Thread: How to concat PUNICODE_STRING

In the process of writing a simple minifilter driver, I can't seem to figure out how to do this. Admittedly, I have extremely limited experience with C/C++ (although I have a decade's worth of other languages). The following works in a C project:

Code:

    PUNICODE_STRING _d;
    _d = malloc(sizeof(UNICODE_STRING));
    NTSTATUS _d_status = RtlUnicodeStringInit(_d, d);
    // Check status...
    // Where _c is an existing PUNICODE_STRING
    NTSTATUS _c_d_status = RtlStringCbCatA(_c, sizeof(_c), _d);
    // Check status...
    printf("_c_d: %wZ\r\n", _c);

When done in a KMDF project, I use ExAllocatePool2 instead. Fails on the first RtlUnicodeStringInit with 0xc0000005.

Sorry, substitute that for L"abc" (or any sample text).

So this works, but changes to TextA affect MainText (as expected).

Code:

    // MainText is PUNICODE_STRING
    NTSTRSAFE_PWSTR TextA = MainText->Buffer;

    UNICODE_STRING TextB;
    RtlInitUnicodeString(&TextB, L"abc");

    NTSTATUS status = RtlStringCbCatW(TextA, MainText->Length + TextB.Length + 2, TextB.Buffer);

For whatever reason, I just assumed there's no reason that call could've failed. Besides, it was RtlUnicodeStringInit which was failing. Well, it'd help if I was initializing the memory with the correct param for Flags. POOL_FLAGS instead of POOL_TYPE got me moving forward.

The following works, as a deeper copy:

Code:

    UNICODE_STRING tst = EMPTY_UNICODE_STRING;
    tst.MaximumLength = MainText->Length + 1;
    tst.Buffer = ExAllocatePool2(POOL_FLAG_NON_PAGED, MainText->Length + 1, DRIVER_TAG);
    if (NULL == tst.Buffer) {
        DbgPrint("ExAllocatePool2 failed!\r\n");
    }
    else {
        RtlCopyUnicodeString(&tst, MainText);
    }

Originally Posted by tmontney

So this works, but changes to TextA affect MainText (as expected).

Code:

    // MainText is PUNICODE_STRING
    NTSTRSAFE_PWSTR TextA = MainText->Buffer;

    UNICODE_STRING TextB;
    RtlInitUnicodeString(&TextB, L"abc");

    NTSTATUS status = RtlStringCbCatW(TextA, MainText->Length + TextB.Length + 2, TextB.Buffer);

Should use the following instead of RtlStringCbCatW:

Code:

status = RtlUnicodeStringCatString(TextA, L"abc");

I'm fumbling my way through this, and realized there's an exact function for appending Unicode with a "string".