[Python-Dev] PEP 471: scandir(fd) and pathlib.Path(name, dir_fd=None) (original) (raw)

Victor Stinner victor.stinner at gmail.com
Tue Jul 1 15:01:26 CEST 2014

2014-07-01 14:26 GMT+02:00 Ben Hoyt <benhoyt at gmail.com>:

Thanks, Victor.

I don't have any experience with dirfd handling, so unfortunately can't really comment here. What advantages does it bring? I notice that even os.listdir() on Python 3.4 doesn't have anything related to file descriptors, so I'd be in favour of not including support.

See https://docs.python.org/dev/library/os.html#dir-fd

The idea is to make sure that you get files from the same directory. Problems occur when a directory is moved or a symlink is modified. Example:

Using unlink("passwd", dir_fd=tmp_copy_fd), you don't have this issue. You are sure that you are working in /tmp/copy directory.

You can imagine a lot of other scenarios to override files and read sensitive files.

Hopefully, the Linux rm commands knows unlinkat() sycall ;-)

haypo at selma$ mkdir -p a/b/c haypo at selma$ strace -e unlinkat rm -rf a unlinkat(5, "c", AT_REMOVEDIR) = 0 unlinkat(4, "b", AT_REMOVEDIR) = 0 unlinkat(AT_FDCWD, "a", AT_REMOVEDIR) = 0 +++ exited with 0 +++

We should implement a similar think in shutil.rmtree().

See also os.fwalk() which is a version of os.walk() providing dir_fd.

We can always add it later.

I would prefer to discuss that right now. My proposition is to accept an int for scandir() and copy the int into DirEntry.dir_fd. It's not that complex :-)

The enhancement of the pathlib module can be done later. By the way, I know that Antoine Pitrou wanted to implemented file descriptors in pathlib, but the feature was rejected or at least delayed.

Victor

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