bpo-43984: Update winreg.SetValueEx to make sure the value set is not -1

Lib/test/test_winreg.py

@@ -113,7 +113,6 @@ def _write_test_data(self, root_key, subkeystr="sub_key",
                       "does not close the actual key!")
         except OSError:
             pass
-
     def _read_test_data(self, root_key, subkeystr="sub_key", OpenKey=OpenKey):
         # Check we can get default value for this key.
         val = QueryValue(root_key, test_key_name)
@@ -340,6 +339,23 @@ def test_setvalueex_value_range(self):
         finally:
             DeleteKey(HKEY_CURRENT_USER, test_key_name)
 
+    def test_setvalueex_negative_one_check(self):
+        # Test for Issue #43984, check -1 was not set by SetValueEx.
+        # Py2Reg, which gets called by SetValueEx, wasn't checking return
+        # value by PyLong_AsUnsignedLong, thus setting -1 as value in the registry.
+        # The implementation now checks PyLong_AsUnsignedLong return value to assure
+        # the value set was not -1.
+        try:
+            with CreateKey(HKEY_CURRENT_USER, test_key_name) as ck:
+                with self.assertRaises(OverflowError):
+                    SetValueEx(ck, "test_name_dword", None, REG_DWORD, -1)
+                    SetValueEx(ck, "test_name_qword", None, REG_QWORD, -1)
+                self.assertRaises(FileNotFoundError, QueryValueEx, ck, "test_name_dword")
+                self.assertRaises(FileNotFoundError, QueryValueEx, ck, "test_name_qword")
+
+        finally:
+            DeleteKey(HKEY_CURRENT_USER, test_key_name)
+
     def test_queryvalueex_return_value(self):
         # Test for Issue #16759, return unsigned int from QueryValueEx.
         # Reg2Py, which gets called by QueryValueEx, was returning a value

Misc/NEWS.d/next/Windows/2021-05-02-15-29-33.bpo-43984.U92jiv.rst

@@ -0,0 +1,3 @@
+:meth:`winreg.SetValueEx` now leaves the target value untouched in the case of conversion errors.
+Previously, ``-1`` would be written in case of such errors.
+

PC/winreg.c

@@ -561,42 +561,54 @@ Py2Reg(PyObject *value, DWORD typ, BYTE **retDataBuf, DWORD *retDataSize)
 {
     Py_ssize_t i,j;
     switch (typ) {
-        case REG_DWORD:
-            if (value != Py_None && !PyLong_Check(value))
-                return FALSE;
-            *retDataBuf = (BYTE *)PyMem_NEW(DWORD, 1);
-            if (*retDataBuf == NULL){
-                PyErr_NoMemory();
-                return FALSE;
-            }
-            *retDataSize = sizeof(DWORD);
-            if (value == Py_None) {
-                DWORD zero = 0;
-                memcpy(*retDataBuf, &zero, sizeof(DWORD));
-            }
-            else {
-                DWORD d = PyLong_AsUnsignedLong(value);
+        case REG_DWORD: 
+            {
+                if (value != Py_None && !PyLong_Check(value)) {
+                    return FALSE;
+                }
+                DWORD d;
+                if (value == Py_None) {
+                    d = 0;
+                }
+                else if (PyLong_Check(value)) {
+                    d = PyLong_AsUnsignedLong(value);
+                    if (d == (DWORD)(-1) && PyErr_Occurred()) {
+                        return FALSE;
+                    }
+                }
+                *retDataBuf = (BYTE *)PyMem_NEW(DWORD, 1);
+                if (*retDataBuf == NULL) {
+                    PyErr_NoMemory();
+                    return FALSE;
+                }
                 memcpy(*retDataBuf, &d, sizeof(DWORD));
+                *retDataSize = sizeof(DWORD);
+                break;
             }
-            break;
-        case REG_QWORD:
-          if (value != Py_None && !PyLong_Check(value))
-                return FALSE;
-            *retDataBuf = (BYTE *)PyMem_NEW(DWORD64, 1);
-            if (*retDataBuf == NULL){
-                PyErr_NoMemory();
-                return FALSE;
-            }
-            *retDataSize = sizeof(DWORD64);
-            if (value == Py_None) {
-                DWORD64 zero = 0;
-                memcpy(*retDataBuf, &zero, sizeof(DWORD64));
-            }
-            else {
-                DWORD64 d = PyLong_AsUnsignedLongLong(value);
+        case REG_QWORD: 
+            {
+                if (value != Py_None && !PyLong_Check(value)) {
+                    return FALSE;
+                }
+                DWORD64 d;
+                if (value == Py_None) {
+                    d = 0;
+                }
+                else if (PyLong_Check(value)) {
+                    d = PyLong_AsUnsignedLongLong(value);
+                    if (d == (DWORD64)(-1) && PyErr_Occurred()) {
+                        return FALSE;
+                    }
+                }
+                *retDataBuf = (BYTE *)PyMem_NEW(DWORD64, 1);
+                if (*retDataBuf == NULL) {
+                    PyErr_NoMemory();
+                    return FALSE;
+                }
                 memcpy(*retDataBuf, &d, sizeof(DWORD64));
+                *retDataSize = sizeof(DWORD64);
+                break;
             }
-            break;
         case REG_SZ:
         case REG_EXPAND_SZ:
             {