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[3.9] bpo-13097: ctypes: limit callback to 1024 arguments (GH-19914) #20453

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Merged
merged 1 commit into from
May 27, 2020
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[3.9] bpo-13097: ctypes: limit callback to 1024 arguments (GH-19914) #20453

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15 changes: 15 additions & 0 deletions Lib/ctypes/test/test_callbacks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -287,6 +287,21 @@ def callback(check, s):
self.assertEqual(s.second, check.second)
self.assertEqual(s.third, check.third)

def test_callback_too_many_args(self):
def func(*args):
return len(args)

CTYPES_MAX_ARGCOUNT = 1024
proto = CFUNCTYPE(c_int, *(c_int,) * CTYPES_MAX_ARGCOUNT)
cb = proto(func)
args1 = (1,) * CTYPES_MAX_ARGCOUNT
self.assertEqual(cb(*args1), CTYPES_MAX_ARGCOUNT)

args2 = (1,) * (CTYPES_MAX_ARGCOUNT + 1)
with self.assertRaises(ArgumentError):
cb(*args2)


################################################################

if __name__ == '__main__':
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-05-06-02-01-25.bpo-13097.Wh5xSK.rst
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@@ -0,0 +1 @@
``ctypes`` now raises an ``ArgumentError`` when a callback is invoked with more than 1024 arguments.
15 changes: 15 additions & 0 deletions Modules/_ctypes/callproc.c
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Expand Up @@ -1072,6 +1072,14 @@ GetComError(HRESULT errcode, GUID *riid, IUnknown *pIunk)
#define IS_PASS_BY_REF(x) (x > 8 || !POW2(x))
#endif

/*
* bpo-13097: Max number of arguments _ctypes_callproc will accept.
*
* This limit is enforced for the `alloca()` call in `_ctypes_callproc`,
* to avoid allocating a massive buffer on the stack.
*/
#define CTYPES_MAX_ARGCOUNT 1024

/*
* Requirements, must be ensured by the caller:
* - argtuple is tuple of arguments
Expand Down Expand Up @@ -1107,6 +1115,13 @@ PyObject *_ctypes_callproc(PPROC pProc,
++argcount;
#endif

if (argcount > CTYPES_MAX_ARGCOUNT)
{
PyErr_Format(PyExc_ArgError, "too many arguments (%zi), maximum is %i",
argcount, CTYPES_MAX_ARGCOUNT);
return NULL;
}

args = (struct argument *)alloca(sizeof(struct argument) * argcount);
if (!args) {
PyErr_NoMemory();
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