Remove superuser checks in pgstattuple

Now that we track initial privileges on extension objects and changes to
those permissions, we can drop the superuser() checks from the various
functions which are part of the pgstattuple extension and rely on the
GRANT system to control access to those functions.

Since a pg_upgrade will preserve the version of the extension which
existed prior to the upgrade, we can't simply modify the existing
functions but instead need to create new functions which remove the
checks and update the SQL-level functions to use the new functions
(and to REVOKE EXECUTE rights on those functions from PUBLIC).

Thanks to Tom and Andres for adding support for extensions to follow
update paths (see: 40b449a), allowing this patch to be much smaller
since no new base version script needed to be included.

Approach suggested by Noah.

Reviewed by Michael Paquier.

1 files changed, 34 insertions, 5 deletions

diff --git a/contrib/pgstattuple/pgstatapprox.c b/contrib/pgstattuple/pgstatapprox.c
index a49ff543d2d..f524fc4e306 100644
--- a/contrib/pgstattuple/pgstatapprox.c
+++ b/contrib/pgstattuple/pgstatapprox.c
@@ -29,6 +29,9 @@
 #include "commands/vacuum.h"
 
 PG_FUNCTION_INFO_V1(pgstattuple_approx);
+PG_FUNCTION_INFO_V1(pgstattuple_approx_v1_5);
+
+Datum pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo);
 
 typedef struct output_type
 {
@@ -204,11 +207,42 @@ statapprox_heap(Relation rel, output_type *stat)
 
 /*
  * Returns estimated live/dead tuple statistics for the given relid.
+ *
+ * The superuser() check here must be kept as the library might be upgraded
+ * without the extension being upgraded, meaning that in pre-1.5 installations
+ * these functions could be called by any user.
  */
 Datum
 pgstattuple_approx(PG_FUNCTION_ARGS)
 {
 	Oid			relid = PG_GETARG_OID(0);
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 (errmsg("must be superuser to use pgstattuple functions"))));
+
+	PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
+}
+
+/*
+ * As of pgstattuple version 1.5, we no longer need to check if the user
+ * is a superuser because we REVOKE EXECUTE on the SQL function from PUBLIC.
+ * Users can then grant access to it based on their policies.
+ *
+ * Otherwise identical to pgstattuple_approx (above).
+ */
+Datum
+pgstattuple_approx_v1_5(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+
+	PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
+}
+
+Datum
+pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo)
+{
 	Relation	rel;
 	output_type stat = {0};
 	TupleDesc	tupdesc;
@@ -217,11 +251,6 @@ pgstattuple_approx(PG_FUNCTION_ARGS)
 	HeapTuple	ret;
 	int			i = 0;
 
-	if (!superuser())
-		ereport(ERROR,
-				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 (errmsg("must be superuser to use pgstattuple functions"))));
-
 	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
 		elog(ERROR, "return type must be a row type");