Securing Your PostgreSQL DB with Roles and Privileges

https://rlopzc.com/posts/securing-your-postgresql-db-with-roles--privileges/

by rlopezc • 3 years ago

117 37 3 years ago

pphysch5• 3 years ago

Has anyone run into issues with too many roles? Like if you want to use RLS and have a role per application-user, with millions of users.

programmarchy2• 3 years ago

Why have a role per user instead of just defining the row policy with the user directly?

pphysch5• 3 years ago

How does that work? With per "user" roles, I can SET ROLE "user-1000" and enter their authz context without changing any of my queries. How would this work without per-user roles?

hn_throwaway_996• 3 years ago

In Postgres a "role" really is equivalent to a user. A user in Postgres is just a role with the ability to log in.

paulryanrogers• 3 years ago

Roles/users are backed by PG tables, so I imagine storing them should be no more difficult. (Assuming partitioning and other native features are available.) Yet I'm not sure how well it would scale all the row checks for read and write access, especially if you also use column level security.

Proxying connections for so many different users would be awkward too, though some proxies apparently can take on a different role for the session and revert when client-side disconnects.

anarazel2• 3 years ago

FWIW, you don't need to use database roles if you want to use RLS. You can instead have some other context indicating the current "application user" and use that in your RLS policies.

pphysch5• 3 years ago

Do I have to add that context to every query, or is it something I can set per cursor/transaction?

aeonsky• 3 years ago

Yes, my team had a direct issue with this on Aurora Postgres, at least. This is PG9 but then kept happening all the way into PG12 until we got rid of all but like 5 roles. Above like 4000 roles we experienced a significant lag on every query, sometimes on the order of seconds. At scaled somewhat linearly. I even wrote to Tom Lane and he said that area of Postgres is poorly optimized.

pphysch5• 3 years ago

Interesting. Why so many roles initially, and how did you safely consolidate to 5?

hn_throwaway_996• 3 years ago

The article starts at the top by saying "To become SOC2 compliant, we needed to remove global access and fine-tune who has access to what schemas and tables."

I've had to go through this SOC2 certification process as well, and I think a much better approach (with a lot of other benefits) is to use client side encryption to encode sensitive data like PII or PHI (personal health info) before you insert it into the DB. That way it's easy to give all of your developers read-only access to essentially the entire DB for things like debugging support while still maintaining SOC2 and other compliance (e.g. HIPAA).

Not saying there isn't also good use cases for roles and privileges (and it's a lot harder to add client-side encryption after the fact), but using client side encryption/decryption is a better approach to this issue IMO (you get more security benefits, and the compliance benefits really just are a consequence of that).

lastofus• 3 years ago

Doesn't encrypting your data before insertion make your data unable to be indexed/searched easily?

webstrand• 3 years ago

For some kinds of data and queries, it doesn't matter if the data in the index is encrypted. For other kinds of data, you could build the index on an expression that produces decrypted or anonymized values. Sadly postgres doesn't have per-index permissions, so you can't prevent a user with access to the table from using all of it's indexes.

hn_throwaway_996• 3 years ago

For indexing/searching on encrypted fields we use a blind index (lots of good resources if you search for that term).

On the other hand, sorting on encrypted fields has proven to be a difficult challenge. There are some possible approaches but they lower the security of your encryption.

rudasn• 3 years ago

How can you do client side encryption with web apps though? While keeping the key on the client, I assume, and allowing multiple browser sessions for the same user?

candiddevmike• 3 years ago

Envelope encryption, where you encrypt a data encryption key (typically symmetric with AES) with other keys (typically asymmetric with RSA). This is how most password safes like bitwarden work.

hn_throwaway_996• 3 years ago

When I say "client side encryption", I'm referring to the database client, which in most web apps is actually code running on a private server (i.e. browser code makes API calls to a server running something like Python, Node or Java, and that server code makes calls to the DB - it's on the server where PII is encrypted).

That said, you can also use the SubtleCrypto API in the browser to encrypt data before it is even sent to the server.

patmorgan232• 3 years ago

I believe by client side they mean the database client, which would be the application backend/server.

_jal2• 3 years ago

That's fine if you want a bucket of bits instead of a database. You can even make it easier by making one big table with an ID and blob, and just serialize | encrypt state to the DB. Easy-peasy.

If you want to use the "R" in RDBMS, though, or report on your data, or use indexes, or anything else that makes it worth running complex DBs instead of a file system, you're stuck using a database as a database.

hn_throwaway_996• 3 years ago

This is wrong and unnecessarily snarky. I don't pre-encrypt all data, just PII/PHI. Doing this, or tokenization with a vaulting servjce, is pretty much standard recommended practice for storing sensitive data.

snagg• 3 years ago

We are big proponent of app-layer encryption as well. We wrote extensively about how we do it for our specific use case: https://www.slashid.dev/blog/app-layer-encryption/

singron• 3 years ago

We've done SOC2 type 1 and 2, and with a few exceptions, you only have to do what you say you do. First you claim you have controls on X, Y, Z, and then your audiors check that. You can just not claim X if you don't want to implement it. If the claim is vague, you have a lot of flexibility for implementation too.

This is a huge reason why SOC2 isn't a very useful certification. Your SOC2 and my SOC2 can be wildly different.

TheNewsIsHere4• 3 years ago

I would qualify this statement. For a competent auditing firm there are non-negotiables to attesting to your own firms compliance, and a discerning (prospective) customer who pays attention and knows how to read those reports can spot places where “you’re trying to get away with it”.

I’d much sooner agree that the flexibility is in implementation. As long as you can hit a control in a reasonable and articulable manner that can be measured and evidenced, you have much flexibility. I see that as the benefit of SOC2. Others see it as an issue.

To your point, last time I led a company through a SOC2 Type 1-2 engagement, we had some standards sourced from NIST that were ahead of industry for the time, and published NIST standards were an authority that the auditing firm was comfortable accepting as compensatory for a control that otherwise would have been absent or out of compliance. So that control was ultimately accepted as “No exceptions during the audit period, but see our notes annex”.

louwrentius3• 3 years ago

Maybe I’m totally out of it, but creating an actual database user for each account of your application sounds like you can rely on database security and don’t run the risk of application bugs causing security vulnerabilities.

This means a more complex database level of roles and privileges, which may be it’s own can of worms, but if you have to choose between problems to have, what would you select?

warent• 3 years ago

I don't think this literally means each user of your app gets their own DB user, rather that you create different db users for different aspects of your app.

What you're describing is what RLS (row-level security) is for, where you log into a generic global "app_user" user with certain permissions that don't include things like admin tables etc, and then define the specific user that is using the session via session variables.

louwrentius3• 3 years ago

I've seen blog posts decades ago from DB admins that actually advocated for a DB account per user account. They stated the DB was totally build for that, but people just don't know. They use what they understand, as in: app people may know too little about database security and privileges and just decide to solve it in code.

patmorgan232• 3 years ago

There are applications that are built to where literally every user gets a database login. For example Dynamics SL (formerly Solomon) is built this way with MS SQL server.

_jal2• 3 years ago

We are heavy postgres users, and we do both SOC2 and a more stringent audit demanded by our corporate parent. Lots of roles, lots of RLS, encrypted media, additional column-level encryption for some specific things for not great reasons).

The postgres roles in particular were a recurring mess until we built provisioning that stuff in to our onboarding automation. If you are going to have individual named users, I highly recommend taking humans out of the process, we make too many mistakes.

And yes, there are multiple advantages to enforcing access control as close to the data as possible. I tend to think of databases as "data structures that can defend themselves" - not just security, but type and data validation, relational references, etc. all can both save you from bugs and help you find them earlier.

louwrentius3• 3 years ago

Yes, as an armchair "expert" that's what I was thinking. But managing swats of SQL: a developer friend said that this is difficult too. I don't know. But if I had to choose, I would make the SQL / DB side rock solid, even if it required some business logic in SQL.

Securing Your PostgreSQL DB with Roles and Privileges

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