Have REASSIGN OWNED work on extensions, too

Per bug #6593, REASSIGN OWNED fails when the affected role has created
an extension.  Even though the user related to the extension is not
nominally the owner, its OID appears on pg_shdepend and thus causes
problems when the user is to be dropped.

This commit adds code to change the "ownership" of the extension itself,
not of the contained objects.  This is fine because it's currently only
called from REASSIGN OWNED, which would also modify the ownership of the
contained objects.  However, this is not sufficient for a working ALTER
OWNER implementation extension.

Back-patch to 9.1, where extensions were introduced.

Bug #6593 reported by Emiliano Leporati.

src/backend/catalog/pg_shdepend.c

@@ -25,6 +25,7 @@
 #include "catalog/pg_conversion.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_default_acl.h"
+#include "catalog/pg_extension.h"
 #include "catalog/pg_foreign_data_wrapper.h"
 #include "catalog/pg_foreign_server.h"
 #include "catalog/pg_language.h"
@@ -1392,6 +1393,10 @@ shdepReassignOwned(List *roleids, Oid newrole)
 					AlterForeignDataWrapperOwner_oid(sdepForm->objid, newrole);
 					break;
 
+				case ExtensionRelationId:
+					AlterExtensionOwner_oid(sdepForm->objid, newrole);
+					break;
+
 				default:
 					elog(ERROR, "unexpected classid %u", sdepForm->classid);
 					break;

src/backend/commands/extension.c

@@ -2789,3 +2789,95 @@ ExecAlterExtensionContentsStmt(AlterExtensionContentsStmt *stmt)
 	if (relation != NULL)
 		relation_close(relation, NoLock);
 }
+
+/*
+ * AlterExtensionOwner_internal
+ *
+ * Internal routine for changing the owner of an extension.  rel must be
+ * pg_extension, already open and suitably locked; it will not be closed.
+ *
+ * Note that this only changes ownership of the extension itself; it doesn't
+ * change the ownership of objects it contains.  Since this function is
+ * currently only called from REASSIGN OWNED, this restriction is okay because
+ * said objects would also be affected by our caller.  But it's not enough for
+ * a full-fledged ALTER OWNER implementation, so beware.
+ */
+static void
+AlterExtensionOwner_internal(Relation rel, Oid extensionOid, Oid newOwnerId)
+{
+	Form_pg_extension extForm;
+	HeapTuple	tup;
+	SysScanDesc	scandesc;
+	ScanKeyData	entry[1];
+
+	Assert(RelationGetRelid(rel) == ExtensionRelationId);
+
+	ScanKeyInit(&entry[0],
+				ObjectIdAttributeNumber,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(extensionOid));
+
+	scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
+								  SnapshotNow, 1, entry);
+
+	/* We assume that there can be at most one matching tuple */
+	tup = systable_getnext(scandesc);
+	if (!HeapTupleIsValid(tup)) /* should not happen */
+		elog(ERROR, "cache lookup failed for extension %u", extensionOid);
+
+	tup = heap_copytuple(tup);
+	systable_endscan(scandesc);
+
+	extForm = (Form_pg_extension) GETSTRUCT(tup);
+
+	/*
+	 * If the new owner is the same as the existing owner, consider the
+	 * command to have succeeded.  This is for dump restoration purposes.
+	 */
+	if (extForm->extowner != newOwnerId)
+	{
+		/* Superusers can always do it */
+		if (!superuser())
+		{
+			/* Otherwise, must be owner of the existing object */
+			if (!pg_extension_ownercheck(HeapTupleGetOid(tup), GetUserId()))
+				aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_EXTENSION,
+							   NameStr(extForm->extname));
+
+			/* Must be able to become new owner */
+			check_is_member_of_role(GetUserId(), newOwnerId);
+
+			/* no privilege checks on namespace are required */
+		}
+
+		/*
+		 * Modify the owner --- okay to scribble on tup because it's a copy
+		 */
+		extForm->extowner = newOwnerId;
+
+		simple_heap_update(rel, &tup->t_self, tup);
+
+		CatalogUpdateIndexes(rel, tup);
+
+		/* Update owner dependency reference */
+		changeDependencyOnOwner(ExtensionRelationId, extensionOid,
+								newOwnerId);
+	}
+
+	heap_freetuple(tup);
+}
+
+/*
+ * Change extension owner, by OID
+ */
+void
+AlterExtensionOwner_oid(Oid extensionOid, Oid newOwnerId)
+{
+	Relation	rel;
+
+	rel = heap_open(ExtensionRelationId, RowExclusiveLock);
+	
+	AlterExtensionOwner_internal(rel, extensionOid, newOwnerId);
+
+	heap_close(rel, NoLock);
+}

src/include/commands/extension.h

@@ -46,4 +46,6 @@ extern char *get_extension_name(Oid ext_oid);
 
 extern void AlterExtensionNamespace(List *names, const char *newschema);
 
+extern void AlterExtensionOwner_oid(Oid extensionOid, Oid newOwnerId);
+
 #endif   /* EXTENSION_H */