From f7a2002e82cfc639d1b6df89012f5d6c623ad545 Mon Sep 17 00:00:00 2001
From: Joe Conway <mail@joeconway.com>
Date: Sat, 23 Nov 2019 10:39:20 -0500
Subject: [PATCH] Add object TRUNCATE hook

All operations with acl permissions checks should have a corresponding hook
so that, for example, mandatory access control (MAC) may be enforced by an
extension. The command TRUNCATE is missing this hook, so add it. Patch by
Yuli Khodorkovskiy with some editorialization by me. Based on the discussion
not back-patched. A separate patch will exercise the hook in the sepgsql
extension.

Author: Yuli Khodorkovskiy
Reviewed-by: Joe Conway
Discussion: https://postgr.es/m/CAFL5wJcomybj1Xdw7qWmPJRpGuFukKgNrDb6uVBaCMgYS9dkaA%40mail.gmail.com
---
 src/backend/catalog/objectaccess.c | 17 +++++++++++++++++
 src/backend/commands/tablecmds.c   |  2 ++
 src/include/catalog/objectaccess.h | 14 +++++++++++++-
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/backend/catalog/objectaccess.c b/src/backend/catalog/objectaccess.c
index b1619b859f..d51d01fe65 100644
--- a/src/backend/catalog/objectaccess.c
+++ b/src/backend/catalog/objectaccess.c
@@ -11,6 +11,7 @@
 #include "postgres.h"
 
 #include "catalog/objectaccess.h"
+#include "catalog/pg_class.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_proc.h"
 
@@ -64,6 +65,22 @@ RunObjectDropHook(Oid classId, Oid objectId, int subId,
 						   (void *) &drop_arg);
 }
 
+/*
+ * RunObjectTruncateHook
+ *
+ * It is the entrypoint of OAT_TRUNCATE event
+ */
+void
+RunObjectTruncateHook(Oid objectId)
+{
+	/* caller should check, but just in case... */
+	Assert(object_access_hook != NULL);
+
+	(*object_access_hook) (OAT_TRUNCATE,
+						   RelationRelationId, objectId, 0,
+						   NULL);
+}
+
 /*
  * RunObjectPostAlterHook
  *
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 45aae5955d..5440eb9015 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1937,6 +1937,8 @@ truncate_check_rel(Oid relid, Form_pg_class reltuple)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("permission denied: \"%s\" is a system catalog",
 						relname)));
+
+	InvokeObjectTruncateHook(relid);
 }
 
 /*
diff --git a/src/include/catalog/objectaccess.h b/src/include/catalog/objectaccess.h
index 0170f1f1e4..9824adf531 100644
--- a/src/include/catalog/objectaccess.h
+++ b/src/include/catalog/objectaccess.h
@@ -37,6 +37,10 @@
  * creation or altering, because OAT_POST_CREATE or OAT_POST_ALTER are
  * sufficient for extensions to track these kind of checks.
  *
+ * OAT_TRUNCATE should be invoked just before truncation of objects. This
+ * event is equivalent to truncate permission on a relation under the
+ * default access control mechanism.
+ *
  * Other types may be added in the future.
  */
 typedef enum ObjectAccessType
@@ -45,7 +49,8 @@ typedef enum ObjectAccessType
 	OAT_DROP,
 	OAT_POST_ALTER,
 	OAT_NAMESPACE_SEARCH,
-	OAT_FUNCTION_EXECUTE
+	OAT_FUNCTION_EXECUTE,
+	OAT_TRUNCATE
 } ObjectAccessType;
 
 /*
@@ -131,6 +136,7 @@ extern void RunObjectPostCreateHook(Oid classId, Oid objectId, int subId,
 									bool is_internal);
 extern void RunObjectDropHook(Oid classId, Oid objectId, int subId,
 							  int dropflags);
+extern void RunObjectTruncateHook(Oid objectId);
 extern void RunObjectPostAlterHook(Oid classId, Oid objectId, int subId,
 								   Oid auxiliaryId, bool is_internal);
 extern bool RunNamespaceSearchHook(Oid objectId, bool ereport_on_violation);
@@ -160,6 +166,12 @@ extern void RunFunctionExecuteHook(Oid objectId);
 							  (dropflags));							\
 	} while(0)
 
+#define InvokeObjectTruncateHook(objectId)							\
+	do {															\
+		if (object_access_hook)										\
+			RunObjectTruncateHook(objectId);						\
+	} while(0)
+
 #define InvokeObjectPostAlterHook(classId,objectId,subId)			\
 	InvokeObjectPostAlterHookArg((classId),(objectId),(subId),		\
 								 InvalidOid,false)