Policy: Disallow policy_templates objects to have duplicate keys

Bug: 1108908
Change-Id: Iff1c506befb6e7703f8858246cdade1493b87f66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2409915
Commit-Queue: Nikita Podguzov <nikitapodguzov@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807662}

components/policy/tools/syntax_check_policy_template_json.py

@@ -7,6 +7,7 @@ Checks a policy_templates.json file for conformity to its syntax specification.
 '''
 
 import argparse
+import ast
 import json
 import os
 import re
@@ -201,6 +202,20 @@ def MergeDict(*dicts):
   return result
 
 
+class DuplicateKeyVisitor(ast.NodeVisitor):
+  def visit_Dict(self, node):
+    seen_keys = set()
+    for i, node_key in enumerate(node.keys):
+      key = ast.literal_eval(node_key)
+      if key in seen_keys:
+        raise ValueError("Duplicate key '%s' in line %d found." %
+                         (key, node.values[i].lineno))
+      seen_keys.add(key)
+
+    # Recursively check for all nested objects.
+    self.generic_visit(node)
+
+
 class PolicyTemplateChecker(object):
 
   def __init__(self):
@@ -1516,7 +1531,12 @@ class PolicyTemplateChecker(object):
   def Main(self, filename, options, original_file_contents, current_version):
     try:
       with open(filename, "rb") as f:
-        data = eval(f.read().decode("UTF-8"))
+        raw_data = f.read().decode("UTF-8")
+        data = eval(raw_data)
+        DuplicateKeyVisitor().visit(ast.parse(raw_data))
+    except ValueError as e:
+      self._Error(str(e))
+      return 1
     except:
       import traceback
       traceback.print_exc(file=sys.stdout)