gh-144069: Fix memory leak in _dbm.open() on failure

Author: VanshAgarwal24036

Lib/test/test_dbm.py

@@ -244,6 +244,10 @@ def setUp(self):
         self.addCleanup(cleaunup_test_dir)
         setup_test_dir()
 
+    def test_open_nonexistent_directory(self):
+        missing_dir = os.path.join(dirname + "_does_not_exist", "test.db")
+        with self.assertRaises(OSError):
+            dbm.open(missing_dir, "c")
 
 class WhichDBTestCase(unittest.TestCase):
     def test_whichdb(self):

Modules/_dbmmodule.c

@@ -85,11 +85,16 @@ newdbmobject(_dbm_state *state, const char *file, int flags, int mode)
     }
     dp->di_size = -1;
     dp->flags = flags;
+    dp->di_dbm = NULL;
     PyObject_GC_Track(dp);
 
     /* See issue #19296 */
-    if ( (dp->di_dbm = dbm_open((char *)file, flags, mode)) == 0 ) {
+    if ( (dp->di_dbm = dbm_open((char *)file, flags, mode)) == NULL ) {
         PyErr_SetFromErrnoWithFilename(state->dbm_error, file);
+        if (dp->di_dbm != NULL) {
+            dbm_close(dp->di_dbm);
+            dp->di_dbm = NULL;
+        }
         Py_DECREF(dp);
         return NULL;
     }