Merge pull request #21602 from github/tausbn/python-port-modification-of-locals

Python: Port ModificationOfLocals.ql

Author: tausbn

python/ql/src/Statements/ModificationOfLocals.ql

@@ -12,10 +12,10 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.ApiGraphs
 
-predicate originIsLocals(ControlFlowNodeWithPointsTo n) {
-  n.pointsTo(_, _, Value::named("locals").getACall())
+predicate originIsLocals(ControlFlowNode n) {
+  API::builtin("locals").getReturn().getAValueReachableFromSource().asCfgNode() = n
 }
 
 predicate modification_of_locals(ControlFlowNode f) {
@@ -37,5 +37,8 @@ where
   // in module level scope `locals() == globals()`
   // see https://docs.python.org/3/library/functions.html#locals
   // FP report in https://github.com/github/codeql/issues/6674
-  not a.getScope() instanceof ModuleScope
+  not a.getScope() instanceof Module and
+  // in class level scope `locals()` reflects the class namespace,
+  // so modifications do take effect.
+  not a.getScope() instanceof Class
 select a, "Modification of the locals() dictionary will have no effect on the local variables."

python/ql/test/query-tests/Statements/general/test.py

@@ -174,3 +174,9 @@ def assert_ok(seq):
 # False positive. ODASA-8042. Fixed in PR #2401.
 class false_positive:
     e = (x for x in [])
+
+# In class-level scope `locals()` reflects the class namespace,
+# so modifications do take effect.
+class MyClass:
+    locals()['x'] = 43  # OK
+    y = x