Thread: Information/schema hiding...
[ 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
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
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, $user still works.. I think the more important question is: "Why is that needed?" (Consider the PATH environmental var, which is fairly analogous to search_path -- that doesn't complain if you add nonexistent directories to it.) -Neil
>> Should information hiding be done in psql(1) or should this be managed >> by the backend and all logic kept out of psql(1)? > > If the intent of this feature is security, it seems totally pointless > to > implement it in psql (leaving aside whether it's actually a good idea > or > not). > > [ WRT to search_path and nonexistent schemas ] *nods* I completely agree that the best place for this to happen is in the backend and not psql. >>> Why is that needed? It's already a no-op AFAIR. It also is >>> incompatible with the existing behavior, in which nonexistent schemas >>> (think "$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
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
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
>>> 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