Handle condition going from privileged to non-privileged user in whic…

…h the cwd disables descent.

Fall back to Mitogen's temporary directory. In relation to mitogen-hq#636.

ansible_mitogen/runner.py

@@ -378,10 +378,15 @@ def _setup_cwd(self):
         """
         For situations like sudo to a non-privileged account, CWD could be
         $HOME of the old account, which could have mode go=, which means it is
-        impossible to restore the old directory, so don't even try.
+        impossible to restore the old directory. Fallback to a neutral temp if so.
         """
         if self.cwd:
-            os.chdir(self.cwd)
+            try:
+                os.chdir(self.cwd)
+            except OSError:
+                LOG.debug('%r: could not CHDIR to %r',
+                          self, self.cwd)
+                self._revert_cwd()
 
     def _setup_environ(self):
         """

docs/changelog.rst

@@ -20,6 +20,7 @@ To avail of fixes in an unreleased version, please download a ZIP file
 v0.2.10 (unreleased)
 --------------------
 
+* :gh:issue:`636` os.chdir fails if the sudo/become user lacks adequate permissions to chdir prior to task
 * :gh:issue:`597` mitogen does not support Ansible 2.8 Python interpreter detection
 * :gh:issue:`655` wait_for_connection gives errors
 * :gh:issue:`672` cannot perform relative import error