Always require SELECT permission for ON CONFLICT DO UPDATE.

The update path of an INSERT ... ON CONFLICT DO UPDATE requires SELECT
permission on the columns of the arbiter index, but it failed to check
for that in the case of an arbiter specified by constraint name.

In addition, for a table with row level security enabled, it failed to
check updated rows against the table's SELECT policies when the update
path was taken (regardless of how the arbiter index was specified).

Backpatch to 9.5 where ON CONFLICT DO UPDATE and RLS were introduced.

Security: CVE-2017-15099

src/backend/catalog/pg_constraint.c

@@ -805,6 +805,104 @@ get_relation_constraint_oid(Oid relid, const char *conname, bool missing_ok)
 	return conOid;
 }
 
+/*
+ * get_relation_constraint_attnos
+ *		Find a constraint on the specified relation with the specified name
+ *		and return the constrained columns.
+ *
+ * Returns a Bitmapset of the column attnos of the constrained columns, with
+ * attnos being offset by FirstLowInvalidHeapAttributeNumber so that system
+ * columns can be represented.
+ *
+ * *constraintOid is set to the OID of the constraint, or InvalidOid on
+ * failure.
+ */
+Bitmapset *
+get_relation_constraint_attnos(Oid relid, const char *conname,
+							   bool missing_ok, Oid *constraintOid)
+{
+	Bitmapset  *conattnos = NULL;
+	Relation	pg_constraint;
+	HeapTuple	tuple;
+	SysScanDesc scan;
+	ScanKeyData skey[1];
+
+	/* Set *constraintOid, to avoid complaints about uninitialized vars */
+	*constraintOid = InvalidOid;
+
+	/*
+	 * Fetch the constraint tuple from pg_constraint.  There may be more than
+	 * one match, because constraints are not required to have unique names;
+	 * if so, error out.
+	 */
+	pg_constraint = heap_open(ConstraintRelationId, AccessShareLock);
+
+	ScanKeyInit(&skey[0],
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(relid));
+
+	scan = systable_beginscan(pg_constraint, ConstraintRelidIndexId, true,
+							  NULL, 1, skey);
+
+	while (HeapTupleIsValid(tuple = systable_getnext(scan)))
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+		Datum		adatum;
+		bool		isNull;
+		ArrayType  *arr;
+		int16	   *attnums;
+		int			numcols;
+		int			i;
+
+		/* Check the constraint name */
+		if (strcmp(NameStr(con->conname), conname) != 0)
+			continue;
+		if (OidIsValid(*constraintOid))
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("table \"%s\" has multiple constraints named \"%s\"",
+							get_rel_name(relid), conname)));
+
+		*constraintOid = HeapTupleGetOid(tuple);
+
+		/* Extract the conkey array, ie, attnums of constrained columns */
+		adatum = heap_getattr(tuple, Anum_pg_constraint_conkey,
+							  RelationGetDescr(pg_constraint), &isNull);
+		if (isNull)
+			continue;			/* no constrained columns */
+
+		arr = DatumGetArrayTypeP(adatum);	/* ensure not toasted */
+		numcols = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			numcols < 0 ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "conkey is not a 1-D smallint array");
+		attnums = (int16 *) ARR_DATA_PTR(arr);
+
+		/* Construct the result value */
+		for (i = 0; i < numcols; i++)
+		{
+			conattnos = bms_add_member(conattnos,
+									   attnums[i] - FirstLowInvalidHeapAttributeNumber);
+		}
+	}
+
+	systable_endscan(scan);
+
+	/* If no such constraint exists, complain */
+	if (!OidIsValid(*constraintOid) && !missing_ok)
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("constraint \"%s\" for table \"%s\" does not exist",
+						conname, get_rel_name(relid))));
+
+	heap_close(pg_constraint, AccessShareLock);
+
+	return conattnos;
+}
+
 /*
  * get_domain_constraint_oid
  *		Find a constraint on the specified domain with the specified name.

src/backend/parser/parse_clause.c

@@ -3164,9 +3164,26 @@ transformOnConflictArbiter(ParseState *pstate,
 
 		pstate->p_namespace = save_namespace;
 
+		/*
+		 * If the arbiter is specified by constraint name, get the constraint
+		 * OID and mark the constrained columns as requiring SELECT privilege,
+		 * in the same way as would have happened if the arbiter had been
+		 * specified by explicit reference to the constraint's index columns.
+		 */
 		if (infer->conname)
-			*constraint = get_relation_constraint_oid(RelationGetRelid(pstate->p_target_relation),
-													  infer->conname, false);
+		{
+			Oid			relid = RelationGetRelid(pstate->p_target_relation);
+			RangeTblEntry *rte = pstate->p_target_rangetblentry;
+			Bitmapset  *conattnos;
+
+			conattnos = get_relation_constraint_attnos(relid, infer->conname,
+													   false, constraint);
+
+			/* Make sure the rel as a whole is marked for SELECT access */
+			rte->requiredPerms |= ACL_SELECT;
+			/* Mark the constrained columns as requiring SELECT access */
+			rte->selectedCols = bms_add_members(rte->selectedCols, conattnos);
+		}
 	}
 
 	/*

src/backend/rewrite/rowsecurity.c

@@ -310,6 +310,8 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 		{
 			List	   *conflict_permissive_policies;
 			List	   *conflict_restrictive_policies;
+			List	   *conflict_select_permissive_policies = NIL;
+			List	   *conflict_select_restrictive_policies = NIL;
 
 			/* Get the policies that apply to the auxiliary UPDATE */
 			get_policies_for_relation(rel, CMD_UPDATE, user_id,
@@ -339,9 +341,6 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 			 */
 			if (rte->requiredPerms & ACL_SELECT)
 			{
-				List	   *conflict_select_permissive_policies = NIL;
-				List	   *conflict_select_restrictive_policies = NIL;
-
 				get_policies_for_relation(rel, CMD_SELECT, user_id,
 										  &conflict_select_permissive_policies,
 										  &conflict_select_restrictive_policies);
@@ -362,6 +361,21 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 								   withCheckOptions,
 								   hasSubLinks,
 								   false);
+
+			/*
+			 * Add ALL/SELECT policies as WCO_RLS_UPDATE_CHECK WCOs, to ensure
+			 * that the final updated row is visible when taking the UPDATE
+			 * path of an INSERT .. ON CONFLICT DO UPDATE, if SELECT rights
+			 * are required for this relation.
+			 */
+			if (rte->requiredPerms & ACL_SELECT)
+				add_with_check_options(rel, rt_index,
+									   WCO_RLS_UPDATE_CHECK,
+									   conflict_select_permissive_policies,
+									   conflict_select_restrictive_policies,
+									   withCheckOptions,
+									   hasSubLinks,
+									   true);
 		}
 	}
 

src/include/catalog/pg_constraint_fn.h

@@ -69,6 +69,8 @@ extern char *ChooseConstraintName(const char *name1, const char *name2,
 extern void AlterConstraintNamespaces(Oid ownerId, Oid oldNspId,
 						  Oid newNspId, bool isType, ObjectAddresses *objsMoved);
 extern Oid	get_relation_constraint_oid(Oid relid, const char *conname, bool missing_ok);
+extern Bitmapset *get_relation_constraint_attnos(Oid relid, const char *conname,
+							   bool missing_ok, Oid *constraintOid);
 extern Oid	get_domain_constraint_oid(Oid typid, const char *conname, bool missing_ok);
 
 extern Bitmapset *get_primary_key_attnos(Oid relid, bool deferrableOk,

src/test/regress/expected/privileges.out

@@ -488,10 +488,22 @@ ERROR:  permission denied for relation atest5
 INSERT INTO atest5(three) VALUES (4) ON CONFLICT (two) DO UPDATE set three = 10; -- fails (due to INSERT)
 ERROR:  permission denied for relation atest5
 -- Check that the columns in the inference require select privileges
--- Error. No privs on four
-INSERT INTO atest5(three) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 10;
+INSERT INTO atest5(four) VALUES (4); -- fail
 ERROR:  permission denied for relation atest5
 SET SESSION AUTHORIZATION regress_user1;
+GRANT INSERT (four) ON atest5 TO regress_user4;
+SET SESSION AUTHORIZATION regress_user4;
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 3; -- fails (due to SELECT)
+ERROR:  permission denied for relation atest5
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT ON CONSTRAINT atest5_four_key DO UPDATE set three = 3; -- fails (due to SELECT)
+ERROR:  permission denied for relation atest5
+INSERT INTO atest5(four) VALUES (4); -- ok
+SET SESSION AUTHORIZATION regress_user1;
+GRANT SELECT (four) ON atest5 TO regress_user4;
+SET SESSION AUTHORIZATION regress_user4;
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 3; -- ok
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT ON CONSTRAINT atest5_four_key DO UPDATE set three = 3; -- ok
+SET SESSION AUTHORIZATION regress_user1;
 REVOKE ALL (one) ON atest5 FROM regress_user4;
 GRANT SELECT (one,two,blue) ON atest6 TO regress_user4;
 SET SESSION AUTHORIZATION regress_user4;

src/test/regress/expected/rowsecurity.out

@@ -3807,9 +3807,10 @@ DROP TABLE r1;
 --
 SET SESSION AUTHORIZATION regress_rls_alice;
 SET row_security = on;
-CREATE TABLE r1 (a int);
+CREATE TABLE r1 (a int PRIMARY KEY);
 CREATE POLICY p1 ON r1 FOR SELECT USING (a < 20);
 CREATE POLICY p2 ON r1 FOR UPDATE USING (a < 20) WITH CHECK (true);
+CREATE POLICY p3 ON r1 FOR INSERT WITH CHECK (true);
 INSERT INTO r1 VALUES (10);
 ALTER TABLE r1 ENABLE ROW LEVEL SECURITY;
 ALTER TABLE r1 FORCE ROW LEVEL SECURITY;
@@ -3836,6 +3837,18 @@ ALTER TABLE r1 FORCE ROW LEVEL SECURITY;
 -- Error
 UPDATE r1 SET a = 30 RETURNING *;
 ERROR:  new row violates row-level security policy for table "r1"
+-- UPDATE path of INSERT ... ON CONFLICT DO UPDATE should also error out
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT (a) DO UPDATE SET a = 30 RETURNING *;
+ERROR:  new row violates row-level security policy for table "r1"
+-- Should still error out without RETURNING (use of arbiter always requires
+-- SELECT permissions)
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT (a) DO UPDATE SET a = 30;
+ERROR:  new row violates row-level security policy for table "r1"
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT ON CONSTRAINT r1_pkey DO UPDATE SET a = 30;
+ERROR:  new row violates row-level security policy for table "r1"
 DROP TABLE r1;
 -- Check dependency handling
 RESET SESSION AUTHORIZATION;

src/test/regress/sql/privileges.sql

@@ -320,9 +320,24 @@ INSERT INTO atest5(two) VALUES (6) ON CONFLICT (two) DO UPDATE set three = EXCLU
 INSERT INTO atest5(two) VALUES (6) ON CONFLICT (two) DO UPDATE set three = EXCLUDED.three;
 INSERT INTO atest5(two) VALUES (6) ON CONFLICT (two) DO UPDATE set one = 8; -- fails (due to UPDATE)
 INSERT INTO atest5(three) VALUES (4) ON CONFLICT (two) DO UPDATE set three = 10; -- fails (due to INSERT)
+
 -- Check that the columns in the inference require select privileges
--- Error. No privs on four
-INSERT INTO atest5(three) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 10;
+INSERT INTO atest5(four) VALUES (4); -- fail
+
+SET SESSION AUTHORIZATION regress_user1;
+GRANT INSERT (four) ON atest5 TO regress_user4;
+SET SESSION AUTHORIZATION regress_user4;
+
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 3; -- fails (due to SELECT)
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT ON CONSTRAINT atest5_four_key DO UPDATE set three = 3; -- fails (due to SELECT)
+INSERT INTO atest5(four) VALUES (4); -- ok
+
+SET SESSION AUTHORIZATION regress_user1;
+GRANT SELECT (four) ON atest5 TO regress_user4;
+SET SESSION AUTHORIZATION regress_user4;
+
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT (four) DO UPDATE set three = 3; -- ok
+INSERT INTO atest5(four) VALUES (4) ON CONFLICT ON CONSTRAINT atest5_four_key DO UPDATE set three = 3; -- ok
 
 SET SESSION AUTHORIZATION regress_user1;
 REVOKE ALL (one) ON atest5 FROM regress_user4;

src/test/regress/sql/rowsecurity.sql

@@ -1674,10 +1674,11 @@ DROP TABLE r1;
 --
 SET SESSION AUTHORIZATION regress_rls_alice;
 SET row_security = on;
-CREATE TABLE r1 (a int);
+CREATE TABLE r1 (a int PRIMARY KEY);
 
 CREATE POLICY p1 ON r1 FOR SELECT USING (a < 20);
 CREATE POLICY p2 ON r1 FOR UPDATE USING (a < 20) WITH CHECK (true);
+CREATE POLICY p3 ON r1 FOR INSERT WITH CHECK (true);
 INSERT INTO r1 VALUES (10);
 ALTER TABLE r1 ENABLE ROW LEVEL SECURITY;
 ALTER TABLE r1 FORCE ROW LEVEL SECURITY;
@@ -1699,6 +1700,17 @@ ALTER TABLE r1 FORCE ROW LEVEL SECURITY;
 -- Error
 UPDATE r1 SET a = 30 RETURNING *;
 
+-- UPDATE path of INSERT ... ON CONFLICT DO UPDATE should also error out
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT (a) DO UPDATE SET a = 30 RETURNING *;
+
+-- Should still error out without RETURNING (use of arbiter always requires
+-- SELECT permissions)
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT (a) DO UPDATE SET a = 30;
+INSERT INTO r1 VALUES (10)
+    ON CONFLICT ON CONSTRAINT r1_pkey DO UPDATE SET a = 30;
+
 DROP TABLE r1;
 
 -- Check dependency handling