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

Doc/library/os.rst

@@ -569,6 +569,39 @@ 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, subject to any
+   constraints imposed by the *nstype* argument (a *nstype* of ``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*
+   subject to any constraints imposed by *nstype*, which is a bit mask specified
+   by combining one or more of the ``CLONE_NEW*`` constants,
+   e.g., as ``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 or newer with glibc 2.14 or newer.
+
+   .. versionadded:: 3.12
+
+   .. seealso::
+
+      The :func:`~os.unshare` function.
+
 .. function:: setpgrp()
 
    Call the system call :c:func:`setpgrp` or ``setpgrp(0, 0)`` depending on
@@ -732,6 +765,46 @@ 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 ``CLONE_*``
+   constants, 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 or newer.
+
+   .. versionadded:: 3.12
+
+   .. seealso::
+
+      The :func:`~os.setns` function.
+
+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

Lib/test/test_posix.py

@@ -2172,6 +2172,58 @@ def test_utime(self):
                 os.utime("path", dir_fd=0)
 
 
+class NamespacesTests(unittest.TestCase):
+    """Tests for os.unshare() and os.setns()."""
+
+    @support.requires_subprocess()
+    def subprocess(self, code):
+        import subprocess
+        with subprocess.Popen((sys.executable, '-c', code),
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            encoding="utf-8"
+        ) as p:
+            p.wait()
+            return (
+                p.returncode,
+                tuple(p.stdout),
+                tuple(p.stderr),
+            )
+
+    @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):
+        rc, out, err = self.subprocess("""if 1:
+            import os
+            import sys
+            fd = os.open('/proc/self/ns/uts', os.O_RDONLY)
+            try:
+                print(os.readlink('/proc/self/ns/uts'))
+                os.unshare(os.CLONE_NEWUTS)
+                print(os.readlink('/proc/self/ns/uts'))
+                os.setns(fd, os.CLONE_NEWUTS)
+                print(os.readlink('/proc/self/ns/uts'))
+            except OSError as e:
+                sys.stderr.write(str(e.errno))
+                sys.exit(2)
+            finally:
+                os.close(fd)
+            """)
+
+        if rc == 2:
+            e = int(err[0])
+            self.assertIn(e, (errno.EPERM, errno.EINVAL, errno.ENOSPC, errno.ENOSYS))
+            self.skipTest(f"could not call os.unshare / os.setns [Errno {e}].")
+
+        self.assertEqual(rc, 0)
+        self.assertEqual(err, ())
+        original, new, back = out
+        self.assertNotEqual(original, new)
+        self.assertEqual(original, back)
+
+
 def tearDownModule():
     support.reap_children()
 

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.

Modules/posixmodule.c

@@ -8588,6 +8588,64 @@ os_pidfd_open_impl(PyObject *module, pid_t pid, unsigned int flags)
 #endif
 
 
+#ifdef HAVE_SETNS
+/*[clinic input]
+os.setns
+  fd: fildes
+    A file descriptor to a namespace.
+  nstype: int = 0
+    Type of namespace.
+
+Move the calling thread into different namespaces.
+[clinic start generated code]*/
+
+static PyObject *
+os_setns_impl(PyObject *module, int fd, int nstype)
+/*[clinic end generated code: output=5dbd055bfb66ecd0 input=42787871226bf3ee]*/
+{
+    int res;
+
+    Py_BEGIN_ALLOW_THREADS
+    res = setns(fd, nstype);
+    Py_END_ALLOW_THREADS
+
+    if (res != 0) {
+        return posix_error();
+    }
+
+    Py_RETURN_NONE;
+}
+#endif
+
+
+#ifdef HAVE_UNSHARE
+/*[clinic input]
+os.unshare
+  flags: int
+    Namespaces to be unshared.
+
+Disassociate parts of a process (or thread) execution context.
+[clinic start generated code]*/
+
+static PyObject *
+os_unshare_impl(PyObject *module, int flags)
+/*[clinic end generated code: output=1b3177906dd237ee input=9e065db3232b8b1b]*/
+{
+    int res;
+
+    Py_BEGIN_ALLOW_THREADS
+    res = unshare(flags);
+    Py_END_ALLOW_THREADS
+
+    if (res != 0) {
+        return posix_error();
+    }
+
+    Py_RETURN_NONE;
+}
+#endif
+
+
 #if defined(HAVE_READLINK) || defined(MS_WINDOWS)
 /*[clinic input]
 os.readlink
@@ -14933,6 +14991,8 @@ static PyMethodDef posix_methods[] = {
     OS__ADD_DLL_DIRECTORY_METHODDEF
     OS__REMOVE_DLL_DIRECTORY_METHODDEF
     OS_WAITSTATUS_TO_EXITCODE_METHODDEF
+    OS_SETNS_METHODDEF
+    OS_UNSHARE_METHODDEF
     {NULL,              NULL}            /* Sentinel */
 };
 
@@ -15378,6 +15438,53 @@ all_ins(PyObject *m)
 #ifdef SCHED_FX
     if (PyModule_AddIntConstant(m, "SCHED_FX", SCHED_FSS)) return -1;
 #endif
+
+/* constants for namespaces */
+#if defined(HAVE_SETNS) || defined(HAVE_UNSHARE)
+#ifdef CLONE_FS
+    if (PyModule_AddIntMacro(m, CLONE_FS)) return -1;
+#endif
+#ifdef CLONE_FILES
+    if (PyModule_AddIntMacro(m, CLONE_FILES)) return -1;
+#endif
+#ifdef CLONE_NEWNS
+    if (PyModule_AddIntMacro(m, CLONE_NEWNS)) return -1;
+#endif
+#ifdef CLONE_NEWCGROUP
+    if (PyModule_AddIntMacro(m, CLONE_NEWCGROUP)) return -1;
+#endif
+#ifdef CLONE_NEWUTS
+    if (PyModule_AddIntMacro(m, CLONE_NEWUTS)) return -1;
+#endif
+#ifdef CLONE_NEWIPC
+    if (PyModule_AddIntMacro(m, CLONE_NEWIPC)) return -1;
+#endif
+#ifdef CLONE_NEWUSER
+    if (PyModule_AddIntMacro(m, CLONE_NEWUSER)) return -1;
+#endif
+#ifdef CLONE_NEWPID
+    if (PyModule_AddIntMacro(m, CLONE_NEWPID)) return -1;
+#endif
+#ifdef CLONE_NEWNET
+    if (PyModule_AddIntMacro(m, CLONE_NEWNET)) return -1;
+#endif
+#ifdef CLONE_NEWTIME
+    if (PyModule_AddIntMacro(m, CLONE_NEWTIME)) return -1;
+#endif
+#ifdef CLONE_SYSVSEM
+    if (PyModule_AddIntMacro(m, CLONE_SYSVSEM)) return -1;
+#endif
+#ifdef CLONE_THREAD
+    if (PyModule_AddIntMacro(m, CLONE_THREAD)) return -1;
+#endif
+#ifdef CLONE_SIGHAND
+    if (PyModule_AddIntMacro(m, CLONE_SIGHAND)) return -1;
+#endif
+#ifdef CLONE_VM
+    if (PyModule_AddIntMacro(m, CLONE_VM)) return -1;
+#endif
+#endif
+
 #endif
 
 #ifdef USE_XATTRS