The init function of the signal module fails to check for errors in a couple of places. The patch replaces PyDict_SetItemString() calls with PyModule_AddIntMacro() and error checks. An exception is unlikely so I'm OK when the patch just lands in 3.4 and 3.5.

CID 1295026 (#41 of 41): Dereference null return value (NULL_RETURNS)
dereference: Dereferencing a pointer that might be null x when calling PyDict_SetItemString

All of the PyModule_AddIntMacro() changes have already been applied in https://github.com/python/cpython/commit/6782b14bcba612e4a39e41992c77306217b91e30.

The remaining parts are:

-    x = PyLong_FromLong((long)NSIG);
-    if (!x || PyDict_SetItemString(d, "NSIG", x) < 0)
+    if (PyModule_AddIntMacro(m, NSIG))
         goto finally;
-    Py_DECREF(x);

---

-     PyExc_IOError, NULL);
-    if (ItimerError != NULL)
-    PyDict_SetItemString(d, "ItimerError", ItimerError);
+                                     PyExc_IOError, NULL);
+    if (PyModule_AddObject(m, "ItimerError", ItimerError))
+        goto finally;

@berkerpeksag I made the requested changes on the PR. PTAL.

New changeset 9541bd321a94f13dc41163a5d7a1a847816fac84 by Berker Peksag (Joannah Nanjekye) in branch 'master':
bpo-24011: Use PyModule_Add{Object,IntMacro} in PyInit__signal() (GH-12765)
https://github.com/python/cpython/commit/9541bd321a94f13dc41163a5d7a1a847816fac84

Thank you, Joannah. There's no need to backport PR 12765 to maintenance branches, so I'm closing this issue as 'fixed'.

There is a regression related to reference count: see bpo-38037.