Extending query rewriting techniques for fine-grained access control

TLDR

Fine‑grained access control at the tuple level is required for large‑user database applications, and enforcing it in application code has many drawbacks that can be avoided by database‑level enforcement. The authors propose a novel fine‑grained access control model based on authorization views that enables authorization‑transparent querying and introduce a new notion of conditional validity. They define authorization views and conditional validity, and provide inference rules to determine query validity. The approach is shown to be practical by extending an existing query optimizer to perform access control checks using these inference rules.

Abstract

Current day database applications, with large numbers of users, require fine-grained access control mechanisms, at the level of individual tuples, not just entire relations/views, to control which parts of the data can be accessed by each user. Fine-grained access control is often enforced in the application code, which has numerous drawbacks; these can be avoided by specifying/enforcing access control at the database level. We present a novel fine-grained access control model based on authorization views that allows "authorization-transparent" querying; that is, user queries can be phrased in terms of the database relations, and are valid if they can be answered using only the information contained in these authorization views. We extend earlier work on authorization-transparent querying by introducing a new notion of validity, conditional validity. We give a powerful set of inference rules to check for query validity. We demonstrate the practicality of our techniques by describing how an existing query optimizer can be extended to perform access control checks by incorporating these inference rules.