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gh-78724: raise RuntimeError's when calling methods on non-ready Struct()'s by skirpichev · Pull Request #143643 · python/cpython · GitHub
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gh-78724: raise RuntimeError's when calling methods on non-ready Struct()'s #143643

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Merged
serhiy-storchaka merged 14 commits into from
Jan 11, 2026
+31 −8
Merged

gh-78724: raise RuntimeError's when calling methods on non-ready Struct()'s #143643

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a1c2603
gh-143379: fix UAF in struct.Struct.pack() when object modified by du…
skirpichev Jan 3, 2026
716e28c
Merge branch 'master' into fix-uaf-s_pack_internal/143379
skirpichev Jan 10, 2026
e611953
address review: implement a different solution with a mutex flag
skirpichev Jan 10, 2026
ab62167
+ clean the mess
skirpichev Jan 10, 2026
3b18427
gh-78724: raise RuntimeError's when calling methods on non-ready Stru…
skirpichev Jan 10, 2026
54dbea8
Merge branch 'master' into deprecate-struct-init/78724
skirpichev Jan 10, 2026
b6c8bed
revert stuff from #143382
skirpichev Jan 10, 2026
f542173
revert deprecations (TBD: a separate pr)
skirpichev Jan 10, 2026
69a5eec
address review: redo patch to use s_codes
skirpichev Jan 10, 2026
0e6af95
Merge branch 'main' into deprecate-struct-init/78724
skirpichev Jan 10, 2026
8ba6b33
address review: -asserts + redo test
skirpichev Jan 10, 2026
ea0f8e2
address review: adjust tests
skirpichev Jan 10, 2026
c71be45
Merge branch 'master' into deprecate-struct-init/78724
skirpichev Jan 11, 2026
b61bddb
address review: revert unrelated change
skirpichev Jan 11, 2026
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12 changes: 12 additions & 0 deletions Lib/test/test_struct.py
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Original file line number Diff line number Diff line change
Expand Up @@ -816,6 +816,18 @@ def test_endian_table_init_subinterpreters(self):
results = executor.map(exec, [code] * 5)
self.assertListEqual(list(results), [None] * 5)

def test_operations_on_half_initialized_Struct(self):
S = struct.Struct.__new__(struct.Struct)

spam = array.array('b', b' ')
self.assertRaises(RuntimeError, S.iter_unpack, 1)
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self.assertRaises(RuntimeError, S.pack, 1)
self.assertRaises(RuntimeError, S.pack_into, 1)

@serhiy-storchaka serhiy-storchaka Jan 10, 2026

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S.pack_into(buffer, offset, v1, v2, ...)

@skirpichev skirpichev Jan 10, 2026

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BTW, I think that argument processing in the struct's functions/methods should be refactored and transformed to the AC. E.g. S.pack_info could check required arguments before validation of the soself struct.

Though, this belongs to a separate issue.

@skirpichev skirpichev Jan 11, 2026

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AC cleanup goes to #143673

self.assertRaises(RuntimeError, S.unpack, spam)
self.assertRaises(RuntimeError, S.unpack_from, spam)
self.assertRaises(RuntimeError, getattr, S, 'format')
self.assertEqual(S.size, -1)


class UnpackIteratorTest(unittest.TestCase):
"""
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-01-10-10-04-08.gh-issue-78724.xkXfxX.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Raise :exc:`RuntimeError`'s when user attempts to call methods on
half-initialized :class:`~struct.Struct` objects, For example, created by
``Struct.__new__(Struct)``. Patch by Sergey B Kirpichev.
32 changes: 20 additions & 12 deletions Modules/_struct.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1698,8 +1698,6 @@ prepare_s(PyStructObject *self)
return -1;
}

self->s_size = size;
self->s_len = len;
codes = PyMem_Malloc((ncodes + 1) * sizeof(formatcode));
if (codes == NULL) {
PyErr_NoMemory();
Expand All @@ -1709,6 +1707,8 @@ prepare_s(PyStructObject *self)
if (self->s_codes != NULL)
PyMem_Free(self->s_codes);
self->s_codes = codes;
self->s_size = size;
self->s_len = len;

s = fmt;
size = 0;
Expand Down Expand Up @@ -1794,8 +1794,6 @@ static int
Struct___init___impl(PyStructObject *self, PyObject *format)
/*[clinic end generated code: output=b8e80862444e92d0 input=192a4575a3dde802]*/
{
int ret = 0;

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if (PyUnicode_Check(format)) {
format = PyUnicode_AsASCIIString(format);
if (format == NULL)
Expand All @@ -1816,8 +1814,10 @@ Struct___init___impl(PyStructObject *self, PyObject *format)

Py_SETREF(self->s_format, format);

ret = prepare_s(self);
return ret;
if (prepare_s(self)) {
return -1;
}
return 0;
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}

static int
Expand Down Expand Up @@ -1897,6 +1897,14 @@ s_unpack_internal(PyStructObject *soself, const char *startfrom,
return NULL;
}

#define ENSURE_STRUCT_IS_READY(self) \
do { \
if (!(self)->s_codes) { \
PyErr_SetString(PyExc_RuntimeError, \
"Struct object is not initialized"); \
return NULL; \
} \
} while (0);

/*[clinic input]
Struct.unpack
Expand All @@ -1917,7 +1925,7 @@ Struct_unpack_impl(PyStructObject *self, Py_buffer *buffer)
/*[clinic end generated code: output=873a24faf02e848a input=3113f8e7038b2f6c]*/
{
_structmodulestate *state = get_struct_state_structinst(self);
assert(self->s_codes != NULL);
ENSURE_STRUCT_IS_READY(self);
if (buffer->len != self->s_size) {
PyErr_Format(state->StructError,
"unpack requires a buffer of %zd bytes",
Expand Down Expand Up @@ -1949,7 +1957,7 @@ Struct_unpack_from_impl(PyStructObject *self, Py_buffer *buffer,
/*[clinic end generated code: output=57fac875e0977316 input=cafd4851d473c894]*/
{
_structmodulestate *state = get_struct_state_structinst(self);
assert(self->s_codes != NULL);
ENSURE_STRUCT_IS_READY(self);

if (offset < 0) {
if (offset + self->s_size > 0) {
Expand Down Expand Up @@ -2101,8 +2109,7 @@ Struct_iter_unpack_impl(PyStructObject *self, PyObject *buffer)
{
_structmodulestate *state = get_struct_state_structinst(self);
unpackiterobject *iter;

assert(self->s_codes != NULL);
ENSURE_STRUCT_IS_READY(self);

if (self->s_size == 0) {
PyErr_Format(state->StructError,
Expand Down Expand Up @@ -2242,8 +2249,8 @@ s_pack(PyObject *self, PyObject *const *args, Py_ssize_t nargs)

/* Validate arguments. */
soself = PyStructObject_CAST(self);
ENSURE_STRUCT_IS_READY(soself);
assert(PyStruct_Check(self, state));
assert(soself->s_codes != NULL);
if (nargs != soself->s_len)
{
PyErr_Format(state->StructError,
Expand Down Expand Up @@ -2285,8 +2292,8 @@ s_pack_into(PyObject *self, PyObject *const *args, Py_ssize_t nargs)

/* Validate arguments. +1 is for the first arg as buffer. */
soself = PyStructObject_CAST(self);
ENSURE_STRUCT_IS_READY(soself);
assert(PyStruct_Check(self, state));
assert(soself->s_codes != NULL);
if (nargs != (soself->s_len + 2))
{
if (nargs == 0) {
Expand Down Expand Up @@ -2373,6 +2380,7 @@ static PyObject *
s_get_format(PyObject *op, void *Py_UNUSED(closure))
{
PyStructObject *self = PyStructObject_CAST(op);
ENSURE_STRUCT_IS_READY(self);
return PyUnicode_FromStringAndSize(PyBytes_AS_STRING(self->s_format),
PyBytes_GET_SIZE(self->s_format));
}
Expand Down
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