Switch user at run time when program runs as root - c++

Question

If some c++ program runs as root and i want to execute some of the commands with different user and read the output of that command and again switch back to root user so can someone guide me how to achieve that in linux OS & c++ ?
Below is the reference code i wrote. Can someone guide me which is correct or not ?
#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

I tried to do it using popen and sudo command as I'm using Ubuntu 18.04 LTS
Please find below code in C++
#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;
}
Please use below command to compile in g++
g++ prog.cpp -o prog -std=c++11
This produces below output (as I don't have any 'user' account)
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
I hope it helps!