Re: Facility for detecting insecure object naming - Mailing list pgsql-hackers

On Wed, Aug 08, 2018 at 09:58:38AM -0400, Tom Lane wrote:
> I'm not sold on #2 either.  That path leads to, for example,
> s/=/OPERATOR(pg_catalog.=)/g everywhere, which is utterly catastrophic
> to both readability and portability of your SQL code.  We *must* find
> a way to do better, not tell people that's what to do.
> 
> When the security team was discussing this issue before, we speculated
> about ideas like inventing a function trust mechanism, so that attacks
> based on search path manipulations would fail even if they managed to
> capture an operator reference.  I'd rather go down that path than
> encourage people to do more schema qualification.

Interesting.  If we got a function trust mechanism, how much qualification
would you then like?  Here are the levels I know about, along with their
implications:


-- (1) Use qualified references and exact match for all objects.
--
-- Always secure, even if schema usage does not conform to ddl-schemas-patterns
-- and function trust is disabled.
--
-- Subject to denial of service from anyone able to CREATE in cube schema or
-- earthdistance schema.
CREATE FUNCTION latitude(earth)
RETURNS float8
LANGUAGE SQL
IMMUTABLE STRICT
PARALLEL SAFE
AS $$SELECT CASE
  WHEN @cube_schema@.cube_ll_coord($1::@cube_schema@.cube, 3)
    OPERATOR(pg_catalog./)
    @extschema@.earth() OPERATOR(pg_catalog.<) -1 THEN -90::pg_catalog.float8
  WHEN @cube_schema@.cube_ll_coord($1::@cube_schema@.cube, 3)
    OPERATOR(pg_catalog./)
    @extschema@.earth() OPERATOR(pg_catalog.>)  1 THEN  90::pg_catalog.float8
  ELSE pg_catalog.degrees(pg_catalog.asin(@cube_schema@.cube_ll_coord(
    $1::@cube_schema@.cube, 3) OPERATOR(pg_catalog./) @extschema@.earth()))
END$$;


-- (2) Use qualified references for objects outside pg_catalog.
--
-- With function trust disabled, this would be subject to privilege escalation
-- from anyone able to CREATE in cube schema.
--
-- Subject to denial of service from anyone able to CREATE in cube schema or
-- earthdistance schema.
CREATE FUNCTION latitude(earth)
RETURNS float8
LANGUAGE SQL
IMMUTABLE STRICT
PARALLEL SAFE
AS $$SELECT CASE
  WHEN @cube_schema@.cube_ll_coord($1, 3)
    /
    @extschema@.earth() < -1 THEN -90::float8
  WHEN @cube_schema@.cube_ll_coord($1, 3)
    /
    @extschema@.earth() >  1 THEN  90::float8
  ELSE degrees(asin(@cube_schema@.cube_ll_coord($1, 3) / @extschema@.earth()))
END$$;


-- (3) "SET search_path" with today's code.
--
-- Security and reliability considerations are the same as (2).  Today, this
-- reduces performance by suppressing optimizations like inlining.
CREATE FUNCTION latitude(earth)
RETURNS float8
LANGUAGE SQL
IMMUTABLE STRICT
PARALLEL SAFE
SET search_path FROM CURRENT
AS $$SELECT CASE
  WHEN cube_ll_coord($1, 3)
    /
    earth() < -1 THEN -90::float8
  WHEN cube_ll_coord($1, 3)
    /
    earth() >  1 THEN  90::float8
  ELSE degrees(asin(cube_ll_coord($1, 3) / earth()))
END$$;


-- (4) Today's code (reformatted).
--
-- Always secure if schema usage conforms to ddl-schemas-patterns, even if
-- function trust is disabled.  If cube schema or earthdistance schema is not in
-- search_path, function doesn't work.
CREATE FUNCTION latitude(earth)
RETURNS float8
LANGUAGE SQL
IMMUTABLE STRICT
PARALLEL SAFE
AS $$SELECT CASE
  WHEN cube_ll_coord($1, 3)
    /
    earth() < -1 THEN -90::float8
  WHEN cube_ll_coord($1, 3)
    /
    earth() >  1 THEN  90::float8
  ELSE degrees(asin(cube_ll_coord($1, 3) / earth()))
END$$;