/* SPDX-License-Identifier: GPL-2.0
 *
 * Copyright (C) 2018-2020 WireGuard LLC. All Rights Reserved.
 */

#include "elevate.h"

#include <Windows.h>
#include <TlHelp32.h>

BOOL
ElevateToSystem(void)
{
    HANDLE CurrentProcessToken, ThreadToken, ProcessSnapshot, WinlogonProcess, WinlogonToken, DuplicatedToken;
    PROCESSENTRY32W ProcessEntry = { .dwSize = sizeof(PROCESSENTRY32W) };
    BOOL Ret;
    DWORD LastError = ERROR_SUCCESS;
    TOKEN_PRIVILEGES Privileges = { .PrivilegeCount = 1, .Privileges = { { .Attributes = SE_PRIVILEGE_ENABLED } } };
    CHAR LocalSystemSid[0x400];
    DWORD RequiredBytes = sizeof(LocalSystemSid);
    struct
    {
        TOKEN_USER MaybeLocalSystem;
        CHAR LargeEnoughForLocalSystem[0x400];
    } TokenUserBuffer;

    Ret = CreateWellKnownSid(WinLocalSystemSid, NULL, &LocalSystemSid, &RequiredBytes);
    LastError = GetLastError();
    if (!Ret)
        goto cleanup;
    Ret = OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &CurrentProcessToken);
    LastError = GetLastError();
    if (!Ret)
        goto cleanup;
    Ret =
        GetTokenInformation(CurrentProcessToken, TokenUser, &TokenUserBuffer, sizeof(TokenUserBuffer), &RequiredBytes);
    LastError = GetLastError();
    CloseHandle(CurrentProcessToken);
    if (!Ret)
        goto cleanup;
    if (EqualSid(TokenUserBuffer.MaybeLocalSystem.User.Sid, LocalSystemSid))
        return TRUE;
    Ret = LookupPrivilegeValueW(NULL, SE_DEBUG_NAME, &Privileges.Privileges[0].Luid);
    LastError = GetLastError();
    if (!Ret)
        goto cleanup;
    ProcessSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
    LastError = GetLastError();
    if (ProcessSnapshot == INVALID_HANDLE_VALUE)
        goto cleanup;
    for (Ret = Process32FirstW(ProcessSnapshot, &ProcessEntry); Ret;
         Ret = Process32NextW(ProcessSnapshot, &ProcessEntry))
    {
        if (_wcsicmp(ProcessEntry.szExeFile, L"winlogon.exe"))
            continue;
        RevertToSelf();
        Ret = ImpersonateSelf(SecurityImpersonation);
        LastError = GetLastError();
        if (!Ret)
            continue;
        Ret = OpenThreadToken(GetCurrentThread(), TOKEN_ADJUST_PRIVILEGES, FALSE, &ThreadToken);
        LastError = GetLastError();
        if (!Ret)
            continue;
        Ret = AdjustTokenPrivileges(ThreadToken, FALSE, &Privileges, sizeof(Privileges), NULL, NULL);
        LastError = GetLastError();
        CloseHandle(ThreadToken);
        if (!Ret)
            continue;

        WinlogonProcess = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, ProcessEntry.th32ProcessID);
        LastError = GetLastError();
        if (!WinlogonProcess)
            continue;
        Ret = OpenProcessToken(WinlogonProcess, TOKEN_IMPERSONATE | TOKEN_DUPLICATE, &WinlogonToken);
        LastError = GetLastError();
        CloseHandle(WinlogonProcess);
        if (!Ret)
            continue;
        Ret = DuplicateToken(WinlogonToken, SecurityImpersonation, &DuplicatedToken);
        LastError = GetLastError();
        CloseHandle(WinlogonToken);
        if (!Ret)
            continue;
        if (!GetTokenInformation(DuplicatedToken, TokenUser, &TokenUserBuffer, sizeof(TokenUserBuffer), &RequiredBytes))
            goto next;
        if (SetLastError(ERROR_ACCESS_DENIED), !EqualSid(TokenUserBuffer.MaybeLocalSystem.User.Sid, LocalSystemSid))
            goto next;
        if (!SetThreadToken(NULL, DuplicatedToken))
            goto next;
        CloseHandle(DuplicatedToken);
        CloseHandle(ProcessSnapshot);
        SetLastError(ERROR_SUCCESS);
        return TRUE;
    next:
        LastError = GetLastError();
        CloseHandle(DuplicatedToken);
    }
    RevertToSelf();
    CloseHandle(ProcessSnapshot);
cleanup:
    SetLastError(LastError);
    return FALSE;
}