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[3.7] bpo-36907: fix refcount bug in _PyStack_UnpackDict() (GH-13381) #13493

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Merged
encukou merged 1 commit into from
May 22, 2019
Merged

[3.7] bpo-36907: fix refcount bug in _PyStack_UnpackDict() (GH-13381) #13493

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17 changes: 17 additions & 0 deletions Lib/test/test_call.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
import struct
import collections
import itertools
import gc


class FunctionCalls(unittest.TestCase):
Expand Down Expand Up @@ -438,6 +439,22 @@ def test_fastcall_keywords(self):
result = _testcapi.pyobject_fastcallkeywords(func, args, kwnames)
self.check_result(result, expected)

def test_fastcall_clearing_dict(self):
# Test bpo-36907: the point of the test is just checking that this
# does not crash.
class IntWithDict:
__slots__ = ["kwargs"]
def __init__(self, **kwargs):
self.kwargs = kwargs
def __int__(self):
self.kwargs.clear()
gc.collect()
return 0
x = IntWithDict(dont_inherit=IntWithDict())
# We test the argument handling of "compile" here, the compilation
# itself is not relevant. When we pass flags=x below, x.__int__() is
# called, which changes the keywords dict.
compile("pass", "", "exec", x, **x.kwargs)

if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-05-17-12-28-24.bpo-36907.rk7kgp.rst
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@@ -0,0 +1,2 @@
Fix a crash when calling a C function with a keyword dict (``f(**kwargs)``)
and changing the dict ``kwargs`` while that function is running.
17 changes: 12 additions & 5 deletions Objects/call.c
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Original file line number Diff line number Diff line change
Expand Up @@ -542,10 +542,14 @@ _PyMethodDef_RawFastCallDict(PyMethodDef *method, PyObject *self,
}

result = (*fastmeth) (self, stack, nargs, kwnames);
if (stack != args) {
if (kwnames != NULL) {
Py_ssize_t i, n = nargs + PyTuple_GET_SIZE(kwnames);
for (i = 0; i < n; i++) {
Py_DECREF(stack[i]);
}
PyMem_Free((PyObject **)stack);
Py_DECREF(kwnames);
}
Py_XDECREF(kwnames);
break;
}

Expand Down Expand Up @@ -1379,8 +1383,11 @@ _PyStack_UnpackDict(PyObject *const *args, Py_ssize_t nargs, PyObject *kwargs,
return -1;
}

/* Copy position arguments (borrowed references) */
memcpy(stack, args, nargs * sizeof(stack[0]));
/* Copy positional arguments */
for (i = 0; i < nargs; i++) {
Py_INCREF(args[i]);
stack[i] = args[i];
}

kwstack = stack + nargs;
pos = i = 0;
Expand All @@ -1389,8 +1396,8 @@ _PyStack_UnpackDict(PyObject *const *args, Py_ssize_t nargs, PyObject *kwargs,
called in the performance critical hot code. */
while (PyDict_Next(kwargs, &pos, &key, &value)) {
Py_INCREF(key);
Py_INCREF(value);
PyTuple_SET_ITEM(kwnames, i, key);
/* The stack contains borrowed references */
kwstack[i] = value;
i++;
}
Expand Down