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gh-117657: Fix __slots__ thread safety in free-threaded build (#119368)

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Fix a race in `PyMember_GetOne` and `PyMember_SetOne` for `Py_T_OBJECT_EX`.
These functions implement `__slots__` accesses for Python objects.
This commit is contained in:
Daniele Parmeggiani 2024-06-17 14:44:54 -04:00 • committed by GitHub
parent 460cc9e14e
commit 362cd2680b
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GPG key ID: B5690EEEBB952194
4 changed files with 77 additions and 12 deletions
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42
Python/structmember.c
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@ -4,8 +4,22 @@
#include "Python.h"
#include "pycore_abstract.h" // _PyNumber_Index()
#include "pycore_long.h" // _PyLong_IsNegative()
#include "pycore_object.h" // _Py_TryIncrefCompare(), FT_ATOMIC_*()
#include "pycore_critical_section.h"
static inline PyObject *
member_get_object(const char *addr, const char *obj_addr, PyMemberDef *l)
{
PyObject *v = FT_ATOMIC_LOAD_PTR(*(PyObject **) addr);
if (v == NULL) {
PyErr_Format(PyExc_AttributeError,
"'%T' object has no attribute '%s'",
(PyObject *)obj_addr, l->name);
}
return v;
}
PyObject *
PyMember_GetOne(const char *obj_addr, PyMemberDef *l)
{
@ -75,15 +89,19 @@ PyMember_GetOne(const char *obj_addr, PyMemberDef *l)
Py_INCREF(v);
break;
case Py_T_OBJECT_EX:
v = *(PyObject **)addr;
if (v == NULL) {
PyObject *obj = (PyObject *)obj_addr;
PyTypeObject *tp = Py_TYPE(obj);
PyErr_Format(PyExc_AttributeError,
"'%.200s' object has no attribute '%s'",
tp->tp_name, l->name);
}
v = member_get_object(addr, obj_addr, l);
#ifndef Py_GIL_DISABLED
Py_XINCREF(v);
#else
if (v != NULL) {
if (!_Py_TryIncrefCompare((PyObject **) addr, v)) {
Py_BEGIN_CRITICAL_SECTION((PyObject *) obj_addr);
v = member_get_object(addr, obj_addr, l);
Py_XINCREF(v);
Py_END_CRITICAL_SECTION();
}
}
#endif
break;
case Py_T_LONGLONG:
v = PyLong_FromLongLong(*(long long *)addr);
@ -92,6 +110,7 @@ PyMember_GetOne(const char *obj_addr, PyMemberDef *l)
v = PyLong_FromUnsignedLongLong(*(unsigned long long *)addr);
break;
case _Py_T_NONE:
// doesn't require free-threading code path
v = Py_NewRef(Py_None);
break;
default:
@ -118,6 +137,9 @@ PyMember_SetOne(char *addr, PyMemberDef *l, PyObject *v)
return -1;
}
#ifdef Py_GIL_DISABLED
PyObject *obj = (PyObject *) addr;
#endif
addr += l->offset;
if ((l->flags & Py_READONLY))
@ -281,8 +303,10 @@ PyMember_SetOne(char *addr, PyMemberDef *l, PyObject *v)
break;
case _Py_T_OBJECT:
case Py_T_OBJECT_EX:
Py_BEGIN_CRITICAL_SECTION(obj);
oldv = *(PyObject **)addr;
*(PyObject **)addr = Py_XNewRef(v);
FT_ATOMIC_STORE_PTR_RELEASE(*(PyObject **)addr, Py_XNewRef(v));
Py_END_CRITICAL_SECTION();
Py_XDECREF(oldv);
break;
case Py_T_CHAR: {