gh-95023: Added os.setns and os.unshare to easily switch between namespaces on Linux

Doc/library/os.rst

@@ -590,6 +590,44 @@ process and user.
  See the documentation for :func:`getgroups` for cases where it may not
  return the same group list set by calling setgroups().
 
+.. function:: setns(fd, nstype=0)
+
+ Reassociate the current thread with a Linux namespace.
+ See the :manpage:`setns(2)` and :manpage:`namespaces(7)` man pages for more
+ details.
+
+ If *fd* refers to a :file:`/proc/{pid}/ns/` link, ``setns()`` reassociates the
+ calling thread with the namespace associated with that link,
+ and *nstype* may be set to one of the
+ :ref:`CLONE_NEW* constants <os-unshare-clone-flags>`
+ to impose constraints on the operation
+ (``0`` means no constraints).
+
+ Since Linux 5.8, *fd* may refer to a PID file descriptor obtained from
+ :func:`~os.pidfd_open`. In this case, ``setns()`` reassociates the calling thread
+ into one or more of the same namespaces as the thread referred to by *fd*.
+ This is subject to any constraints imposed by *nstype*,
+ which is a bit mask combining one or more of the
+ :ref:`CLONE_NEW* constants <os-unshare-clone-flags>`,
+ e.g. ``setns(fd, os.CLONE_NEWUTS | os.CLONE_NEWPID)``.
+ The caller's memberships in unspecified namespaces are left unchanged.
+
+ *fd* can be any object with a :meth:`~io.IOBase.fileno` method, or a raw file descriptor.
+
+ This example reassociates the thread with the ``init`` process's network namespace::
+
+ fd = os.open("/proc/1/ns/net", os.O_RDONLY)
+ os.setns(fd, os.CLONE_NEWNET)
+ os.close(fd)
+
+ .. availability:: Linux >= 3.0 with glibc >= 2.14.
+
+ .. versionadded:: 3.12
+
+ .. seealso::
+
+ The :func:`~os.unshare` function.
+
 .. function:: setpgrp()
 
  Call the system call :c:func:`setpgrp` or ``setpgrp(0, 0)`` depending on
@@ -756,6 +794,49 @@ process and user.
  The function is now always available and is also available on Windows.
 
 
+.. function:: unshare(flags)
+
+ Disassociate parts of the process execution context, and move them into a
+ newly created namespace.
+ See the :manpage:`unshare(2)`
+ man page for more details.
+ The *flags* argument is a bit mask, combining zero or more of the
+ :ref:`CLONE_* constants <os-unshare-clone-flags>`,
+ that specifies which parts of the execution context should be
+ unshared from their existing associations and moved to a new namespace.
+ If the *flags* argument is ``0``, no changes are made to the calling process's
+ execution context.
+
+ .. availability:: Linux >= 2.6.16.
+
+ .. versionadded:: 3.12
+
+ .. seealso::
+
+ The :func:`~os.setns` function.
+
+.. _os-unshare-clone-flags:
+
+Flags to the :func:`unshare` function, if the implementation supports them.
+See :manpage:`unshare(2)` in the Linux manual
+for their exact effect and availability.
+
+.. data:: CLONE_FILES
+ CLONE_FS
+ CLONE_NEWCGROUP
+ CLONE_NEWIPC
+ CLONE_NEWNET
+ CLONE_NEWNS
+ CLONE_NEWPID
+ CLONE_NEWTIME
+ CLONE_NEWUSER
+ CLONE_NEWUTS
+ CLONE_SIGHAND
+ CLONE_SYSVSEM
+ CLONE_THREAD
+ CLONE_VM
+
+
 .. _os-newstreams:
 
 File Object Creation

Include/internal/pycore_global_strings.h

@@ -489,6 +489,7 @@ struct _Py_global_strings {
  STRUCT_FOR_ID(node_depth)
  STRUCT_FOR_ID(node_offset)
  STRUCT_FOR_ID(ns)
+ STRUCT_FOR_ID(nstype)
  STRUCT_FOR_ID(number)
  STRUCT_FOR_ID(obj)
  STRUCT_FOR_ID(object)

Lib/test/test_posix.py

@@ -2194,6 +2194,53 @@ def test_utime(self):
  os.utime("path", dir_fd=0)
 
 
+class NamespacesTests(unittest.TestCase):
+ """Tests for os.unshare() and os.setns()."""
+
+ @unittest.skipUnless(hasattr(os, 'unshare'), 'needs os.unshare()')
+ @unittest.skipUnless(hasattr(os, 'setns'), 'needs os.setns()')
+ @unittest.skipUnless(os.path.exists('/proc/self/ns/uts'), 'need /proc/self/ns/uts')
+ @support.requires_linux_version(3, 0, 0)
+ def test_unshare_setns(self):
+ code = """if 1:
+ import errno
+ import os
+ import sys
+ fd = os.open('/proc/self/ns/uts', os.O_RDONLY)
+ try:
+ original = os.readlink('/proc/self/ns/uts')
+ try:
+ os.unshare(os.CLONE_NEWUTS)
+ except OSError as e:
+ if e.errno == errno.ENOSPC:
+ # skip test if limit is exceeded
+ sys.exit()
+ raise
+ new = os.readlink('/proc/self/ns/uts')
+ if original == new:
+ raise Exception('os.unshare failed')
+ os.setns(fd, os.CLONE_NEWUTS)
+ restored = os.readlink('/proc/self/ns/uts')
+ if original != restored:
+ raise Exception('os.setns failed')
+ except PermissionError:
+ # The calling process did not have the required privileges
+ # for this operation
+ pass
+ except OSError as e:
+ # Skip the test on these errors:
+ # - ENOSYS: syscall not available
+ # - EINVAL: kernel was not configured with the CONFIG_UTS_NS option
+ # - ENOMEM: not enough memory
+ if e.errno not in (errno.ENOSYS, errno.EINVAL, errno.ENOMEM):
+ raise
+ finally:
+ os.close(fd)
+ """
+
+ assert_python_ok("-c", code)
+
+
 def tearDownModule():
  support.reap_children()
 

Misc/ACKS

@@ -344,6 +344,7 @@ Hervé Coatanhay
 Riccardo Coccioli
 Nick Coghlan
 Josh Cogliati
+Noam Cohen
 Dave Cole
 Terrence Cole
 Benjamin Collar

Misc/NEWS.d/next/Core and Builtins/2022-07-20-09-04-55.gh-issue-95023.bs-xd7.rst

@@ -0,0 +1 @@
+Implement :func:`os.setns` and :func:`os.unshare` for Linux. Patch by Noam Cohen.