Convert WCHAR * to UNICODE STRING

Question

First try at windows driver development. How can I convert a WCHAR array (coming from user-space) to a UNICODE_STRING (in kernel mode) assuming that the WCHAR array is not null-terminated?

Should I verify if it ends with null and if it doesn't allocate a new buffer (+2 for the null) and then use the RtlAnsiXXX functions? What is the proper way?

Thanks!

Answer 1

To initialize UNICODE_STRING from wchar array use RtlInitUnicodeString.

WCHAR array has to be null-terminated.

So if you checked and wchar-string is not null terminated, you should allocate a new buffer(+sizeof(WCHAR) for null), copy array content and then call RtlInitUnicodeString.

To check if wchar-string from user-mode is null-terminated I am using:

BOOLEAN IsStringTerminated(PWCHAR Array, USHORT ArrayLength, USHORT *StringLength)
{
    BOOLEAN bStringIsTerminated = FALSE;
    USHORT uiIndex = 0;

    *StringLength = 0;

    while(uiIndex < ArrayLength && bStringIsTerminated == FALSE)
    {
        if(Array[uiIndex] == L'\0')
        {
            *StringLength = uiIndex + 1;
            bStringIsTerminated = TRUE;
        }
        else
        {
            uiIndex++;
        }
    }

    return bStringIsTerminated;
}

Answer 2

The WCHAR array does not have to be NULL-terminated. UNICODE_STRING structure was designed for counted strings, and as such, works with non NULL-terminated WCHAR arrays-- you will have to know the length, of course.

For example, you can use RtlInitEmptyUnicodeString.