Re: Reworks for Access Control facilities (r2363)

Heikki Linnakangas wrote:
> KaiGai Kohei wrote:
>> When we create a new object, we can provide an explicit security context
>> to be assigned on the new object, instead of the default one.
>
> To get started, do we really need that feature? It would make for a
> significantly smaller patch if there was no explicit security labels on
> objects.

The importance of the feature is relatively minor than MAC itself.
So, I can agree to omit code corresponding to statement support
from the first patch. (IIRC, about 300-400 lines can be reduced.)
But it will be necessary feature at the next step, because DBA cannot
create a special purpose table without statement support.

For example, if security policy allows DBA to create read-writable
table (in default) and read-only table. He cannot set up read-only
table without explicit security label support.

>>>> On the other hand, the default PG model allows to bypass checks on
>>>> certain objects. For example, column-level privileges are only checked
>>>> when a user does not have enough permissions on the target table.
>>>> If "SELECT a,b FROM t" is given, pg_attribute_aclcheck() may not invoked
>>>> when user has needed privileges on the table t.
>>> Hmm, I see. Yes, it does seem like we'd need to change such permission
>>> checks to accommodate both models.
>> I'm not clear why we need to rework the permission checks here.
>> DAC and MAC perform orthogonally and independently.
>> DAC allows to override column-level privileges by table-level privileges
>> according to the default PG's model. It seems to me fine.
>> On the other hand, MAC checks both of permissions. It is also fine.
>
> I meant we need to refactor the code doing the permission checks. The
> existing checks are doing the right thing for DAC, but as you point out,
> if the MAC checks are within pg_*_aclcheck() functions,
> pg_attribute_aclcheck() needs to be called even if you have privilege on
> the table.

I think we already learned refactoring DAC checks need widespread code
changes and pushes a burden to reviewers.

In this case, I think the point just after invocation of ExecCheckRTEPerms()
in ExecCheckRTPerms() is the best point to put SE-PgSQL's checks.
Needless to say, its specification should be clearly documented.

Thanks,
--
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>