gh-109351: Fix crash when compiling AST with invalid NamedExpr (#109352)

Author: JelleZijlstra

Lib/test/test_compile.py

@@ -443,6 +443,33 @@ def f():
         self.assertIn("_A__mangled_mod", A.f.__code__.co_varnames)
         self.assertIn("__package__", A.f.__code__.co_varnames)
 
+    def test_compile_invalid_namedexpr(self):
+        # gh-109351
+        m = ast.Module(
+            body=[
+                ast.Expr(
+                    value=ast.ListComp(
+                        elt=ast.NamedExpr(
+                            target=ast.Constant(value=1),
+                            value=ast.Constant(value=3),
+                        ),
+                        generators=[
+                            ast.comprehension(
+                                target=ast.Name(id="x", ctx=ast.Store()),
+                                iter=ast.Name(id="y", ctx=ast.Load()),
+                                ifs=[],
+                                is_async=0,
+                            )
+                        ],
+                    )
+                )
+            ],
+            type_ignores=[],
+        )
+
+        with self.assertRaisesRegex(TypeError, "NamedExpr target must be a Name"):
+            compile(ast.fix_missing_locations(m), "<file>", "exec")
+
     def test_compile_ast(self):
         fname = __file__
         if fname.lower().endswith('pyc'):

Misc/NEWS.d/next/Core and Builtins/2023-09-12-16-00-42.gh-issue-109351.kznGeR.rst

@@ -0,0 +1,2 @@
+Fix crash when compiling an invalid AST involving a named (walrus)
+expression.

Python/ast.c

@@ -381,6 +381,11 @@ validate_expr(struct validator *state, expr_ty exp, expr_context_ty ctx)
         ret = validate_exprs(state, exp->v.Tuple.elts, ctx, 0);
         break;
     case NamedExpr_kind:
+        if (exp->v.NamedExpr.target->kind != Name_kind) {
+            PyErr_SetString(PyExc_TypeError,
+                            "NamedExpr target must be a Name");
+            return 0;
+        }
         ret = validate_expr(state, exp->v.NamedExpr.value, Load);
         break;
     /* This last case doesn't have any checking. */