8000 bpo-38368: Added fix for ctypes crash when handling arrays in structs… by vsajip · Pull Request #16589 · python/cpython · GitHub
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bpo-38368: Added fix for ctypes crash when handling arrays in structs… #16589

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Merged
merged 8 commits into from
Oct 8, 2019
Merged

bpo-38368: Added fix for ctypes crash when handling arrays in structs… #16589

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03934da
bpo-38368: Added fix for ctypes crash when handling arrays in structs…
vsajip Oct 4, 2019
5c947c7
Simplified handling of ctypes structs/unions containing arrays.
vsajip Oct 5, 2019
fd976d3
Added some more test logic.
vsajip Oct 5, 2019
2b07ffe
Changes in response to review comments.
vsajip Oct 5, 2019
4942f5c
Reverted to single-allocation strategy for easier backing out on fail…
vsajip Oct 5, 2019
b440691
Amended incorrect assertion.
vsajip Oct 5, 2019
8bc7ca9
Moved assertion out of condition.
vsajip Oct 5, 2019
f2f02a4
Changed the name of a #defined constant to be more descriptive,
vsajip Oct 8, 2019
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Changes in response to review comments.
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@vsajip
vsajip committed Oct 5, 2019
commit 2b07ffe235389ca7d771f40f616b075a3471a817
6 changes: 4 additions & 2 deletions Modules/_ctypes/stgdict.c
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Expand Up @@ -729,8 +729,8 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
if (PyCArrayTypeObject_Check(desc)) {
Py_ssize_t length = dict->length;
StgDictObject *edict;
ffi_type * dummy_struct;
ffi_type ** dummy_fields;
ffi_type *dummy_struct;
ffi_type **dummy_fields;
Py_ssize_t dummy_index;

edict = PyType_stgdict(dict->proto);
Expand All @@ -745,11 +745,13 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
/* Do separate allocations for now. */
dummy_struct = PyMem_New(ffi_type, 1);
if (dummy_struct == NULL) {
Py_DECREF(pair);
PyErr_NoMemory();
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I think there should be a Py_DECREF(pair); here.

return -1;
}
dummy_fields = PyMem_New(ffi_type *, length + 1);
if (dummy_fields == NULL) {
Py_DECREF(pair);
PyErr_NoMemory();
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I think dummy_struct should be freed here. Also, pair should be decrefed.

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Well, the problem is that we're doing these allocations in a loop, and unless we keep some sort of linked list or dynamically allocated structure to keep track of all our allocations (both dummy_struct and dummy_fields in earlier iterations of the loop), we will leak this memory in an Out Of Memory (OOM) situation. I'm not aware that we currently do this type of recovery for these internal allocations in an OOM situation, but happy to be proved wrong.

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I will have a think about an alternative allocation strategy which allows an easier recovery, but it will be potentially a little harder to follow the logic compared to what's there now.

return -1;
}
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