bpo-16576: Add checks for bitfields passed by value to functions. (pythonGH-17097)

Author: vsajip

Lib/ctypes/test/test_structures.py

@@ -656,6 +656,87 @@ class Test5(Structure):
         self.assertEqual(test5.nested.an_int, 0)
         self.assertEqual(test5.another_int, 0)
 
+    #@unittest.skipIf('s390' in MACHINE, 'Test causes segfault on S390')
+    def test_bitfield_by_value(self):
+        # See bpo-16576
+
+        # These should mirror the structures in Modules/_ctypes/_ctypes_test.c
+
+        class Test6(Structure):
+            _fields_ = [
+                ('A', c_int, 1),
+                ('B', c_int, 2),
+                ('C', c_int, 3),
+                ('D', c_int, 2),
+            ]
+
+        test6 = Test6()
+        # As these are signed int fields, all are logically -1 due to sign
+        # extension.
+        test6.A = 1
+        test6.B = 3
+        test6.C = 7
+        test6.D = 3
+        dll = CDLL(_ctypes_test.__file__)
+        with self.assertRaises(TypeError) as ctx:
+            func = dll._testfunc_bitfield_by_value1
+            func.restype = c_long
+            func.argtypes = (Test6,)
+            result = func(test6)
+        self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
+                         'a struct/union with a bitfield by value, which is '
+                         'unsupported.')
+        # passing by reference should be OK
+        func = dll._testfunc_bitfield_by_reference1
+        func.restype = c_long
+        func.argtypes = (POINTER(Test6),)
+        result = func(byref(test6))
+        self.assertEqual(result, -4)
+        self.assertEqual(test6.A, 0)
+        self.assertEqual(test6.B, 0)
+        self.assertEqual(test6.C, 0)
+        self.assertEqual(test6.D, 0)
+
+        class Test7(Structure):
+            _fields_ = [
+                ('A', c_uint, 1),
+                ('B', c_uint, 2),
+                ('C', c_uint, 3),
+                ('D', c_uint, 2),
+            ]
+        test7 = Test7()
+        test7.A = 1
+        test7.B = 3
+        test7.C = 7
+        test7.D = 3
+        func = dll._testfunc_bitfield_by_reference2
+        func.restype = c_long
+        func.argtypes = (POINTER(Test7),)
+        result = func(byref(test7))
+        self.assertEqual(result, 14)
+        self.assertEqual(test7.A, 0)
+        self.assertEqual(test7.B, 0)
+        self.assertEqual(test7.C, 0)
+        self.assertEqual(test7.D, 0)
+
+        # for a union with bitfields, the union check happens first
+        class Test8(Union):
+            _fields_ = [
+                ('A', c_int, 1),
+                ('B', c_int, 2),
+                ('C', c_int, 3),
+                ('D', c_int, 2),
+            ]
+
+        test8 = Test8()
+        with self.assertRaises(TypeError) as ctx:
+            func = dll._testfunc_bitfield_by_value2
+            func.restype = c_long
+            func.argtypes = (Test8,)
+            result = func(test8)
+        self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
+                         'a union by value, which is unsupported.')
+
 class PointerMemberTestCase(unittest.TestCase):
 
     def test(self):

Modules/_ctypes/_ctypes.c

@@ -2400,11 +2400,18 @@ converters_from_argtypes(PyObject *ob)
                 }
                 return NULL;
             }
-            /*
             if (stgdict->flags & TYPEFLAG_HASBITFIELD) {
-                printf("found stgdict with bitfield\n");
+                Py_DECREF(converters);
+                Py_DECREF(ob);
+                if (!PyErr_Occurred()) {
+                    PyErr_Format(PyExc_TypeError,
+                                 "item %zd in _argtypes_ passes a struct/"
+                                 "union with a bitfield by value, which is "
+                                 "unsupported.",
+                                 i + 1);
+                }
+                return NULL;
             }
-            */
         }
 
         if (_PyObject_LookupAttrId(tp, &PyId_from_param, &cnv) <= 0) {

Modules/_ctypes/_ctypes_test.c

@@ -194,6 +194,56 @@ _testfunc_union_by_reference3(Test5 *in) {
     return result;
 }
 
+typedef struct {
+    signed int A: 1, B:2, C:3, D:2;
+} Test6;
+
+EXPORT(long)
+_testfunc_bitfield_by_value1(Test6 in) {
+    long result = in.A + in.B + in.C + in.D;
+
+    /* As the struct is passed by value, changes to it shouldn't be
+     * reflected in the caller.
+     */
+    memset(&in, 0, sizeof(in));
+    return result;
+}
+
+EXPORT(long)
+_testfunc_bitfield_by_reference1(Test6 *in) {
+    long result = in->A + in->B + in->C + in->D;
+
+    memset(in, 0, sizeof(Test6));
+    return result;
+}
+
+typedef struct {
+    unsigned int A: 1, B:2, C:3, D:2;
+} Test7;
+
+EXPORT(long)
+_testfunc_bitfield_by_reference2(Test7 *in) {
+    long result = in->A + in->B + in->C + in->D;
+
+    memset(in, 0, sizeof(Test7));
+    return result;
+}
+
+typedef union {
+    signed int A: 1, B:2, C:3, D:2;
+} Test8;
+
+EXPORT(long)
+_testfunc_bitfield_by_value2(Test8 in) {
+    long result = in.A + in.B + in.C + in.D;
+
+    /* As the struct is passed by value, changes to it shouldn't be
+     * reflected in the caller.
+     */
+    memset(&in, 0, sizeof(in));
+    return result;
+}
+
 EXPORT(void)testfunc_array(int values[4])
 {
     printf("testfunc_array %d %d %d %d\n",