8000 Windows: os.stat() returns random times on ERROR_ACCESS_DENIED · Issue #114273 · python/cpython · GitHub
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danny0838 opened this issue Jan 18, 2024 · 6 comments
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Windows: os.stat() returns random times on ERROR_ACCESS_DENIED #114273

danny0838 opened this issue Jan 18, 2024 · 6 comments
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OS-windows type-bug An unexpected behavior, bug, or error

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@danny0838
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danny0838 commented Jan 18, 2024 •
edited by Eclips4
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Bug report

Bug description:

When retrieving the timestamp of an inaccessible file (or directory) in Windows, such as:

os.path.getmtime('C:\\System Volume Information')

, a negative value such as -11644246396.230042 is returned in Python 3.12.

In Python < 3.12, a normal timestamp such as 1705600376.5800736 is returned instead.

This may break many scripts as most of them don't expect a negative value.

CPython versions tested on:

3.12

Operating systems tested on:

Windows
@danny0838 danny0838 added the type-bug An unexpected behavior, bug, or error label Jan 18, 2024
@serhiy-storchaka
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serhiy-storchaka commented Jan 19, 2024 •
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>>> time.gmtime(1705600376.5800736)
time.struct_time(tm_year=2024, tm_mon=1, tm_mday=18, tm_hour=17, tm_min=52, tm_sec=56, tm_wday=3, tm_yday=18, tm_isdst=0)

It is approximately the time of the report. Perhaps the time of the request.

>>> time.gmtime(-11644246396.230042)
time.struct_time(tm_year=1601, tm_mon=1, tm_mday=3, tm_hour=15, tm_min=6, tm_sec=43, tm_wday=2, tm_yday=3, tm_isdst=0)

It is suspiciously close to the start of Win32 epoch https://devblogs.microsoft.com/oldnewthing/20090306-00/?p=18913.

@vstinner, were there some changes in time conversion that can be related to this? Or maybe Python 3.11 and 3.12 executables have different capabilities, so Win32 API returns different result? cc @zooba

danny0838 added a commit to danny0838/PyWebScrapBook that referenced this issue Jan 19, 2024
@danny0838
Fix template error for negative timestamp
c3e658e 
- A negative timestamp may be returned by os.stat() for an inaccessible file in Python 3.12:
  python/cpython#114273
- Add datetime to template global.
@vstinner
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On Windows, os.stat() calls win32_xstat_slow_impl() which calls:

    DWORD access = FILE_READ_ATTRIBUTES;
    DWORD flags = FILE_FLAG_BACKUP_SEMANTICS; /* Allow opening directories. */
    if (!traverse) {
        flags |= FILE_FLAG_OPEN_REPARSE_POINT; 
    }                   
                        
    hFile = CreateFileW(path, access, 0, NULL, OPEN_EXISTING, flags, NULL);

CreateFileW() returns INVALID_HANDLE_VALUE when trying to open C:\System Volume Information path. In this case, basicInfo is left unmodified, whereas the structure is allocated on the stack.

In short, os.stat() returns random values to timestamps (such as st_mtime) on C:\System Volume Information: when CreateFileW() returns INVALID_HANDLE_VALUE. The value depends on the state of the stack memory, in short it's "undefined" or "random".

In fact, CreateFileW() fails with ERROR_ACCESS_DENIED (error code 5). In this case, attributes_from_dir() is called and it works. Problem: basicInfo is not filled by this function (and is left unchanged).

cc @zooba @eryksun

@vstinner
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Note: os.path.getmtime('C:\\System Volume Information') returns the expected modified time if the code is run as an administrator. The problem only occurs on "access denied". For example, if I run the script in a SSH shell, I'm an administrator, and the code works as expected.

@vstinner vstinner changed the title Negative timestamp for an inaccessible file in Python 3.12/Windows Windows: os.stat() returns random times on ERROR_ACCESS_DENIED Jan 19, 2024
@zooba
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zooba commented Jan 22, 2024

This is fixed in 3.13 already. See #111877.

@zooba zooba closed this as not planned Won't fix, can't repro, duplicate, stale Jan 22, 2024
@zooba
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zooba commented Jan 22, 2024

It's also been backported, so the next 3.12 will have the fix. I think it missed the last update because of a lack of reviewers.

@vstinner
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I confirm that the fix works as expected. On the current main branch, os.path.getmtime('C:\\System Volume Information') returns a valid timestamp, rather than an invalid negative timestamp.

I also confirm that the code works as expected in the current 3.11 and 3.12 branches.

@vstinner vstinner mentioned this issue Jan 23, 2024
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