GeezerVison is showing github.com — `posixpath.realpath('secretlink')` raises · Issue #118447 · python/cpython
posixpath.realpath('secretlink') raises #118447
DescriptionBug report
Bug description:
GNU coreutils realpath -m doesn't raise an error for secret symlinks (no read permission):
wannes@Stefans-iMac dirs % sudo ls -l secret-symlink
l--------- 1 wannes staff 44 Jun 30 2023 secret-symlink -> /Users/wannes/path-picker/link-test/dirs/dir
wannes@Stefans-iMac dirs % grealpath -m secret-symlink
/Users/wannes/path-picker/link-test/dirs/secret-symlink But posixpath.realpath() does:
>>> import posixpath
>>> posixpath.realpath("secret-symlink")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<frozen posixpath>", line 435, in realpath
File "<frozen posixpath>", line 495, in _joinrealpath
PermissionError: [Errno 13] Permission denied: 'secret-symlink'CPython versions tested on:
3.12
Operating systems tested on:
macOS
Linked PRs
Activityeryksun commented on Apr 30, 2024 Setting permissions on a symlink is a BSD (including macOS) feature. Linux doesn't allow it. Testing this should be limited to platforms with os.chmod in os.supports_follow_symlinks. nineteendo commented on May 2, 2024 ContributorAuthor More actions Upon closer inspection, this is a bug in coreutils:
wannes@Stefans-iMac dirs % sudo ls -l secret-recursive-symlink
l--------- 1 wannes staff 40 Jun 30 2023 secret-recursive-symlink -> /Users/wannes/path-picker/link-test/dirs
wannes@Stefans-iMac dirs % sudo realpath secret-recursive-symlink/..
/Users/wannes/path-picker/link-test
wannes@Stefans-iMac dirs % grealpath -m secret-recursive-symlink/..
/Users/wannes/path-picker/link-test/dirs barneygale commented on May 2, 2024 I wouldn't expect os.path.realpath(..., strict=False) to raise OSError, no matter what coreutils does! nineteendo commented on May 2, 2024 ContributorAuthor More actions That's probably a reason which this is not part of POSIX... I expected you needed permission to follow it, not to determine the real location.
Return the canonical path of the specified filename, eliminating any symbolic links encountered in the path.
We can't eliminate this symlink, because we don't know where it points to, which we need to know for determining the parent directory. Also, coreutils doesn't even raise an error in strict mode:
wannes@Stefans-iMac ~ % ln -s . src
wannes@Stefans-iMac ~ % grealpath -e src/..
/Users
wannes@Stefans-iMac ~ % chmod -h 000 src
wannes@Stefans-iMac ~ % grealpath -e src/..
/Users/wannes Raising an error here will lead to the fewest bugs.
eryksun commented on May 2, 2024 On macOS and NetBSD, fcntl() supports F_GETPATH. In that case, you could try to open "secret-symlink" and query the resolved path, e.g. target = os.fsdecode(fcntl.fcntl(fd, fcntl.F_GETPATH, bytes(1024))). You may have to revisit the design of fcntl.fcntl() to make it use an internal buffer bigger than 1024 bytes, though I think that's currently the maximum path length supported by macOS. nineteendo commented on May 2, 2024 ContributorAuthor More actions That works:
>>> import fcntl
>>> import os
>>> os.symlink('.', 'src')
>>> os.chmod('src', 0o000, follow_symlinks=False)
>>> os.readlink('src')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
PermissionError: [Errno 13] Permission denied: 'src'
>>> fd = os.open('src', os.O_RDONLY)
>>> os.fsdecode(fcntl.fcntl(fd, fcntl.F_GETPATH, bytes(1024))).rstrip('\x00')
'/Users/wannes'But I think it might be cleaner to fix this in readlink... nineteendo commented on May 3, 2024 ContributorAuthor More actions But it doesn't work for broken symlinks:
>>> import fcntl
>>> import os
>>> open('tmp', 'w', encoding='utf-8')
<_io.TextIOWrapper name='tmp' mode='w' encoding='utf-8'>
>>> os.symlink('tmp', 'dst')
>>> os.unlink('tmp')
>>> os.chmod('dst', 0o000, follow_symlinks=False)
>>> os.readlink('dst')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
PermissionError: [Errno 13] Permission denied: 'dst'
>>> fd = os.open('dst', os.O_RDONLY)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: 'dst'added a commit that references this issue on May 18, 2024GH-118447: Fix handling of unreadable symlinks in `os.path.realpath()` ( nineteendo commented on May 22, 2024 ContributorAuthor More actions With the FreeBSD test failures fixed, we can close this.
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