How to get name associated with open HANDLE

Question

What's the easiest way to get the filename associated with an open HANDLE in Win32?

Answer 1

There is a correct (although undocumented) way to do this on Windows XP which also works with directories -- the same method GetFinalPathNameByHandle uses on Windows Vista and later.

Here are the eneded declarations. Some of these are already in WInternl.h and MountMgr.h but I just put them here anyway:

#include "stdafx.h"
#include <Windows.h>
#include <assert.h>

enum OBJECT_INFORMATION_CLASS { ObjectNameInformation = 1 };
enum FILE_INFORMATION_CLASS { FileNameInformation = 9 };
struct FILE_NAME_INFORMATION { ULONG FileNameLength; WCHAR FileName[1]; };
struct IO_STATUS_BLOCK { PVOID Dummy; ULONG_PTR Information; };
struct UNICODE_STRING { USHORT Length; USHORT MaximumLength; PWSTR Buffer; };
struct MOUNTMGR_TARGET_NAME { USHORT DeviceNameLength; WCHAR DeviceName[1]; };
struct MOUNTMGR_VOLUME_PATHS { ULONG MultiSzLength; WCHAR MultiSz[1]; };

extern "C" NTSYSAPI NTSTATUS NTAPI NtQueryObject(IN HANDLE Handle OPTIONAL,
    IN OBJECT_INFORMATION_CLASS ObjectInformationClass,
    OUT PVOID ObjectInformation OPTIONAL, IN ULONG ObjectInformationLength,
    OUT PULONG ReturnLength OPTIONAL);
extern "C" NTSYSAPI NTSTATUS NTAPI NtQueryInformationFile(IN HANDLE FileHandle,
    OUT PIO_STATUS_BLOCK IoStatusBlock, OUT PVOID FileInformation,
    IN ULONG Length, IN FILE_INFORMATION_CLASS FileInformationClass);

#define MOUNTMGRCONTROLTYPE ((ULONG) 'm')
#define IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH \
    CTL_CODE(MOUNTMGRCONTROLTYPE, 12, METHOD_BUFFERED, FILE_ANY_ACCESS)

union ANY_BUFFER {
    MOUNTMGR_TARGET_NAME TargetName;
    MOUNTMGR_VOLUME_PATHS TargetPaths;
    FILE_NAME_INFORMATION NameInfo;
    UNICODE_STRING UnicodeString;
    WCHAR Buffer[USHRT_MAX];
};

Here's the core function:

LPWSTR GetFilePath(HANDLE hFile)
{
    static ANY_BUFFER nameFull, nameRel, nameMnt;
    ULONG returnedLength; IO_STATUS_BLOCK iosb; NTSTATUS status;
    status = NtQueryObject(hFile, ObjectNameInformation,
        nameFull.Buffer, sizeof(nameFull.Buffer), &returnedLength);
    assert(status == 0);
    status = NtQueryInformationFile(hFile, &iosb, nameRel.Buffer,
        sizeof(nameRel.Buffer), FileNameInformation);
    assert(status == 0);
    //I'm not sure how this works with network paths...
    assert(nameFull.UnicodeString.Length >= nameRel.NameInfo.FileNameLength);
    nameMnt.TargetName.DeviceNameLength = (USHORT)(
        nameFull.UnicodeString.Length - nameRel.NameInfo.FileNameLength);
    wcsncpy(nameMnt.TargetName.DeviceName, nameFull.UnicodeString.Buffer,
        nameMnt.TargetName.DeviceNameLength / sizeof(WCHAR));
    HANDLE hMountPointMgr = CreateFile(_T("\\\\.\\MountPointManager"),
        0, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
        NULL, OPEN_EXISTING, 0, NULL);
    __try
    {
        DWORD bytesReturned;
        BOOL success = DeviceIoControl(hMountPointMgr,
            IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH, &nameMnt,
            sizeof(nameMnt), &nameMnt, sizeof(nameMnt),
            &bytesReturned, NULL);
        assert(success && nameMnt.TargetPaths.MultiSzLength > 0);
        wcsncat(nameMnt.TargetPaths.MultiSz, nameRel.NameInfo.FileName,
            nameRel.NameInfo.FileNameLength / sizeof(WCHAR));
        return nameMnt.TargetPaths.MultiSz;
    }
    __finally { CloseHandle(hMountPointMgr); }
}

and here's an example usage:

int _tmain(int argc, _TCHAR* argv[])
{
    HANDLE hFile = CreateFile(_T("\\\\.\\C:\\Windows\\Notepad.exe"),
        0, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
    assert(hFile != NULL && hFile != INVALID_HANDLE_VALUE);
    __try
    {
        wprintf(L"%s\n", GetFilePath(hFile));
        //  Prints:
        //  C:\Windows\notepad.exe
    }
    __finally { CloseHandle(hFile); }
    return 0;
}

Answer 2

I tried the code posted by Mehrdad here. It works, but with limitations:

1. It should not be used for network shares because the MountPointManager may hang for a very long time.
2. It uses undocumented API (IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH) I don't like that very much
3. It does not support USB devices that create virtual COM ports (I need that in my project)

I also studied other approaches like GetFileInformationByHandleEx() and GetFinalPathNameByHandle(), but these are useless as they return only Path + Filename but without drive. Additionally GetFinalPathNameByHandle() also has the hanging bug.

The GetMappedFileName() approach in the MSDN (posted by Max here) is also very limited:

1. It works only with real files
2. The file size must not be zero bytes
3. Directories, Network and COM ports are not supported
4. The code is clumsy

So I wrote my own code. I tested it on Win XP and on Win 7, 8, and 10. It works perfectly.

NOTE: You do NOT need any additional LIB file to compile this code!

CPP FILE:

t_NtQueryObject NtQueryObject()
{
    static t_NtQueryObject f_NtQueryObject = NULL;
    if (!f_NtQueryObject)
    {
        HMODULE h_NtDll = GetModuleHandle(L"Ntdll.dll"); // Ntdll is loaded into EVERY process!
        f_NtQueryObject = (t_NtQueryObject)GetProcAddress(h_NtDll, "NtQueryObject");
    }
    return f_NtQueryObject;
}


// returns
// "\Device\HarddiskVolume3"                                (Harddisk Drive)
// "\Device\HarddiskVolume3\Temp"                           (Harddisk Directory)
// "\Device\HarddiskVolume3\Temp\transparent.jpeg"          (Harddisk File)
// "\Device\Harddisk1\DP(1)0-0+6\foto.jpg"                  (USB stick)
// "\Device\TrueCryptVolumeP\Data\Passwords.txt"            (Truecrypt Volume)
// "\Device\Floppy0\Autoexec.bat"                           (Floppy disk)
// "\Device\CdRom1\VIDEO_TS\VTS_01_0.VOB"                   (DVD drive)
// "\Device\Serial1"                                        (real COM port)
// "\Device\USBSER000"                                      (virtual COM port)
// "\Device\Mup\ComputerName\C$\Boot.ini"                   (network drive share,  Windows 7)
// "\Device\LanmanRedirector\ComputerName\C$\Boot.ini"      (network drive share,  Windwos XP)
// "\Device\LanmanRedirector\ComputerName\Shares\Dance.m3u" (network folder share, Windwos XP)
// "\Device\Afd"                                            (internet socket)
// "\Device\Console000F"                                    (unique name for any Console handle)
// "\Device\NamedPipe\Pipename"                             (named pipe)
// "\BaseNamedObjects\Objectname"                           (named mutex, named event, named semaphore)
// "\REGISTRY\MACHINE\SOFTWARE\Classes\.txt"                (HKEY_CLASSES_ROOT\.txt)
DWORD GetNtPathFromHandle(HANDLE h_File, CString* ps_NTPath)
{
    if (h_File == 0 || h_File == INVALID_HANDLE_VALUE)
        return ERROR_INVALID_HANDLE;

    // NtQueryObject() returns STATUS_INVALID_HANDLE for Console handles
    if (IsConsoleHandle(h_File))
    {
        ps_NTPath->Format(L"\\Device\\Console%04X", (DWORD)(DWORD_PTR)h_File);
        return 0;
    }

    BYTE  u8_Buffer[2000];
    DWORD u32_ReqLength = 0;

    UNICODE_STRING* pk_Info = &((OBJECT_NAME_INFORMATION*)u8_Buffer)->Name;
    pk_Info->Buffer = 0;
    pk_Info->Length = 0;

    // IMPORTANT: The return value from NtQueryObject is bullshit! (driver bug?)
    // - The function may return STATUS_NOT_SUPPORTED although it has successfully written to the buffer.
    // - The function returns STATUS_SUCCESS although h_File == 0xFFFFFFFF
    NtQueryObject()(h_File, ObjectNameInformation, u8_Buffer, sizeof(u8_Buffer), &u32_ReqLength);

    // On error pk_Info->Buffer is NULL
    if (!pk_Info->Buffer || !pk_Info->Length)
        return ERROR_FILE_NOT_FOUND;

    pk_Info->Buffer[pk_Info->Length /2] = 0; // Length in Bytes!

    *ps_NTPath = pk_Info->Buffer;
    return 0;
}

// converts
// "\Device\HarddiskVolume3"                                -> "E:"
// "\Device\HarddiskVolume3\Temp"                           -> "E:\Temp"
// "\Device\HarddiskVolume3\Temp\transparent.jpeg"          -> "E:\Temp\transparent.jpeg"
// "\Device\Harddisk1\DP(1)0-0+6\foto.jpg"                  -> "I:\foto.jpg"
// "\Device\TrueCryptVolumeP\Data\Passwords.txt"            -> "P:\Data\Passwords.txt"
// "\Device\Floppy0\Autoexec.bat"                           -> "A:\Autoexec.bat"
// "\Device\CdRom1\VIDEO_TS\VTS_01_0.VOB"                   -> "H:\VIDEO_TS\VTS_01_0.VOB"
// "\Device\Serial1"                                        -> "COM1"
// "\Device\USBSER000"                                      -> "COM4"
// "\Device\Mup\ComputerName\C$\Boot.ini"                   -> "\\ComputerName\C$\Boot.ini"
// "\Device\LanmanRedirector\ComputerName\C$\Boot.ini"      -> "\\ComputerName\C$\Boot.ini"
// "\Device\LanmanRedirector\ComputerName\Shares\Dance.m3u" -> "\\ComputerName\Shares\Dance.m3u"
// returns an error for any other device type
DWORD GetDosPathFromNtPath(const WCHAR* u16_NTPath, CString* ps_DosPath)
{
    DWORD u32_Error;

    if (wcsnicmp(u16_NTPath, L"\\Device\\Serial", 14) == 0 || // e.g. "Serial1"
        wcsnicmp(u16_NTPath, L"\\Device\\UsbSer", 14) == 0)   // e.g. "USBSER000"
    {
        HKEY h_Key; 
        if (u32_Error = RegOpenKeyEx(HKEY_LOCAL_MACHINE, L"Hardware\\DeviceMap\\SerialComm", 0, KEY_QUERY_VALUE, &h_Key))
            return u32_Error;

        WCHAR u16_ComPort[50];

        DWORD u32_Type;
        DWORD u32_Size = sizeof(u16_ComPort); 
        if (u32_Error = RegQueryValueEx(h_Key, u16_NTPath, 0, &u32_Type, (BYTE*)u16_ComPort, &u32_Size))
        {
            RegCloseKey(h_Key);
            return ERROR_UNKNOWN_PORT;
        }

        *ps_DosPath = u16_ComPort;
        RegCloseKey(h_Key);
        return 0;
    }

    if (wcsnicmp(u16_NTPath, L"\\Device\\LanmanRedirector\\", 25) == 0) // Win XP
    {
        *ps_DosPath  = L"\\\\";
        *ps_DosPath += (u16_NTPath + 25);
        return 0;
    }

    if (wcsnicmp(u16_NTPath, L"\\Device\\Mup\\", 12) == 0) // Win 7
    {
        *ps_DosPath  = L"\\\\";
        *ps_DosPath += (u16_NTPath + 12);
        return 0;
    }

    WCHAR u16_Drives[300];
    if (!GetLogicalDriveStrings(300, u16_Drives))
        return GetLastError();

    WCHAR* u16_Drv = u16_Drives;
    while (u16_Drv[0])
    {
        WCHAR* u16_Next = u16_Drv +wcslen(u16_Drv) +1;

        u16_Drv[2] = 0; // the backslash is not allowed for QueryDosDevice()

        WCHAR u16_NtVolume[1000];
        u16_NtVolume[0] = 0;

        // may return multiple strings!
        // returns very weird strings for network shares
        if (!QueryDosDevice(u16_Drv, u16_NtVolume, sizeof(u16_NtVolume) /2))
            return GetLastError();

        int s32_Len = (int)wcslen(u16_NtVolume);
        if (s32_Len > 0 && wcsnicmp(u16_NTPath, u16_NtVolume, s32_Len) == 0)
        {
            *ps_DosPath  =  u16_Drv;
            *ps_DosPath += (u16_NTPath + s32_Len);
            return 0;
        }

        u16_Drv = u16_Next;
    }
    return ERROR_BAD_PATHNAME;
}

HEADER FILE:

#pragma warning(disable: 4996) // wcsnicmp deprecated
#include <winternl.h>

// This makro assures that INVALID_HANDLE_VALUE (0xFFFFFFFF) returns FALSE
#define IsConsoleHandle(h) (((((ULONG_PTR)h) & 0x10000003) == 0x3) ? TRUE : FALSE)

enum OBJECT_INFORMATION_CLASS 
{
    ObjectBasicInformation, 
    ObjectNameInformation,
    ObjectTypeInformation, 
    ObjectAllInformation, 
    ObjectDataInformation
};

struct OBJECT_NAME_INFORMATION 
{
    UNICODE_STRING Name; // defined in winternl.h
    WCHAR NameBuffer;
};

typedef NTSTATUS (NTAPI* t_NtQueryObject)(HANDLE Handle, OBJECT_INFORMATION_CLASS Info, PVOID Buffer, ULONG BufferSize, PULONG ReturnLength);   

Answer 3

edit Thanks for the comments about this being Vista or Server 2008 only. I missed that in the page. Guess I should have read the whole article ;)

It looks like you can use GetFileInformationByHandleEx() to get this information.

You'll likely want to do something like:

GetFileInformationByHandleEx( fileHandle, FILE_NAME_INFO, lpFileInformation, sizeof(FILE_NAME_INFO));

Double check the MSDN page to make sure I haven't misled you too badly :)

Cheers,

Taylor