NetLocalGroupEnum access violation enumerating local groups

Question

Hello,

I fall into problem of using correectly NetLocalGroupEnum api

When debugging I notice a weird pointer value set to 0xFFFFFFFFF. (screenshot joined)

Has anybody a working code snippet for this API call ?

Thanks in advance :)

Answer 1

The cause of the access violation is the improper casting of &workingDword to a (PDWORD_PTR). In an x64 build a DWORD_PTR is a 64-bit value. The workingDword variable should be a DWORD_PTR, not a DWORD.

Also, the call will allocate memory that must be freed with NetApiBufferFree and return that address in the pBytes variable. The call to malloc is not needed.

    DWORD dwentriesread{}, dwtotalentries{};
    DWORD_PTR resumehandle{};
    LPBYTE pbuf{};

    auto ret = NetLocalGroupEnum(
        NULL, // servername
        0, // level
        &pbuf, // bufptr
        MAX_PREFERRED_LENGTH, // prefmaxlen
        &dwentriesread, // entries read
        &dwtotalentries, // total entries
        &resumehandle // resume handle
    );

    if (ret == NERR_Success)
    {
        printf_s("Entries read: %u, total entries: %u\n", dwentriesread, dwtotalentries);
        for (ULONG i = 0; i < dwentriesread; i++)
        {
            LOCALGROUP_INFO_0 lgi = ((PLOCALGROUP_INFO_0)pbuf)[i];
            printf_s("Group name: %ls\n", lgi.lgrpi0_name);
        }
    }
    else
    {
        printf_s("NetLocalGroupEnum returned %u\n", ret);
    }


    if (pbuf)
        NetApiBufferFree(pbuf);

Answer 2

Hi RLWA32,

thanks for your help :)

I didn't realized that I should use a 64 bits dword pointer

declaring p_resume_handle like this make it working

.....
DWORD    totalentries = 0;
// declare a working 64 bits dword
DWORD_PTR    workingDword64 = 0;
PDWORD_PTR    p_resume_handle = &workingDword64;

	pBytes = NULL;


	ntStatus= NetLocalGroupEnum(
		/*[in]      LPCWSTR*/    NULL,
		/*[in]      DWORD*/      level,
		/*[out]     LPBYTE * */ &pBytes,
		/*[in]      DWORD */      MAX_PREFERRED_LENGTH,
		/*[out]     LPDWORD*/    &entriesread,
		/*[out]     LPDWORD*/    &totalentries,
		/*[in, out] PDWORD_PTR */ p_resume_handle
	);
	wprintf(L"NetGroupEnum: %d\n", ntStatus);