[Python-checkins] bpo-37138: fix undefined behaviour with memcpy() on NULL array (GH-13867)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/6e053079ac3fe50ffbe9128bcf766298168c31cb
commit: 6e053079ac3fe50ffbe9128bcf766298168c31cb
branch: 3.8
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019-06-07T11:25:53-07:00
summary:

bpo-37138: fix undefined behaviour with memcpy() on NULL array (GH-13867)

(cherry picked from commit 1f9531764cc0f8dbca1d8f429d162dc28282f4b4)

Co-authored-by: Jeroen Demeyer <J.Demeyer at UGent.be>

files:
M Objects/classobject.c

diff --git a/Objects/classobject.c b/Objects/classobject.c
index ffd3f875c0e7..2415ed14cb15 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -71,7 +71,11 @@ method_vectorcall(PyObject *method, PyObject *const *args,
         }
         /* use borrowed references */
         newargs[0] = self;
-        memcpy(newargs + 1, args, totalargs * sizeof(PyObject *));
+        if (totalargs) { /* bpo-37138: if totalargs == 0, then args may be
+                          * NULL and calling memcpy() with a NULL pointer
+                          * is undefined behaviour. */
+            memcpy(newargs + 1, args, totalargs * sizeof(PyObject *));
+        }
         result = _PyObject_Vectorcall(func, newargs, nargs+1, kwnames);
         PyMem_Free(newargs);
     }