fix(detector): detect property-backed attribute replay

kernelguard.py

@@ -2459,6 +2459,95 @@ def _has_ver(expr: ast.AST | None) -> bool:
                 ),
             }]
 
+        # Fourth pass: replay from an attribute on captured state that the
+        # entrypoint fills after a state-only fast path.
+        #
+        # Pattern: if hasattr(_state, "value"): return _state.value
+        #          _state.value = data.clone()
+        #          return _state.value
+        params = {
+            arg.arg
+            for args in (node.args.posonlyargs, node.args.args, node.args.kwonlyargs)
+            for arg in args
+        }
+        if node.args.vararg is not None:
+            params.add(node.args.vararg.arg)
+        if node.args.kwarg is not None:
+            params.add(node.args.kwarg.arg)
+
+        global_names = {
+            name
+            for stmt in node.body
+            if isinstance(stmt, ast.Global)
+            for name in stmt.names
+        }
+        local_names = {
+            target.id
+            for stmt in node.body
+            if isinstance(stmt, (ast.Assign, ast.AnnAssign, ast.AugAssign))
+            for target in (
+                stmt.targets if isinstance(stmt, ast.Assign)
+                else [stmt.target]
+            )
+            if isinstance(target, ast.Name) and target.id not in global_names
+        }
+        captured = _expr_names(node) - params - local_names
+
+        mutated_attrs: set[tuple[str, str]] = set()
+        attr_sources: dict[str, tuple[str, str]] = {}
+
+        for child in ast.walk(node):
+            if not isinstance(child, ast.Assign):
+                continue
+            if isinstance(child.value, ast.Attribute):
+                source_root = _ast_root_name(child.value)
+                if source_root in captured:
+                    for target in child.targets:
+                        if isinstance(target, ast.Name):
+                            attr_sources[target.id] = (source_root, child.value.attr)
+            for target in child.targets:
+                if not isinstance(target, ast.Attribute):
+                    continue
+                target_root = _ast_root_name(target)
+                if target_root in captured:
+                    mutated_attrs.add((target_root, target.attr))
+
+        if mutated_attrs:
+            for child in ast.walk(node):
+                if not isinstance(child, ast.If):
+                    continue
+                if _body_has_calls(child.body):
+                    continue
+                if _expr_names(child.test) & params:
+                    continue
+
+                returns_replayed_attr = False
+                for stmt in child.body:
+                    if not isinstance(stmt, ast.Return) or stmt.value is None:
+                        continue
+                    if (isinstance(stmt.value, ast.Name)
+                            and attr_sources.get(stmt.value.id) in mutated_attrs):
+                        returns_replayed_attr = True
+                        break
+                    if not isinstance(stmt.value, ast.Attribute):
+                        continue
+                    attr_key = (_ast_root_name(stmt.value), stmt.value.attr)
+                    if attr_key in mutated_attrs:
+                        returns_replayed_attr = True
+                        break
+
+                if not returns_replayed_attr:
+                    continue
+
+                return [{
+                    "pattern": "LAST_CALL_REPLAY",
+                    "severity": "critical",
+                    "evidence": (
+                        f"{entrypoint_name} returns an attribute from captured "
+                        "state mutated by the entrypoint"
+                    ),
+                }]
+
     return []