Disable the use of anchors when parsing yaml

This can be used as a DDoS attack

Closes-Bug: 1785657
Change-Id: Icf460fea113e9279715cae87df3ef88a77575e04

mistral/event_engine/default_event_engine.py

@@ -23,7 +23,6 @@
 from oslo_service import threadgroup
 from oslo_utils import fnmatch
 import six
-import yaml
 
 from mistral import context as auth_ctx
 from mistral.db.v2 import api as db_api
@@ -33,6 +32,7 @@
 from mistral import messaging as mistral_messaging
 from mistral.rpc import clients as rpc
 from mistral.services import security
+from mistral.utils import safe_yaml
 
 
 LOG = logging.getLogger(__name__)
@@ -83,8 +83,8 @@ def __init__(self):
                 config = cf.read()
 
             try:
-                definition_cfg = yaml.safe_load(config)
-            except yaml.YAMLError as err:
+                definition_cfg = safe_yaml.load(config)
+            except safe_yaml.YAMLError as err:
                 if hasattr(err, 'problem_mark'):
                     mark = err.problem_mark
                     errmsg = (

mistral/lang/parser.py

@@ -15,7 +15,6 @@
 
 import cachetools
 import threading
-import yaml
 from yaml import error
 
 import six
@@ -27,6 +26,7 @@
 from mistral.lang.v2 import tasks as tasks_v2
 from mistral.lang.v2 import workbook as wb_v2
 from mistral.lang.v2 import workflows as wf_v2
+from mistral.utils import safe_yaml
 
 V2_0 = '2.0'
 
@@ -50,7 +50,7 @@ def parse_yaml(text):
     """
 
     try:
-        return yaml.safe_load(text) or {}
+        return safe_yaml.load(text) or {}
     except error.YAMLError as e:
         raise exc.DSLParsingException(
             "Definition could not be parsed: %s\n" % e

mistral/services/workflows.py

@@ -12,12 +12,12 @@
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
 
-import yaml
 
 from mistral.db.v2 import api as db_api
 from mistral import exceptions as exc
 from mistral.lang import parser as spec_parser
 from mistral import services
+from mistral.utils import safe_yaml
 from mistral.workflow import states
 from mistral_lib import utils
 from oslo_log import log as logging
@@ -95,7 +95,7 @@ def _append_all_workflows(definition, is_system, scope, namespace,
                           wf_list_spec, db_wfs):
     wfs = wf_list_spec.get_workflows()
 
-    wfs_yaml = yaml.load(definition) if len(wfs) != 1 else None
+    wfs_yaml = safe_yaml.load(definition) if len(wfs) != 1 else None
 
     for wf_spec in wfs:
         if len(wfs) != 1:
@@ -135,7 +135,7 @@ def update_workflows(definition, scope='private', identifier=None,
 
     db_wfs = []
 
-    wfs_yaml = yaml.load(definition) if len(wfs) != 1 else None
+    wfs_yaml = safe_yaml.load(definition) if len(wfs) != 1 else None
 
     with db_api.transaction():
         for wf_spec in wfs:
@@ -205,7 +205,7 @@ def _update_workflow(wf_spec, definition, scope, identifier=None,
 
 
 def _cut_wf_definition_from_all(wfs_yaml, wf_name):
-    return yaml.dump({
+    return safe_yaml.dump({
         'version': wfs_yaml['version'],
         wf_name: wfs_yaml[wf_name]
     })

mistral/tests/unit/lang/v2/base.py

@@ -14,11 +14,11 @@
 
 import copy
 
-import yaml
 
 from mistral import exceptions as exc
 from mistral.lang import parser as spec_parser
 from mistral.tests.unit import base
+from mistral.utils import safe_yaml
 from mistral_lib import utils
 
 
@@ -75,9 +75,10 @@ def _parse_dsl_spec(self, dsl_file=None, add_tasks=False,
             dsl_yaml = base.get_resource(self._resource_path + '/' + dsl_file)
 
             if changes:
-                dsl_dict = yaml.safe_load(dsl_yaml)
+                dsl_dict = safe_yaml.safe_load(dsl_yaml)
                 utils.merge_dicts(dsl_dict, changes)
-                dsl_yaml = yaml.safe_dump(dsl_dict, default_flow_style=False)
+                dsl_yaml = safe_yaml.safe_dump(dsl_dict,
+                                               default_flow_style=False)
         else:
             dsl_dict = copy.deepcopy(self._dsl_blank)
 
@@ -87,7 +88,7 @@ def _parse_dsl_spec(self, dsl_file=None, add_tasks=False,
             if changes:
                 utils.merge_dicts(dsl_dict, changes)
 
-            dsl_yaml = yaml.safe_dump(dsl_dict, default_flow_style=False)
+            dsl_yaml = safe_yaml.safe_dump(dsl_dict, default_flow_style=False)
 
         if not expect_error:
             return self._spec_parser(dsl_yaml)

mistral/tests/unit/utils/test_safeLoader.py

@@ -0,0 +1,70 @@
+#  Copyright 2019 - Nokia Corporation
+#
+#  Licensed under the Apache License, Version 2.0 (the "License"); you may
+#  not use this file except in compliance with the License. You may obtain
+#  a copy of the License at
+#
+#  http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#  License for the specific language governing permissions and limitations
+#  under the License.
+
+from unittest import TestCase
+
+from mistral.utils import safe_yaml
+
+
+class TestSafeLoader(TestCase):
+    def test_safe_load(self):
+        yaml_text = """
+        version: '2.0'
+
+        wf1:
+          type: direct
+
+          input:
+            - a: &a ["lol","lol","lol","lol","lol"]
+            - b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
+            - c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
+            - d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
+            - e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
+            - f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
+            - g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
+            - h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
+            - i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]
+
+
+          tasks:
+            hello:
+              action: std.echo output="Hello"
+              wait-before: 1
+              publish:
+                result: <% task(hello).result %>
+        """
+
+        result = {
+            'version': '2.0',
+            'wf1':
+                {'type': 'direct',
+                 'input': [
+                     {'a': '&a ["lol","lol","lol","lol","lol"]'},
+                     {'b': '&b [*a,*a,*a,*a,*a,*a,*a,*a,*a]'},
+                     {'c': '&c [*b,*b,*b,*b,*b,*b,*b,*b,*b]'},
+                     {'d': '&d [*c,*c,*c,*c,*c,*c,*c,*c,*c]'},
+                     {'e': '&e [*d,*d,*d,*d,*d,*d,*d,*d,*d]'},
+                     {'f': '&f [*e,*e,*e,*e,*e,*e,*e,*e,*e]'},
+                     {'g': '&g [*f,*f,*f,*f,*f,*f,*f,*f,*f]'},
+                     {'h': '&h [*g,*g,*g,*g,*g,*g,*g,*g,*g]'},
+                     {'i': '&i [*h,*h,*h,*h,*h,*h,*h,*h,*h]'}],
+                 'tasks':
+                    {'hello': {
+                        'action': 'std.echo output="Hello"',
+                        'wait-before': 1, 'publish':
+                            {'result': '<% task(hello).result %>'}
+                    }}
+                 }
+        }
+        self.assertEqual(result, safe_yaml.load(yaml_text))

mistral/utils/safe_yaml.py

@@ -0,0 +1,62 @@
+#  Copyright 2019 - Nokia Corporation
+#
+#  Licensed under the Apache License, Version 2.0 (the "License"); you may
+#  not use this file except in compliance with the License. You may obtain
+#  a copy of the License at
+#
+#  http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#  License for the specific language governing permissions and limitations
+#  under the License.
+
+import yaml
+from yaml import *  # noqa
+
+yaml.SafeDumper.ignore_aliases = lambda *args: True
+
+
+class SafeLoader(yaml.SafeLoader):
+    """Treat '@', '&', '*' as plain string.
+
+       Anchors are not used in mistral workflow. It's better to
+       disable them completely. Anchors can be used as an exploit to a
+       Denial of service attack through expansion (Billion Laughs)
+       see https://en.wikipedia.org/wiki/Billion_laughs_attack.
+       Also this module uses the safe loader by default which is always
+       a better loader.
+
+       When using yaml module to load a yaml file or a string use this
+       module instead of yaml.
+
+       Example:
+         import mistral.utils.safe_yaml as safe_yaml
+         ...
+         ...
+
+         safe_yaml.load(...)
+
+    """
+
+    def fetch_alias(self):
+        return self.fetch_plain()
+
+    def fetch_anchor(self):
+        return self.fetch_plain()
+
+    def check_plain(self):
+        # Modified: allow '@'
+        if self.peek() == '@':
+            return True
+        else:
+            return super(SafeLoader, self).check_plain()
+
+
+def load(stream):
+    return yaml.load(stream, SafeLoader)
+
+
+def safe_load(stream):
+    return load(stream)