[issue45710] Junction/symbolic folder access error on Windows 11

[Eryk Sun]

Eryk Sun  added the comment:

All we can do here is document the store app's limitation on cross-volume 
reparse points (junctions, symlinks) in "%UserProfile%\AppData". I suppose it's 
a rare enough problem that it can just be closed as a third-party issue.

--
resolution: works for me -> third party
stage:  -> resolved
status: open -> closed

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[issue45710] Junction/symbolic folder access error on Windows 11

[Fabio Storino]

Fabio Storino  added the comment:

Hello, Eryk. Just to let you know that a regular Python installation was able 
to access my junction folder in AppData and run scripts there.

Thank you for the information on how store apps handle reads/writes in the 
AppData folder.

This is my first bug report. Should I mark this issue as closed?

--
resolution:  -> works for me

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[issue45710] Junction/symbolic folder access error on Windows 11

[Eryk Sun]

Eryk Sun  added the comment:

> does this or does this not look to you like a bug in CPython?

It's better to leave the detailed explanation of limits up to the document 
that's referenced for further information [1], but this issue isn't even 
briefly mentioned there. Maybe it would help some people to mention the store 
package's [2] limitation on using reparse points in "%UserProfile%\AppData", 
but this is the first I've seen of this issue, and I hadn't even considered the 
problem beforehand. I don't see why it would ever be necessary to use a 
cross-volume reparse point in the application-data tree.

Also, maybe this is a bug in the operation system that could get fixed in the 
future. It could be unintended behavior in the filesystem filter that 
virtualizes access to "%UserProfile%\AppData". Maybe someone used a target 
device hint as a convenience in the design, without thinking about how it would 
limit the resolution of reparse points. 

---
[1] 
https://docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes
[2] https://docs.python.org/3.10/using/windows.html#the-microsoft-store-package

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[issue45710] Junction/symbolic folder access error on Windows 11

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Eryk, does this or does this not look to you like a bug in CPython?  I don't 
know enough to tell.

--
nosy: +terry.reedy

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[issue45710] Junction/symbolic folder access error on Windows 11

[Eryk Sun]

Eryk Sun  added the comment:

It's not completely surprising that attempting to traverse a name-surrogate 
reparse point under "%UserProfile%\AppData" fails when using the store app. If 
you can't or won't move the mountpoint up to %UserProfile%, or anywhere else 
outside of the application-data tree, then I suggest using a regular Python 
installation from python.org.

The error in Windows 11 is ERROR_MOUNT_POINT_NOT_RESOLVED (649), based on the 
NT status code STATUS_MOUNT_POINT_NOT_RESOLVED. This error status is associated 
with the kernel routines IoCreateFileSpecifyDeviceObjectHint() [1] and 
IoCreateFileEx() [2]:

IoCreateFileEx returns this status value if the DriverContext
parameter is not NULL and if the file or directory name contains
a mount point that resolves to a volume other than the one to
which the specified device object is attached. This device 
object is specified by the DeviceObjectHint member of the 
IO_DRIVER_CREATE_CONTEXT structure.

A filter driver can use this feature to open a path on a particular volume or 
filesystem device (i.e. the device hint) and bypass other filter drivers that 
are attached to the device stack. However, if path parsing traverses a reparse 
point to another filesystem, it has to fail with 
STATUS_MOUNT_POINT_NOT_RESOLVED. Note that a reparse point that targets a path 
in the same filesystem works fine. For example:

>>> path = os.path.join(os.environ['appdata'], 'spam')
>>> os.lstat(path).st_reparse_tag == stat.IO_REPARSE_TAG_MOUNT_POINT
True
>>> os.path.realpath(path)
'C:\\Temp\\spam'
>>> os.path.exists(os.path.join(path, 'eggs.py'))
True
>>> subprocess.call(['python', os.path.join(path, 'eggs.py')])
works fine
0

The case of a cross-device mountpoint or symlink under "%UserProfile%\AppData" 
also fails when using the store app in Windows 10. However, the error in 
Windows 10 is ERROR_INVALID_FUNCTION (1), from the status code 
STATUS_NOT_IMPLEMENTED, so the underlying implementation details must be quite 
different. I was able to work around the limitation somewhat in Windows 10 (but 
not Windows 11) by first changing to the mountpoint directory and accessing 
relative paths. This doesn't work when running a script, however, since the 
interpreter tries to open the fully-qualified path, which has to traverse the 
mountpoint or symlink.

---
[1 
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/nf-ntddk-iocreatefilespecifydeviceobjecthint
[2] 
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/nf-ntddk-iocreatefileex.

--
nosy: +eryksun

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[issue45710] Junction/symbolic folder access error on Windows 11

[Fabio Storino]

New submission from Fabio Storino :

After upgrading to Windows 11 I can't run Python scripts from a junction folder 
anymore. Everything else works as before on that folder.

Background: I have Minecraft installed on a second volume (E:\Games\Minecraft). 
I created a junction folder at %appdata%\.minecraft pointing to that folder. 
When I try to run a Python script from that folder I get this error:

---
python: can't open file 'C:\Users\x\AppData\Roaming\.minecraft\test.py': 
[Errno 22] Invalid argument
---

When trying to debug in VS Code, I get a more detailed error:

---
Traceback (most recent call last):
  File "C:\Program 
Files\WindowsApps\PythonSoftwareFoundation.Python.3.9_3.9.2032.0_x64
__qbz5n2kfra8p0\lib\ntpath.py", line 647, in realpath
path = _getfinalpathname(path)
OSError: [WinError 649] The create operation failed because the name
contained at least one mount point which resolves to a volume to
which the specified device object is not attached:
'c:\\Users\\x\\AppData\\Roaming\\.minecraft'
---

When trying to open that junction folder in Python's IDLE I get the following 
error message:

---
[Window Title] Location is not available

[Content] C:\Users\x\AppData\Roaming\.minecraft is not accessible.

The create operation failed because the name contained at least one
mount point which resolves to a volume to which the specified device
object is not attached.
---

I tried creating a symbolic directory link instead of a junction, but got the 
same message.

I can run the same scripts directly from the target folder (E:\Games\Minecraft).

I can also run them from the junction folder from an Ubuntu terminal on WSL2 
(Windows Subsystem for Linux).

I tried this with Python 3.9 and 3.10 (WSL2 uses Python 3.8).

--
components: Windows
messages: 405677
nosy: fstorino, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Junction/symbolic folder access error on Windows 11
type: behavior
versions: Python 3.10, Python 3.9

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