[ACCEPTED]-Determine path to registry key from HKEY handle in C++-handle

Use LoadLibrary and NtQueryKey exported function as in the following 2 code snippet.

#include <windows.h>
#include <string>

typedef LONG NTSTATUS;

#ifndef STATUS_SUCCESS
#define STATUS_SUCCESS ((NTSTATUS)0x00000000L)
#endif

#ifndef STATUS_BUFFER_TOO_SMALL
#define STATUS_BUFFER_TOO_SMALL ((NTSTATUS)0xC0000023L)
#endif

std::wstring GetKeyPathFromKKEY(HKEY key)
{
    std::wstring keyPath;
    if (key != NULL)
    {
        HMODULE dll = LoadLibrary(L"ntdll.dll");
        if (dll != NULL) {
            typedef DWORD (__stdcall *NtQueryKeyType)(
                HANDLE  KeyHandle,
                int KeyInformationClass,
                PVOID  KeyInformation,
                ULONG  Length,
                PULONG  ResultLength);

            NtQueryKeyType func = reinterpret_cast<NtQueryKeyType>(::GetProcAddress(dll, "NtQueryKey"));

            if (func != NULL) {
                DWORD size = 0;
                DWORD result = 0;
                result = func(key, 3, 0, 0, &size);
                if (result == STATUS_BUFFER_TOO_SMALL)
                {
                    size = size + 2;
                    wchar_t* buffer = new (std::nothrow) wchar_t[size/sizeof(wchar_t)]; // size is in bytes
                    if (buffer != NULL)
                    {
                        result = func(key, 3, buffer, size, &size);
                        if (result == STATUS_SUCCESS)
                        {
                            buffer[size / sizeof(wchar_t)] = L'\0';
                            keyPath = std::wstring(buffer + 2);
                        }

                        delete[] buffer;
                    }
                }
            }

            FreeLibrary(dll);
        }
    }
    return keyPath;
}

int _tmain(int argc, _TCHAR* argv[])
{
    HKEY key = NULL;
    LONG ret = ERROR_SUCCESS;

    ret = RegOpenKey(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft", &key);
    if (ret == ERROR_SUCCESS)
    {
        wprintf_s(L"Key path for %p is '%s'.", key, GetKeyPathFromKKEY(key).c_str());    
        RegCloseKey(key);
    }

    return 0;
}

This will print the key path 1 on the console:

Key path for 00000FDC is '\REGISTRY\MACHINE\SOFTWARE\Microsoft'.

I was excited to find this article and its 8 well liked solution. Until I found that 7 my system's NTDLL.DLL did not have NtQueryKeyType.

After 6 some hunting around, I ran across ZwQueryKey 5 in the DDK forums.

It is in C#, but here 4 is the solution that works for me:

enum KEY_INFORMATION_CLASS
{
    KeyBasicInformation,            // A KEY_BASIC_INFORMATION structure is supplied.
    KeyNodeInformation,             // A KEY_NODE_INFORMATION structure is supplied.
    KeyFullInformation,             // A KEY_FULL_INFORMATION structure is supplied.
    KeyNameInformation,             // A KEY_NAME_INFORMATION structure is supplied.
    KeyCachedInformation,           // A KEY_CACHED_INFORMATION structure is supplied.
    KeyFlagsInformation,            // Reserved for system use.
    KeyVirtualizationInformation,   // A KEY_VIRTUALIZATION_INFORMATION structure is supplied.
    KeyHandleTagsInformation,       // Reserved for system use.
    MaxKeyInfoClass                 // The maximum value in this enumeration type.
}
[StructLayout(LayoutKind.Sequential)]
public struct KEY_NAME_INFORMATION
{
    public UInt32 NameLength;     // The size, in bytes, of the key name string in the Name array.
    public char[] Name;           // An array of wide characters that contains the name of the key.
                                  // This character string is not null-terminated.
                                  // Only the first element in this array is included in the
                                  //    KEY_NAME_INFORMATION structure definition.
                                  //    The storage for the remaining elements in the array immediately
                                  //    follows this element.
}

[DllImport("ntdll.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern int ZwQueryKey(IntPtr hKey, KEY_INFORMATION_CLASS KeyInformationClass, IntPtr lpKeyInformation, int Length, out int ResultLength);

public static String GetHKeyName(IntPtr hKey)
{
    String result = String.Empty;
    IntPtr pKNI = IntPtr.Zero;

    int needed = 0;
    int status = ZwQueryKey(hKey, KEY_INFORMATION_CLASS.KeyNameInformation, IntPtr.Zero, 0, out needed);
    if ((UInt32)status == 0xC0000023)   // STATUS_BUFFER_TOO_SMALL
    {
        pKNI = Marshal.AllocHGlobal(sizeof(UInt32) + needed + 4 /*paranoia*/);
        status = ZwQueryKey(hKey, KEY_INFORMATION_CLASS.KeyNameInformation, pKNI, needed, out needed);
        if (status == 0)    // STATUS_SUCCESS
        {
            char[] bytes = new char[2 + needed + 2];
            Marshal.Copy(pKNI, bytes, 0, needed);
            // startIndex == 2  skips the NameLength field of the structure (2 chars == 4 bytes)
            // needed/2         reduces value from bytes to chars
            //  needed/2 - 2    reduces length to not include the NameLength
            result = new String(bytes, 2, (needed/2)-2);
        }
    }
    Marshal.FreeHGlobal(pKNI);
    return result;
}

I've only 3 ever tried it while running as Administrator, which 2 may be required.

The result is a bit oddly 1 formatted: \REGISTRY\MACHINE\SOFTWARE\company\product for example, instead of HKEY_LOCAL_MACHINE\SOFTWARE\company\product.

Nominally no because it's just a handle 8 and there is no API that I know of to let 7 you do this in the normal Windows API's.

HOWEVER 6 the Native API has lots of functions some 5 of which can give you handles open for given 4 files and the like so there maybe something 3 similar for the Registry. That and RegMon 2 by SysInternals may do something like this 1 but you'll have to Google I'm afraid :/

You can use RegSaveKey and write it to a file, then 8 look at the file.

Alternatively you can 7 keep a global map of HKEYs to LPCWSTRs and 6 add entries when you open them and do lookups 5 whenever.

You may also be able to do something 4 with the !reg command in WinDBG / NTSD, but 3 you can't just give it the HKEY. You'll 2 have to do some other trickery to get the 1 info you want out of it.

Since std::wstring allows to construct string from pointer 16 and count of characters, and the kernel 15 string always return the count of bytes, it 14 is not necessary to terminated the string 13 with NUL. I do not suggest that to add size 12 or to offset the pointer by constant number 11 directly, it's better to use the real data 10 type like the structure types instead, and 9 std::vector<UCHAR> instead of new for dynamic memory allocating. I 8 modified the code from highly upvoted answer 7 as the followings.

The legacy way, obtaining 6 the function pointer from ntdll.dll dynamically:

#include <ntstatus.h>
#define WIN32_NO_STATUS
#include <windows.h>
#include <winternl.h>
#include <string>
#include <vector>

#define REG_KEY_PATH_LENGTH 1024

typedef enum _KEY_INFORMATION_CLASS {
    KeyBasicInformation,
    KeyNodeInformation,
    KeyFullInformation,
    KeyNameInformation,
    KeyCachedInformation,
    KeyFlagsInformation,
    KeyVirtualizationInformation,
    KeyHandleTagsInformation,
    KeyTrustInformation,
    KeyLayerInformation,
    MaxKeyInfoClass
} KEY_INFORMATION_CLASS;

typedef struct _KEY_NAME_INFORMATION {
    ULONG NameLength;
    WCHAR Name[1];
} KEY_NAME_INFORMATION, *PKEY_NAME_INFORMATION;

typedef NTSTATUS (NTAPI *PFN_NtQueryKey)(
    __in        HANDLE  /* KeyHandle */,
    __in        KEY_INFORMATION_CLASS /* KeyInformationClass */,
    __out_opt   PVOID   /* KeyInformation */,
    __in        ULONG   /* Length */,
    __out       ULONG * /* ResultLength */
);

std::wstring RegQueryKeyPath(HKEY hKey)
{
    std::wstring keyPath;

    if (hKey != NULL)
    {
        HMODULE hinstDLL = GetModuleHandleW(L"ntdll.dll");
        if (hinstDLL != NULL)
        {
            FARPROC pfn = GetProcAddress(hinstDLL, "NtQueryKey");
            if (pfn != NULL)
            {
                NTSTATUS Status;

                std::vector<UCHAR> Buffer(FIELD_OFFSET(KEY_NAME_INFORMATION, Name) + sizeof(WCHAR) * REG_KEY_PATH_LENGTH);
                KEY_NAME_INFORMATION *pkni;
                ULONG Length;

            TryAgain:
                Status = reinterpret_cast<PFN_NtQueryKey>(pfn)(hKey, KeyNameInformation, Buffer.data(), Buffer.size(), &Length);
                switch (Status) {
                case STATUS_BUFFER_TOO_SMALL:
                case STATUS_BUFFER_OVERFLOW:
                    Buffer.resize(Length);
                    goto TryAgain;
                case STATUS_SUCCESS:
                    pkni = reinterpret_cast<KEY_NAME_INFORMATION *>(Buffer.data());
                    keyPath.assign(pkni->Name, pkni->NameLength / sizeof(WCHAR));
                default:
                    break;
                }
            }
        }
    }

    return keyPath;
}

If 5 you are using Visual Studio 2015 or above, ntdll.lib is 4 included by default, so I suggest that linking 3 to ntdll.dll statically:

#include <ntstatus.h>
#define WIN32_NO_STATUS
#include <windows.h>
#include <winternl.h>
#pragma comment(lib, "ntdll")
#include <string>
#include <vector>

#define REG_KEY_PATH_LENGTH 1024

typedef enum _KEY_INFORMATION_CLASS {
    KeyBasicInformation,
    KeyNodeInformation,
    KeyFullInformation,
    KeyNameInformation,
    KeyCachedInformation,
    KeyFlagsInformation,
    KeyVirtualizationInformation,
    KeyHandleTagsInformation,
    KeyTrustInformation,
    KeyLayerInformation,
    MaxKeyInfoClass
} KEY_INFORMATION_CLASS;

typedef struct _KEY_NAME_INFORMATION {
    ULONG NameLength;
    WCHAR Name[1];
} KEY_NAME_INFORMATION, *PKEY_NAME_INFORMATION;

EXTERN_C NTSYSAPI NTSTATUS NTAPI NtQueryKey(
    __in        HANDLE  /* KeyHandle */,
    __in        KEY_INFORMATION_CLASS /* KeyInformationClass */,
    __out_opt   PVOID   /* KeyInformation */,
    __in        ULONG   /* Length */,
    __out       ULONG * /* ResultLength */
);

std::wstring RegQueryKeyPath(HKEY hKey)
{
    std::wstring keyPath;

    NTSTATUS Status;

    std::vector<UCHAR> Buffer(FIELD_OFFSET(KEY_NAME_INFORMATION, Name) + sizeof(WCHAR) * REG_KEY_PATH_LENGTH);
    KEY_NAME_INFORMATION *pkni;
    ULONG Length;

TryAgain:
    Status = NtQueryKey(hKey, KeyNameInformation, Buffer.data(), Buffer.size(), &Length);
    switch (Status) {
    case STATUS_BUFFER_TOO_SMALL:
    case STATUS_BUFFER_OVERFLOW:
        Buffer.resize(Length);
        goto TryAgain;
    case STATUS_SUCCESS:
        pkni = reinterpret_cast<KEY_NAME_INFORMATION *>(Buffer.data());
        keyPath.assign(pkni->Name, pkni->NameLength / sizeof(WCHAR));
    default:
        break;
    }

    return keyPath;
}

Note that NtQueryKey returned STATUS_BUFFER_OVERFLOW but 2 not STATUS_BUFFER_TOO_SMALL on Windows 10 if the supplied buffer 1 is insufficient.

For ntsd/windbg:

!handle yourhandle 4

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