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  1. Core ReactOS
  2. CORE-18789

FILE_APPEND_DATA not handled correctly in NtCreateFile & friends

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Details

    • Bug
    • Resolution: Unresolved
    • Major
    • None
    • NTCore
    • None

    Description

      1. Create a blank file test.txt with e.g. Notepad and add some contents, then close it.
      2. Open that file with an NtCreateFile (or ZwCreateFile) with the following flags:

          Status = ZwCreateFile(&FileHandle,
                                FILE_APPEND_DATA | SYNCHRONIZE,
                                &ObjectAttributes,
                                &Iosb,
                                NULL,
                                FILE_ATTRIBUTE_NORMAL,
                                FILE_SHARE_READ,
                                FILE_OPEN_IF,
                                FILE_NON_DIRECTORY_FILE | FILE_SYNCHRONOUS_IO_NONALERT |
                                  FILE_SEQUENTIAL_ONLY | FILE_WRITE_THROUGH,
                                NULL,
                                0);
      

      (ObjectAttributes needs to be initialized obviously...)
      3. Write new data with NtWriteFile (or ZwWriteFile):

              Status = ZwWriteFile(FileHandle, NULL, NULL, NULL, &Iosb,
                                   chBuffer, uRead, NULL, NULL);
      

      (chBuffer: data buffer; uRead: number of bytes to write.)
      Note that according to MSDN, and as it happens on Windows, since the file is opened with FILE_APPEND_DATA | SYNCHRONIZE, data is/should be always appended [1,2], even if no explicit file offset has been specified in the ZwWriteFile call or the file pointer explicitly positioned manually before the write operations.

      [1]: https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/nf-wdm-zwcreatefile#remarks
      [2]: https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/nf-wdm-zwwritefile

      On Windows: such code works as expected: new data gets appended to the end of the file.
      On ReactOS: code doesn't work, and data gets written at the beginning of the file, overwriting any existing data.

      I attach an interactive console program that illustrates all that; it can be run on Windows (2003+) or ReactOS and behaviour can be manually compared.

      Attachments

        1. 0001-Fixed.patch
          0.9 kB
          zecarlos1957
        2. AppendData.png
          35 kB
          zecarlos1957

        Activity

          People

            Unassigned Unassigned
            hbelusca hbelusca
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            Watchers:
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            Dates

              Created:
              Updated: