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

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",