Re: security label support, part.2

2010/7/22 KaiGai Kohei <kaigai@ak.jp.nec.com>:
> Thanks for your reviewing.
>> 1. I am inclined to suggest the syntax SECURITY LABEL ON ... IS ...,
>> following COMMENT ON (it's also somewhat similar to the GRANT syntax).
>>   While the hook in ExecCheckRTPerms() will only allow meaningful
>> permissions checks on the use of relations, there will presumably be
>> ongoing demand to add additional hooks to cover other types of
>> objects, and I'd rather add label support all at once rather than
>> bit-by-bit.  I also think that the SECURITY LABEL syntax is more
>> future-proof; we don't need to worry about conflicts in other parts of
>> the grammar.
>>
> Hmm. Indeed, we cannot deny the possibility to conflict with other part
> in the future, if we use ALTER xxx statement here.
>
> But, right now, we have no statement that starts in noun, rather than verb.
> The "comment" is a noun, but "comment on" is a phrasal-verb, isn't it?
>
> How about RELABEL <object> TO <label>, instead?

Well, I like SECURITY LABEL better because it's more clear about what
kind of label we're talking about, but if there's consensus on some
other option it's OK with me.  Actually, we need to work the security
provider name in there too, I think, so perhaps SECURITY LABEL FOR
provider ON object IS labeltext.  I realize it's slightly odd
grammatically, but it's no worse than the COMMENT syntax.

>> 2. Similarly, the design of the hook in secabel.h is way too
>> short-sighted and won't scale to any other object type.  We don't need
>> or want one hook per object type here.  Use an ObjectAddress.
>>
> I think the relation type is an exceptional object class, because of
> the recursion due to the table inheritances.
> For other object classes, I also think one security hook which takes
> ObjectAddress as an argument is enough to implement.
>
> So, I expect we need two hooks on relabeling eventually.
> (One for relation, one for other object classes)

Please explain in more detail.

>> 3. I am firmly of the view that we want to allow multiple security
>> providers.  I think the way this should work here is that we should
>> keep a list somewhere of security providers known to the system, which
>> loadable modules should add themselves to.  Each such security
>> provider should be represented by a struct containing, at least, a
>> name and a function that gets called on relabel.  The labels should be
>> stored in the catalog.  That way there is never any possibility of one
>> security provider getting a label that was originally applied by some
>> other security provider.  If we were storing these labels in pg_class
>> or pg_attribute or similar, the storage cost for this might be worth
>> worrying about, but as this is a separate catalog, it's not.
>>
> What I'm worrying about is that we cannot estimate amount of works when
> we expand the concept to row-level security. We will need to revise the
> implementation, if individual user tuples have its security label in the
> future version.
> If we don't support multiple labels right now, it will not be feature
> degradation, even if it will be hard to implement multiple label support
> for each user tuples. :(

I think it is 100% clear that row-level security will require
completely separate infrastructure, and therefore I'm not even a tiny
bit worried about this.  :-)

--
Robert Haas
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