Fix two crashers.

Lib/test/crashers/borrowed_ref_3.py

-"""
-PyDict_GetItem() returns a borrowed reference.
-There are probably a number of places that are open to attacks
-such as the following one, in bltinmodule.c:min_max().
-"""
-
-class KeyFunc(object):
-    def __call__(self, n):
-        del d['key']
-        return 1
-
-
-d = {'key': KeyFunc()}
-min(range(10), **d)

Lib/test/crashers/borrowed_ref_4.py

-"""
-PyDict_GetItem() returns a borrowed reference.
-This attack is against ceval.c:IMPORT_NAME, which calls an
-object (__builtin__.__import__) without holding a reference to it.
-"""
-
-import types
-import __builtin__
-
-
-class X(object):
-    def __getattr__(self, name):
-        # this is called with name == '__bases__' by PyObject_IsInstance()
-        # during the unbound method call -- it frees the unbound method
-        # itself before it invokes its im_func.
-        del __builtin__.__import__
-        return ()
-
-pseudoclass = X()
-
-class Y(object):
-    def __call__(self, *args):
-        # 'self' was freed already
-        print self, args
-
-# make an unbound method
-__builtin__.__import__ = types.MethodType(Y(), None, (pseudoclass, str))
-import spam

Python/bltinmodule.c

@@ -1245,11 +1245,14 @@ min_max(PyObject *args, PyObject *kwds, int op)
 				"%s() got an unexpected keyword argument", name);
 			return NULL;
 		}
+		Py_INCREF(keyfunc);
 	}
 
 	it = PyObject_GetIter(v);
-	if (it == NULL)
+	if (it == NULL) {
+		Py_XDECREF(keyfunc);
 		return NULL;
+	}
 
 	maxitem = NULL; /* the result */
 	maxval = NULL;  /* the value associated with the result */
@@ -1298,6 +1301,7 @@ min_max(PyObject *args, PyObject *kwds, int op)
 	else
 		Py_DECREF(maxval);
 	Py_DECREF(it);
+	Py_XDECREF(keyfunc);
 	return maxitem;
 
 Fail_it_item_and_val:
@@ -1308,6 +1312,7 @@ Fail_it:
 	Py_XDECREF(maxval);
 	Py_XDECREF(maxitem);
 	Py_DECREF(it);
+	Py_XDECREF(keyfunc);
 	return NULL;
 }
 

Python/ceval.c

@@ -2066,6 +2066,7 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 						"__import__ not found");
 				break;
 			}
+			Py_INCREF(x);
 			v = POP();
 			u = TOP();
 			if (PyInt_AsLong(u) != -1 || PyErr_Occurred())
@@ -2087,11 +2088,14 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 			Py_DECREF(u);
 			if (w == NULL) {
 				u = POP();
+				Py_DECREF(x);
 				x = NULL;
 				break;
 			}
 			READ_TIMESTAMP(intr0);
-			x = PyEval_CallObject(x, w);
+			v = x;
+			x = PyEval_CallObject(v, w);
+			Py_DECREF(v);
 			READ_TIMESTAMP(intr1);
 			Py_DECREF(w);
 			SET_TOP(x);