bpo-30245: Fix possible overflow when organize struct.pack_into error message (#1682)

1 files changed, 10 insertions, 0 deletions

diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index 02d50b2..b2a5f42 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -599,6 +599,16 @@ class StructTest(unittest.TestCase):
                 'offset -11 out of range for 10-byte buffer'):
             struct.pack_into('<B', byte_list, -11, 123)
 
+    def test_boundary_error_message_with_large_offset(self):
+        # Test overflows cause by large offset and value size (issue 30245)
+        regex = (
+            r'pack_into requires a buffer of at least ' + str(sys.maxsize + 4) +
+            r' bytes for packing 4 bytes at offset ' + str(sys.maxsize) +
+            r' \(actual buffer size is 10\)'
+        )
+        with self.assertRaisesRegex(struct.error, regex):
+            struct.pack_into('<I', bytearray(10), sys.maxsize, 1)
+
     def test_issue29802(self):
         # When the second argument of struct.unpack() was of wrong type
         # the Struct object was decrefed twice and the reference to