Re: RLS Design

On 01/07/14 21:51, Robert Haas wrote:
> On Tue, Jul 1, 2014 at 3:20 PM, Dean Rasheed <dean.a.rasheed@gmail.com> wrote:
>>
>> That seems like a pretty strong argument.
>>
>> If RLS quals are instead regarded as constraints on access, and
>> multiple policies apply, then it seems that the quals should now be
>> combined with AND rather than OR, right?
> Yeah, maybe.  I intuitively feel that OR would be more useful, so it
> would be nice to find a design where that makes sense.
Looking at the use cases we described earlier in 
http://www.postgresql.org/message-id/attachment/32196/mini-rim.sql I see 
more OR than AND, for instance 'if the row is sensitive then the user 
must be related to the row' which translates to (NOT sensitive) OR the 
user is related.

An addition to that rule could be a breakglass method or other reasons 
to access, e.g.
(NOT sensitive) OR user is related OR break glass OR legally required 
access.

>    But it depends
> a lot, in my view, on what syntax we end up with.  For example,
> suppose we add just one command:
>
> ALTER TABLE table_name FILTER [ role_name | PUBLIC ] USING qual;
>
> If the given role inherits from multiple roles that have different
> filters, I think the user will naturally expect all of the filters to
> be applied.

Suppose a building administrator gives a single person that has multiple 
roles multiple key cards to access appropriate rooms in a building. You 
could draw a venn diagram of the rooms those key cards open, and the 
intuition here probably is that the person can enter any room if one of 
the key cards matches, not all cards.

>     But you could do it other ways.  For example:
>
> ALTER TABLE table_name [ NO ] ROW LEVEL SECURITY;
> ALTER TABLE table_name GRANT ROW ACCESS TO role_name USING qual;
>
> If a table is set to NO ROW LEVEL SECURITY then it behaves just like
> it does now: anyone who accesses it sees all the rows, restricted to
> those columns for which they have permission.  If the table is set to
> ROW LEVEL SECURITY then the default is to show no rows.  The second
> command then allows access to a subset of the rows for a give role
> name.  In this case, it is probably logical for access to be combined
> via OR.
>
regards,
Yeb Havinga