Backport of:

From 7d512c8e4442a896d56505be3e78f1156f443465 Mon Sep 17 00:00:00 2001
From: Riccardo Schirone <ret2libc@users.noreply.github.com>
Date: Wed, 13 Nov 2019 14:54:21 +0100
Subject: [PATCH] Use Py_CLEAR instead of Py_DECREF to also set the variable to
 NULL (#1616)

These files contain loops that convert system data into python objects
and during the process they create objects and dereference their
refcounts after they have been added to the resulting list.

However, in case of errors during the creation of those python objects,
the refcount to previously allocated objects is dropped again with
Py_XDECREF, which should be a no-op in case the paramater is NULL. Even
so, in most of these loops the variables pointing to the objects are
never set to NULL, even after Py_DECREF is called at the end of the loop
iteration. This means, after the first iteration, if an error occurs
those python objects will get their refcount dropped two times,
resulting in a possible double-free.
---
 psutil/_psutil_aix.c     | 18 +++++++-------
 psutil/_psutil_bsd.c     | 30 +++++++++++-----------
 psutil/_psutil_linux.c   | 14 +++++------
 psutil/_psutil_osx.c     | 39 ++++++++++++++---------------
 psutil/_psutil_sunos.c   | 43 ++++++++++++++++----------------
 psutil/_psutil_windows.c | 54 ++++++++++++++++++++--------------------
 6 files changed, 97 insertions(+), 101 deletions(-)

--- a/psutil/_psutil_linux.c
+++ b/psutil/_psutil_linux.c
@@ -232,9 +232,9 @@ psutil_disk_partitions(PyObject *self, P
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
     }
     endmntent(file);
     return py_retlist;
@@ -488,10 +488,10 @@ psutil_users(PyObject *self, PyObject *a
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
     endutent();
     return py_retlist;
