[Python-checkins] bpo-41252: Fix incorrect refcounting in _ssl.c's _servername_callback() (GH-21407)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/54babbe976531d4d1c21ea415f71e7c6846e15bc
commit: 54babbe976531d4d1c21ea415f71e7c6846e15bc
branch: 3.8
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2020-07-09T03:15:36-07:00
summary:

bpo-41252: Fix incorrect refcounting in _ssl.c's _servername_callback() (GH-21407)

(cherry picked from commit ee96f32ca24779656d3c8736d26671fc3689f0a3)

Co-authored-by: Zackery Spytz <zspytz at gmail.com>

files:
A Misc/NEWS.d/next/Core and Builtins/2020-07-08-21-55-23.bpo-41252.nBWL-Y.rst
M Modules/_ssl.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-07-08-21-55-23.bpo-41252.nBWL-Y.rst b/Misc/NEWS.d/next/Core and Builtins/2020-07-08-21-55-23.bpo-41252.nBWL-Y.rst
new file mode 100644
index 0000000000000..65f3189c83ec6
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-07-08-21-55-23.bpo-41252.nBWL-Y.rst	
@@ -0,0 +1 @@
+Fix incorrect refcounting in _ssl.c's ``_servername_callback()``.
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 8ee2c170368fd..1944393e54890 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -4548,11 +4548,12 @@ _servername_callback(SSL *s, int *al, void *args)
          * back into a str object, but still as an A-label (bpo-28414)
          */
         servername_str = PyUnicode_FromEncodedObject(servername_bytes, "ascii", NULL);
-        Py_DECREF(servername_bytes);
         if (servername_str == NULL) {
             PyErr_WriteUnraisable(servername_bytes);
+            Py_DECREF(servername_bytes);
             goto error;
         }
+        Py_DECREF(servername_bytes);
         result = PyObject_CallFunctionObjArgs(
             ssl_ctx->set_sni_cb, ssl_socket, servername_str,
             ssl_ctx, NULL);