Python startup should not require passwd entry

[bbi5291]

BPO	10496
Nosy	@loewis, @birkenfeld, @arekm, @vstinner, @tiran, @tarekziade, @ned-deily, @merwok, @bitdancer, @IIIIllllIIIIllllIIIIllllIIIIllllIIIIll, @serhiy-storchaka, @matrixise, @seirl, @yan12125, @surajssd, @izbyshev, @Cinerar, @miss-islington, @pxinwr
PRs	bpo-10496 Runing Inside docker container from non root user raises KeyError #3403 bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error #10919 [3.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10924 [3.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10924 [3.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10924 [3.6] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10925 [3.6] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10925 [2.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10930 [2.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10930 [2.7] bpo-10496: posixpath.expanduser() catchs pwd.getpwuid() error (GH-10919) #10930 bpo-10496: distutils check_environ() handles getpwuid() error #10931 bpo-10496: distutils check_environ() handles getpwuid() error #10931 bpo-10496: distutils check_environ() handles getpwuid() error #10931 [3.7] bpo-10496: distutils check_environ() handles getpwuid() error (GH-10931) #11212 [2.7] bpo-10496: distutils check_environ() handles getpwuid() error (GH-10931) #11213 bpo-31904: posixpath.expanduser() handles user home of None #23530
Files	bug.c nonexistent_user.patch user.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/merwok'
closed_at = <Date 2018-12-18.16:37:38.410>
created_at = <Date 2010-11-22.00:59:48.070>
labels = ['3.7', 'tests', '3.8', 'type-bug', 'library']
title = 'Python startup should not require passwd entry'
updated_at = <Date 2020-12-17.20:40:51.564>
user = 'https://bugs.python.org/bbi5291'

bugs.python.org fields:

activity = <Date 2020-12-17.20:40:51.564>
actor = 'pxinwr'
assignee = 'eric.araujo'
closed = True
closed_date = <Date 2018-12-18.16:37:38.410>
closer = 'vstinner'
components = ['Library (Lib)', 'Tests']
creation = <Date 2010-11-22.00:59:48.070>
creator = 'bbi5291'
dependencies = []
files = ['19760', '21896', '47211']
hgrepos = []
issue_num = 10496
keywords = ['patch', 'needs review']
message_count = 50.0
messages = ['122086', '122272', '122640', '132771', '133626', '133674', '133675', '133676', '133742', '133743', '133830', '134984', '134987', '135044', '135047', '135195', '135551', '135592', '135596', '155530', '155534', '156373', '193987', '257513', '270771', '272115', '282502', '282503', '282504', '302176', '302355', '303943', '304128', '331100', '331103', '331108', '331115', '331123', '331125', '331127', '331128', '331129', '331133', '331135', '331136', '331163', '332065', '332067', '332070', '332071']
nosy_count = 29.0
nosy_names = ['loewis', 'georg.brandl', 'arekm', 'vstinner', 'christian.heimes', 'nadeem.vawda', 'tarek', 'ned.deily', 'eric.araujo', 'grahamd', 'r.david.murray', 'neologix', 'filippo', 'xuanji', 'bbi5291', 'Denis.Barmenkov', 'aikinci', 'serhiy.storchaka', 'matrixise', 'zaytsev', 'antoine.pietri', 'yan12125', 'Jonathon Reinhart', 'surajd', 'izbyshev', 'cinerar', 'Nicholas Brown', 'miss-islington', 'pxinwr']
pr_nums = ['3403', '10919', '10924', '10924', '10924', '10925', '10925', '10930', '10930', '10930', '10931', '10931', '10931', '11212', '11213', '23530']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue10496'
versions = ['Python 2.7', 'Python 3.7', 'Python 3.8']

[bbi5291]

This bug is Linux-specific.

When Python cannot find the home directory of the user invoking it, it prints "'import site' failed; use -v for traceback".

This occurs only when both of these conditions are met:

1. /etc/passwd contains no entry for the current real UID
2. the HOME environment variable does not exist

To duplicate this bug, compile and run the attached program as root.
(This program assumes that 12345 is not a legitimate user on your system, and that Python is at /usr/bin/python ; if this is not the case then edit it accordingly.)

[ned-deily]

The problem is reproducible on a current Debian Linux system although with different results for current versions of Python (only security issues are accepted against 2.6). Unlike with 2.6, 3.1 reports no error. 2.7 and 3.2 both fail with an exception:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site.py", line 548, in <module>
    main()
  File "/usr/lib/python2.7/site.py", line 530, in main
    known_paths = addusersitepackages(known_paths)
  File "/usr/lib/python2.7/site.py", line 257, in addusersitepackages
    user_site = getusersitepackages()
  File "/usr/lib/python2.7/site.py", line 232, in getusersitepackages
    user_base = getuserbase() # this will also set USER_BASE
  File "/usr/lib/python2.7/site.py", line 222, in getuserbase
    USER_BASE = get_config_var('userbase')
  File "/usr/lib/python2.7/sysconfig.py", line 541, in get_config_var
    return get_config_vars().get(name)
  File "/usr/lib/python2.7/sysconfig.py", line 449, in get_config_vars
    _CONFIG_VARS['userbase'] = _getuserbase()
  File "/usr/lib/python2.7/sysconfig.py", line 198, in _getuserbase
    return env_base if env_base else joinuser("~", ".local")
  File "/usr/lib/python2.7/sysconfig.py", line 185, in joinuser
    return os.path.expanduser(os.path.join(*args))
  File "/usr/lib/python2.7/posixpath.py", line 256, in expanduser
    userhome = pwd.getpwuid(os.getuid()).pw_dir
KeyError: 'getpwuid(): uid not found: 12345'

[IIIIllllIIIIllllIIIIllllIIIIllllIIIIll]

I tried running bug.c using the svn head of python and got this:

Could not find platform independent libraries <prefix>
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Fatal Python error: Py_Initialize: Unable to get the locale encoding
LookupError: no codec search functions registered: can't find encoding
Aborted

[DenisBarmenkov]

I saw similar error on Python 2.6 installed on freeBSD.
I had test SVN server and wrote pre-commit hook using python. When remote developer commited his changes to repository, hook called os.path.expanduser and exception was raised:
# File "/usr/local/lib/python2.6/posixpath.py", line 259, in expanduser
# userhome = pwd.getpwuid(os.getuid()).pw_dir
#KeyError: 'getpwuid(): uid not found: 12345'

So its not a just-Linux issue.

[vstinner]

This issue remembers me the issue bpo-6612 (failure if the current directory was removed): the fix was to ignore os.getcwd().

Attached patch ignores os.path.expanduser() error (KeyError) and keeps ~ in the path. Example without HOME var and with an non existent user (uid 12345):

----------------------

$ env -i ./python
>>> import sysconfig
>>> sysconfig.get_config_var('userbase')
'~/.local'

>>> sysconfig.get_paths(scheme='posix_user', expand=False)
{'platstdlib': '{userbase}/lib/python{py_version_short}', 'platlib': '{userbase}/lib/python{py_version_short}/site-packages', 'purelib': '{userbase}/lib/python{py_version_short}/site-packages', 'stdlib': '{userbase}/lib/python{py_version_short}', 'scripts': '{userbase}/bin', 'include': '{userbase}/include/python{py_version_short}', 'data': '{userbase}'}

>>> sysconfig.get_paths(scheme='posix_user')              
{'platstdlib': '~/.local/lib/python3.3', 'platlib': '~/.local/lib/python3.3/site-packages', 'purelib': '~/.local/lib/python3.3/site-packages', 'stdlib': '~/.local/lib/python3.3', 'scripts': '~/.local/bin', 'include': '~/.local/include/python3.3', 'data': '~/.local'}

---

Example with an existant user but without HOME var:
----------------------

marge$ env -i ./python
>>> import sysconfig
>>> sysconfig.get_config_var('userbase')
'/home/haypo/.local'
>>> sysconfig.get_paths(scheme='posix_user')      
{'platstdlib': '/home/haypo/.local/lib/python3.3', 'platlib': '/home/haypo/.local/lib/python3.3/site-packages', 'purelib': '/home/haypo/.local/lib/python3.3/site-packages', 'stdlib': '/home/haypo/.local/lib/python3.3', 'scripts': '/home/haypo/.local/bin', 'include': '/home/haypo/.local/include/python3.3', 'data': '/home/haypo/.local'}

---

[merwok]

Can someone explain how it can happen that a user has no home directory?

[bbi5291]

I discovered this while I was implementing and testing a sandbox for automatic evaluation of programs.

[merwok]

Can you be more precise? IOW, why is this a Python bug rather than a system misconfiguration? Note that I don’t know a lot about POSIX, so I’m open to change my mind.

[neologix]

I'm not sure whether POSIX warrants anything about this behavior, but nothing prevents a process from running with a UID not listed in /etc/passwd (or NIS, whatever). For example, sudo allows running a command with a UID not listed in the password database, see http://linux.die.net/man/5/sudoers :
"""
targetpw

If set, sudo will prompt for the password of the user specified by the -u flag (defaults to root) instead of the password of the invoking user. Note that this precludes the use of a uid not listed in the passwd database as an argument to the -u flag. This flag is off by default.
"""

UIDs not backed by users are useful for example if you're working with a sandbox, or virtual users such as in some FTP servers http://www.proftpd.org/docs/howto/VirtualUsers.html :
"""
Question: What makes a user "virtual", then?
Answer: A virtual user is, quite simply, a user that is not defined in the system /etc/passwd file. This file associates a user name, given by the system administrator, to a user ID (commonly shortened to UID) and a group ID (GID), among other details. The Unix kernel does not deal with users in terms of their user names; it only "knows" about UIDs and GIDs. This means that an application like proftpd can look up the IDs to use for a given user name however it sees fit. Using /etc/passwd is not strictly required.
"""

[vstinner]

Because the patch is simple (just add a try/except), I think that it doesn't matter if only few people use users without entry in /etc/passwd and we should fix this issue.

[merwok]

It’s not just a try/except, it’s a behavior change: after the patch, paths returned by sysconfig may not be fully expanded paths. I would like Tarek to make a call on this.

[vstinner]

I would like Tarek to make a call on this.

So Tarek, what do you think?