Ensure COPY TO on an RLS-enabled table copies no more than it should.

The COPY documentation is quite clear that "COPY relation TO" copies
rows from only the named table, not any inheritance children it may
have.  However, if you enabled row-level security on the table then
this stopped being true, because the code forgot to apply the ONLY
modifier in the "SELECT ... FROM relation" query that it constructs
in order to allow RLS predicates to be attached.  Fix that.

Report and patch by Antonin Houska (comment adjustments and test case
by me).  Back-patch to all supported branches.

Discussion: https://postgr.es/m/3472.1675251957@antos

src/backend/commands/copy.c

@@ -244,11 +244,14 @@ DoCopy(ParseState *pstate, const CopyStmt *stmt,
 
 			/*
 			 * Build RangeVar for from clause, fully qualified based on the
-			 * relation which we have opened and locked.
+			 * relation which we have opened and locked.  Use "ONLY" so that
+			 * COPY retrieves rows from only the target table not any
+			 * inheritance children, the same as when RLS doesn't apply.
 			 */
 			from = makeRangeVar(get_namespace_name(RelationGetNamespace(rel)),
 								pstrdup(RelationGetRelationName(rel)),
 								-1);
+			from->inh = false;	/* apply ONLY */
 
 			/* Build query */
 			select = makeNode(SelectStmt);

src/backend/commands/copyto.c

@@ -508,8 +508,8 @@ BeginCopyTo(ParseState *pstate,
 		/*
 		 * With row-level security and a user using "COPY relation TO", we
 		 * have to convert the "COPY relation TO" to a query-based COPY (eg:
-		 * "COPY (SELECT * FROM relation) TO"), to allow the rewriter to add
+		 * "COPY (SELECT * FROM ONLY relation) TO"), to allow the rewriter to
-		 * in any RLS clauses.
+		 * add in any RLS clauses.
 		 *
 		 * When this happens, we are passed in the relid of the originally
 		 * found relation (which we have locked).  As the planner will look up

src/test/regress/expected/rowsecurity.out

@@ -3255,6 +3255,42 @@ ERROR:  permission denied for table copy_rel_to
 SET row_security TO ON;
 COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
 ERROR:  permission denied for table copy_rel_to
+-- Check behavior with a child table.
+RESET SESSION AUTHORIZATION;
+SET row_security TO ON;
+CREATE TABLE copy_rel_to_child () INHERITS (copy_rel_to);
+INSERT INTO copy_rel_to_child VALUES (1, 'one'), (2, 'two');
+-- Check COPY TO as Superuser/owner.
+RESET SESSION AUTHORIZATION;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ',';
+1,c4ca4238a0b923820dcc509a6f75849b
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ',';
+1,c4ca4238a0b923820dcc509a6f75849b
+-- Check COPY TO as user with permissions.
+SET SESSION AUTHORIZATION regress_rls_bob;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - would be affected by RLS
+ERROR:  query would be affected by row-level security policy for table "copy_rel_to"
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+-- Check COPY TO as user with permissions and BYPASSRLS
+SET SESSION AUTHORIZATION regress_rls_exempt_user;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+1,c4ca4238a0b923820dcc509a6f75849b
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+1,c4ca4238a0b923820dcc509a6f75849b
+-- Check COPY TO as user without permissions. SET row_security TO OFF;
+SET SESSION AUTHORIZATION regress_rls_carol;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
+ERROR:  permission denied for table copy_rel_to
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
+ERROR:  permission denied for table copy_rel_to
 -- Check COPY FROM as Superuser/owner.
 RESET SESSION AUTHORIZATION;
 SET row_security TO OFF;
@@ -3285,6 +3321,7 @@ ERROR:  permission denied for table copy_t
 RESET SESSION AUTHORIZATION;
 DROP TABLE copy_t;
 DROP TABLE copy_rel_to CASCADE;
+NOTICE:  drop cascades to table copy_rel_to_child
 -- Check WHERE CURRENT OF
 SET SESSION AUTHORIZATION regress_rls_alice;
 CREATE TABLE current_check (currentid int, payload text, rlsuser text);

src/test/regress/sql/rowsecurity.sql

@@ -1265,6 +1265,40 @@ COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
 SET row_security TO ON;
 COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
 
+-- Check behavior with a child table.
+RESET SESSION AUTHORIZATION;
+SET row_security TO ON;
+CREATE TABLE copy_rel_to_child () INHERITS (copy_rel_to);
+INSERT INTO copy_rel_to_child VALUES (1, 'one'), (2, 'two');
+
+-- Check COPY TO as Superuser/owner.
+RESET SESSION AUTHORIZATION;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ',';
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ',';
+
+-- Check COPY TO as user with permissions.
+SET SESSION AUTHORIZATION regress_rls_bob;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - would be affected by RLS
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+
+-- Check COPY TO as user with permissions and BYPASSRLS
+SET SESSION AUTHORIZATION regress_rls_exempt_user;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --ok
+
+-- Check COPY TO as user without permissions. SET row_security TO OFF;
+SET SESSION AUTHORIZATION regress_rls_carol;
+SET row_security TO OFF;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
+SET row_security TO ON;
+COPY copy_rel_to TO STDOUT WITH DELIMITER ','; --fail - permission denied
+
 -- Check COPY FROM as Superuser/owner.
 RESET SESSION AUTHORIZATION;
 SET row_security TO OFF;