Fixes Issue #3745: Fix hashlib to always reject unicode and non

buffer-api supporting objects as input no matter how it was compiled
(built in implementations or external openssl library).

Modules/hashlib.h

@@ -0,0 +1,28 @@
+/* Common code for use by all hashlib related modules. */
+
+/*
+ * Given a PyObject* obj, fill in the Py_buffer* viewp with the result
+ * of PyObject_GetBuffer.  Sets and exception and issues a return NULL
+ * on any errors.
+ */
+#define GET_BUFFER_VIEW_OR_ERROUT(obj, viewp) do { \
+        if (PyUnicode_Check((obj))) { \
+            PyErr_SetString(PyExc_TypeError, \
+                            "Unicode-objects must be encoded before hashing");\
+            return NULL; \
+        } \
+        if (!PyObject_CheckBuffer((obj))) { \
+            PyErr_SetString(PyExc_TypeError, \
+                            "object supporting the buffer API required"); \
+            return NULL; \
+        } \
+        if (PyObject_GetBuffer((obj), (viewp), PyBUF_SIMPLE) == -1) { \
+            return NULL; \
+        } \
+        if ((viewp)->ndim > 1) { \
+            PyErr_SetString(PyExc_BufferError, \
+                            "Buffer must be single dimension"); \
+            PyBuffer_Release((viewp)); \
+            return NULL; \
+        } \
+    } while(0);