Thread: Strange permission problem regarding pg_settings

Hi

I installed a postgres-application (which was developed on debian
woody) on red hat 9 today, using the postgres 7.3 rpms from redhad.
One of my the triggers uses the pg_settings table (more precisely, it
updates that table to change the search_path temporarily). With the
postgres 7.3 (and 7.4 too) installed on my debian development system,
this worked fine. On redhat 9, however, I get an "pg_settings:
permission denied" error when my trigger is executed.

The same thing happens when I try altering the pg_settings table from
the commandline. (But of course works, when connected as superuser). I
double-checked the permissions set on both the pg_settings view, and
the set_config(text, text, bool)-function called from the update-rule
for pg_settings, and both seem to be correct (and the same as on the
debian machine).

As I needed to get the thing running, I now solved the problem by
making the user that my app connects as a superuser, but I'd like to
get rid of this again...

Are there any more permission I could check, or perhaps some
config-option in postgres.conf that I could try?

greetings, Florian Pflug

PS: I also tried moving the postgres-data-dir away, and creating a
fresh one with initdb - but with no success - still "pg_settings:
permission denied"

Florian G. Pflug wrote:
> I installed a postgres-application (which was developed on debian woody)
> on red hat 9 today, using the postgres 7.3 rpms from redhad.
> One of my the triggers uses the pg_settings table (more precisely, it
> updates that table to change the search_path temporarily). With the
> postgres 7.3 (and 7.4 too) installed on my debian development system,
> this worked fine. On redhat 9, however, I get an "pg_settings:
> permission denied" error when my trigger is executed.

I've got Red Hat 9 here, but it is hard to guess what might be wrong
without seeing some details. Can you post a self-contained example that
recreates the problem?

Joe

On Dec 10, 2003, at 8:19 AM, Joe Conway wrote:
> Florian G. Pflug wrote:
>> I installed a postgres-application (which was developed on debian
>> woody) on red hat 9 today, using the postgres 7.3 rpms from redhad.
>> One of my the triggers uses the pg_settings table (more precisely, it
>> updates that table to change the search_path temporarily). With the
>> postgres 7.3 (and 7.4 too) installed on my debian development system,
>> this worked fine. On redhat 9, however, I get an "pg_settings:
>> permission denied" error when my trigger is executed.
> I've got Red Hat 9 here, but it is hard to guess what might be wrong
> without seeing some details. Can you post a self-contained example
> that recreates the problem?

This is what I did:
As user postgres (connected to template1)
.) create user testuser password 'pw' nocreatedb nocreateuser
.) create database testdb owner testuser encoding 'utf-8'

As user testuser (connected to testdb) :
.) update pg_settings set setting='public' where name='search_path' ;
this gives "pg_settings: permission denied"

.) select set_config('search_path', 'public', 'f') ;
this works, and sets the search_path as expected to 'public'

On debian(woody), with a woody-backport of postgresql-7.3 installed
(the packages for sid recompiled for woody, and installed with dpkg),
the "update pg_settings..." statement works.

As soon as I remove the "nocreateuser" from the "create user
testuser...." line (or alter the user afterwards), it works on redhat
too (but the user is superuser then, of course...)

If you need further information, or want me to test something, just say
so ;-)

greetings, Florian Pflug

"Florian G. Pflug" <fgp@phlo.org> writes:
> As user testuser (connected to testdb) :
> .) update pg_settings set setting='public' where name='search_path' ;
> this gives "pg_settings: permission denied"

Hm.  Works fine here.  What do you get from

select relacl, relacl is null from pg_class where relname = 'pg_settings';


            regards, tom lane

On Dec 10, 2003, at 5:35 PM, Tom Lane wrote:
> "Florian G. Pflug" <fgp@phlo.org> writes:
>> As user testuser (connected to testdb) :
>> .) update pg_settings set setting='public' where name='search_path' ;
>> this gives "pg_settings: permission denied"
> Hm.  Works fine here.  What do you get from
> select relacl, relacl is null from pg_class where relname =
> 'pg_settings';

testdb=> select relacl, relacl is null from pg_class where relname =
'pg_settings' ;
  relacl | ?column?
--------+----------
  {=r}   | f
(1 row)

mfg, Florian Pflug

Tom Lane wrote:
> "Florian G. Pflug" <fgp@phlo.org> writes:
>>As user testuser (connected to testdb) :
>>.) update pg_settings set setting='public' where name='search_path' ;
>>this gives "pg_settings: permission denied"
>
> Hm.  Works fine here.  What do you get from
>
> select relacl, relacl is null from pg_class where relname = 'pg_settings';

Works fine here too, on RH9:

Welcome to psql 7.3.5, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
        \h for help with SQL commands
        \? for help on internal slash commands
        \g or terminate with semicolon to execute query
        \q to quit

regression=# \c template1
You are now connected to database template1.
template1=# create user testuser password 'pw' nocreatedb nocreateuser;
CREATE USER
template1=# create database testdb owner testuser encoding 'utf-8';
CREATE DATABASE
template1=# \c testdb testuser
You are now connected to database testdb as user testuser.
testdb=> update pg_settings set setting='public' where name='search_path' ;
  set_config
------------
  public
(1 row)

testdb=> select relacl, relacl is null from pg_class where relname =
'pg_settings';
  relacl | ?column?
--------+----------
  {=r}   | f
(1 row)


Joe

Joe Conway <mail@joeconway.com> writes:
> Works fine here too, on RH9:

> testdb=> update pg_settings set setting='public' where name='search_path' ;
>   set_config
> ------------
>   public
> (1 row)

> testdb=> select relacl, relacl is null from pg_class where relname =
> 'pg_settings';
>   relacl | ?column?
> --------+----------
>   {=r}   | f
> (1 row)

Hm.  By rights it *should* fail, since the ACL is clearly not granting
UPDATE permissions to anybody.

The fact that it fails to fail seems to be because the rules on
pg_settings rewrite the UPDATE into DO INSTEAD NOTHING (which does
nothing, in particular makes no permission checks) and a SELECT,
which only requires read-permission on pg_settings.  This is probably
bogus and we ought to see what we can do about fixing it.  (And we'd
better fix initdb to grant UPDATE on pg_settings to public, too.)

Now, why does Florian see a permissions failure (which is really the
*right* behavior) when we don't?  He didn't say exactly which PG version
he was running, but I see a likely-related bug fix between 7.3.2 and
7.3.3:

2003-02-13 16:40  tgl

    * src/backend/rewrite/rewriteHandler.c (REL7_3_STABLE): Repair rule
    permissions-checking bug reported by Tim Burgess 10-Feb-02: the
    table(s) modified by the original query would get checked for the
    type of write permission needed by a rule query.

This fix may need to be rethought.  I'm not sure though where is a clean
place to plug in the UPDATE permissions check given that the rules for
this case do not generate any UPDATE query.

            regards, tom lane

Tom Lane wrote:
> Now, why does Florian see a permissions failure (which is really the
> *right* behavior) when we don't?  He didn't say exactly which PG version
> he was running, but I see a likely-related bug fix between 7.3.2 and
> 7.3.3:

That seems to be it:

# psql regression
Welcome to psql 7.3.2, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
        \h for help with SQL commands
        \? for help on internal slash commands
        \g or terminate with semicolon to execute query
        \q to quit

regression=# \c template1
You are now connected to database template1.
template1=# create user testuser password 'pw' nocreatedb nocreateuser;
CREATE USER
template1=# create database testdb owner testuser encoding 'utf-8';
CREATE DATABASE
template1=# \c testdb testuser
You are now connected to database testdb as user testuser.
testdb=> update pg_settings set setting='public' where name='search_path' ;
ERROR:  pg_settings: permission denied

> This fix may need to be rethought.  I'm not sure though where is a clean
> place to plug in the UPDATE permissions check given that the rules for
> this case do not generate any UPDATE query.

Do you want me to take a look at this, or are you planning to?

Joe

Joe Conway <mail@joeconway.com> writes:
> Tom Lane wrote:
>> This fix may need to be rethought.  I'm not sure though where is a clean
>> place to plug in the UPDATE permissions check given that the rules for
>> this case do not generate any UPDATE query.

> Do you want me to take a look at this, or are you planning to?

If you have any ideas, feel free to take a shot.  I've not thought of
anything I like.

I suspect the fact that the pre-patch code made the "right" permissions
check was really coincidental, and that the correct fix will not involve
reversion of that patch but rather adding a facility somewhere to ensure
that the original view gets properly permission-checked even if there's
a DO INSTEAD NOTHING rule.  However, before biting that bullet it'd
probably be good to understand in detail what's happening in both the
7.3.2 and CVS-tip code.  I have not looked at just why that patch
changes this example's behavior.

            regards, tom lane

Tom Lane said:
> Hm.  By rights it *should* fail, since the ACL is clearly not granting
UPDATE permissions to anybody.
>
> The fact that it fails to fail seems to be because the rules on
> pg_settings rewrite the UPDATE into DO INSTEAD NOTHING (which does
nothing, in particular makes no permission checks) and a SELECT, which
only requires read-permission on pg_settings.  This is probably bogus
and we ought to see what we can do about fixing it.  (And we'd better
fix initdb to grant UPDATE on pg_settings to public, too.)
>
> Now, why does Florian see a permissions failure (which is really the
*right* behavior) when we don't?  He didn't say exactly which PG version
he was running, but I see a likely-related bug fix between 7.3.2 and
7.3.3:
Sorry for not specifing the exact postgres versions involved initially - I
believed that the problem were different default on redhat and debian, or
different compiling options...

RedHat-9: postgres 7.3.2-3
debian: postgres 7.3.2r1-5 (sid backport)

I tried setting the relacl for the pg_settings table to {=rw}, but I still
get permission denied. To double-check, I then set it to {=}, and this
lets not only the update fail, but also select now gives "permission
denied" (The correct behaviour I believe).

greetings, Florian Pflug

"Florian Pflug" <fgp@phlo.org> writes:
> Sorry for not specifing the exact postgres versions involved initially - I
> believed that the problem were different default on redhat and debian, or
> different compiling options...

> RedHat-9: postgres 7.3.2-3
> debian: postgres 7.3.2r1-5 (sid backport)

Hm, could the debian version have that rewrite patch, even though it
claims to be 7.3.2?  I'd have expected the behavior to be the same
if they're both straight 7.3.2.

> I tried setting the relacl for the pg_settings table to {=rw}, but I still
> get permission denied.

This does not surprise me; the original code was just plain buggy.
I suspect it is applying some completely inappropriate check (like
checking some other permission bit than UPDATE), so that the apparently
correct failure is really coincidental, and it still fails when it
should succeed.  Unfortunately I don't have a running copy of 7.3.2 to
trace through ...

Anyway, in the short run I'd suggest updating to 7.3.5, which will let
you do the UPDATE even though it really shouldn't :-(.  The cleanups
I'm worried about making are for future development.

            regards, tom lane

On Thu, 2003-12-11 at 16:26, Tom Lane wrote:
> "Florian Pflug" <fgp@phlo.org> writes:
> > Sorry for not specifing the exact postgres versions involved initially - I
> > believed that the problem were different default on redhat and debian, or
> > different compiling options...
>
> > RedHat-9: postgres 7.3.2-3
> > debian: postgres 7.3.2r1-5 (sid backport)
>
> Hm, could the debian version have that rewrite patch, even though it
> claims to be 7.3.2?  I'd have expected the behavior to be the same
> if they're both straight 7.3.2.

Debian 7.3.2r1-5 included several patches that would later be released
in 7.3.3.

--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight, UK                             http://www.lfix.co.uk/oliver
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839  932A 614D 4C34 3E1D 0C1C
                 ========================================
     "The spirit of the Lord GOD is upon me; because the
      LORD hath anointed me to preach good tidings unto the
      meek; he hath sent me to bind up the brokenhearted, to
      proclaim liberty to the captives, and the opening of
      the prison to them that are bound."
                                        Isaiah 61:1

Tom Lane wrote:
> This does not surprise me; the original code was just plain buggy.
> I suspect it is applying some completely inappropriate check (like
> checking some other permission bit than UPDATE), so that the apparently
> correct failure is really coincidental, and it still fails when it
> should succeed.  Unfortunately I don't have a running copy of 7.3.2 to
> trace through ...

I saw something similar the other day on my copy of 7.3.2. I'll try to
work through this, but it may be the weekend before I have time to
really dig in.

Joe

On Thu, Dec 11, 2003 at 11:26:14AM -0500, Tom Lane wrote:
> Anyway, in the short run I'd suggest updating to 7.3.5, which will let
> you do the UPDATE even though it really shouldn't :-(.  The cleanups
> I'm worried about making are for future development.

First, thanks to everyone involved in tracking down this problem - you have
been of invaluable help to me - I surely would have spent many useless hours
on debugging this without your help.

Am I right to assume that updating to 7.4 will have the same effekt as
updating to 7.3.5? I ask because I plan to update to 7.4 sometime anyway,
and util then it doesn't really hurt to connect as superuser, since this
isn't a production system for the moment.

greetings, Florian Pflug

On Fri, Dec 12, 2003 at 04:24:32AM +0100, Florian G. Pflug wrote:

> Am I right to assume that updating to 7.4 will have the same effekt as
> updating to 7.3.5? I ask because I plan to update to 7.4 sometime anyway,
> and util then it doesn't really hurt to connect as superuser, since this
> isn't a production system for the moment.

No, you're not.  You can update to 7.3.5 by just dropping the new
executables into place (after stopping the postmaster, of course).
Going to 7.4 will require you to dump all your data and reload.
(I'm assuming you are running 7.3.4 ...)

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"La experiencia nos dice que el hombre peló millones de veces las patatas,
pero era forzoso admitir la posibilidad de que en un caso entre millones,
las patatas pelarían al hombre" (Ijon Tichy)

Alvaro Herrera <alvherre@dcc.uchile.cl> writes:
> On Fri, Dec 12, 2003 at 04:24:32AM +0100, Florian G. Pflug wrote:
>> Am I right to assume that updating to 7.4 will have the same effekt as
>> updating to 7.3.5?

> No, you're not.  You can update to 7.3.5 by just dropping the new
> executables into place (after stopping the postmaster, of course).

I think he was asking whether 7.4 will behave the same as 7.3.5 with
respect to this particular permissions issue.  Which it will.  You're
correct that getting to 7.3.5 should be less painful (which is why
I suggested it) --- but if he wants to jump to 7.4, no reason why not.

            regards, tom lane

Tom Lane wrote:
> I suspect the fact that the pre-patch code made the "right" permissions
> check was really coincidental, and that the correct fix will not involve
> reversion of that patch but rather adding a facility somewhere to ensure
> that the original view gets properly permission-checked even if there's
> a DO INSTEAD NOTHING rule.  However, before biting that bullet it'd
> probably be good to understand in detail what's happening in both the
> 7.3.2 and CVS-tip code.  I have not looked at just why that patch
> changes this example's behavior.
>

I just started looking at this again. There is definitely an issue in
cvs tip:

create table t(f1 int, f2 text);
insert into t values(1, 'abc');
create view v as select * from t;
CREATE RULE v_upd AS ON UPDATE TO v DO INSTEAD
   UPDATE t SET f1 = NEW.f1, f2 = NEW.f2 WHERE f1 = OLD.f1;
create user user1;

-- this fails; as it should, I think
\c - user1
update v set f2 = 'def' where f1 = 1;
ERROR:  permission denied for relation v

-- so grant SELECT on the view
\c - postgres
grant select on v to public;

-- this should fail, but doesn't
\c - user1
update v set f2 = 'def' where f1 = 1;
UPDATE 1


On 7.3.2 that last section of the above script gives:

\c - user1
update v set f2 = 'def' where f1 = 1;
ERROR:  v: permission denied

The comment associated with the change says this:

  * Also, we must disable write-access checking in all the RT entries
  * copied from the main query.  This is safe since in fact the rule
  * action won't write on them, and it's necessary because the rule
  * action may have a different commandType than the main query, causing
  * ExecCheckRTEPerms() to make an inappropriate check.  The read-access
  * checks can be left enabled, although they're probably redundant.
  */

So SELECT permissions get checked for user1, but write-access does not.
The underlying table should be checked for permissions based on the rule
owner per rewriteDefine.c around line 439 (line 387 in 7.3.2):

  /*
   * We want the rule's table references to be checked as though by the
   * rule owner, not the user referencing the rule.  Therefore, scan
   * through the rule's rtables and set the checkAsUser field on all
   * rtable entries.
   */

Since the rule owner in this case is also the creator of the table, the
UPDATE suceeds.

ISTM that we want the relations in the un-rewritten query checked based
on the basis of the user referencing the rule and for the modes used in
the un-rewritten query -- suggesting the change need be reverted. Then
we want the rule's table references checked based on rule owner and
actual operations performed. It looks like this part should be what's
happening.

I went back to the original complaint -- here is the example on a 7.3.2
installation:

regression=# create table table1 (test1 integer);
grant insert on table1 to pleb;
create rule test_rule as on insert to table1 do update table2 set test2
= 2 where test2 = 0;
\c - pleb;
insert into table1 values (1);
CREATE TABLE
regression=# create table table2 (test2 integer);
CREATE TABLE
regression=# create user pleb;
ERROR:  CREATE USER: user name "pleb" already exists
regression=# grant insert on table1 to pleb;
GRANT
regression=# create rule test_rule as on insert to table1 do update
table2 set test2 = 2 where test2 = 0;
CREATE RULE
regression=# \c - pleb;
You are now connected as new user pleb.
regression=> insert into table1 values (1);
ERROR:  table1: permission denied

A few NOTICES placed in ExecCheckRTEPerms() reveals this:

regression=> insert into table1 values (1);
NOTICE:  relOid = 1245674
NOTICE:  userid = 101
NOTICE:  operation = CMD_INSERT
NOTICE:  relOid = 1245674
NOTICE:  userid = 101
NOTICE:  operation = CMD_UPDATE
ERROR:  table1: permission denied

regression=> select oid, relname from pg_class where relname like 'table%';
    oid   | relname
---------+---------
  1245674 | table1
  1245676 | table2
(2 rows)

It seems that second pass through ExecCheckRTEPerms() is not doing the
right thing. It ought to be checking table2 (not table1) for UPDATE as
userid == 1 (not 101), shouldn't it?

Any thoughts on where to look next?

Thanks,

Joe

[ please respect moving of thread to pg-hackers ]

Joe Conway <mail@joeconway.com> writes:
> ISTM that we want the relations in the un-rewritten query checked based
> on the basis of the user referencing the rule and for the modes used in
> the un-rewritten query -- suggesting the change need be reverted.

Reverting the change will bring back the bug for which it was created.
It does seem though that we have an inadequate model of how to perform
permission checks.  In particular, the "write" flag bit in RTEs is
context dependent: it can mean insert, update, or delete permission
depending on the surrounding command.

The problem the earlier bug report identified is really that when an RTE
is copied from one query to another, the meaning of its "write" flag bit
changes --- incorrectly --- if the new query is of a different type.
I thought when making that patch that we could make an end-run around
this problem by zeroing out the flag bit, but what we're now realizing
is that that leaves us with no check at all in some scenarios (because
the original query will be dropped completely when INSTEAD is specified).

I begin to think that the only real solution is to change the RTE
representation to identify the exact permission bits to be checked for
each entry (say, replace the read and write booleans with a permission
bitmask).  Then a view reference specifying INSERT permission check
could be copied into an UPDATE query without changing its permission
semantics.

This would be a fairly extensive change though.  Does anyone see an
easier way?

Also, does anyone see a case where it would be correct for the checked
permission to change when an RTE is copied to a query of a different
type?

            regards, tom lane

I wrote
> "Florian Pflug" <fgp@phlo.org> writes:
>> I tried setting the relacl for the pg_settings table to {=rw}, but I still
>> get permission denied.

> This does not surprise me; the original code was just plain buggy.
> I suspect it is applying some completely inappropriate check (like
> checking some other permission bit than UPDATE), so that the apparently
> correct failure is really coincidental, and it still fails when it
> should succeed.

I've finished tracing through this, and it turns out to be a combination
of factors.  ExecCheckRTEPerms sees pg_settings referenced with
checkForWrite in a SELECT query, which it thinks means a SELECT FOR
UPDATE.  It happens that this requires the same UPDATE permission as a
real UPDATE, so the aclcheck() call that gets issued is, more or less by
chance, the correct thing: a check for UPDATE privilege on pg_settings.
But that fails, and the reason it fails is the "usecatupd" defense
against allowing anyone to update a system catalog.  This latter defense
obviously predates the existence of updatable views in the system
schema.  What I've done about it is to disable the check in the case of
a view relation, which seems to be the minimum workable loosening of the
check ... but maybe it deserves a more complete rethink.

I have also reverted the broken change of 13-Feb-03 in rewriteHandler.c.
Upshot is that:
  * loss of view permission checking is fixed in 7.3.*, 7.4.*, and HEAD;
  * 7.4.* and HEAD will correctly allow UPDATE on pg_settings, although
    this depends on a chance coincidence;
  * the bug Tim Burgess complained of here is back:
    http://archives.postgresql.org/pgsql-bugs/2003-02/msg00038.php

Per previous discussion, the best way to fix Tim's problem and make the
pg_settings behavior less coincidental seems to require a change in RTE
representation, so it will only be fixable in 7.5.  I will work on that
next ...

            regards, tom lane