[issue28353] os.fwalk() unhandled exception when error occurs accessing symbolic link target
Samson Lee added the comment: This is definitely a bug because there is no way an unhandled exception like this is acceptable behaviour. The behaviour is that the fwalk iteration will stop and there is no way to recover / continue. Also fwalk takes an onerror callback function that won't be called with this error. -- ___ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28353> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue28353] os.fwalk() unhandled exception when error occurs accessing symbolic link target
Samson Lee added the comment: Sorry, the target file needs to be in a directory you don't have permission to access: $ mkdir handsoff $ sudo chown root:root handsoff $ sudo chmod 700 handsoff $ ln -s handsoff/anything blah -- ___ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28353> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue28353] os.fwalk() unhandled exception when error occurs accessing symbolic link target
Samson Lee added the comment: Similar to http://bugs.python.org/issue25860 -- nosy: +serhiy.storchaka ___ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28353> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue28353] os.fwalk() unhandled exception when error occurs accessing symbolic link target
New submission from Samson Lee:
The bug is os.fwalk() crashes with unhandled exception when there is an error
accessing symbolic link targets.
To reproduce the bug, create a symbolic link that targets a file that you do not
have permission to access:
$ touch handsoff
$ sudo chown root:root handsoff
$ sudo chmod 700 handsoff
$ ln -s handsoff blah
Now, os.fwalk() fails:
>>> for root, dirs, files, fd in os.fwalk('.'):
... print(root, dirs, files)
...
Traceback (most recent call last):
File "test_fwalk_permission_error.py", line 3, in
for root, dirs, files, fd in os.fwalk('.'):
File "/usr/lib64/python3.5/os.py", line 520, in fwalk
yield from _fwalk(topfd, top, topdown, onerror, follow_symlinks)
File "/usr/lib64/python3.5/os.py", line 537, in _fwalk
if st.S_ISDIR(stat(name, dir_fd=topfd).st_mode):
PermissionError: [Errno 13] Permission denied: 'blah'
The cause of the problem is in this part of os.py:
for name in names:
try:
# Here, we don't use AT_SYMLINK_NOFOLLOW to be consistent with
# walk() which reports symlinks to directories as directories.
# We do however check for symlinks before recursing into
# a subdirectory.
if st.S_ISDIR(stat(name, dir_fd=topfd).st_mode):
dirs.append(name)
else:
nondirs.append(name)
except FileNotFoundError:
try:
# Add dangling symlinks, ignore disappeared files
if st.S_ISLNK(stat(name, dir_fd=topfd, follow_symlinks=False)
.st_mode):
nondirs.append(name)
except FileNotFoundError:
continue
To fix it, simply replace FileNotFoundError with more general OSError.
Cheers
--
components: Library (Lib)
messages: 278016
nosy: Samson Lee
priority: normal
severity: normal
status: open
title: os.fwalk() unhandled exception when error occurs accessing symbolic link
target
versions: Python 3.5, Python 3.6
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[issue25860] os.fwalk() silently skips remaining directories when error occurs
Changes by Samson Lee <sammo2...@gmail.com>: -- nosy: +hynek, neologix ___ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25860> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue25860] os.fwalk() silently skips remaining directories when error occurs
Changes by Samson Lee <sammo2...@gmail.com>: -- nosy: +benhoyt, haypo ___ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25860> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue25860] os.fwalk() silently skips remaining directories when error occurs
New submission from Samson Lee:
I noticed os.fwalk() produced different results as os.walk(). It turned out
that os.fwalk() skips all remaining directories when OSError occurs (e.g. due
to PermissionError).
To reproduce the bug, first create a test directory structure:
$ mkdir 1; touch 1/a
$ mkdir 2; touch 2/b
$ mkdir 3; touch 3/c
$ mkdir 4; touch 4/c
At this stage, everything is okay, both os.fwalk() os.walk() produce the same
results:
>>> import os
>>> for root, dirs, files in os.walk('.'):
... dirs.sort()
... print(root, dirs, files)
. ['1', '2', '3', '4'] []
./1 [] ['a']
./2 [] ['b']
./3 [] ['c']
./4 [] ['d']
>>> for root, dirs, files, fd in os.fwalk('.'):
... dirs.sort()
... print(root, dirs, files)
. ['1', '2', '3', '4'] []
./1 [] ['a']
./2 [] ['b']
./3 [] ['c']
./4 [] ['d']
To introduce an error, force a PermissionError on one of the directories:
$ sudo chown root:root 2
$ sudo chmod 700 2
Now, the os.fwalk() results are different (trust me, os.walk() is still okay):
>>> for root, dirs, files, fd in os.fwalk('.'):
... dirs.sort()
... print(root, dirs, files)
. ['1', '2', '3', '4'] []
./1 [] ['a']
So it seems that os.fwalk skips remaining directories after an error occurs.
The cause of the problem is in this part of os.py:
for name in dirs:
try:
orig_st = stat(name, dir_fd=topfd, follow_symlinks=follow_symlinks)
dirfd = open(name, O_RDONLY, dir_fd=topfd)
except OSError as err:
if onerror is not None:
onerror(err)
break
To fix it, simply replace break with continue. Patch attached.
Cheers
--
components: Library (Lib)
files: fwalk-silently-skips-dirs-when-error-occurs.patch
keywords: patch
messages: 256377
nosy: Samson Lee
priority: normal
severity: normal
status: open
title: os.fwalk() silently skips remaining directories when error occurs
type: behavior
versions: Python 3.4, Python 3.5
Added file:
http://bugs.python.org/file41304/fwalk-silently-skips-dirs-when-error-occurs.patch
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