Re: [RFC] Interface of Row Level Security

On Thu, May 24, 2012 at 12:00 PM, Kohei KaiGai <kaigai@kaigai.gr.jp> wrote:
>> Another issue, BTW, are FOREIGN KEY constraints. Should you be allowed to
>> created references to rows which are invisible to you, or should FOREIGN KEY
>> constraints be exempt from security policies? I'd say they shouldn't be, i.e.
>> the policy WHERE clause should be added to constraint checking queries like
>> usual. But maybe I'm missing some reason why that'd be undesirable…
>>
> I agree. The row level security policy should not be applied during FK checks
> (or other internal stuff; to be harmless). At the previous discussion, it was
> issued that iteration of FK/PK proving enables malicious one to estimate
> existence of invisible tuple and its key value, although they cannot see the
> actual values. It is well documented limitation, thus, user should not use row-
> level security (or should not use natural key) if they cannot accept
> this limitation.

You say "I agree", but it seems to me that you and Florian are in fact
taking opposite positions.

FWIW, I'm inclined to think that you should NOT be able to create a
row that references an invisible row.  You might end up with that
situation anyway, because we don't know what the semantics of the
security policy are: rows might become visible or invisible after the
fact, and we can't police that.  But I think that if you take the
opposite position that the select queries inside fkey triggers ought
to be exempt from security policy, then you need to build some new
mechanism to make that happen, which seems like extra work for no
benefit.

--
Robert Haas
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