[python-win32] python-win32 Digest, Vol 162, Issue 4

[Goku Balu]

So if we deny WRITE then SYNCHRONIZE will be denied which will in-turn
affect READ. Is there a way to deny WRITE alone without affecting
file/folder read?

Thanks,
Goku


On Tue, Sep 20, 2016 at 9:30 PM, <python-win32-request at python.org> wrote:

>
> >
> > That doesn't seem like a bug to me. GENERIC_WRITE represents several
> > permissions mashed together, including FILE_WRITE and read control.
> >
> > Perhaps try with just FILE_WRITE on its own?
>
> For a file or directory, GENERIC_WRITE (0x80000000) gets mapped to
> FILE_GENERIC_WRITE, which includes the following standard rights
> (upper 16 bits):
>
>     SYNCHRONIZE  = 0x00100000
>     READ_CONTROL = 0x00020000
>
> and File-object specific rights (lower 16 bits):
>
>     FILE_WRITE_ATTRIBUTES = 0x00000100
>     FILE_WRITE_EA         = 0x00000010
>     FILE_APPEND_DATA      = 0x00000004
>     FILE_WRITE_DATA       = 0x00000002
>
> The relevant access right that's being denied in this case is SYNCHRONIZE.
>
> For example, SetCurrentDirectory uses a synchronous directory handle,
> i.e. it calls NtOpenfile with desired access SYNCHRONIZE |
> FILE_TRAVERSE and open option FILE_SYNCHRONOUS_IO_NONALERT. Similarly,
> for listing a directory, FindFirstFile uses a synchronous handle with
> SYNCHRONIZE | FILE_LIST_DIRECTORY access.
>
> The open option FILE_SYNCHRONOUS_IO_NONALERT is defined as follows:
>
>     All operations on the file are performed synchronously.
>     Waits in the system that synchronize I/O queuing and
>     completion are not subject to alerts. This flag also
>     causes the I/O system to maintain the file-position
>     context. If this flag is set, the SYNCHRONIZE flag must
>     be set in the DesiredAccess parameter.
>
> For example, when FindFirstFile calls NtQueryDirectoryFile
> (FileBothDirectoryInformation) to list the directory, the system call
> sees the handle is opened for synchronous access, so it waits to
> acquire the File object's Lock before calling the filesystem driver
> (e.g. NTFS). Then it waits again to complete the request.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-win32/attachments/20160923/39c88514/attachment.html>