Re: Updates of SE-PostgreSQL 8.4devel patches (r1704)

Heikki Linnakangas wrote:
> KaiGai Kohei wrote:
>> As I promised last week, SE-PostgreSQL patches are revised here:
>
> I think I now understand what sepgsqlCheckProcedureInstall is trying to
> achieve. It's trying to stop attacks where you trick another user to run
> your malicious code. We had a serious vulnerability of that kind a while
> ago (http://archives.postgresql.org//pgsql-hackers/2008-01/msg00268.php)
> when ANALYZE and VACUUM FULL ran expression and partial index predicates
> with (typically) superuser privileges.
>
> It seems that sepgsqlCheckProcedureInstall is trying to provide a more
> thorough solution to the trojan horse problem than what we did back
> then. It stops you from installing an untrusted function as a type
> input/output function, operator implementing function etc. Now that
> could be useful on its own, quite apart from the rest of the
> SE-PostgreSQL patch, in which case I'd like to see that implemented as a
> separate patch, so that you can use the facility even if you're not
> using SE-PostgreSQL.

Yes, the purpose of sepgsqlCheckProcedureInstall() is to prevent users
to invoke functions installed by other malicious/untrusted one, typically
known as trojan-horse.

Basically, I can agree the vanilla PostgreSQL also provide similar stuff
to prevent to install "untrusted" functions as a part of system internal
codes. If we have such a facility as a basis, we can implement
sepgsqlCheckProcedureInstall() hook more simple and easier to maintenance.

[snip]
>> + case ConversionRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_conversion, conproc, newtup,
>> oldtup);
>> + break;
>
> This ought to be unnecessary now. Only C-functions can be installed as
> conversion procs, and a C function can do anything, so there's little
> point in checking this anymore.

We should not assume only C-functions can be installed on pg_conversion
(and other internal stuff), because a superuser can update system catalog
by hand.

Example)
postgres=# CREATE OR REPLACE FUNCTION testfn()
postgres-# RETURNS int LANGUAGE sql AS 'SELECT 1';
CREATE FUNCTION
postgres=# UPDATE pg_conversion SET conproc = 'testfn'::regproc where oid=11276;
UPDATE 1
postgres=# set client_encoding = 'sjis';
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and repeat your command.
Failed.
!>

SE-PostgreSQL intends to acquire them and apply access control policy
in this case also.

Aside note: sepgsqlCheckDatabaseInstallModule() check permissions on
a newly installed C-library file, to prevent to load a file deployed
by untrusted client.

>> + case ForeignDataWrapperRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_foreign_data_wrapper,
>> fdwvalidator, newtup, oldtup);
>> + break;
>
> Hmm, calls to fdwvalidator are not at all performance critical, so maybe
> we should just check execute permission when it's called.

If pg_proc_aclcheck() on its invocation, it is not necessary to check
on the installation time.

[snip]
>> + case OperatorRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_operator, oprcode, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_operator, oprrest, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_operator, oprjoin, newtup, oldtup);
>> + break;
>
> oprcode is checked for execute permission when the operator is used. For
> oprrest and oprjoin, we could add checks into the planner where they're
> called. (pg_operator.oprcom and pg_operator.oprnegate are missing?)

If runtime checks are added, it is more desirable.

>> + case TSParserRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_ts_parser, prsstart, newtup,
>> oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_ts_parser, prstoken, newtup,
>> oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_ts_parser, prsend, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_ts_parser, prsheadline, newtup,
>> oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_ts_parser, prslextype, newtup,
>> oldtup);
>> + break;
>> + + case TSTemplateRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_ts_template, tmplinit, newtup,
>> oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_ts_template, tmpllexize, newtup,
>> oldtup);
>> + break;
>
> Not sure about these. Maybe we should add checks to where these are called.

I'll check the behavior of them tomorrow.

>> + case TypeRelationId:
>> + CHECK_PROC_INSTALL_PERM(pg_type, typinput, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typoutput, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typreceive, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typsend, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typmodin, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typmodout, newtup, oldtup);
>> + CHECK_PROC_INSTALL_PERM(pg_type, typanalyze, newtup, oldtup);
>> + break;
>
> Hmm, input/output functions have to be in C, so I'm not concerned about
> those. send/receive and typmodin/typmodout are a bit problematic.
> ANALYZE calls typanalyze as the table owner, so I think that's safe.
>
>
> All of these require the victim to willingly (although indirectly) call
> a non-security definer function created by the attacker, with varying
> degrees of difficultness in tricking someone to do that. Can't you just
> create a policy that forbids creating non-security definer functions in
> the first place? It's much more coarse-grained, but would probably be
> enough in practice.

I think it is possible, and I welcome the vanilla PostgreSQL also have
such a facility. It also make easier to maintain SE-PostgreSQL code. :-)
The issue it what policy should be applied on the vanilla side.

The following rules may be able to be a draft.
- Any installed functions should not security definer.
- Any installed functions should be owned by superuser.
(to prevent replacement by normal users.)

What is your opinion? I'll try to consider it more...

Thanks,
--
KaiGai Kohei <kaigai(at)kaigai(dot)gr(dot)jp>