Author eryksun
Recipients CrouZ, eryksun, paul.moore, steve.dower, tim.golden, zach.ware
Date 2019-11-18.21:53:30
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Message-id <1574114010.51.0.850493288264.issue38822@roundup.psfhosted.org>
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In attributes_from_dir() in Modules/posixmodule.c, a trailing backslash or slash should be stripped from the lpFileName parameter of FindFirstFileW. Otherwise the call opens the directory via NtOpenFile, instead of opening its parent directory. Even if opening the directory is successful, which we don't expect in this case, FindFirstFileW forcibly fails the call with ERROR_FILE_NOT_FOUND (2) because it expects a filename filter (e.g. "*") for the internal NtQueryDirectoryFile[Ex] system call.

Care needs to be taken to not strip the trailing slash of the root directory of a DOS drive because that creates a drive-relative path (e.g. "C:"). It is expected that FindFirstFileW will fail for the root of a DOS drive or UNC share, since there's no parent directory to open.

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"System Volume Information" explicitly grants access only to the SYSTEM account. Implicitly we have read-attributes access to this directory because we have read-data (i.e. list-directory) access to the root directory. Great, but even for 0 desired access, CreateFileW requests both read-attributes and synchronize access, even for overlapped I/O (i.e. kernel File objects created by CreateFileW can always be waited on). So even an elevated administrator normally can't open this directory to query information. However, backup and restore privileges are in effect when an open requests backup semantics, which we already do. We could extend os.stat to temporarily enable SeBackupPrivilege if the caller has it. 

It's also possible to open the directory with a native NtOpenFile or NtCreateFile system call, without the FILE_SYNCHRONOUS_IO_NONALERT option and without requesting SYNCHRONIZE access -- i.e. the File object will be asynchronous and not waitable.
History
Date User Action Args
2019-11-18 21:53:30eryksunsetrecipients: + eryksun, paul.moore, tim.golden, CrouZ, zach.ware, steve.dower
2019-11-18 21:53:30eryksunsetmessageid: <1574114010.51.0.850493288264.issue38822@roundup.psfhosted.org>
2019-11-18 21:53:30eryksunlinkissue38822 messages
2019-11-18 21:53:30eryksuncreate