CODEWITHSUNDEEP
c++windowsfile-ioexe
kdod
kdod

Reputation: 13

Why Am I Writing 0 bytes with WriteFile?

I'm trying to make a program that finds the next .exe file in a user-defined directory and writes a flag to it (for a computer security class).

It's currently writing 0 bytes, and I'm not sure why.

Here is my code so far:

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <Windows.h>
#include <fstream>

using namespace std;

typedef wchar_t wchar;

struct thePlague{
    long int origBytes;
    wchar_t flag[6];
};

void main() {
WIN32_FIND_DATA findFileData; //Windows structure that receives info about a found file or directory
HANDLE hFind = INVALID_HANDLE_VALUE; //Handle that holds whether or not a file was successfully found with FindNextFile
LARGE_INTEGER fileSize;
wchar szDir[MAX_PATH];
DWORD dwError = 0;

wchar directory[MAX_PATH];
wcout<<L"Please enter a directory: ";
wcin>>directory;

// Check that the input path plus 7 is not longer than MAX_PATH.
// 7 characters are for the "\*.exe" plus NULL appended below.
if (wcslen(directory) > (MAX_PATH - 7)) {
    wcout<<L"\nDirectory is too long\n";
    return;
}

wcout<<L"Target directory is: "<<directory<<endl;

// Prepare string for use with FindFile functions.  First, copy the
// string to a buffer, then append '\*' to the directory name.

wcscpy(szDir, directory);
wcscat(szDir, L"\\*.exe");

//Find the first file in the directory

hFind = FindFirstFile(szDir, &findFileData);

if (hFind == INVALID_HANDLE_VALUE) {
    wcout<<L"FindFirstFile Failed"<<GetLastError()<<endl;
    return;
}

do {
    fileSize.LowPart = findFileData.nFileSizeLow;
    fileSize.HighPart = findFileData.nFileSizeHigh;
    wcout<<findFileData.cFileName<<L" "<<fileSize.QuadPart<<L" bytes\n";

    DWORD dwBytesWritten = 0; //# of bytes written by WriteFile
    wchar_t *buffer = (wchar *)malloc(sizeof(thePlague)); //A buffer the size of our struct (infection flag)
    wofstream writeToBuffer(buffer, ios::binary); //Open the buffer for writing
    thePlague newVictim; //New infection flag

    writeToBuffer.write((const wchar_t*)&newVictim, sizeof(thePlague));
    writeToBuffer.close();

    DWORD dwErrorFlag;

    dwErrorFlag = WriteFile(hFind, //The handle holding the file we are writing to
              buffer, //The buffer holding what we want to write to the file, in this case a struct
              sizeof(thePlague), //How many bytes to write to the file
              &dwBytesWritten, //Where to store the # of bytes successfully written
              NULL //Where to write to incase of overlap
              );

    if (dwErrorFlag == false)
        wcout<<L"Error was: "<<GetLastError()<<endl;

    wcout<<L"# of bytes written: "<<dwBytesWritten<<endl;

} while(FindNextFile(hFind, &findFileData) != 0);


FindClose(hFind);
return;
}

When I run this, I get:

Please enter a directory: C:\Infect
Target directory is: C:\Infect
hello.exe 65536 bytes
Error was: 6
# of bytes written: 0
Press any key to continue . . .

I know this is an ERROR_INVALID_HANDLE, but how do I fix this?

Upvotes: 0

Views: 2120

Answers (2)

Emerick Rogul
Emerick Rogul

Reputation: 6804

FindFirstFile returns a search handle, but WriteFile requires an open file handle. Use CreateFile to open the file before writing to it with WriteFile.

Upvotes: 3

nos
nos

Reputation: 229324

You need to open the file before writing to it. Your HANDLE hFind is just a handle to iterate over directories/files, not an open handle to a file.

Use CreateFile() to open the file

Upvotes: 6

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