gh-106831: Fix NULL check of d2i_SSL_SESSION() result in _ssl.c (#106832)

Author: sobolevn

Misc/NEWS.d/next/Library/2023-07-17-21-45-15.gh-issue-106831.RqVq9X.rst

@@ -0,0 +1,2 @@
+Fix potential missing ``NULL`` check of ``d2i_SSL_SESSION`` result in
+``_ssl.c``.

Modules/_ssl.c

@@ -2808,7 +2808,7 @@ _ssl_session_dup(SSL_SESSION *session) {
     /* get length */
     slen = i2d_SSL_SESSION(session, NULL);
     if (slen == 0 || slen > 0xFF00) {
-        PyErr_SetString(PyExc_ValueError, "i2d() failed.");
+        PyErr_SetString(PyExc_ValueError, "i2d() failed");
         goto error;
     }
     if ((senc = PyMem_Malloc(slen)) == NULL) {
@@ -2817,12 +2817,13 @@ _ssl_session_dup(SSL_SESSION *session) {
     }
     p = senc;
     if (!i2d_SSL_SESSION(session, &p)) {
-        PyErr_SetString(PyExc_ValueError, "i2d() failed.");
+        PyErr_SetString(PyExc_ValueError, "i2d() failed");
         goto error;
     }
     const_p = senc;
     newsession = d2i_SSL_SESSION(NULL, &const_p, slen);
-    if (session == NULL) {
+    if (newsession == NULL) {
+        PyErr_SetString(PyExc_ValueError, "d2i() failed");
         goto error;
     }
     PyMem_Free(senc);