runas-stdio: A variant of runas which takes all its parameters as UTF-8 strings via stdio.

runas-stdio.cpp

// Released into the public domain.
// http://creativecommons.org/publicdomain/zero/1.0/

#include <string>

#include <cstdio>

#include <fcntl.h>
#include <io.h>
#include <windows.h>

/** The name of the program, taken from wargv[0]. */
static const wchar_t *progname = L"runas-stdio";

static std::wstring widen(std::string str)
{
	if (str.length() == 0)
	{
		return std::wstring();
	}

	// what's the size?
	int size = MultiByteToWideChar(CP_UTF8, 0, str.c_str(), static_cast<int>(str.length()), nullptr, 0);
	if (size == 0)
	{
		fwprintf(stderr, L"%ls: Failed to deduce buffer size for wide string: %lu\n", progname, GetLastError());
		abort();
	}

	std::wstring ret(static_cast<unsigned int>(size), L'\0');

	if (MultiByteToWideChar(CP_UTF8, 0, str.c_str(), static_cast<int>(str.length()), &ret[0], static_cast<int>(ret.size())) != size)
	{
		fwprintf(stderr, L"%ls: Failed to convert UTF-8 string to wide string: %lu\n", progname, GetLastError());
		abort();
	}

	return ret;
}

static std::string readUntilNul(const wchar_t *readingWhat)
{
	std::string ret;
	int c;
	for (;;)
	{
		c = fgetc(stdin);
		if (c == '\0')
		{
			break;
		}
		else if (c == EOF)
		{
			fwprintf(stderr, L"%ls: Encountered error or EOF while reading \n", readingWhat);
			abort();
		}
		else
		{
			ret += static_cast<char>(c);
		}
	}
	return ret;
}

int wmain(int argc, wchar_t **wargv)
{
	if (argc > 0 && wargv != nullptr && wargv[0] != nullptr && wargv[0][0] != L'\0')
	{
		progname = wargv[0];
	}

	if (argc > 1)
	{
		fwprintf(stderr,
			L"\n"
			L"Usage: %ls\n"
			L"\n"
			L"Send the following information in UTF-8 on stdin:\n"
			L"1. The username (DOMAIN\\User or [email protected]).\n"
			L"2. A NUL byte.\n"
			L"3. The password.\n"
			L"4. A NUL byte.\n"
			L"5. The full command line to execute.\n"
			L"6. A NUL byte.\n",
			progname
		);
		return 1;
	}

	// set stdin to binary
	_setmode(_fileno(stdin), _O_BINARY);

	// username, then password, then command
	std::string username = readUntilNul(L"username");
	std::string password = readUntilNul(L"password");
	std::string command = readUntilNul(L"command");

	std::string::size_type backslash = username.find("\\");
	bool haveDomain = false;
	std::string domain;
	if (backslash != std::string::npos)
	{
		// split username into domain and password
		haveDomain = true;
		domain = username.substr(0, backslash);
		username = username.substr(backslash + 1);
	}

	// we'll need this as a modifiable buffer
	std::wstring wideCommand = widen(command);

	// go
	STARTUPINFOW si;
	memset(&si, 0, sizeof(si));
	si.cb = sizeof(si);
	PROCESS_INFORMATION pi;
	int ret = CreateProcessWithLogonW(
		widen(username).c_str(),
		haveDomain ? widen(domain).c_str() : nullptr,
		widen(password).c_str(),
		LOGON_WITH_PROFILE,
		nullptr,  // application name (part of command line)
		&wideCommand[0],
		CREATE_DEFAULT_ERROR_MODE | CREATE_UNICODE_ENVIRONMENT,
		nullptr,  // environment (inherit)
		nullptr,  // working dir (inherit)
		&si,
		&pi
	);
	if (ret == 0)
	{
		fwprintf(stderr, L"%ls: Process launch failed: %lu\n", progname, ret);
		abort();
	}

	CloseHandle(pi.hProcess);
	CloseHandle(pi.hThread);

	return 0;
}