[issue30044] shutil.copystat should (allow to) copy ownership, and other attributes

[Eryk Sun]

Eryk Sun <eryksun at gmail.com> added the comment:

In Windows, I wouldn't expect shutil.copy2 to preserve the owner and ACLs. They change whenever a file gets copied via CopyFileExW [1]. Keeping them exactly as in the source file generally requires a privileged backup and restore operation, such as via BackupRead [2] and BackupWrite [3]. Unless the caller has SeRestorePrivilege, the owner can only be set to one of the SIDs in the caller's groups that are flagged as SE_GROUP_OWNER, which is usually just the user's SID or, for an admin, the Administrators SID. Also, for copying the system ACL, adding or removing audit and scoped-policy-identifier entries requires SeSecurityPrivilege.

CopyFileExW copies all data streams in a file, which is typically just the anonymous data stream, but an NTFS/ReFS file can have multiple named data streams. For metadata, it copies the change and modify timestamps (but not the create and access timestamps), file attributes (readonly, hidden, system, archive, temporary, not-content-indexed), extended attributes, and resource attributes [4]. 

Separating this functionality into shutil.copy and shutil.copystat would be fairly involved. These functions could be left as is and just document the discrepancy in shutil.copy2, or new functions could be implemented in the nt or _winapi module to list the data streams in a file and get/set file attributes and system resource attributes. Supporting extended attributes would require the native NT API, and for little benefit since they're mostly used for "$Kernel." prefixed attributes that can only be set by kernel-mode callers such as drivers.

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[1]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-copyfileexw
[2]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-backupread
[3]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-backupwrite
[4]: Resource attributes are like extended attributes, but a named resource attribute is a tuple of one or more items with a given data type (integer, string, or bytes) that's stored as an entry in the file's system ACL. Keeping them in the SACL allows conditional access/audit entries to reference them in an access check or access audit. Unlike audit entries in the SACL, reading and writing resource attributes doesn't require SeSecurityPrivilege.

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nosy: +eryksun

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<https://bugs.python.org/issue30044>
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