bpo-36907: fix refcount bug in _PyStack_UnpackDict() (GH-13381)

1 files changed, 12 insertions, 5 deletions

diff --git a/Objects/call.c b/Objects/call.c
index 337ca81..cb9ccd9 100644
--- a/Objects/call.c
+++ b/Objects/call.c
@@ -544,10 +544,14 @@ _PyMethodDef_RawFastCallDict(PyMethodDef *method, PyObject *self,
         }
 
         result = (*fastmeth) (self, stack, nargs, kwnames);
-        if (stack != args) {
+        if (kwnames != NULL) {
+            Py_ssize_t i, n = nargs + PyTuple_GET_SIZE(kwnames);
+            for (i = 0; i < n; i++) {
+                Py_DECREF(stack[i]);
+            }
             PyMem_Free((PyObject **)stack);
+            Py_DECREF(kwnames);
         }
-        Py_XDECREF(kwnames);
         break;
     }
 
@@ -1334,8 +1338,11 @@ _PyStack_UnpackDict(PyObject *const *args, Py_ssize_t nargs, PyObject *kwargs,
         return -1;
     }
 
-    /* Copy position arguments (borrowed references) */
-    memcpy(stack, args, nargs * sizeof(stack[0]));
+    /* Copy positional arguments */
+    for (i = 0; i < nargs; i++) {
+        Py_INCREF(args[i]);
+        stack[i] = args[i];
+    }
 
     kwstack = stack + nargs;
     pos = i = 0;
@@ -1344,8 +1351,8 @@ _PyStack_UnpackDict(PyObject *const *args, Py_ssize_t nargs, PyObject *kwargs,
        called in the performance critical hot code. */
     while (PyDict_Next(kwargs, &pos, &key, &value)) {
         Py_INCREF(key);
+        Py_INCREF(value);
         PyTuple_SET_ITEM(kwnames, i, key);
-        /* The stack contains borrowed references */
         kwstack[i] = value;
         i++;
     }