Fix ALTER EXTENSION SET SCHEMA with objects outside an extension's schema

As coded, the code would use as a base comparison the namespace OID from
the first object scanned in pg_depend when switching its namespace
dependency entry to the new one, and use it as a base of comparison for
any follow-up checks.  It would also be used as the old namespace OID to
switch *from* for the extension's pg_depend entry.  Hence, if the first
object scanned has a namespace different than the one stored in the
extension, we would finish by:
- Not checking that the extension objects map with the extension's
schema.
- Not switching the extension -> namespace dependency entry to the new
namespace provided by the user, making ALTER EXTENSION ineffective.

This issue exists since this command has been introduced in d9572c4 for
relocatable extension, so backpatch all the way down to 11.  The test
case has been provided by Heikki, that I have tweaked a bit to show the
effects on pg_depend for the extension.

Reported-by: Heikki Linnakangas
Author: Michael Paquier, Heikki Linnakangas
Discussion: https://postgr.es/m/20eea594-a05b-4c31-491b-007b6fceef28@iki.fi
Backpatch-through: 11

1 files changed, 4 insertions, 7 deletions

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index f3f44b7f6de..7e81d848190 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -2706,7 +2706,7 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 {
 	Oid			extensionOid;
 	Oid			nspOid;
-	Oid			oldNspOid = InvalidOid;
+	Oid			oldNspOid;
 	AclResult	aclresult;
 	Relation	extRel;
 	ScanKeyData key[2];
@@ -2789,6 +2789,9 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 
 	objsMoved = new_object_addresses();
 
+	/* store the OID of the namespace to-be-changed */
+	oldNspOid = extForm->extnamespace;
+
 	/*
 	 * Scan pg_depend to find objects that depend directly on the extension,
 	 * and alter each one's schema.
@@ -2835,12 +2838,6 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 												 objsMoved);
 
 		/*
-		 * Remember previous namespace of first object that has one
-		 */
-		if (oldNspOid == InvalidOid && dep_oldNspOid != InvalidOid)
-			oldNspOid = dep_oldNspOid;
-
-		/*
 		 * If not all the objects had the same old namespace (ignoring any
 		 * that are not in namespaces), complain.
 		 */