Thread: proposal: schema private functions
Hi
I would to introduce new flag for routines - PRIVATE. Routines with this flag can be called only from other routines assigned with same schema. Because these routines are not available for top queries, we can hide these functions from some outputs like \df ..
Example:
CREATE SCHEMA s1;
CREATE SCHEMA s2;
CREATE OR REPLACE FUNCTION s1.nested()
RETURNS int AS $$
BEGIN
RETURN random()*1000;
END;
$$ PRIVATE;
SELECT s1.nested(); -- fails - it is top query
CREATE OR REPLACE FUNCTION s1.fx()
RETURNS int AS $$
BEGIN
RETURN s1.nested();
END;
$$ LANGUAGE plpgsql;
SELECT s1.fx(); -- will work
CREATE OR REPLACE FUNCTION s2.fx()
RETURNS int AS $$
BEGIN
RETURN s1.nested();
END;
$$ LANGUAGE plpgsql;
SELECT s2.fx(); -- fails - it call private function from other schema.
This proposal is simple, and strong enough to separate functions that can be directly callable and auxiliary functions, that can be called from other functions.
I wrote PoC implementation, and it is not hard, and it should not to impact performance. I introduced query_owner_nspid into query environment. When any functions has flag private, then query_owner_nspid should be same like function namespace id.
Comments, notes?
Pavel
Attachment
Couldn't this be handled by having a new permission on FUNCTIONs
("CALL"?) to distinguish EXECUTE?
This would have to be made backwards-compatible, possibly by
automatically granting CALL ON ALL FUNCTIONS to public at schema create
time and/or PG upgrade time, which the schema owner could then REVOKE,
or by requiring CALL permission only functions marked PRIVATE.
Because initially a schema has no functions, the owner can revoke this
grant to public before creating any functions, thus there would be no
race contition. A race condition could be made less likely still by
having CALL not imply EXECUTE (users would have to have both to
successfully call a given function).
I would agree that a PRIVATE keyword would be a syntactically convenient
way to say that in its absence then public gets granted CALL on the
given function. But IMO it shouldn't be necessary, and either way
permissions machinery should be involved.
What do other SQL databases do? Does any have a PRIVATE keyword for
FUNCTIONs?
Using permissions has the net effect of making visibility more
fine-grained.
Regarding \df, I'm not sure that hiding function names one cannot call
is worthwhile, but if it were, then there are several options depending
on whether confidentiality of function names is to be a security
feature: RLS on the pg_catalog.pg_proc table (provides confidentiality),
or having a system view on it or filtering in psql (no real
confidentiality).
All that said, being able to have PRIVATE schemas, tables, views,
functions, FDWs, variables, maybe even roles, is definitly appealing,
mainly for code organization reasons.
I didn't understand how PRIVATE would help reduce the need for SECURITY
DEFINER. Can you explain?
Nico
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2018-08-23 17:18 GMT+02:00 Nico Williams <nico@cryptonector.com>:
Couldn't this be handled by having a new permission on FUNCTIONs
("CALL"?) to distinguish EXECUTE?
I don't understand to this questions. Private functions will be functions still - there is not necessity to call these functions differently.
This would have to be made backwards-compatible, possibly by
automatically granting CALL ON ALL FUNCTIONS to public at schema create
time and/or PG upgrade time, which the schema owner could then REVOKE,
or by requiring CALL permission only functions marked PRIVATE.
Because initially a schema has no functions, the owner can revoke this
grant to public before creating any functions, thus there would be no
race contition. A race condition could be made less likely still by
having CALL not imply EXECUTE (users would have to have both to
successfully call a given function).
I would agree that a PRIVATE keyword would be a syntactically convenient
way to say that in its absence then public gets granted CALL on the
given function. But IMO it shouldn't be necessary, and either way
permissions machinery should be involved.
What do other SQL databases do? Does any have a PRIVATE keyword for
FUNCTIONs?
The private flag, what I propose, has not relations to access rights - the limiting factor is scope. The system of access rights is not touched by this feature.
The other databases has not PRIVATE keyword, what I know - but have some different mechanism how to hide some internal API
PL/SQL package functions are by default "private" if are not mentioned in package header.
Using permissions has the net effect of making visibility more
fine-grained.
Regarding \df, I'm not sure that hiding function names one cannot call
is worthwhile, but if it were, then there are several options depending
on whether confidentiality of function names is to be a security
feature: RLS on the pg_catalog.pg_proc table (provides confidentiality),
or having a system view on it or filtering in psql (no real
confidentiality).
Probably private objects (functions) should not be visible in \df .. maybe \dfP or some similar can be used.
All that said, being able to have PRIVATE schemas, tables, views,
functions, FDWs, variables, maybe even roles, is definitly appealing,
mainly for code organization reasons.
I didn't understand how PRIVATE would help reduce the need for SECURITY
DEFINER. Can you explain?
sure. Any object marked as private - is not accessible directly .. You want to protect these objects against access in wrong order, .. but sometimes you should to use data (or features) of these objects. Now, you should to use security definer functions and any user can call these functions, and then the access to protected objects is controlled. But you should to use security definer functions. When you use private flag, then this object can be accessed only from function (procedure, ...) from same schema. And if some user doesn't create right for schema, then he hasn't free access to private objects. But this user can use any non private objects from the schema, if has necessary rights, and then the access to private objects is controlled and security definer functions are not necessary.
Nico
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