bpo-34695: sqlite3: Fix crash if Cache.get() is called before __init__()

Lib/sqlite3/test/regression.py

@@ -397,6 +397,17 @@ def callback(*args):
         del ref
         support.gc_collect()
 
+    def CheckBpo34695(self):
+        """
+        The interpreter shouldn't crash in case Cache.__init__() is not
+        called.
+        """
+        cache = sqlite.Cache.__new__(sqlite.Cache, lambda x: x)
+        self.assertRaisesRegex(sqlite.ProgrammingError, r'Cache\.__init__',
+                               cache.get, 42)
+        self.assertRaisesRegex(sqlite.ProgrammingError, r'Cache\.__init__',
+                               cache.display)
+
 
 def suite():
     regression_suite = unittest.makeSuite(RegressionTests, "Check")

Misc/NEWS.d/next/Library/2018-09-15-18-58-31.bpo-34695.Ts0-Kt.rst

@@ -0,0 +1 @@
+Fix crash if :meth:`sqlite3.Cache.get` is called before ``__init__``.

Modules/_sqlite/cache.c

@@ -22,6 +22,7 @@
  */
 
 #include "cache.h"
+#include "module.h"
 #include <limits.h>
 
 /* only used internally */
@@ -112,13 +113,26 @@ void pysqlite_cache_dealloc(pysqlite_Cache* self)
     Py_TYPE(self)->tp_free((PyObject*)self);
 }
 
+static int pysqlite_check_cache(pysqlite_Cache *self) {
+    if (self->factory == NULL) {
+        PyErr_SetString(pysqlite_ProgrammingError,
+                        "Cache.__init__ was not called or failed.");
+        return 0;
+    }
+    return 1;
+}
+
 PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args)
 {
     PyObject* key = args;
     pysqlite_Node* node;
     pysqlite_Node* ptr;
     PyObject* data;
 
+    if (!pysqlite_check_cache(self)) {
+        return NULL;
+    }
+
     node = (pysqlite_Node*)PyDict_GetItem(self->mapping, key);
     if (node) {
         /* an entry for this key already exists in the cache */
@@ -218,6 +232,10 @@ PyObject* pysqlite_cache_display(pysqlite_Cache* self, PyObject* args)
     PyObject* nextkey;
     PyObject* display_str;
 
+    if (!pysqlite_check_cache(self)) {
+        return NULL;
+    }
+
     ptr = self->first;
 
     while (ptr) {