From de52944f389c85943f35049cc9cdf9ea0a3ca380 Mon Sep 17 00:00:00 2001
From: Joshua Haberman <haberman@google.com>
Date: Mon, 11 Dec 2023 16:55:43 -0800
Subject: [PATCH] [Python/upb] Fixed SEGV when attempting to delete a message
 attribute

Deleting an attribute is not allowed in any Proto Python implementation, but upb was not checking for this case.

PiperOrigin-RevId: 589995449
---
 python/google/protobuf/internal/message_test.py | 11 +++++++++++
 python/message.c                                |  6 ++++++
 2 files changed, 17 insertions(+)

diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index b0f1ae784fa6..a6223c2a7edf 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -1340,6 +1340,17 @@ def testFieldPresence(self):
     self.assertEqual(False, message.optional_bool)
     self.assertEqual(0, message.optional_nested_message.bb)
 
+  def testDel(self):
+    msg = unittest_pb2.TestAllTypes()
+
+    # Fields cannot be deleted.
+    with self.assertRaises(AttributeError):
+      del msg.optional_int32
+    with self.assertRaises(AttributeError):
+      del msg.optional_bool
+    with self.assertRaises(AttributeError):
+      del msg.repeated_nested_message
+
   def testAssignInvalidEnum(self):
     """Assigning an invalid enum number is not allowed in proto2."""
     m = unittest_pb2.TestAllTypes()
diff --git a/python/message.c b/python/message.c
index 2aea2c5a9ff9..2cca1c1f0f19 100644
--- a/python/message.c
+++ b/python/message.c
@@ -1005,6 +1005,12 @@ __attribute__((flatten)) static PyObject* PyUpb_Message_GetAttr(
 static int PyUpb_Message_SetAttr(PyObject* _self, PyObject* attr,
                                  PyObject* value) {
   PyUpb_Message* self = (void*)_self;
+
+  if (value == NULL) {
+    PyErr_SetString(PyExc_AttributeError, "Cannot delete field attribute");
+    return -1;
+  }
+
   const upb_FieldDef* field;
   if (!PyUpb_Message_LookupName(self, attr, &field, NULL,
                                 PyExc_AttributeError)) {