Make contrib modules' installation scripts more secure.

Hostile objects located within the installation-time search_path could
capture references in an extension's installation or upgrade script.
If the extension is being installed with superuser privileges, this
opens the door to privilege escalation.  While such hazards have existed
all along, their urgency increases with the v13 "trusted extensions"
feature, because that lets a non-superuser control the installation path
for a superuser-privileged script.  Therefore, make a number of changes
to make such situations more secure:

* Tweak the construction of the installation-time search_path to ensure
that references to objects in pg_catalog can't be subverted; and
explicitly add pg_temp to the end of the path to prevent attacks using
temporary objects.

* Disable check_function_bodies within installation/upgrade scripts,
so that any security gaps in SQL-language or PL-language function bodies
cannot create a risk of unwanted installation-time code execution.

* Adjust lookup of type input/receive functions and join estimator
functions to complain if there are multiple candidate functions.  This
prevents capture of references to functions whose signature is not the
first one checked; and it's arguably more user-friendly anyway.

* Modify various contrib upgrade scripts to ensure that catalog
modification queries are executed with secure search paths.  (These
are in-place modifications with no extension version changes, since
it is the update process itself that is at issue, not the end result.)

Extensions that depend on other extensions cannot be made fully secure
by these methods alone; therefore, revert the "trusted" marking that
commit eb67623c9 applied to earthdistance and hstore_plperl, pending
some better solution to that set of issues.

Also add documentation around these issues, to help extension authors
write secure installation scripts.

Patch by me, following an observation by Andres Freund; thanks
to Noah Misch for review.

Security: CVE-2020-14350

contrib/intarray/intarray--1.1--1.2.sql

@@ -7,23 +7,38 @@
 -- We use to_regprocedure() so that query doesn't fail if run against 9.6beta1 definitions,
 -- wherein the signatures have been updated already.  In that case to_regprocedure() will
 -- return NULL and no updates will happen.
+DO LANGUAGE plpgsql
+$$
+DECLARE
+  my_schema pg_catalog.text := pg_catalog.quote_ident(pg_catalog.current_schema());
+  old_path pg_catalog.text := pg_catalog.current_setting('search_path');
+BEGIN
+-- for safety, transiently set search_path to just pg_catalog+pg_temp
+PERFORM pg_catalog.set_config('search_path', 'pg_catalog, pg_temp', true);
 
 UPDATE pg_catalog.pg_proc SET
   proargtypes = pg_catalog.array_to_string(newtypes::pg_catalog.oid[], ' ')::pg_catalog.oidvector,
   pronargs = pg_catalog.array_length(newtypes, 1)
 FROM (VALUES
-(NULL::pg_catalog.text, NULL::pg_catalog.regtype[]), -- establish column types
+(NULL::pg_catalog.text, NULL::pg_catalog.text[]), -- establish column types
 ('g_int_consistent(internal,_int4,int4,oid,internal)', '{internal,_int4,int2,oid,internal}'),
 ('g_intbig_consistent(internal,internal,int4,oid,internal)', '{internal,_int4,int2,oid,internal}'),
-('g_intbig_same(internal,internal,internal)', '{intbig_gkey,intbig_gkey,internal}'),
+('g_intbig_same(internal,internal,internal)', '{SCH.intbig_gkey,SCH.intbig_gkey,internal}'),
 ('ginint4_queryextract(internal,internal,int2,internal,internal,internal,internal)', '{_int4,internal,int2,internal,internal,internal,internal}'),
 ('ginint4_consistent(internal,int2,internal,int4,internal,internal,internal,internal)', '{internal,int2,_int4,int4,internal,internal,internal,internal}')
-) AS update_data (oldproc, newtypes)
-WHERE oid = pg_catalog.to_regprocedure(oldproc);
+) AS update_data (oldproc, newtypestext),
+LATERAL (
+  SELECT array_agg(replace(typ, 'SCH', my_schema)::regtype) as newtypes FROM unnest(newtypestext) typ
+) ls
+WHERE oid = to_regprocedure(my_schema || '.' || replace(oldproc, 'SCH', my_schema));
 
 UPDATE pg_catalog.pg_proc SET
-  prorettype = 'intbig_gkey'::pg_catalog.regtype
-WHERE oid = pg_catalog.to_regprocedure('g_intbig_union(internal,internal)');
+  prorettype = (my_schema || '.intbig_gkey')::pg_catalog.regtype
+WHERE oid = pg_catalog.to_regprocedure(my_schema || '.g_intbig_union(internal,internal)');
+
+PERFORM pg_catalog.set_config('search_path', old_path, true);
+END
+$$;
 
 ALTER FUNCTION bqarr_in(cstring) PARALLEL SAFE;
 ALTER FUNCTION bqarr_out(query_int) PARALLEL SAFE;

contrib/intarray/intarray--unpackaged--1.0.sql

@@ -84,13 +84,23 @@ ALTER EXTENSION intarray ADD function ginint4_consistent(internal,smallint,inter
 -- entries.  This is ugly as can be, but there's no other way to do it
 -- while preserving the identities (OIDs) of the functions.
 
+DO LANGUAGE plpgsql
+$$
+DECLARE
+  my_schema_unquoted pg_catalog.text := pg_catalog.current_schema();
+  my_schema pg_catalog.text := pg_catalog.quote_ident(pg_catalog.current_schema());
+  old_path pg_catalog.text := pg_catalog.current_setting('search_path');
+BEGIN
+-- for safety, transiently set search_path to just pg_catalog+pg_temp
+PERFORM pg_catalog.set_config('search_path', 'pg_catalog, pg_temp', true);
+
 UPDATE pg_catalog.pg_proc
 SET pronargs = 7, proargtypes = '2281 2281 21 2281 2281 2281 2281'
-WHERE oid = 'ginint4_queryextract(internal,internal,smallint,internal,internal)'::pg_catalog.regprocedure;
+WHERE oid = (my_schema || '.ginint4_queryextract(internal,internal,smallint,internal,internal)')::pg_catalog.regprocedure;
 
 UPDATE pg_catalog.pg_proc
 SET pronargs = 8, proargtypes = '2281 21 2281 23 2281 2281 2281 2281'
-WHERE oid = 'ginint4_consistent(internal,smallint,internal,integer,internal,internal)'::pg_catalog.regprocedure;
+WHERE oid = (my_schema || '.ginint4_consistent(internal,smallint,internal,integer,internal,internal)')::pg_catalog.regprocedure;
 
 -- intarray also relies on the core function ginarrayextract, which changed
 -- signature in 9.1.  To support upgrading, pg_catalog contains entries
@@ -104,8 +114,12 @@ SET amproc = 'pg_catalog.ginarrayextract(anyarray,internal,internal)'::pg_catalo
 WHERE amprocfamily =
   (SELECT oid FROM pg_catalog.pg_opfamily WHERE opfname = 'gin__int_ops' AND
      opfnamespace = (SELECT oid FROM pg_catalog.pg_namespace
-                     WHERE nspname = pg_catalog.current_schema()))
+                     WHERE nspname = my_schema_unquoted))
   AND amproclefttype = 'integer[]'::pg_catalog.regtype
   AND amprocrighttype = 'integer[]'::pg_catalog.regtype
   AND amprocnum = 2
   AND amproc = 'pg_catalog.ginarrayextract(anyarray,internal)'::pg_catalog.regprocedure;
+
+PERFORM pg_catalog.set_config('search_path', old_path, true);
+END
+$$;