Properly deserializes built-in exceptions

If the remote target and the caller have different python
versions, then built-in exceptions raised by the remote target
will not be properly deserialized on the caller. Because of this,
oslo.messaging will simply raise a RemoteError, instead of any
expected exceptions the caller might expect.

This patch addresses this issue.

Closes-Bug: #1630795

Change-Id: I6d9eaf5497e746be9766731172406ec624ef9ba7

oslo_messaging/_drivers/common.py

@@ -33,6 +33,7 @@ from oslo_messaging import _utils as utils
 LOG = logging.getLogger(__name__)
 
 _EXCEPTIONS_MODULE = 'exceptions' if six.PY2 else 'builtins'
+_EXCEPTIONS_MODULES = ['exceptions', 'builtins']
 
 
 '''RPC Envelope Version.
@@ -208,6 +209,13 @@ def deserialize_remote_exception(data, allowed_remote_exmods):
     name = failure.get('class')
     module = failure.get('module')
 
+    # the remote service which raised the given exception might have a
+    # different python version than the caller. For example, the caller might
+    # run python 2.7, while the remote service might run python 3.4. Thus,
+    # the exception module will be "builtins" instead of "exceptions".
+    if module in _EXCEPTIONS_MODULES:
+        module = _EXCEPTIONS_MODULE
+
     # NOTE(ameade): We DO NOT want to allow just any module to be imported, in
     # order to prevent arbitrary code execution.
     if module != _EXCEPTIONS_MODULE and module not in allowed_remote_exmods:

oslo_messaging/tests/test_exception_serialization.py

@@ -26,6 +26,7 @@ from oslo_messaging.tests import utils as test_utils
 load_tests = testscenarios.load_tests_apply_scenarios
 
 EXCEPTIONS_MODULE = 'exceptions' if six.PY2 else 'builtins'
+OTHER_EXCEPTIONS_MODULE = 'builtins' if six.PY2 else 'exceptions'
 
 
 class NovaStyleException(Exception):
@@ -149,6 +150,17 @@ class DeserializeRemoteExceptionTestCase(test_utils.BaseTestCase):
               remote_name='Exception',
               remote_args=('test\ntraceback\ntraceback\n', ),
               remote_kwargs={})),
+        ('different_python_versions',
+         dict(allowed=_standard_allowed,
+              clsname='Exception',
+              modname=OTHER_EXCEPTIONS_MODULE,
+              cls=Exception,
+              args=['test'],
+              kwargs={},
+              str='test\ntraceback\ntraceback\n',
+              remote_name='Exception',
+              remote_args=('test\ntraceback\ntraceback\n', ),
+              remote_kwargs={})),
         ('nova_style',
          dict(allowed=_standard_allowed,
               clsname='NovaStyleException',