[Python-checkins] gh-99952: [ctypes] fix refcount issues in from_param() result. (#100169)
gpshead
webhook-mailer at python.org
Thu Jan 26 03:28:40 EST 2023
https://github.com/python/cpython/commit/dfad678d7024ab86d265d84ed45999e031a03691
commit: dfad678d7024ab86d265d84ed45999e031a03691
branch: main
author: Yukihiro Nakadaira <yukihiro.nakadaira at gmail.com>
committer: gpshead <greg at krypto.org>
date: 2023-01-26T00:28:34-08:00
summary:
gh-99952: [ctypes] fix refcount issues in from_param() result. (#100169)
Fixes a reference counting issue with `ctypes.Structure` when a `from_param()` method call is used and the structure size is larger than a C pointer `sizeof(void*)`.
This problem existed for a very long time, but became more apparent in 3.8+ by change likely due to garbage collection cleanup timing changes.
files:
A Misc/NEWS.d/next/Library/2022-12-11-14-38-59.gh-issue-99952.IYGLzr.rst
M Lib/test/test_ctypes/test_parameters.py
M Modules/_ctypes/_ctypes.c
M Modules/_ctypes/_ctypes_test.c
diff --git a/Lib/test/test_ctypes/test_parameters.py b/Lib/test/test_ctypes/test_parameters.py
index 22d290db1bcb..06cc95107b79 100644
--- a/Lib/test/test_ctypes/test_parameters.py
+++ b/Lib/test/test_ctypes/test_parameters.py
@@ -266,6 +266,58 @@ def test_parameter_repr(self):
self.assertRegex(repr(c_wchar_p.from_param('hihi')), r"^<cparam 'Z' \(0x[A-Fa-f0-9]+\)>$")
self.assertRegex(repr(c_void_p.from_param(0x12)), r"^<cparam 'P' \(0x0*12\)>$")
+ @test.support.cpython_only
+ def test_from_param_result_refcount(self):
+ # Issue #99952
+ import _ctypes_test
+ from ctypes import PyDLL, c_int, c_void_p, py_object, Structure
+
+ class X(Structure):
+ """This struct size is <= sizeof(void*)."""
+ _fields_ = [("a", c_void_p)]
+
+ def __del__(self):
+ trace.append(4)
+
+ @classmethod
+ def from_param(cls, value):
+ trace.append(2)
+ return cls()
+
+ PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
+ PyList_Append.restype = c_int
+ PyList_Append.argtypes = [py_object, py_object, X]
+
+ trace = []
+ trace.append(1)
+ PyList_Append(trace, 3, "dummy")
+ trace.append(5)
+
+ self.assertEqual(trace, [1, 2, 3, 4, 5])
+
+ class Y(Structure):
+ """This struct size is > sizeof(void*)."""
+ _fields_ = [("a", c_void_p), ("b", c_void_p)]
+
+ def __del__(self):
+ trace.append(4)
+
+ @classmethod
+ def from_param(cls, value):
+ trace.append(2)
+ return cls()
+
+ PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
+ PyList_Append.restype = c_int
+ PyList_Append.argtypes = [py_object, py_object, Y]
+
+ trace = []
+ trace.append(1)
+ PyList_Append(trace, 3, "dummy")
+ trace.append(5)
+
+ self.assertEqual(trace, [1, 2, 3, 4, 5])
+
################################################################
if __name__ == '__main__':
diff --git a/Misc/NEWS.d/next/Library/2022-12-11-14-38-59.gh-issue-99952.IYGLzr.rst b/Misc/NEWS.d/next/Library/2022-12-11-14-38-59.gh-issue-99952.IYGLzr.rst
new file mode 100644
index 000000000000..09ec96124953
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-12-11-14-38-59.gh-issue-99952.IYGLzr.rst
@@ -0,0 +1,2 @@
+Fix a reference undercounting issue in :class:`ctypes.Structure` with ``from_param()``
+results larger than a C pointer.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 272cafb5a9a3..8690f2c1b078 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -412,6 +412,7 @@ _ctypes_alloc_format_string_with_shape(int ndim, const Py_ssize_t *shape,
typedef struct {
PyObject_HEAD
void *ptr;
+ PyObject *keep; // If set, a reference to the original CDataObject.
} StructParamObject;
@@ -419,6 +420,7 @@ static void
StructParam_dealloc(PyObject *myself)
{
StructParamObject *self = (StructParamObject *)myself;
+ Py_XDECREF(self->keep);
PyMem_Free(self->ptr);
Py_TYPE(self)->tp_free(myself);
}
@@ -466,6 +468,7 @@ StructUnionType_paramfunc(CDataObject *self)
StructParamObject *struct_param = (StructParamObject *)obj;
struct_param->ptr = ptr;
+ struct_param->keep = Py_NewRef(self);
} else {
ptr = self->b_ptr;
obj = Py_NewRef(self);
diff --git a/Modules/_ctypes/_ctypes_test.c b/Modules/_ctypes/_ctypes_test.c
index e1f91b476a49..a8811d03cc91 100644
--- a/Modules/_ctypes/_ctypes_test.c
+++ b/Modules/_ctypes/_ctypes_test.c
@@ -1047,6 +1047,12 @@ EXPORT(long) _test_i38748_runCallback(_test_i38748_funcType callback, int a, int
#endif
+EXPORT(int)
+_testfunc_pylist_append(PyObject *list, PyObject *item)
+{
+ return PyList_Append(list, item);
+}
+
static struct PyModuleDef_Slot _ctypes_test_slots[] = {
{0, NULL}
};
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