Обсуждение: Users, Roles and Connection Pooling

On Wed, 2019-10-02 at 08:46 +1000, Matt Andrews wrote:
> Here’s a question I’ve been asking for a while and just can’t find an
> answer to, so I thought I’d ask it here. The answer could be
> subjective, but here goes...
> 
> When a web app connects to Postgres via a connection pooler, what is
> the best way to manage privileges for the connecting user? Especially
> when their is a complex hierarchy of privileges?
> 
> Should each signed up user have their own role which inherits from
> whichever roles they are members of? This means that the connection
> pool role should then be granted in every user?
> 
> Does creating a Postgres role for every app user scale? Roles can
> only have names, is an email address a good name for individual app
> users?
> 
> Are their any resources out there that anyone knows of that addresses
> these questions?
> 
> There’s plenty of stuff out there on roles and permissions, I’ve read
> a lot of it, but not much on dealing with individual app users
> through a connection pool. 
> 
> I’m thinking that any queries should start with SET ROLE ‘username’
> and end with RESET ROLE. Is this how it could work?
> 
> Any help would be greatly appreciated. 

A couple of pointers:

- The role that the application server connects with should be a
  member of each database role it wants to become through SET ROLE.

- Yes, you will have to start with SET ROLE.
  RESET ROLE should be executed by the pool when it gets a connection
  back.

- This is a good setup if you don't have too many users.  Metadata
  queries will start getting slow if you get into the tens of thousands
  of users, maybe earlier.

  The advantages are that you can make use of PostgreSQL's rich
  permission concept and row level security.

- The name of the user might as well be an e-mail address, as long
  as it does not exceed 63 bytes.

- Make use of user groups and grant privileges on that level rather
  than to the individual users.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com

Greetings,

* Laurenz Albe (laurenz.albe@cybertec.at) wrote:
> A couple of pointers:

I generally agree with these comments.

> - This is a good setup if you don't have too many users.  Metadata
>   queries will start getting slow if you get into the tens of thousands
>   of users, maybe earlier.

While this seems plausible- I'd love to hear about exactly what you've
seen start to be a problem when getting up to that many users.  Are you
just referring to things like \du?  Or..?

Thanks,

Stephen

I have little experience in this area, but it seems like having a Postgres role for every application user is the right way to do things. It’s just that it also seems really inconvenient.

For example how to map an application’s users/people table to Postgres roles? The pg_role name field is limited to 64 bytes, you can’t create a foreign key to pg_role. What’s the answer? Use UUIDs as usernames or something?

There’s very little out there on this topic, but surely this has been done before. 

On Wed, 2 Oct 2019 at 17:43, Stephen Frost <sfrost@snowman.net> wrote:

Greetings,

* Laurenz Albe (laurenz.albe@cybertec.at) wrote:
> A couple of pointers:

I generally agree with these comments.

> - This is a good setup if you don't have too many users.  Metadata
>   queries will start getting slow if you get into the tens of thousands
>   of users, maybe earlier.

While this seems plausible- I'd love to hear about exactly what you've
seen start to be a problem when getting up to that many users.  Are you
just referring to things like \du?  Or..?

Thanks,

Stephen

Greetings,

(we don't top-post on these lists, fyi, please reply in-line and trim)

* Matt Andrews (mattandrews@massey.com.au) wrote:
> I have little experience in this area, but it seems like having a Postgres
> role for every application user is the right way to do things. It’s just
> that it also seems really inconvenient.

I agree that there are some drawbacks to it.

> For example how to map an application’s users/people table to Postgres
> roles? The pg_role name field is limited to 64 bytes, you can’t create a
> foreign key to pg_role. What’s the answer? Use UUIDs as usernames or
> something?

Yeah, it would be nice to have an answer to the FK issue when it comes
to roles (and possibly other things..).  The limit on length is annoying
but I'm not sure that it's show-stopper.  I don't think using UUIDs is a
good idea, at all...

> There’s very little out there on this topic, but surely this has been done
> before.

Oh, absolutely, but with compromises, particularly around FKs and such.

Thanks,

Stephen

> On Wed, 2019-10-02 at 08:46 +1000, Matt Andrews wrote:
> > Here’s a question I’ve been asking for a while and just can’t find an
> > answer to, so I thought I’d ask it here. The answer could be
> > subjective, but here goes...
> > 
> > When a web app connects to Postgres via a connection pooler, what is
> > the best way to manage privileges for the connecting user? Especially
> > when their is a complex hierarchy of privileges?
> > 
> > Should each signed up user have their own role which inherits from
> > whichever roles they are members of? This means that the connection
> > pool role should then be granted in every user?
> > 
> > Does creating a Postgres role for every app user scale? Roles can
> > only have names, is an email address a good name for individual app
> > users?
> > 
> > Are their any resources out there that anyone knows of that addresses
> > these questions?
> > 
> > There’s plenty of stuff out there on roles and permissions, I’ve read
> > a lot of it, but not much on dealing with individual app users
> > through a connection pool. 
> > 
> > I’m thinking that any queries should start with SET ROLE ‘username’
> > and end with RESET ROLE. Is this how it could work?
> > 
> > Any help would be greatly appreciated. 

I can't help with questions about scale but I like to give roles/users
almost no permissions at all. i.e. They can't select, insert, update
or delete anything. All they have permission to do is to execute stored
functions that were installed by a role with the necessary permissions
and they are security defining functions so the permissions of the role
that created them apply when the functions are called. This means that
there will never be any successful SQL injection, even if the application
code is buggy, so it's more important for web applications, but I apply
this method to internal systems as well. This approach might help with
scaling because fewer users might be needed but I'm not sure.

cheers,
raf

On 10/2/19 5:27 PM, raf wrote:
>>
> I can't help with questions about scale but I like to give roles/users
> almost no permissions at all. i.e. They can't select, insert, update
> or delete anything. All they have permission to do is to execute stored
> functions that were installed by a role with the necessary permissions
> and they are security defining functions so the permissions of the role
> that created them apply when the functions are called. This means that
> there will never be any successful SQL injection, even if the application
> code is buggy, so it's more important for web applications, but I apply
> this method to internal systems as well. This approach might help with
> scaling because fewer users might be needed but I'm not sure.
>
> cheers,
> raf
>
>
How easy is it to introduce an new function call all the way up to the 
app user?  Does this approach preclude making use of any query 
generation techniques available?

Rob Sargent wrote:

> On 10/2/19 5:27 PM, raf wrote:
> > > 
> > I can't help with questions about scale but I like to give roles/users
> > almost no permissions at all. i.e. They can't select, insert, update
> > or delete anything. All they have permission to do is to execute stored
> > functions that were installed by a role with the necessary permissions
> > and they are security defining functions so the permissions of the role
> > that created them apply when the functions are called. This means that
> > there will never be any successful SQL injection, even if the application
> > code is buggy, so it's more important for web applications, but I apply
> > this method to internal systems as well. This approach might help with
> > scaling because fewer users might be needed but I'm not sure.
> > 
> > cheers,
> > raf
> > 
> How easy is it to introduce an new function call all the way up to the app
> user?

It's easy when you have the right tools to make it
easy: i.e. you write the stored function, then run a
tool to generate the python class for the result set
and the python function that the client applications
can then call to execute the stored function and return
its results.

> Does this approach preclude making use of any query generation
> techniques available?

Yes, it does. I'm happy to write my own plpgsql and
sql. I find that usually results in faster results
(mainly by reducing the temptation to process data
outside the database) as well as being more secure.

I once worked in a job were I couldn't go home until
some program had finished and it was sucking data out
of the database just to summarise it and insert the
summaries. It tooks hours. I replaced it with a stored
procedure that took two minutes and I started going
home much earlier. Rightly or wrongly, that made me
prefer prcessing data inside the database.

cheers,
raf