bpo-13097: ctypes: limit callback to 1024 arguments (GH-19914)

ctypes now raises an ArgumentError when a callback
is invoked with more than 1024 arguments.

The ctypes module allocates arguments on the stack in
ctypes_callproc() using alloca(), which is problematic
when large numbers of arguments are passed. Instead
of a stack overflow, this commit raises an ArgumentError
if more than 1024 parameters are passed.

1 files changed, 15 insertions, 0 deletions

diff --git a/Lib/ctypes/test/test_callbacks.py b/Lib/ctypes/test/test_callbacks.py
index f622093..937a06d 100644
--- a/Lib/ctypes/test/test_callbacks.py
+++ b/Lib/ctypes/test/test_callbacks.py
@@ -287,6 +287,21 @@ class SampleCallbacksTestCase(unittest.TestCase):
         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__':