https://github.com/python/cpython/commit/57ba3b0c6e87264fc42ecf31780ec7c598380347 commit: 57ba3b0c6e87264fc42ecf31780ec7c598380347 branch: 3.13 author: Miss Islington (bot) <[email protected]> committer: Yhg1s <[email protected]> date: 2024-09-02T12:47:18+02:00 summary:
[3.13] gh-122527: Fix a crash on deallocation of `PyStructSequence` (GH-122577) (#122625) gh-122527: Fix a crash on deallocation of `PyStructSequence` (GH-122577) The `PyStructSequence` destructor would crash if it was deallocated after its type's dictionary was cleared by the GC, because it couldn't compute the "real size" of the instance. This could occur with relatively straightforward code in the free-threaded build or with a reference cycle involving the type in the default build, due to differing orders in which `tp_clear()` was called. Account for the non-sequence fields in `tp_basicsize` and use that, along with `Py_SIZE()`, to compute the "real" size of a `PyStructSequence` in the dealloc function. This avoids the accesses to the type's dictionary during dealloc, which were unsafe. (cherry picked from commit 4b63cd170e5dd840bffc80922f09f2d69932ff5c) Co-authored-by: Sam Gross <[email protected]> files: A Misc/NEWS.d/next/Core_and_Builtins/2024-08-01-19-13-58.gh-issue-122527.eztso6.rst M Lib/test/test_structseq.py M Lib/test/test_sys.py M Objects/structseq.c diff --git a/Lib/test/test_structseq.py b/Lib/test/test_structseq.py index 6aec63e2603412..d0bc0bd7b61520 100644 --- a/Lib/test/test_structseq.py +++ b/Lib/test/test_structseq.py @@ -2,8 +2,10 @@ import os import pickle import re +import textwrap import time import unittest +from test.support import script_helper class StructSeqTest(unittest.TestCase): @@ -342,6 +344,17 @@ def test_copy_replace_with_unnamed_fields(self): with self.assertRaisesRegex(TypeError, error_message): copy.replace(r, st_mode=1, error=2) + def test_reference_cycle(self): + # gh-122527: Check that a structseq that's part of a reference cycle + # with its own type doesn't crash. Previously, if the type's dictionary + # was cleared first, the structseq instance would crash in the + # destructor. + script_helper.assert_python_ok("-c", textwrap.dedent(r""" + import time + t = time.gmtime() + type(t).refcyle = t + """)) + if __name__ == "__main__": unittest.main() diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py index 8008b6b586f930..3d2bcf2358f413 100644 --- a/Lib/test/test_sys.py +++ b/Lib/test/test_sys.py @@ -1822,7 +1822,8 @@ def test_pythontypes(self): # symtable entry # XXX # sys.flags - check(sys.flags, vsize('') + self.P * len(sys.flags)) + # FIXME: The +1 will not be necessary once gh-122575 is fixed + check(sys.flags, vsize('') + self.P * (1 + len(sys.flags))) def test_asyncgen_hooks(self): old = sys.get_asyncgen_hooks() diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-08-01-19-13-58.gh-issue-122527.eztso6.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-08-01-19-13-58.gh-issue-122527.eztso6.rst new file mode 100644 index 00000000000000..f697ed99d0c523 --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-08-01-19-13-58.gh-issue-122527.eztso6.rst @@ -0,0 +1,4 @@ +Fix a crash that occurred when a ``PyStructSequence`` was deallocated after +its type's dictionary was cleared by the GC. The type's +:c:member:`~PyTypeObject.tp_basicsize` now accounts for non-sequence fields +that aren't included in the :c:macro:`Py_SIZE` of the sequence. diff --git a/Objects/structseq.c b/Objects/structseq.c index d8289f2638db0f..94f09b3ee0a337 100644 --- a/Objects/structseq.c +++ b/Objects/structseq.c @@ -41,12 +41,20 @@ get_type_attr_as_size(PyTypeObject *tp, PyObject *name) get_type_attr_as_size(tp, &_Py_ID(n_sequence_fields)) #define REAL_SIZE_TP(tp) \ get_type_attr_as_size(tp, &_Py_ID(n_fields)) -#define REAL_SIZE(op) REAL_SIZE_TP(Py_TYPE(op)) +#define REAL_SIZE(op) get_real_size((PyObject *)op) #define UNNAMED_FIELDS_TP(tp) \ get_type_attr_as_size(tp, &_Py_ID(n_unnamed_fields)) #define UNNAMED_FIELDS(op) UNNAMED_FIELDS_TP(Py_TYPE(op)) +static Py_ssize_t +get_real_size(PyObject *op) +{ + // Compute the real size from the visible size (i.e., Py_SIZE()) and the + // number of non-sequence fields accounted for in tp_basicsize. + Py_ssize_t hidden = Py_TYPE(op)->tp_basicsize - offsetof(PyStructSequence, ob_item); + return Py_SIZE(op) + hidden / sizeof(PyObject *); +} PyObject * PyStructSequence_New(PyTypeObject *type) @@ -120,6 +128,9 @@ structseq_dealloc(PyStructSequence *obj) PyObject_GC_UnTrack(obj); PyTypeObject *tp = Py_TYPE(obj); + // gh-122527: We can't use REAL_SIZE_TP() or any macros that access the + // type's dictionary here, because the dictionary may have already been + // cleared by the garbage collector. size = REAL_SIZE(obj); for (i = 0; i < size; ++i) { Py_XDECREF(obj->ob_item[i]); @@ -565,10 +576,14 @@ initialize_members(PyStructSequence_Desc *desc, static void initialize_static_fields(PyTypeObject *type, PyStructSequence_Desc *desc, - PyMemberDef *tp_members, unsigned long tp_flags) + PyMemberDef *tp_members, Py_ssize_t n_members, + unsigned long tp_flags) { type->tp_name = desc->name; - type->tp_basicsize = sizeof(PyStructSequence) - sizeof(PyObject *); + // Account for hidden members in tp_basicsize because they are not + // included in the variable size. + Py_ssize_t n_hidden = n_members - desc->n_in_sequence; + type->tp_basicsize = sizeof(PyStructSequence) + (n_hidden - 1) * sizeof(PyObject *); type->tp_itemsize = sizeof(PyObject *); type->tp_dealloc = (destructor)structseq_dealloc; type->tp_repr = (reprfunc)structseq_repr; @@ -621,7 +636,7 @@ _PyStructSequence_InitBuiltinWithFlags(PyInterpreterState *interp, if (members == NULL) { goto error; } - initialize_static_fields(type, desc, members, tp_flags); + initialize_static_fields(type, desc, members, n_members, tp_flags); _Py_SetImmortal((PyObject *)type); } @@ -684,7 +699,7 @@ PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc) if (members == NULL) { return -1; } - initialize_static_fields(type, desc, members, 0); + initialize_static_fields(type, desc, members, n_members, 0); if (initialize_static_type(type, desc, n_members, n_unnamed_members) < 0) { PyMem_Free(members); return -1; @@ -760,7 +775,8 @@ _PyStructSequence_NewType(PyStructSequence_Desc *desc, unsigned long tp_flags) /* The name in this PyType_Spec is statically allocated so it is */ /* expected that it'll outlive the PyType_Spec */ spec.name = desc->name; - spec.basicsize = sizeof(PyStructSequence) - sizeof(PyObject *); + Py_ssize_t hidden = n_members - desc->n_in_sequence; + spec.basicsize = (int)(sizeof(PyStructSequence) + (hidden - 1) * sizeof(PyObject *)); spec.itemsize = sizeof(PyObject *); spec.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | tp_flags; spec.slots = slots; _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
