python
diff --git a/‎Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst‎
Lines changed: 3 additions & 0 deletions b/‎Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst‎
Lines changed: 3 additions & 0 deletions
diff --git a/‎Modules/posixmodule.c‎
Lines changed: 19 additions & 0 deletions b/‎Modules/posixmodule.c‎
Lines changed: 19 additions & 0 deletions
@@ -0,0 +1,3 @@
+Fix ``os.getgrouplist()``: on macOS, the ``getgrouplist()`` function returns a
+non-zero value without setting ``errno`` if the group list is too small. Double
+the list size and call it again in this case.
@@ -6999,10 +6999,29 @@ posix_getgrouplist(PyObject *self, PyObject *args)
     if (groups == NULL)
         return PyErr_NoMemory();
 
+#ifdef __APPLE__
+    while (getgrouplist(user, basegid, groups, &ngroups)) {
+        /* On macOS, getgrouplist() returns a non-zero value without setting
+           errno if the group list is too small. Double the list size and call
+           it again in this case. */
+        PyMem_Free(groups);
+
+        if (ngroups > INT_MAX / 2) {
+            return PyErr_NoMemory();
+        }
+        ngroups *= 2;
+
+        groups = PyMem_New(int, ngroups);
+        if (groups == NULL) {
+            return PyErr_NoMemory();
+        }
+    }
+#else
     if (getgrouplist(user, basegid, groups, &ngroups) == -1) {
         PyMem_Del(groups);
         return posix_error();
     }
+#endif
 
 #ifdef _Py_MEMORY_SANITIZER
     /* Clang memory sanitizer libc intercepts don't know getgrouplist. */
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fix ``os.getgrouplist()``: on macOS, the ``getgrouplist()`` function returns a
	`2`	+non-zero value without setting ``errno`` if the group list is too small. Double
	`3`	`+the list size and call it again in this case.`