From c9ade5e6be7ffec47f10d6d59818998bf03125a8 Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Tue, 10 Mar 2026 18:29:23 +0200 Subject: [PATCH] gh-145743: Fix inconsistency after calling Struct.__init__() with invalid format (GH-145744) Only set the format attribute after successful (re-)initialization. (cherry picked from commit 3f33bf83e8496737b86333bc9ec55dc3ccb3faca) Co-authored-by: Serhiy Storchaka --- Lib/test/test_struct.py | 20 ++++++++++++++++++-- Modules/_struct.c | 29 +++++++++++++++-------------- 2 files changed, 33 insertions(+), 16 deletions(-) diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py index a3f8fad7a9a0f9..0105027403ae19 100644 --- a/Lib/test/test_struct.py +++ b/Lib/test/test_struct.py @@ -579,8 +579,24 @@ def test_Struct_reinitialization(self): # Issue 9422: there was a memory leak when reinitializing a # Struct instance. This test can be used to detect the leak # when running with regrtest -L. - s = struct.Struct('i') - s.__init__('ii') + s = struct.Struct('>h') + s.__init__('>hh') + self.assertEqual(s.format, '>hh') + packed = b'\x00\x01\x00\x02' + self.assertEqual(s.pack(1, 2), packed) + self.assertEqual(s.unpack(packed), (1, 2)) + + with self.assertRaises(UnicodeEncodeError): + s.__init__('\udc00') + self.assertEqual(s.format, '>hh') + self.assertEqual(s.pack(1, 2), packed) + self.assertEqual(s.unpack(packed), (1, 2)) + + with self.assertRaises(struct.error): + s.__init__('$') + self.assertEqual(s.format, '>hh') + self.assertEqual(s.pack(1, 2), packed) + self.assertEqual(s.unpack(packed), (1, 2)) def check_sizeof(self, format_str, number_of_codes): # The size of 'PyStructObject' diff --git a/Modules/_struct.c b/Modules/_struct.c index c3ca125e41ab64..93b913955538b6 100644 --- a/Modules/_struct.c +++ b/Modules/_struct.c @@ -1420,11 +1420,11 @@ align(Py_ssize_t size, char c, const formatdef *e) /* calculate the size of a format string */ static int -prepare_s(PyStructObject *self) +prepare_s(PyStructObject *self, PyObject *format) { const formatdef *f; const formatdef *e; - formatcode *codes; + formatcode *codes, *codes0; const char *s; const char *fmt; @@ -1434,8 +1434,8 @@ prepare_s(PyStructObject *self) _structmodulestate *state = get_struct_state_structinst(self); - fmt = PyBytes_AS_STRING(self->s_format); - if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(self->s_format)) { + fmt = PyBytes_AS_STRING(format); + if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(format)) { PyErr_SetString(state->StructError, "embedded null character"); return -1; @@ -1511,13 +1511,7 @@ prepare_s(PyStructObject *self) PyErr_NoMemory(); return -1; } - /* Free any s_codes value left over from a previous initialization. */ - if (self->s_codes != NULL) - PyMem_Free(self->s_codes); - self->s_codes = codes; - self->s_size = size; - self->s_len = len; - + codes0 = codes; s = fmt; size = 0; while ((c = *s++) != '\0') { @@ -1557,6 +1551,14 @@ prepare_s(PyStructObject *self) codes->size = 0; codes->repeat = 0; + /* Free any s_codes value left over from a previous initialization. */ + if (self->s_codes != NULL) + PyMem_Free(self->s_codes); + self->s_codes = codes0; + self->s_size = size; + self->s_len = len; + Py_XSETREF(self->s_format, Py_NewRef(format)); + return 0; overflow: @@ -1622,9 +1624,8 @@ Struct___init___impl(PyStructObject *self, PyObject *format) return -1; } - Py_SETREF(self->s_format, format); - - ret = prepare_s(self); + ret = prepare_s(self, format); + Py_DECREF(format); return ret; }