Make inherited TRUNCATE perform access permission checks on parent table only.

Previously, TRUNCATE command through a parent table checked the
permissions on not only the parent table but also the children tables
inherited from it. This was a bug and inherited queries should perform
access permission checks on the parent table only. This commit fixes
that bug.

Back-patch to all supported branches.

Author: Amit Langote
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CAHGQGwFHdSvifhJE+-GSNqUHSfbiKxaeQQ7HGcYz6SC2n_oDcg@mail.gmail.com

src/backend/commands/tablecmds.c

@@ -262,7 +262,9 @@ struct DropRelationCallbackState
 #define		ATT_COMPOSITE_TYPE		0x0010
 #define		ATT_FOREIGN_TABLE		0x0020
 
-static void truncate_check_rel(Relation rel);
+static void truncate_check_rel(Oid relid, Form_pg_class reltuple);
+static void truncate_check_perms(Oid relid, Form_pg_class reltuple);
+static void truncate_check_activity(Relation rel);
 static List *MergeAttributes(List *schema, List *supers, char relpersistence,
 				List **supOids, List **supconstr, int *supOidCount);
 static bool MergeCheckConstraint(List *constraints, char *name, Node *expr);
@@ -1018,7 +1020,11 @@ ExecuteTruncate(TruncateStmt *stmt)
 			heap_close(rel, lockmode);
 			continue;
 		}
-		truncate_check_rel(rel);
+
+		truncate_check_rel(myrelid, rel->rd_rel);
+		truncate_check_perms(myrelid, rel->rd_rel);
+		truncate_check_activity(rel);
+
 		rels = lappend(rels, rel);
 		relids = lappend_oid(relids, myrelid);
 
@@ -1054,7 +1060,15 @@ ExecuteTruncate(TruncateStmt *stmt)
 					continue;
 				}
 
-				truncate_check_rel(rel);
+				/*
+				 * Inherited TRUNCATE commands perform access
+				 * permission checks on the parent table only.
+				 * So we skip checking the children's permissions
+				 * and don't call truncate_check_perms() here.
+				 */
+				truncate_check_rel(RelationGetRelid(rel), rel->rd_rel);
+				truncate_check_activity(rel);
+
 				rels = lappend(rels, rel);
 				relids = lappend_oid(relids, childrelid);
 			}
@@ -1088,7 +1102,9 @@ ExecuteTruncate(TruncateStmt *stmt)
 				ereport(NOTICE,
 						(errmsg("truncate cascades to table \"%s\"",
 								RelationGetRelationName(rel))));
-				truncate_check_rel(rel);
+				truncate_check_rel(relid, rel->rd_rel);
+				truncate_check_perms(relid, rel->rd_rel);
+				truncate_check_activity(rel);
 				rels = lappend(rels, rel);
 				relids = lappend_oid(relids, relid);
 			}
@@ -1289,30 +1305,45 @@ ExecuteTruncate(TruncateStmt *stmt)
  * Check that a given rel is safe to truncate.  Subroutine for ExecuteTruncate
  */
 static void
-truncate_check_rel(Relation rel)
+truncate_check_rel(Oid relid, Form_pg_class reltuple)
 {
-	AclResult	aclresult;
+	char	   *relname = NameStr(reltuple->relname);
 
 	/* Only allow truncate on regular tables */
-	if (rel->rd_rel->relkind != RELKIND_RELATION)
+	if (reltuple->relkind != RELKIND_RELATION)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table",
-						RelationGetRelationName(rel))));
+				 errmsg("\"%s\" is not a table", relname)));
 
-	/* Permissions checks */
-	aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
-								  ACL_TRUNCATE);
-	if (aclresult != ACLCHECK_OK)
-		aclcheck_error(aclresult, ACL_KIND_CLASS,
-					   RelationGetRelationName(rel));
-
-	if (!allowSystemTableMods && IsSystemRelation(rel))
+	if (!allowSystemTableMods && IsSystemClass(relid, reltuple))
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("permission denied: \"%s\" is a system catalog",
-						RelationGetRelationName(rel))));
+						relname)));
+}
 
+/*
+ * Check that current user has the permission to truncate given relation.
+ */
+static void
+truncate_check_perms(Oid relid, Form_pg_class reltuple)
+{
+	char	   *relname = NameStr(reltuple->relname);
+	AclResult	aclresult;
+
+	/* Permissions checks */
+	aclresult = pg_class_aclcheck(relid, GetUserId(), ACL_TRUNCATE);
+	if (aclresult != ACLCHECK_OK)
+		aclcheck_error(aclresult, ACL_KIND_CLASS, relname);
+}
+
+/*
+ * Set of extra sanity checks to check if a given relation is safe to
+ * truncate.
+ */
+static void
+truncate_check_activity(Relation rel)
+{
 	/*
 	 * Don't allow truncate on temp tables of other backends ... their local
 	 * buffer manager is not going to cope.

src/test/regress/expected/privileges.out

@@ -656,6 +656,27 @@ SELECT oid FROM atestp2; -- ok
 -----
 (0 rows)
 
+-- child's permissions do not apply when operating on parent
+SET SESSION AUTHORIZATION regressuser1;
+REVOKE ALL ON atestc FROM regressuser2;
+GRANT ALL ON atestp1 TO regressuser2;
+SET SESSION AUTHORIZATION regressuser2;
+SELECT f2 FROM atestp1; -- ok
+ f2 
+----
+(0 rows)
+
+SELECT f2 FROM atestc; -- fail
+ERROR:  permission denied for relation atestc
+DELETE FROM atestp1; -- ok
+DELETE FROM atestc; -- fail
+ERROR:  permission denied for relation atestc
+UPDATE atestp1 SET f1 = 1; -- ok
+UPDATE atestc SET f1 = 1; -- fail
+ERROR:  permission denied for relation atestc
+TRUNCATE atestp1; -- ok
+TRUNCATE atestc; -- fail
+ERROR:  permission denied for relation atestc
 -- privileges on functions, languages
 -- switch to superuser
 \c -

src/test/regress/sql/privileges.sql

@@ -414,6 +414,20 @@ SELECT fy FROM atestp2; -- ok
 SELECT atestp2 FROM atestp2; -- ok
 SELECT oid FROM atestp2; -- ok
 
+-- child's permissions do not apply when operating on parent
+SET SESSION AUTHORIZATION regressuser1;
+REVOKE ALL ON atestc FROM regressuser2;
+GRANT ALL ON atestp1 TO regressuser2;
+SET SESSION AUTHORIZATION regressuser2;
+SELECT f2 FROM atestp1; -- ok
+SELECT f2 FROM atestc; -- fail
+DELETE FROM atestp1; -- ok
+DELETE FROM atestc; -- fail
+UPDATE atestp1 SET f1 = 1; -- ok
+UPDATE atestc SET f1 = 1; -- fail
+TRUNCATE atestp1; -- ok
+TRUNCATE atestc; -- fail
+
 -- privileges on functions, languages
 
 -- switch to superuser