Merge pull request #8890 from tausbn/python-add-global-attribute-writes

Python: Add support for global attribute writes

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/Attributes.qll

@@ -92,6 +92,32 @@ private class AttributeAssignmentAsAttrWrite extends AttrWrite, CfgNode {
   override string getAttributeName() { result = node.getName() }
 }
 
+/**
+ * An attribute assignment where the object is a global variable: `global_var.attr = value`.
+ *
+ * Syntactically, this is identical to the situation that is covered by
+ * `AttributeAssignmentAsAttrWrite`, however in this case we want to behave as if the object that is
+ * being written is the underlying `ModuleVariableNode`.
+ */
+private class GlobalAttributeAssignmentAsAttrWrite extends AttrWrite, CfgNode {
+  override AttributeAssignmentNode node;
+
+  override Node getValue() { result.asCfgNode() = node.getValue() }
+
+  override Node getObject() {
+    result.(ModuleVariableNode).getVariable() = node.getObject().getNode().(Name).getVariable()
+  }
+
+  override ExprNode getAttributeNameExpr() {
+    // Attribute names don't exist as `Node`s in the control flow graph, as they can only ever be
+    // identifiers, and are therefore represented directly as strings.
+    // Use `getAttributeName` to access the name of the attribute.
+    none()
+  }
+
+  override string getAttributeName() { result = node.getName() }
+}
+
 /** Represents `CallNode`s that may refer to calls to built-in functions or classes. */
 private class BuiltInCallNode extends CallNode {
   string name;

python/ql/test/experimental/dataflow/typetracking/attribute_tests.py

@@ -49,6 +49,24 @@ def test_create_with_foo():
     x = create_with_foo() # $ tracked=foo
     print(x.foo) # $ tracked=foo tracked
 
+def test_global_attribute_assignment():
+    global global_var
+    global_var.foo = tracked # $ tracked tracked=foo
+
+def test_global_attribute_read():
+    x = global_var.foo # $ tracked tracked=foo
+
+def test_local_attribute_assignment():
+    # Same as `test_global_attribute_assignment`, but the assigned variable is not global
+    # In this case, we don't want flow going to the `ModuleVariableNode` for `local_var` 
+    # (which is referenced in `test_local_attribute_read`).
+    local_var = object() # $ tracked=foo
+    local_var.foo = tracked # $ tracked tracked=foo
+
+def test_local_attribute_read():
+    x = local_var.foo
+
+
 # ------------------------------------------------------------------------------
 # Attributes assigned statically to a class
 # ------------------------------------------------------------------------------