Replace eval with function matching

Using eval in code is not safe and may lead to security
risks, especially given that query itself is supplied by a user.

This refactors the code making is presumably safe
and prone to code injections, which are possible with eval.

Story: 2011539
Task: 52866
Change-Id: If629023052aa2c067c419bba10837f77bcc3e59c
Signed-off-by: Dmitriy Rabotyagov <dmitriy@adria-cloud.com>

releasenotes/notes/grap_query_eval_fixup-9232ce40ad85993e.yaml

@@ -0,0 +1,5 @@
+---
+security:
+  - |
+    A security issue in the entity graph querying mechanism has been fixed.
+    This change hardens the query parser against malicious input.

vitrage/graph/query.py

@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import operator
 from oslo_log import log as logging
 
 from vitrage.common.exception import VitrageError
@@ -21,13 +22,21 @@ LOG = logging.getLogger(__name__)
 operators = [
     '<',
     '<=',
-    # '=',
     '==',
     '!=',
     '>=',
     '>',
 ]
 
+ops = {
+    '<': operator.lt,
+    '<=': operator.le,
+    '==': operator.eq,
+    '!=': operator.ne,
+    '>=': operator.ge,
+    '>': operator.gt,
+}
+
 logical_operations = [
     'and',
     'or'
@@ -64,10 +73,7 @@ def create_predicate(query_dict):
     :return: a predicate "match(item)"
     """
     try:
-        expression = _create_query_expression(query=query_dict)
-        LOG.debug('create_predicate::%s', expression)
-        expression = 'lambda item: ' + expression
-        return eval(expression)
+        return _create_query_function(query=query_dict)
     except Exception as e:
         LOG.error('invalid query format %s. Exception: %s',
                   query_dict, e)
@@ -75,46 +81,42 @@ def create_predicate(query_dict):
                            query_dict, e)
 
 
-def _create_query_expression(query, parent_operator=None):
-    expressions = []
+def _create_query_function(query, parent_operator=None):
 
     # First element or element under logical operation
     if not parent_operator and isinstance(query, dict):
         (key, value) = query.copy().popitem()
-        return _create_query_expression(value, key)
+        return _create_query_function(value, key)
 
     # Continue recursion on logical (and/or) operation
     elif parent_operator in logical_operations and isinstance(query, list):
-        for val in query:
-            expressions.append(_create_query_expression(val))
-        return _join_logical_operator(parent_operator, expressions)
+        predicates = [_create_query_function(val) for val in query]
+
+        if not predicates:
+            return lambda item: False
+
+        if parent_operator == 'and':
+            return lambda item: all(p(item) for p in predicates)
+        elif parent_operator == 'or':
+            return lambda item: any(p(item) for p in predicates)
 
     # Recursion evaluate leaf (stop condition)
     elif parent_operator in operators:
-        for key, val in query.items():
-            expressions.append('item.get(' + _evaluable_str(key) + ')' +
-                               parent_operator + ' ' + _evaluable_str(val))
-        return _join_logical_operator('and', expressions)
+        predicates = []
+        op_func = ops[parent_operator]
+        for field, value in query.items():
+            predicates.append(
+                lambda item, f=field, v=value: op_func(item.get(f), v)
+            )
+
+        # Multiple conditions under a comparison operator are implicitly 'and'
+        if len(predicates) > 1:
+            return lambda item: all(p(item) for p in predicates)
+        elif predicates:
+            return predicates[0]
+        else:
+            return lambda item: False
+
     else:
         raise VitrageError('invalid partial query format',
                            parent_operator, query)
-
-
-def _evaluable_str(value):
-    """wrap string/unicode with back tick"""
-    if isinstance(value, str):
-        return '\'' + value + '\''
-    else:
-        return str(value)
-
-
-def _join_logical_operator(op, expressions):
-    """Create an expressions string
-
-    Example input:
-        op='AND'
-        expressions=['a == b', 'c < d']
-    Example output: (a == b AND c < d)
-    """
-    separator = ' ' + op + ' '
-    return '(' + separator.join(expressions) + ')'