This patch does two things:

1) Changes the semantics of assign_search_path()/'SET search_path' so 
that you can't set your search path to a schema you don't have USAGE 
privs for.

2) Changes psql's \dn query and its schema tab completion query to 
incorporate ACL checking so that \dn only lists schemas that a user has 
USAGE privs on.


Rationale:

1) "SET search_path = 'noaccess';" shouldn't look like it succeeds when 
the user doesn't have USAGE privs in the schema 'noaccess'.  Currently, 
the SET command succeeds and a list of objects in the schema also works 
leading the user to believe that they're working in an empty schema.  
'SET search_path' should have its behavior modified so that it fails 
the same way that on the file system when an unprivileged user types 
'cd noaccess'.

2) If a users doesn't have access to a schema, they shouldn't see it in 
the listings provided by psql(1).  If a user wants to know, they can 
query the catalogs by hand (until there's some kind of row level 
security on the system catalogs?), but what they don't have access to, 
probably doesn't interest them or they shouldn't have flaunted in their 
face.  This also changes the behavior of tab completion for schemas.



Problems:

% psql test usr
test=> SET search_path = public,foo;
ERROR:  permission denied for schema foo
test=> \c test dba
You are now connected to database "test" as user "dba".
test=# ALTER USER usr SET search_path = 'foo';
ALTER USER
test=# \c test usr
You are now connected to database "test" as user "usr".
test=> \dn
       List of schemas
         Name        | Owner
--------------------+-------
  information_schema | sean
  pg_catalog         | sean
  public             | sean
(3 rows)

test=> show search_path ;
  search_path
-------------
  foo
(1 row)


And that's the only problem I've found with this patch, but I wasn't 
about ready to put in the extra foo in the ALTER USER command to have 
it prevent an invalid search_path from being set.  -sc





-- 
Sean Chittenden
Thu, 8 Apr 2004 20:00:34 -0700
Sean Chittenden <sean@chittenden.org>
Checking for USAGE on SET search_path...
Sean Chittenden <sean@chittenden.org> writes:
> This patch does two things:

> 1) Changes the semantics of assign_search_path()/'SET search_path' so 
> that you can't set your search path to a schema you don't have USAGE 
> privs for.

Why is that needed?  It's already a no-op AFAIR.  It also is
incompatible with the existing behavior, in which nonexistent schemas
(think "$user") are dropped silently rather than noisily.  Your patch
also breaks the previous careful tweak to allow ALTER DATABASE SET
to succeed when mentioning a schema not present in the current database.

> 2) Changes psql's \dn query and its schema tab completion query to 
> incorporate ACL checking so that \dn only lists schemas that a user has 
> USAGE privs on.

This requires considerable discussion.  Should \df only list functions
you are allowed to call?  \dt only tables you are allowed to read?
\h only commands you are allowed to execute?

I'm not that thrilled with patches that propose basic changes in
behavior and have not been justified by any preceding discussion
on pghackers...

			regards, tom lane

Fri, 09 Apr 2004 02:07:14 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Checking for USAGE on SET search_path... 
[ Discussion moved from patches@ to hackers@ ]

The gist of the discussion being: what are the ramifications of having 
PostgreSQL and psql(1) hide information/schema bits that a user doesn't 
have access to.  This would have to be backend enforced, which would 
mean changing the system catalogs to include some form of row level 
security so that SELECTs from the system catalogs would only return the 
rows that a user has privs to see.  In more practical terms, in 
psql(1), the consequences would be:

\dn	only shows schemas/namespaces that a user has access to
\df	could only show functions that a user can execute (or are visible 
by namespace)
\dt	only shows tables that you have some kind of privileges on

etc.  Not much can be done about \l.  That said, what are the thoughts 
of the other developers/admins?  Is hiding schema information a good 
thing?  Do people think that the concept of "secure by default" should 
apply to schema information inside of the database?  Should information 
hiding be done in psql(1) or should this be managed by the backend and 
all logic kept out of psql(1)?  For sure, the advantage of having it 
managed in the backend is that *all* clients (psql, pgadmin, 
phpPgAdmin, etc.) would pick up the schema structure hiding.

[ Thread from patches@ + response below ]

>> This patch does two things:
>
>> 1) Changes the semantics of assign_search_path()/'SET search_path' so
>> that you can't set your search path to a schema you don't have USAGE
>> privs for.
>
> Why is that needed?  It's already a no-op AFAIR.  It also is
> incompatible with the existing behavior, in which nonexistent schemas
> (think "$user") are dropped silently rather than noisily.

Actually, $user still works... and shouldn't:

test=# CREATE SCHEMA usr;
CREATE SCHEMA
test=# \c test usr
You are now connected to database "test" as user "usr".
test=> SET search_path = '$user';
SET
test=> \dn
       List of schemas
         Name        | Owner
--------------------+-------
  information_schema | sean
  pg_catalog         | sean
  public             | sean
(3 rows)

When the list element is '$user', the loop skips processing and doesn't 
try and resolve $user to usr and then test to see if usr exists.

> Your patch
> also breaks the previous careful tweak to allow ALTER DATABASE SET
> to succeed when mentioning a schema not present in the current 
> database.

This I haven't investigated...  Should you be able to run ALTER 
DATABASE SET if you're in a different database?  *shrug*  I'd say no, 
but I'm biased because I've never used ALTER DATABASE SET outside of 
the current database.  Would it be acceptable to have all SET commands 
succeed without checking if the current database is different than the 
database that's being acted on?  That's no different than the current 
behavior.

>> 2) Changes psql's \dn query and its schema tab completion query to
>> incorporate ACL checking so that \dn only lists schemas that a user 
>> has
>> USAGE privs on.
>
> This requires considerable discussion.

Okey dokey...  sending email to hackers@.

> Should \df only list functions
> you are allowed to call?  \dt only tables you are allowed to read?
> \h only commands you are allowed to execute?

IMHO, yes... but \h doesn't execute a query and shouldn't exercise any 
control on what's shown/displayed.  PostgreSQL is a rather open 
database to non-admins.  If PostgreSQL were a file system and a 
database cluster is the root node, the layout would essentially be:

/[databases]/[schemas]/[tables]/[columns]

and the perms on that file system would be:

find / -type d -exec chmod 755 {} \;
find / -type f -exec chmod 600 {} \;

and schemas would be mod 711 (find / -type d -depth 2 -exec chmod 711 
{} \;).  Users can essentially browse the structure of the entire file 
system/database.  As an admin (network, system, database, or 
otherwise), I want to expose to a user only what they need to be 
exposed to.  Changing a database/directory so that only a user or group 
has access to it (mod 750/700) can only happen through modifications to 
pg_hba.conf.  *shudders*  PostgreSQL makes itself "secure" by default 
by turning off network access.  Once a user is connected, however, 
PostgreSQL is an open book and reminds me of the olden days when 
/etc/passwd contained crypt(3)'ed passwords and home directories were 
created mod 755 or umasks were 0 by default and a mask of 022 was a 
umask for the "overly paranoid."

-sc

-- 
Sean Chittenden


Sun, 11 Apr 2004 14:10:12 -0700
Sean Chittenden <sean@chittenden.org>
Information/schema hiding...


Sean Chittenden wrote:

> Is hiding schema information a good thing?  Do people think that the 
> concept of "secure by default" should apply to schema information 
> inside of the database?  Should information hiding be done in psql(1) 
> or should this be managed by the backend and all logic kept out of 
> psql(1)?  For sure, the advantage of having it managed in the backend 
> is that *all* clients (psql, pgadmin, phpPgAdmin, etc.) would pick up 
> the schema structure hiding.
>

Anywhere else but the backend is pointless, IMNSHO. You might be 
interested in my recent posting about zero knowledge users here:

http://archives.postgresql.org/pgsql-hackers/2004-04/msg00144.php


cheers

andrew


Sun, 11 Apr 2004 18:37:41 -0400
Andrew Dunstan <andrew@dunslane.net>
Re: Information/schema hiding...
On Sun, 2004-04-11 at 17:10, Sean Chittenden wrote:
> Should information hiding be done in psql(1) or should this be managed
> by the backend and all logic kept out of psql(1)?

If the intent of this feature is security, it seems totally pointless to
implement it in psql (leaving aside whether it's actually a good idea or
not).

[ WRT to search_path and nonexistent schemas ]

> > Why is that needed?  It's already a no-op AFAIR.  It also is
> > incompatible with the existing behavior, in which nonexistent schemas
> > (think "$user") are dropped silently rather than noisily.
> 
> Actually, $user still works..

I think the more important question is: "Why is that needed?"

(Consider the PATH environmental var, which is fairly analogous to
search_path -- that doesn't complain if you add nonexistent directories
to it.)

-Neil



Sun, 11 Apr 2004 18:50:24 -0400
Neil Conway <neilc@samurai.com>
Re: Information/schema hiding...
>> Should information hiding be done in psql(1) or should this be managed
>> by the backend and all logic kept out of psql(1)?
>
> If the intent of this feature is security, it seems totally pointless 
> to
> implement it in psql (leaving aside whether it's actually a good idea 
> or
> not).
>
> [ WRT to search_path and nonexistent schemas ]

*nods*  I completely agree that the best place for this to happen is in 
the backend and not psql.

>>> Why is that needed?  It's already a no-op AFAIR.  It also is
>>> incompatible with the existing behavior, in which nonexistent schemas
>>> (think "$user") are dropped silently rather than noisily.
>>
>> Actually, $user still works..
>
> I think the more important question is: "Why is that needed?"

Two reasons come to mind.  First, If you change your search_path to a 
valid schema that you have no access to and try and look for database 
objects, you get the impression that its an empty schema and not a 
schema that you don't have access to.  To prevent this, I changed the 
behavior of SET search_path so that it validates its input.  A warning 
may be appropriate, but I'd rather have the SET search_path fail than 
the CREATE [object] fail.  Second, SET search_path, in my mind, is 
little different than ALTER TABLE ADD CONSTRAINT: it's input can be 
validated and permissions can be checked, therefor should it should be.

> (Consider the PATH environmental var, which is fairly analogous to
> search_path -- that doesn't complain if you add nonexistent directories
> to it.)

Actually, search_path is closer in functionality to a union of the 
chdir(2) syscall and the PATH environment variable.  Any argument to 
chdir(2) is validated by the operating system and chdir(2) is a system 
call - not a library call - for this very reason.  Can you imagine a 
world where chdir(2) didn't validate the existence of directories as 
well as the permissions?

-sc

-- 
Sean Chittenden


Sun, 11 Apr 2004 23:37:26 -0700
Sean Chittenden <sean@chittenden.org>
Re: Information/schema hiding...
Sean Chittenden <sean@chittenden.org> writes:
> Two reasons come to mind.  First, If you change your search_path to a 
> valid schema that you have no access to and try and look for database 
> objects, you get the impression that its an empty schema and not a 
> schema that you don't have access to.  To prevent this, I changed the 
> behavior of SET search_path so that it validates its input.

You can't actually do that.  In many (most?) situations, the search_path
value is fixed before a backend even starts; if you try to error out
because you don't like the contents, you'll prevent backends from
starting at all.

Also consider the situation where backend A creates, deletes, or changes
the permissions on schemas that are mentioned in backend B's search
path.  In the existing code these cases behave consistently and much
the same as Unix PATH searching does: at all times your effective path
consists of those elements of PATH that actually exist and are readable.

It would be possible to make interactive SET behave differently from the
non-interactive case, but I don't think that would be an improvement in
understandability or usability.  It's certainly not worth doing if the
only argument for changing is the one you give above.

			regards, tom lane

Mon, 12 Apr 2004 08:15:42 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Information/schema hiding... 
I said:
> Sean Chittenden <sean@chittenden.org> writes:
>> To prevent this, I changed the 
>> behavior of SET search_path so that it validates its input.

> ... It would be possible to make interactive SET behave differently
> from the non-interactive case,

Wait a minute --- scratch what I said above; interactive "SET
search_path" already does behave differently from noninteractive.
So what did your patch change exactly?

			regards, tom lane

Mon, 12 Apr 2004 09:34:23 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Information/schema hiding... 
>>> To prevent this, I changed the
>>> behavior of SET search_path so that it validates its input.
>
>> ... It would be possible to make interactive SET behave differently
>> from the non-interactive case,
>
> Wait a minute --- scratch what I said above; interactive "SET
> search_path" already does behave differently from noninteractive.
> So what did your patch change exactly?

I think (don't know all of the ways there are to SET search_path), the 
interactive way to SET search_path.  :)  It changed assign_search_path 
in catalog/namespace.c, iirc.  I said in my original email that someone 
could still do ALTER USER SET search_path and have that work without 
checking.

-sc

-- 
Sean Chittenden


Mon, 12 Apr 2004 13:05:55 -0700
Sean Chittenden <sean@chittenden.org>
Re: Information/schema hiding... 