update/common/updatehelper.cpp

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <windows.h>

// Needed for CreateToolhelp32Snapshot
#include <tlhelp32.h>

#include <stdio.h>
#include <direct.h>
#include "shlobj.h"

// Needed for PathAppendW
#include <shlwapi.h>

#include "updatehelper.h"
#include "updateutils_win.h"

#ifdef MOZ_MAINTENANCE_SERVICE
#  include "mozilla/UniquePtr.h"
#  include "pathhash.h"
#  include "registrycertificates.h"
#  include "uachelper.h"

using mozilla::MakeUnique;
using mozilla::UniquePtr;
#endif

BOOL PathGetSiblingFilePath(LPWSTR destinationBuffer, LPCWSTR siblingFilePath,
                            LPCWSTR newFileName);

/**
 * Obtains the path of a file in the same directory as the specified file.
 *
 * @param  destinationBuffer A buffer of size MAX_PATH + 1 to store the result.
 * @param  siblingFilePath   The path of another file in the same directory
 * @param  newFileName       The filename of another file in the same directory
 * @return TRUE if successful
 */
BOOL PathGetSiblingFilePath(LPWSTR destinationBuffer, LPCWSTR siblingFilePath,
                            LPCWSTR newFileName) {
  if (wcslen(siblingFilePath) > MAX_PATH) {
    return FALSE;
  }

  wcsncpy(destinationBuffer, siblingFilePath, MAX_PATH + 1);
  if (!PathRemoveFileSpecW(destinationBuffer)) {
    return FALSE;
  }

  return PathAppendSafe(destinationBuffer, newFileName);
}

/**
 * Obtains the path of the secure directory used to write the status and log
 * files for updates applied with an elevated updater or an updater that is
 * launched using the maintenance service.
 *
 * Example
 * Destination buffer value:
 *   C:\Program Files (x86)\Mozilla Maintenance Service\UpdateLogs
 *
 * @param  outBuf
 *         A buffer of size MAX_PATH + 1 to store the result.
 * @return TRUE if successful
 */
BOOL GetSecureOutputDirectoryPath(LPWSTR outBuf) {
  PWSTR progFilesX86;
  if (FAILED(SHGetKnownFolderPath(FOLDERID_ProgramFilesX86, KF_FLAG_CREATE,
                                  nullptr, &progFilesX86))) {
    return FALSE;
  }
  if (wcslen(progFilesX86) > MAX_PATH) {
    CoTaskMemFree(progFilesX86);
    return FALSE;
  }
  wcsncpy(outBuf, progFilesX86, MAX_PATH + 1);
  CoTaskMemFree(progFilesX86);

  if (!PathAppendSafe(outBuf, L"Mozilla Maintenance Service")) {
    return FALSE;
  }

  // Create the Maintenance Service directory in case it doesn't exist.
  if (!CreateDirectoryW(outBuf, nullptr) &&
      GetLastError() != ERROR_ALREADY_EXISTS) {
    return FALSE;
  }

  if (!PathAppendSafe(outBuf, L"UpdateLogs")) {
    return FALSE;
  }

  // Create the secure update output directory in case it doesn't exist.
  if (!CreateDirectoryW(outBuf, nullptr) &&
      GetLastError() != ERROR_ALREADY_EXISTS) {
    return FALSE;
  }

  return TRUE;
}

/**
 * Obtains the name of the update output file using the update patch directory
 * path and file extension (must include the '.' separator) passed to this
 * function.
 *
 * Example
 * Patch directory path parameter:
 *   C:\ProgramData\Mozilla\updates\0123456789ABCDEF\updates\0
 * File extension parameter:
 *   .status
 * Destination buffer value:
 *   0123456789ABCDEF.status
 *
 * @param  patchDirPath
 *         The path to the update patch directory.
 * @param  fileExt
 *         The file extension for the file including the '.' separator.
 * @param  outBuf
 *         A buffer of size MAX_PATH + 1 to store the result.
 * @return TRUE if successful
 */
BOOL GetSecureOutputFileName(LPCWSTR patchDirPath, LPCWSTR fileExt,
                             LPWSTR outBuf) {
  size_t fullPathLen = wcslen(patchDirPath);
  if (fullPathLen > MAX_PATH) {
    return FALSE;
  }

  size_t relPathLen = wcslen(PATCH_DIR_PATH);
  if (relPathLen > fullPathLen) {
    return FALSE;
  }

  // The patch directory path must end with updates\0 for updates applied with
  // an elevated updater or an updater that is launched using the maintenance
  // service.
  if (_wcsnicmp(patchDirPath + fullPathLen - relPathLen, PATCH_DIR_PATH,
                relPathLen) != 0) {
    return FALSE;
  }

  wcsncpy(outBuf, patchDirPath, MAX_PATH + 1);
  if (!PathRemoveFileSpecW(outBuf)) {
    return FALSE;
  }

  if (!PathRemoveFileSpecW(outBuf)) {
    return FALSE;
  }

  PathStripPathW(outBuf);

  size_t outBufLen = wcslen(outBuf);
  size_t fileExtLen = wcslen(fileExt);
  if (outBufLen + fileExtLen > MAX_PATH) {
    return FALSE;
  }

  wcsncat(outBuf, fileExt, fileExtLen);

  return TRUE;
}

/**
 * Obtains the full path of the secure update output file using the update patch
 * directory path and file extension (must include the '.' separator) passed to
 * this function.
 *
 * Example
 * Patch directory path parameter:
 *   C:\ProgramData\Mozilla\updates\0123456789ABCDEF\updates\0
 * File extension parameter:
 *   .status
 * Destination buffer value:
 *   C:\Program Files (x86)\Mozilla Maintenance
 *     Service\UpdateLogs\0123456789ABCDEF.status
 *
 * @param  patchDirPath
 *         The path to the update patch directory.
 * @param  fileExt
 *         The file extension for the file including the '.' separator.
 * @param  outBuf
 *         A buffer of size MAX_PATH + 1 to store the result.
 * @return TRUE if successful
 */
BOOL GetSecureOutputFilePath(LPCWSTR patchDirPath, LPCWSTR fileExt,
                             LPWSTR outBuf) {
  if (!GetSecureOutputDirectoryPath(outBuf)) {
    return FALSE;
  }

  WCHAR statusFileName[MAX_PATH + 1] = {L'\0'};
  if (!GetSecureOutputFileName(patchDirPath, fileExt, statusFileName)) {
    return FALSE;
  }

  return PathAppendSafe(outBuf, statusFileName);
}

/**
 * Writes a UUID to the ID file in the secure output directory. This is used by
 * the unelevated updater to determine whether an existing update status file in
 * the secure output directory has been updated.
 *
 * @param  patchDirPath
 *         The path to the update patch directory.
 * @return TRUE if successful
 */
BOOL WriteSecureIDFile(LPCWSTR patchDirPath) {
  WCHAR uuidString[MAX_PATH + 1] = {L'\0'};
  if (!GetUUIDString(uuidString)) {
    return FALSE;
  }

  WCHAR idFilePath[MAX_PATH + 1] = {L'\0'};
  if (!GetSecureOutputFilePath(patchDirPath, L".id", idFilePath)) {
    return FALSE;
  }

  FILE* idFile = _wfopen(idFilePath, L"wb+");
  if (idFile == nullptr) {
    return FALSE;
  }

  if (fprintf(idFile, "%ls\n", uuidString) == -1) {
    fclose(idFile);
    return FALSE;
  }

  fclose(idFile);

  return TRUE;
}

/**
 * Removes the update status and log files from the secure output directory.
 *
 * @param  patchDirPath
 *         The path to the update patch directory.
 */
void RemoveSecureOutputFiles(LPCWSTR patchDirPath) {
  WCHAR filePath[MAX_PATH + 1] = {L'\0'};
  if (GetSecureOutputFilePath(patchDirPath, L".id", filePath)) {
    (void)_wremove(filePath);
  }
  if (GetSecureOutputFilePath(patchDirPath, L".status", filePath)) {
    (void)_wremove(filePath);
  }
  if (GetSecureOutputFilePath(patchDirPath, L".log", filePath)) {
    (void)_wremove(filePath);
  }
}

#ifdef MOZ_MAINTENANCE_SERVICE
/**
 * Starts the upgrade process for update of the service if it is
 * already installed.
 *
 * @param  installDir the installation directory where
 *         maintenanceservice_installer.exe is located.
 * @return TRUE if successful
 */
BOOL StartServiceUpdate(LPCWSTR installDir) {
  // Get a handle to the local computer SCM database
  SC_HANDLE manager = OpenSCManager(nullptr, nullptr, SC_MANAGER_ALL_ACCESS);
  if (!manager) {
    return FALSE;
  }

  // Open the service
  SC_HANDLE svc = OpenServiceW(manager, SVC_NAME, SERVICE_ALL_ACCESS);
  if (!svc) {
    CloseServiceHandle(manager);
    return FALSE;
  }

  // If we reach here, then the service is installed, so
  // proceed with upgrading it.

  CloseServiceHandle(manager);

  // The service exists and we opened it, get the config bytes needed
  DWORD bytesNeeded;
  if (!QueryServiceConfigW(svc, nullptr, 0, &bytesNeeded) &&
      GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
    CloseServiceHandle(svc);
    return FALSE;
  }

  // Get the service config information, in particular we want the binary
  // path of the service.
  UniquePtr<char[]> serviceConfigBuffer = MakeUnique<char[]>(bytesNeeded);
  if (!QueryServiceConfigW(
          svc,
          reinterpret_cast<QUERY_SERVICE_CONFIGW*>(serviceConfigBuffer.get()),
          bytesNeeded, &bytesNeeded)) {
    CloseServiceHandle(svc);
    return FALSE;
  }

  CloseServiceHandle(svc);

  QUERY_SERVICE_CONFIGW& serviceConfig =
      *reinterpret_cast<QUERY_SERVICE_CONFIGW*>(serviceConfigBuffer.get());

  PathUnquoteSpacesW(serviceConfig.lpBinaryPathName);

  // Obtain the temp path of the maintenance service binary
  WCHAR tmpService[MAX_PATH + 1] = {L'\0'};
  if (!PathGetSiblingFilePath(tmpService, serviceConfig.lpBinaryPathName,
                              L"maintenanceservice_tmp.exe")) {
    return FALSE;
  }

  if (wcslen(installDir) > MAX_PATH) {
    return FALSE;
  }

  // Get the new maintenance service path from the install dir
  WCHAR newMaintServicePath[MAX_PATH + 1] = {L'\0'};
  wcsncpy(newMaintServicePath, installDir, MAX_PATH);
  PathAppendSafe(newMaintServicePath, L"maintenanceservice.exe");

  // Copy the temp file in alongside the maintenace service.
  // This is a requirement for maintenance service upgrades.
  if (!CopyFileW(newMaintServicePath, tmpService, FALSE)) {
    return FALSE;
  }

  // Check that the copied file's certificate matches the expected name and
  // issuer stored in the registry for this installation and that the
  // certificate is trusted by the system's certificate store.
  if (!DoesBinaryMatchAllowedCertificates(installDir, tmpService)) {
    DeleteFileW(tmpService);
    return FALSE;
  }

  // Start the upgrade comparison process
  STARTUPINFOW si = {0};
  si.cb = sizeof(STARTUPINFOW);
  // No particular desktop because no UI
  si.lpDesktop = const_cast<LPWSTR>(L"");  // -Wwritable-strings
  PROCESS_INFORMATION pi = {0};
  WCHAR cmdLine[64] = {'\0'};
  wcsncpy(cmdLine, L"dummyparam.exe upgrade",
          sizeof(cmdLine) / sizeof(cmdLine[0]) - 1);
  BOOL svcUpdateProcessStarted =
      CreateProcessW(tmpService, cmdLine, nullptr, nullptr, FALSE, 0, nullptr,
                     installDir, &si, &pi);
  if (svcUpdateProcessStarted) {
    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);
  }
  return svcUpdateProcessStarted;
}

/**
 * Executes a maintenance service command
 *
 * @param  argc    The total number of arguments in argv
 * @param  argv    An array of null terminated strings to pass to the service,
 * @return ERROR_SUCCESS if the service command was started.
 *         Less than 16000, a windows system error code from StartServiceW
 *         More than 20000, 20000 + the last state of the service constant if
 *         the last state is something other than stopped.
 *         17001 if the SCM could not be opened
 *         17002 if the service could not be opened
 */
DWORD
StartServiceCommand(int argc, LPCWSTR* argv) {
  DWORD lastState = WaitForServiceStop(SVC_NAME, 5);
  if (lastState != SERVICE_STOPPED) {
    return 20000 + lastState;
  }

  // Get a handle to the SCM database.
  SC_HANDLE serviceManager = OpenSCManager(
      nullptr, nullptr, SC_MANAGER_CONNECT | SC_MANAGER_ENUMERATE_SERVICE);
  if (!serviceManager) {
    return 17001;
  }

  // Get a handle to the service.
  SC_HANDLE service = OpenServiceW(serviceManager, SVC_NAME, SERVICE_START);
  if (!service) {
    CloseServiceHandle(serviceManager);
    return 17002;
  }

  // Wait at most 5 seconds trying to start the service in case of errors
  // like ERROR_SERVICE_DATABASE_LOCKED or ERROR_SERVICE_REQUEST_TIMEOUT.
  const DWORD maxWaitMS = 5000;
  DWORD currentWaitMS = 0;
  DWORD lastError = ERROR_SUCCESS;
  while (currentWaitMS < maxWaitMS) {
    BOOL result = StartServiceW(service, argc, argv);
    if (result) {
      lastError = ERROR_SUCCESS;
      break;
    } else {
      lastError = GetLastError();
    }
    Sleep(100);
    currentWaitMS += 100;
  }
  CloseServiceHandle(service);
  CloseServiceHandle(serviceManager);
  return lastError;
}

/**
 * Launch a service initiated action for a software update with the
 * specified arguments.
 *
 * @param  argc    The total number of arguments in argv
 * @param  argv    An array of null terminated strings to pass to the exePath,
 *                 argv[0] must be the path to the updater.exe
 * @return ERROR_SUCCESS if successful
 */
DWORD
LaunchServiceSoftwareUpdateCommand(int argc, LPCWSTR* argv) {
  // The service command is the same as the updater.exe command line except
  // it has 4 extra args:
  // 0) The name of the service, automatically added by Windows
  // 1) "MozillaMaintenance" (I think this is redundant with 0)
  // 2) The command being executed, which is "software-update"
  // 3) The path to updater.exe (from argv[0])
  LPCWSTR* updaterServiceArgv = new LPCWSTR[argc + 2];
  updaterServiceArgv[0] = L"MozillaMaintenance";
  updaterServiceArgv[1] = L"software-update";

  for (int i = 0; i < argc; ++i) {
    updaterServiceArgv[i + 2] = argv[i];
  }

  // Execute the service command by starting the service with
  // the passed in arguments.
  DWORD ret = StartServiceCommand(argc + 2, updaterServiceArgv);
  delete[] updaterServiceArgv;
  return ret;
}

/**
 * Writes a specific failure code for the update status to a file in the secure
 * output directory. The status file's name without the '.' separator and
 * extension is the same as the update directory name.
 *
 * @param  patchDirPath
 *         The path of the update patch directory.
 * @param  errorCode
 *         Error code to set
 * @return TRUE if successful
 */
BOOL WriteStatusFailure(LPCWSTR patchDirPath, int errorCode) {
  WCHAR statusFilePath[MAX_PATH + 1] = {L'\0'};
  if (!GetSecureOutputFilePath(patchDirPath, L".status", statusFilePath)) {
    return FALSE;
  }

  HANDLE hStatusFile = CreateFileW(statusFilePath, GENERIC_WRITE, 0, nullptr,
                                   CREATE_ALWAYS, 0, nullptr);
  if (hStatusFile == INVALID_HANDLE_VALUE) {
    return FALSE;
  }

  char failure[32];
  sprintf(failure, "failed: %d", errorCode);
  DWORD toWrite = strlen(failure);
  DWORD wrote;
  BOOL ok = WriteFile(hStatusFile, failure, toWrite, &wrote, nullptr);
  CloseHandle(hStatusFile);

  if (!ok || wrote != toWrite) {
    return FALSE;
  }

  return TRUE;
}

/**
 * Waits for a service to enter a stopped state.
 * This function does not stop the service, it just blocks until the service
 * is stopped.
 *
 * @param  serviceName     The service to wait for.
 * @param  maxWaitSeconds  The maximum number of seconds to wait
 * @return state of the service after a timeout or when stopped.
 *         A value of 255 is returned for an error. Typical values are:
 *         SERVICE_STOPPED 0x00000001
 *         SERVICE_START_PENDING 0x00000002
 *         SERVICE_STOP_PENDING 0x00000003
 *         SERVICE_RUNNING 0x00000004
 *         SERVICE_CONTINUE_PENDING 0x00000005
 *         SERVICE_PAUSE_PENDING 0x00000006
 *         SERVICE_PAUSED 0x00000007
 *         last status not set 0x000000CF
 *         Could no query status 0x000000DF
 *         Could not open service, access denied 0x000000EB
 *         Could not open service, invalid handle 0x000000EC
 *         Could not open service, invalid name 0x000000ED
 *         Could not open service, does not exist 0x000000EE
 *         Could not open service, other error 0x000000EF
 *         Could not open SCM, access denied 0x000000FD
 *         Could not open SCM, database does not exist 0x000000FE;
 *         Could not open SCM, other error 0x000000FF;
 * Note: The strange choice of error codes above SERVICE_PAUSED are chosen
 * in case Windows comes out with other service stats higher than 7, they
 * would likely call it 8 and above.  JS code that uses this in TestAUSHelper
 * only handles values up to 255 so that's why we don't use GetLastError
 * directly.
 */
DWORD
WaitForServiceStop(LPCWSTR serviceName, DWORD maxWaitSeconds) {
  // 0x000000CF is defined above to be not set
  DWORD lastServiceState = 0x000000CF;

  // Get a handle to the SCM database.
  SC_HANDLE serviceManager = OpenSCManager(
      nullptr, nullptr, SC_MANAGER_CONNECT | SC_MANAGER_ENUMERATE_SERVICE);
  if (!serviceManager) {
    DWORD lastError = GetLastError();
    switch (lastError) {
      case ERROR_ACCESS_DENIED:
        return 0x000000FD;
      case ERROR_DATABASE_DOES_NOT_EXIST:
        return 0x000000FE;
      default:
        return 0x000000FF;
    }
  }

  // Get a handle to the service.
  SC_HANDLE service =
      OpenServiceW(serviceManager, serviceName, SERVICE_QUERY_STATUS);
  if (!service) {
    DWORD lastError = GetLastError();
    CloseServiceHandle(serviceManager);
    switch (lastError) {
      case ERROR_ACCESS_DENIED:
        return 0x000000EB;
      case ERROR_INVALID_HANDLE:
        return 0x000000EC;
      case ERROR_INVALID_NAME:
        return 0x000000ED;
      case ERROR_SERVICE_DOES_NOT_EXIST:
        return 0x000000EE;
      default:
        return 0x000000EF;
    }
  }

  DWORD currentWaitMS = 0;
  SERVICE_STATUS_PROCESS ssp;
  ssp.dwCurrentState = lastServiceState;
  while (currentWaitMS < maxWaitSeconds * 1000) {
    DWORD bytesNeeded;
    if (!QueryServiceStatusEx(service, SC_STATUS_PROCESS_INFO, (LPBYTE)&ssp,
                              sizeof(SERVICE_STATUS_PROCESS), &bytesNeeded)) {
      DWORD lastError = GetLastError();
      switch (lastError) {
        case ERROR_INVALID_HANDLE:
          ssp.dwCurrentState = 0x000000D9;
          break;
        case ERROR_ACCESS_DENIED:
          ssp.dwCurrentState = 0x000000DA;
          break;
        case ERROR_INSUFFICIENT_BUFFER:
          ssp.dwCurrentState = 0x000000DB;
          break;
        case ERROR_INVALID_PARAMETER:
          ssp.dwCurrentState = 0x000000DC;
          break;
        case ERROR_INVALID_LEVEL:
          ssp.dwCurrentState = 0x000000DD;
          break;
        case ERROR_SHUTDOWN_IN_PROGRESS:
          ssp.dwCurrentState = 0x000000DE;
          break;
        // These 3 errors can occur when the service is not yet stopped but
        // it is stopping.
        case ERROR_INVALID_SERVICE_CONTROL:
        case ERROR_SERVICE_CANNOT_ACCEPT_CTRL:
        case ERROR_SERVICE_NOT_ACTIVE:
          currentWaitMS += 50;
          Sleep(50);
          continue;
        default:
          ssp.dwCurrentState = 0x000000DF;
      }

      // We couldn't query the status so just break out
      break;
    }

    // The service is already in use.
    if (ssp.dwCurrentState == SERVICE_STOPPED) {
      break;
    }
    currentWaitMS += 50;
    Sleep(50);
  }

  lastServiceState = ssp.dwCurrentState;
  CloseServiceHandle(service);
  CloseServiceHandle(serviceManager);
  return lastServiceState;
}
#endif

/**
 * Determines if there is at least one process running for the specified
 * application. A match will be found across any session for any user.
 *
 * @param process The process to check for existance
 * @return ERROR_NOT_FOUND if the process was not found
 *         ERROR_SUCCESS if the process was found and there were no errors
 *         Other Win32 system error code for other errors
 **/
DWORD
IsProcessRunning(LPCWSTR filename) {
  // Take a snapshot of all processes in the system.
  HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
  if (INVALID_HANDLE_VALUE == snapshot) {
    return GetLastError();
  }

  PROCESSENTRY32W processEntry;
  processEntry.dwSize = sizeof(PROCESSENTRY32W);
  if (!Process32FirstW(snapshot, &processEntry)) {
    DWORD lastError = GetLastError();
    CloseHandle(snapshot);
    return lastError;
  }

  do {
    if (wcsicmp(filename, processEntry.szExeFile) == 0) {
      CloseHandle(snapshot);
      return ERROR_SUCCESS;
    }
  } while (Process32NextW(snapshot, &processEntry));
  CloseHandle(snapshot);
  return ERROR_NOT_FOUND;
}

/**
 * Waits for the specified application to exit.
 *
 * @param filename   The application to wait for.
 * @param maxSeconds The maximum amount of seconds to wait for all
 *                   instances of the application to exit.
 * @return  ERROR_SUCCESS if no instances of the application exist
 *          WAIT_TIMEOUT if the process is still running after maxSeconds.
 *          Any other Win32 system error code.
 */
DWORD
WaitForProcessExit(LPCWSTR filename, DWORD maxSeconds) {
  DWORD applicationRunningError = WAIT_TIMEOUT;
  for (DWORD i = 0; i < maxSeconds; i++) {
    DWORD applicationRunningError = IsProcessRunning(filename);
    if (ERROR_NOT_FOUND == applicationRunningError) {
      return ERROR_SUCCESS;
    }
    Sleep(1000);
  }

  if (ERROR_SUCCESS == applicationRunningError) {
    return WAIT_TIMEOUT;
  }

  return applicationRunningError;
}

#ifdef MOZ_MAINTENANCE_SERVICE
/**
 *  Determines if the fallback key exists or not
 *
 *  @return TRUE if the fallback key exists and there was no error checking
 */
BOOL DoesFallbackKeyExist() {
  HKEY testOnlyFallbackKey;
  if (RegOpenKeyExW(HKEY_LOCAL_MACHINE, TEST_ONLY_FALLBACK_KEY_PATH, 0,
                    KEY_READ | KEY_WOW64_64KEY,
                    &testOnlyFallbackKey) != ERROR_SUCCESS) {
    return FALSE;
  }

  RegCloseKey(testOnlyFallbackKey);
  return TRUE;
}

/**
 * Determines if the file system for the specified file handle is local
 * @param file path to check the filesystem type for, must be at most MAX_PATH
 * @param isLocal out parameter which will hold TRUE if the drive is local
 * @return TRUE if the call succeeded
 */
BOOL IsLocalFile(LPCWSTR file, BOOL& isLocal) {
  WCHAR rootPath[MAX_PATH + 1] = {L'\0'};
  if (wcslen(file) > MAX_PATH) {
    return FALSE;
  }

  wcsncpy(rootPath, file, MAX_PATH);
  PathStripToRootW(rootPath);
  isLocal = GetDriveTypeW(rootPath) == DRIVE_FIXED;
  return TRUE;
}

/**
 * Determines the DWORD value of a registry key value
 *
 * @param key       The base key to where the value name exists
 * @param valueName The name of the value
 * @param retValue  Out parameter which will hold the value
 * @return TRUE on success
 */
static BOOL GetDWORDValue(HKEY key, LPCWSTR valueName, DWORD& retValue) {
  DWORD regDWORDValueSize = sizeof(DWORD);
  LONG retCode =
      RegQueryValueExW(key, valueName, 0, nullptr,
                       reinterpret_cast<LPBYTE>(&retValue), &regDWORDValueSize);
  return ERROR_SUCCESS == retCode;
}

/**
 * Determines if the the system's elevation type allows
 * unprmopted elevation.
 *
 * @param isUnpromptedElevation Out parameter which specifies if unprompted
 *                              elevation is allowed.
 * @return TRUE if the user can actually elevate and the value was obtained
 *         successfully.
 */
BOOL IsUnpromptedElevation(BOOL& isUnpromptedElevation) {
  if (!UACHelper::CanUserElevate()) {
    return FALSE;
  }

  LPCWSTR UACBaseRegKey =
      L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
  HKEY baseKey;
  LONG retCode =
      RegOpenKeyExW(HKEY_LOCAL_MACHINE, UACBaseRegKey, 0, KEY_READ, &baseKey);
  if (retCode != ERROR_SUCCESS) {
    return FALSE;
  }

  DWORD consent, secureDesktop;
  BOOL success = GetDWORDValue(baseKey, L"ConsentPromptBehaviorAdmin", consent);
  success = success &&
            GetDWORDValue(baseKey, L"PromptOnSecureDesktop", secureDesktop);

  RegCloseKey(baseKey);
  if (success) {
    isUnpromptedElevation = !consent && !secureDesktop;
  }

  return success;
}
#endif