有帮助!