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bpo-34543: Fix SystemErrors and segfaults with uninitialized Structs #14777

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bpo-34543: Fix SystemErrors and segfaults with uninitialized Structs #14777

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11 changes: 11 additions & 0 deletions Lib/test/test_struct.py
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Original file line number Diff line number Diff line change
Expand Up @@ -652,6 +652,17 @@ def test_format_attr(self):
s2 = struct.Struct(s.format.encode())
self.assertEqual(s2.format, s.format)

def test_uninitialized_struct(self):
s = struct.Struct.__new__(struct.Struct)
with self.assertRaises(ValueError):
s.format
with self.assertRaises(ValueError):
s.size
for meth in s.iter_unpack, s.pack, s.unpack, s.unpack_from:
self.assertRaises(ValueError, meth, b'0')
self.assertRaises(ValueError, s.pack_into, bytearray(1), 0, b'0')
self.assertRaises(ValueError, s.__sizeof__)
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@aeros aeros Jul 15, 2019 •
edited
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Also, realized this after submitting the approval. This is quite minor, and I still approve of the PR either way. Instead of using s.__sizeof__, I would recommend using sys.getsizeof(s):

Suggested change
self.assertRaises(ValueError, s.__sizeof__)
self.assertRaises(ValueError, sys.getsizeof(s))

In general, it seems to be preferable to use functions instead of directly accessing the special object attributes when possible. If you had a specific reason for not using sys.getsizeof(), let me know. Here's the a link to the function defintion and the docs. I looked over it, but I'm not very experienced with the python c-api. I mostly rely on the docs when it comes to the modules implemented in c.



class UnpackIteratorTest(unittest.TestCase):
"""
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-07-14-16-32-15.bpo-34543.2Sguv-.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :exc:`SystemError`\ s and segfaults with uninitialized
:class:`struct.Struct`\ s.
21 changes: 14 additions & 7 deletions Modules/_struct.c
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,12 @@ get_size_t(PyObject *v, size_t *p)

#define RANGE_ERROR(x, f, flag, mask) return _range_error(f, flag)

#define CHECK_INITIALIZED(self) \
if (self->s_codes == NULL) { \
PyErr_SetString(PyExc_ValueError, \
"Struct.__init__() wasn't called"); \
return NULL; \
}

/* Floating point helpers */

Expand Down Expand Up @@ -1533,7 +1539,7 @@ static PyObject *
Struct_unpack_impl(PyStructObject *self, Py_buffer *buffer)
/*[clinic end generated code: output=873a24faf02e848a input=3113f8e7038b2f6c]*/
{
assert(self->s_codes != NULL);
CHECK_INITIALIZED(self);
if (buffer->len != self->s_size) {
PyErr_Format(StructError,
"unpack requires a buffer of %zd bytes",
Expand Down Expand Up @@ -1564,8 +1570,7 @@ Struct_unpack_from_impl(PyStructObject *self, Py_buffer *buffer,
Py_ssize_t offset)
/*[clinic end generated code: output=57fac875e0977316 input=cafd4851d473c894]*/
{
assert(self->s_codes != NULL);

CHECK_INITIALIZED(self);
if (offset < 0) {
if (offset + self->s_size > 0) {
PyErr_Format(StructError,
Expand Down Expand Up @@ -1714,8 +1719,7 @@ Struct_iter_unpack(PyStructObject *self, PyObject *buffer)
{
unpackiterobject *iter;

assert(self->s_codes != NULL);

CHECK_INITIALIZED(self);
if (self->s_size == 0) {
PyErr_Format(StructError,
"cannot iteratively unpack with a struct of length 0");
Expand Down Expand Up @@ -1851,7 +1855,7 @@ s_pack(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
/* Validate arguments. */
soself = (PyStructObject *)self;
assert(PyStruct_Check(self));
assert(soself->s_codes != NULL);
CHECK_INITIALIZED(soself);
if (nargs != soself->s_len)
{
PyErr_Format(StructError,
Expand Down Expand Up @@ -1891,7 +1895,7 @@ s_pack_into(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
/* Validate arguments. +1 is for the first arg as buffer. */
soself = (PyStructObject *)self;
assert(PyStruct_Check(self));
assert(soself->s_codes != NULL);
CHECK_INITIALIZED(soself);
if (nargs != (soself->s_len + 2))
{
if (nargs == 0) {
Expand Down Expand Up @@ -1977,13 +1981,15 @@ s_pack_into(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
static PyObject *
s_get_format(PyStructObject *self, void *unused)
{
CHECK_INITIALIZED(self);
return PyUnicode_FromStringAndSize(PyBytes_AS_STRING(self->s_format),
PyBytes_GET_SIZE(self->s_format));
}

static PyObject *
s_get_size(PyStructObject *self, void *unused)
{
CHECK_INITIALIZED(self);
return PyLong_FromSsize_t(self->s_size);
}

Expand All @@ -1995,6 +2001,7 @@ s_sizeof(PyStructObject *self, void *unused)
{
Py_ssize_t size;
formatcode *code;
CHECK_INITIALIZED(self);

size = _PyObject_SIZE(Py_TYPE(self)) + sizeof(formatcode);
for (code = self->s_codes; code->fmtdef != NULL; code++)
Expand Down