commit 06a1b8915d6674e40f0dccc422ca2c06212392d8
author Ammar Askar <ammar@ammaraskar.com> Fri May 22 16:10:55 2020 +0000
committer GitHub <noreply@github.com> Fri May 22 12:10:55 2020 -0400
tree 4e264812ac42171eaca4bf1f19c78b4fe5c27e7e
parent 30d5a7364db9e65ccabbdce2c20b84fe2fb233fb

bpo-40705: Fix use-after-free in _zoneinfo's module_free (GH-20280)

Modules/_zoneinfo.c

diff --git a/Modules/_zoneinfo.c b/Modules/_zoneinfo.c
index d7e7157..d852c76 100644
--- a/Modules/_zoneinfo.c
+++ b/Modules/_zoneinfo.c
@@ -2490,6 +2490,7 @@
 static int
 initialize_caches()
 {
+    // TODO: Move to a PyModule_GetState / PEP 573 based caching system.
     if (TIMEDELTA_CACHE == NULL) {
         TIMEDELTA_CACHE = PyDict_New();
     }
@@ -2603,14 +2604,16 @@
 
     xdecref_ttinfo(&NO_TTINFO);
 
-    Py_XDECREF(TIMEDELTA_CACHE);
-    if (!Py_REFCNT(TIMEDELTA_CACHE)) {
-        TIMEDELTA_CACHE = NULL;
+    if (TIMEDELTA_CACHE != NULL && Py_REFCNT(TIMEDELTA_CACHE) > 1) {
+        Py_DECREF(TIMEDELTA_CACHE);
+    } else {
+        Py_CLEAR(TIMEDELTA_CACHE);
     }
 
-    Py_XDECREF(ZONEINFO_WEAK_CACHE);
-    if (!Py_REFCNT(ZONEINFO_WEAK_CACHE)) {
-        ZONEINFO_WEAK_CACHE = NULL;
+    if (ZONEINFO_WEAK_CACHE != NULL && Py_REFCNT(ZONEINFO_WEAK_CACHE) > 1) {
+        Py_DECREF(ZONEINFO_WEAK_CACHE);
+    } else {
+        Py_CLEAR(ZONEINFO_WEAK_CACHE);
     }
 
     strong_cache_free(ZONEINFO_STRONG_CACHE);