Issue 28353: os.fwalk() unhandled exception when error occurs accessing symbolic link target (original) (raw)

Created on 2016-10-04 07:06 by Samson Lee, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (16)

msg278016 - (view)

Author: Samson Lee (Samson Lee)

Date: 2016-10-04 07:06

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 <module>
    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

msg278017 - (view)

Author: Samson Lee (Samson Lee)

Date: 2016-10-04 07:08

msg278018 - (view)

Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer)

Date: 2016-10-04 07:45

I can't reproduce the issue.

$ mkdir testdir $ touch testdir/handsoff $ sudo chown root:root testdir/handsoff $ sudo chmod 700 testdir/handsoff $ ln -s handsoff testdir/blah $ python3.5

import os list(os.walk('testdir')) [('testdir', [], ['handsoff', 'blah'])] list(os.fwalk('testdir')) [('testdir', [], ['handsoff', 'blah'], 3)]

Ubuntu 16.04, Linux 4.4, tested on ext4 and tmpfs filesystems.

msg278024 - (view)

Author: Samson Lee (Samson Lee)

Date: 2016-10-04 09:07

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

msg278044 - (view)

Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer)

Date: 2016-10-04 14:45

Yes, there is a difference between os.walk() and os.fwalk() in some cases. I don't know whether it was introduced deliberately or by accident. os.fwalk() was added in , FileNotFoundError is used since .

msg278118 - (view)

Author: Samson Lee (Samson Lee)

Date: 2016-10-05 10:49

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.

msg278178 - (view)

Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer)

Date: 2016-10-06 07:15

Here is a patch with tests. Needed to test it on Windows.

msg279393 - (view)

Author: Roundup Robot (python-dev) (Python triager)

Date: 2016-10-25 11:35

New changeset fe1fea4ded04 by Serhiy Storchaka in branch '3.5': Issue #28353: os.fwalk() no longer fails on broken links. https://hg.python.org/cpython/rev/fe1fea4ded04

New changeset e99ec3c77a63 by Serhiy Storchaka in branch '3.6': Issue #28353: os.fwalk() no longer fails on broken links. https://hg.python.org/cpython/rev/e99ec3c77a63

New changeset 33a1a3dd0051 by Serhiy Storchaka in branch 'default': Issue #28353: os.fwalk() no longer fails on broken links. https://hg.python.org/cpython/rev/33a1a3dd0051

msg279418 - (view)

Author: Roundup Robot (python-dev) (Python triager)

Date: 2016-10-25 16:03

New changeset ec12e16ea6a1 by Serhiy Storchaka in branch '3.6': Issue #28353: Try to fix tests. https://hg.python.org/cpython/rev/ec12e16ea6a1

New changeset a0913dbadea6 by Serhiy Storchaka in branch 'default': Issue #28353: Try to fix tests. https://hg.python.org/cpython/rev/a0913dbadea6

msg279422 - (view)

Author: Roundup Robot (python-dev) (Python triager)

Date: 2016-10-25 17:20

New changeset 470224ec16b6 by Serhiy Storchaka in branch '3.5': Issue #28353: Fixed tests of os.fwalk() with broken links. https://hg.python.org/cpython/rev/470224ec16b6

msg279581 - (view)

Author: Xiang Zhang (xiang.zhang) * (Python committer)

Date: 2016-10-28 04:54

Serhiy, after your commits, test_os requires root privileges or it'll fail. This is not the case before.

[cpython]$ ./python -m test test_os Run tests sequentially 0:00:00 [1/1] test_os test test_os crashed -- Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/libregrtest/runtest.py", line 164, in runtest_inner test_runner() File "/home/angwer/cpython/Lib/test/libregrtest/runtest.py", line 163, in test_runner support.run_unittest(tests) File "/home/angwer/cpython/Lib/test/support/init.py", line 1849, in run_unittest _run_suite(suite) File "/home/angwer/cpython/Lib/test/support/init.py", line 1824, in _run_suite raise TestFailed(err) test.support.TestFailed: multiple errors occurred; run in verbose mode for details

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/libregrtest/runtest.py", line 167, in runtest_inner test_time = time.time() - start_time File "/home/angwer/cpython/Lib/test/libregrtest/save_env.py", line 278, in exit restore(original) File "/home/angwer/cpython/Lib/test/libregrtest/save_env.py", line 235, in restore_files support.rmtree(fn) File "/home/angwer/cpython/Lib/test/support/init.py", line 377, in rmtree _rmtree(path) File "/home/angwer/cpython/Lib/shutil.py", line 474, in rmtree _rmtree_safe_fd(fd, path, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 412, in _rmtree_safe_fd _rmtree_safe_fd(dirfd, fullname, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 412, in _rmtree_safe_fd _rmtree_safe_fd(dirfd, fullname, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 408, in _rmtree_safe_fd onerror(os.open, fullname, sys.exc_info()) File "/home/angwer/cpython/Lib/shutil.py", line 406, in _rmtree_safe_fd dirfd = os.open(name, os.O_RDONLY, dir_fd=topfd) PermissionError: [Errno 13] Permission denied: 'SUB21'

'test_os' left behind directory '@test_23400_tmp' and it couldn't be removed: [Errno 13] Permission denied: 'SUB21' test_os failed

1 test failed: test_os

Total duration: 292 ms Tests result: FAILURE Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/support/init.py", line 914, in temp_dir yield path File "/home/angwer/cpython/Lib/test/support/init.py", line 963, in temp_cwd yield cwd_dir File "/home/angwer/cpython/Lib/test/libregrtest/main.py", line 468, in main self._main(tests, kwargs) File "/home/angwer/cpython/Lib/test/libregrtest/main.py", line 497, in _main sys.exit(len(self.bad) > 0 or self.interrupted) SystemExit: True

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "/home/angwer/cpython/Lib/runpy.py", line 193, in _run_module_as_main "main", mod_spec) File "/home/angwer/cpython/Lib/runpy.py", line 85, in _run_code exec(code, run_globals) File "/home/angwer/cpython/Lib/test/main.py", line 2, in main() File "/home/angwer/cpython/Lib/test/libregrtest/main.py", line 532, in main Regrtest().main(tests=tests, **kwargs) File "/home/angwer/cpython/Lib/test/libregrtest/main.py", line 468, in main self._main(tests, kwargs) File "/home/angwer/cpython/Lib/contextlib.py", line 100, in exit self.gen.throw(type, value, traceback) File "/home/angwer/cpython/Lib/test/support/init.py", line 963, in temp_cwd yield cwd_dir File "/home/angwer/cpython/Lib/contextlib.py", line 100, in exit self.gen.throw(type, value, traceback) File "/home/angwer/cpython/Lib/test/support/init.py", line 917, in temp_dir rmtree(path) File "/home/angwer/cpython/Lib/test/support/init.py", line 377, in rmtree _rmtree(path) File "/home/angwer/cpython/Lib/shutil.py", line 474, in rmtree _rmtree_safe_fd(fd, path, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 412, in _rmtree_safe_fd _rmtree_safe_fd(dirfd, fullname, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 412, in _rmtree_safe_fd _rmtree_safe_fd(dirfd, fullname, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 412, in _rmtree_safe_fd _rmtree_safe_fd(dirfd, fullname, onerror) File "/home/angwer/cpython/Lib/shutil.py", line 408, in _rmtree_safe_fd onerror(os.open, fullname, sys.exc_info()) File "/home/angwer/cpython/Lib/shutil.py", line 406, in _rmtree_safe_fd dirfd = os.open(name, os.O_RDONLY, dir_fd=topfd) PermissionError: [Errno 13] Permission denied: 'SUB21'

msg279582 - (view)

Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer)

Date: 2016-10-28 06:00

Hmm, tests were passed when I ran them before committing. Seems this is heisenbug.

msg279583 - (view)

Author: Xiang Zhang (xiang.zhang) * (Python committer)

Date: 2016-10-28 06:14

Seems like the dir you add breaks other cases. I change addCleanUp to os.chmod and get:

====================================================================== FAIL: test_file_like_path (test.test_os.BytesWalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 950, in test_file_like_path self.test_walk_prune(_PathLike(self.walk_path)) File "/home/angwer/cpython/Lib/test/test_os.py", line 941, in test_walk_prune self.assertEqual(len(all), 2) AssertionError: 3 != 2

====================================================================== FAIL: test_walk_bottom_up (test.test_os.BytesWalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 956, in test_walk_bottom_up self.assertEqual(len(all), 4, all) AssertionError: 5 != 4 : [('@test_24702_tmp/TEST1/SUB2/SUB21', [], ['tmp3']), ('@test_24702_tmp/TEST1/SUB2', ['link', 'SUB21'], ['tmp3', 'broken_link3', 'broken_link', 'broken_link2']), ('@test_24702_tmp/TEST1/SUB1/SUB11', [], []), ('@test_24702_tmp/TEST1/SUB1', ['SUB11'], ['tmp2']), ('@test_24702_tmp/TEST1', ['SUB2', 'SUB1'], ['tmp1'])]

====================================================================== FAIL: test_walk_prune (test.test_os.BytesWalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 941, in test_walk_prune self.assertEqual(len(all), 2) AssertionError: 3 != 2

====================================================================== FAIL: test_walk_topdown (test.test_os.BytesWalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 916, in test_walk_topdown self.assertEqual(len(all), 4) AssertionError: 5 != 4

====================================================================== FAIL: test_file_like_path (test.test_os.FwalkTests)

====================================================================== FAIL: test_walk_bottom_up (test.test_os.FwalkTests)

====================================================================== FAIL: test_walk_prune (test.test_os.FwalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 941, in test_walk_prune self.assertEqual(len(all), 2) AssertionError: 3 != 2

====================================================================== FAIL: test_walk_topdown (test.test_os.FwalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 916, in test_walk_topdown self.assertEqual(len(all), 4) AssertionError: 5 != 4

====================================================================== FAIL: test_file_like_path (test.test_os.WalkTests)

====================================================================== FAIL: test_walk_bottom_up (test.test_os.WalkTests)

====================================================================== FAIL: test_walk_prune (test.test_os.WalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 941, in test_walk_prune self.assertEqual(len(all), 2) AssertionError: 3 != 2

====================================================================== FAIL: test_walk_topdown (test.test_os.WalkTests)

Traceback (most recent call last): File "/home/angwer/cpython/Lib/test/test_os.py", line 916, in test_walk_topdown self.assertEqual(len(all), 4) AssertionError: 5 != 4

msg279584 - (view)

Author: Roundup Robot (python-dev) (Python triager)

Date: 2016-10-28 06:19

New changeset 655510dd46fd by Serhiy Storchaka in branch '3.5': Issue #28353: Make test_os.WalkTests.test_walk_bad_dir stable. https://hg.python.org/cpython/rev/655510dd46fd

New changeset df28e536f19d by Serhiy Storchaka in branch '3.6': Issue #28353: Make test_os.WalkTests.test_walk_bad_dir stable. https://hg.python.org/cpython/rev/df28e536f19d

New changeset aa891d13e1cf by Serhiy Storchaka in branch 'default': Issue #28353: Make test_os.WalkTests.test_walk_bad_dir stable. https://hg.python.org/cpython/rev/aa891d13e1cf

msg279585 - (view)

Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer)

Date: 2016-10-28 06:23

test_walk_bad_dir renamed one of subdirs and tearDown failed to clean up changed tree. An error happened depending on the order of listed subdirectories: ['SUB1', 'SUB2'] -- passed, ['SUB2', 'SUB1'] -- failed.

msg279586 - (view)

Author: Xiang Zhang (xiang.zhang) * (Python committer)

Date: 2016-10-28 06:26

It works. Close. :-)

History

Date

User

Action

Args

2022-04-11 14:58:37

admin

set

github: 72539

2017-03-31 16:36:09

dstufft

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pull_requests: + <pull%5Frequest851>

2016-10-28 06:26:12

xiang.zhang

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status: open -> closed

messages: +

2016-10-28 06:23:36

serhiy.storchaka

set

messages: +

2016-10-28 06:19:47

python-dev

set

messages: +

2016-10-28 06:14:27

xiang.zhang

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messages: +

2016-10-28 06:00:30

serhiy.storchaka

set

messages: +

2016-10-28 04:54:54

xiang.zhang

set

status: closed -> open
nosy: + xiang.zhang
messages: +

2016-10-26 08🔞07

serhiy.storchaka

set

status: open -> closed
resolution: fixed
stage: patch review -> resolved

2016-10-25 17:20:52

python-dev

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messages: +

2016-10-25 16:03:55

python-dev

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messages: +

2016-10-25 11:35:35

python-dev

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nosy: + python-dev
messages: +

2016-10-25 10:50:34

serhiy.storchaka

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assignee: serhiy.storchaka

2016-10-06 07:15:33

serhiy.storchaka

set

files: + fwalk_oserror.patch
keywords: + patch

2016-10-06 07:15:05

serhiy.storchaka

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messages: +
stage: patch review

2016-10-05 10:49:35

Samson Lee

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messages: +

2016-10-05 04:50:20

Mariatta

set

nosy: + Mariatta

2016-10-04 14:45:16

serhiy.storchaka

set

versions: + Python 3.7
nosy: + loewis, neologix, hynek

messages: +

type: behavior

2016-10-04 09:07:52

Samson Lee

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messages: +

2016-10-04 07:45:40

serhiy.storchaka

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messages: +

2016-10-04 07:08:56

Samson Lee

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nosy: + serhiy.storchaka
messages: +

2016-10-04 07:06:56

Samson Lee

create