Issue 28075: os.stat fails when access is denied

doing os.stat on the directory c:\config.msi gives different results on my Windows 10 machine, when done with py27 and py35
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Python 2.7.12 (v2.7.12:d33e0cf91556, Jun 27 2016, 15:24:40) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.stat('c:\\config.msi')
nt.stat_result(st_mode=16895, st_ino=0L, st_dev=0L, st_nlink=0, st_uid=0, st_gid=0, st_size=2891776L, st_atime=1473584558L, st_mtime=1473584558L, st_ctime=1449228297L)

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Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.stat('c:\\config.msi')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
PermissionError: [WinError 5] Zugriff verweigert: 'c:\\config.msi'

-> Access denied

Python 3's os.stat tries to open a handle for the file or directory in order to call GetFileInformationByHandle. Opening a file handle via CreateFile requests at least FILE_READ_ATTRIBUTES and SYNCHRONIZE access when it calls NtCreateFile. If access is denied, os.stat is supposed to fall back on the basic WIN32_FIND_DATA information from FindFirstFile. However, it's not working as intended. For example:

    >>> import os
    >>> os.mkdir('test')
    >>> os.system('icacls test /deny Users:(S,RA)')
    processed file: test
    Successfully processed 1 files; Failed processing 0 files
    0

    >>> os.stat('test')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    PermissionError: [WinError 5] Access is denied: 'test'

The problem is that it's mistakenly checking for ERROR_SHARING_VIOLATION instead of ERROR_ACCESS_DENIED. Technically, getting a sharing violation should be impossible here. That only applies to requesting execute (traverse), read (list), write (add file), append (add subdirectory), or delete access for the contents of the file or directory, not its metadata.

After modifying the code to instead check for ERROR_ACCESS_DENIED, os.stat correctly falls back on using the file attributes from the WIN32_FIND_DATA:

    >>> os.stat('test')
    os.stat_result(st_mode=16895, st_ino=0, st_dev=0, st_nlink=0, 
    st_uid=0, st_gid=0, st_size=0, st_atime=1473589600, 
    st_mtime=1473589600, st_ctime=1473589600)

I overlooked attempting to open a paging-file for any access, which is hard coded as a sharing violation. The attached patch checks for both cases.

New changeset eabb86463462 by Berker Peksag in branch '3.5':
Issue #28075: Check for ERROR_ACCESS_DENIED in Windows implementation of os.stat()
https://hg.python.org/cpython/rev/eabb86463462

New changeset 4071a7cf6437 by Berker Peksag in branch '3.6':
Issue #28075: Merge from 3.5
https://hg.python.org/cpython/rev/4071a7cf6437

New changeset b04d5864e59a by Berker Peksag in branch 'default':
Issue #28075: Merge from 3.6
https://hg.python.org/cpython/rev/b04d5864e59a

Thanks, Eryk.

New changeset 20c4ad866620 by Berker Peksag in branch '3.5':
Issue #28075: Fix test_access_denied in Python 3.5
https://hg.python.org/cpython/rev/20c4ad866620

versions: + Python 3.7
nosy: + berker.peksag

messages: + msg276792
resolution: fixed
stage: patch review -> resolved

versions: + Python 3.6