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

1 files changed, 23 insertions, 10 deletions

diff --git a/contrib/citext/citext--unpackaged--1.0.sql b/contrib/citext/citext--unpackaged--1.0.sql
index ef6d6b06396..4061a0aeff2 100644
--- a/contrib/citext/citext--unpackaged--1.0.sql
+++ b/contrib/citext/citext--unpackaged--1.0.sql
@@ -89,8 +89,17 @@ ALTER EXTENSION citext ADD function translate(citext,citext,text);
 -- default collation is pinned.
 --
 
+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);
+
 WITH RECURSIVE typeoids(typoid) AS
-  ( SELECT 'citext'::pg_catalog.regtype UNION
+  ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
     SELECT oid FROM pg_catalog.pg_type, typeoids
       WHERE typelem = typoid OR typbasetype = typoid )
 UPDATE pg_catalog.pg_type SET typcollation = 100
@@ -98,7 +107,7 @@ FROM typeoids
 WHERE oid = typeoids.typoid;
 
 WITH RECURSIVE typeoids(typoid) AS
-  ( SELECT 'citext'::pg_catalog.regtype UNION
+  ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
     SELECT oid FROM pg_catalog.pg_type, typeoids
       WHERE typelem = typoid OR typbasetype = typoid )
 UPDATE pg_catalog.pg_attribute SET attcollation = 100
@@ -113,7 +122,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, '^0', '100')::pg_catalog.oidvector
 WHERE indclass[0] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -124,7 +133,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[1] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -135,7 +144,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[2] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -146,7 +155,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[3] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -157,7 +166,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[4] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -168,7 +177,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[5] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -179,7 +188,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[6] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -190,7 +199,7 @@ UPDATE pg_catalog.pg_index SET indcollation =
   pg_catalog.regexp_replace(indcollation::pg_catalog.text, E'^(\\d+ \\d+ \\d+ \\d+ \\d+ \\d+ \\d+) 0', E'\\1 100')::pg_catalog.oidvector
 WHERE indclass[7] IN (
   WITH RECURSIVE typeoids(typoid) AS
-    ( SELECT 'citext'::pg_catalog.regtype UNION
+    ( SELECT (my_schema || '.citext')::pg_catalog.regtype UNION
       SELECT oid FROM pg_catalog.pg_type, typeoids
         WHERE typelem = typoid OR typbasetype = typoid )
   SELECT oid FROM pg_catalog.pg_opclass, typeoids
@@ -198,3 +207,7 @@ WHERE indclass[7] IN (
 );
 
 -- somewhat arbitrarily, we assume no citext indexes have more than 8 columns
+
+PERFORM pg_catalog.set_config('search_path', old_path, true);
+END
+$$;