Disallow converting a table to a view if row security is present.

When DefineQueryRewrite() is about to convert a table to a view, it checks
the table for features unavailable to views.  For example, it rejects tables
having triggers.  It omits to reject tables having relrowsecurity or a
pg_policy record. Fix that. To faciliate the repair, invent
relation_has_policies() which indicates the presence of policies on a
relation even when row security is disabled for that relation.

Reported by Noah Misch. Patch by me, review by Stephen Frost. Back-patch
to 9.5 where RLS was introduced.

src/backend/commands/policy.c

@@ -1037,3 +1037,32 @@ get_relation_policy_oid(Oid relid, const char *policy_name, bool missing_ok)
 
 	return policy_oid;
 }
+
+/*
+ * relation_has_policies - Determine if relation has any policies
+ */
+bool
+relation_has_policies(Relation rel)
+{
+	Relation	catalog;
+	ScanKeyData skey;
+	SysScanDesc sscan;
+	HeapTuple	policy_tuple;
+	bool		ret = false;
+
+	catalog = heap_open(PolicyRelationId, AccessShareLock);
+	ScanKeyInit(&skey,
+				Anum_pg_policy_polrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(rel)));
+	sscan = systable_beginscan(catalog, PolicyPolrelidPolnameIndexId, true,
+							   NULL, 1, &skey);
+	policy_tuple = systable_getnext(sscan);
+	if (HeapTupleIsValid(policy_tuple))
+		ret = true;
+
+	systable_endscan(sscan);
+	heap_close(catalog, AccessShareLock);
+
+	return ret;
+}

src/backend/rewrite/rewriteDefine.c

@@ -27,6 +27,7 @@
 #include "catalog/objectaccess.h"
 #include "catalog/pg_rewrite.h"
 #include "catalog/storage.h"
+#include "commands/policy.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
 #include "parser/parse_utilcmd.h"
@@ -410,11 +411,12 @@ DefineQueryRewrite(char *rulename,
 		 *
 		 * If so, check that the relation is empty because the storage for the
 		 * relation is going to be deleted.  Also insist that the rel not have
-		 * any triggers, indexes, or child tables.  (Note: these tests are too
+		 * any triggers, indexes, child tables, policies, or RLS enabled.
-		 * strict, because they will reject relations that once had such but
+		 * (Note: these tests are too strict, because they will reject
-		 * don't anymore.  But we don't really care, because this whole
+		 * relations that once had such but don't anymore.  But we don't
-		 * business of converting relations to views is just a kluge to allow
+		 * really care, because this whole business of converting relations
-		 * dump/reload of views that participate in circular dependencies.)
+		 * to views is just a kluge to allow dump/reload of views that
+		 * participate in circular dependencies.)
 		 */
 		if (event_relation->rd_rel->relkind != RELKIND_VIEW &&
 			event_relation->rd_rel->relkind != RELKIND_MATVIEW)
@@ -451,6 +453,18 @@ DefineQueryRewrite(char *rulename,
 						 errmsg("could not convert table \"%s\" to a view because it has child tables",
 								RelationGetRelationName(event_relation))));
 
+			if (event_relation->rd_rel->relrowsecurity)
+				ereport(ERROR,
+						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						 errmsg("could not convert table \"%s\" to a view because it has row security enabled",
+								RelationGetRelationName(event_relation))));
+
+			if (relation_has_policies(event_relation))
+				ereport(ERROR,
+						(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						 errmsg("could not convert table \"%s\" to a view because it has row security policies",
+								RelationGetRelationName(event_relation))));
+
 			RelisBecomingView = true;
 		}
 	}

src/include/commands/policy.h

@@ -31,5 +31,6 @@ extern Oid get_relation_policy_oid(Oid relid, const char *policy_name,
 
 extern ObjectAddress rename_policy(RenameStmt *stmt);
 
+extern bool relation_has_policies(Relation rel);
 
 #endif   /* POLICY_H */

src/test/regress/expected/rowsecurity.out

@@ -2997,6 +2997,29 @@ DROP ROLE bob; -- succeeds
 ROLLBACK TO q;
 ROLLBACK; -- cleanup
 --
+-- Converting table to view
+--
+BEGIN;
+SET ROW_SECURITY = FORCE;
+CREATE TABLE t (c int);
+CREATE POLICY p ON t USING (c % 2 = 1);
+ALTER TABLE t ENABLE ROW LEVEL SECURITY;
+SAVEPOINT q;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- fails due to row level security enabled
+ERROR:  could not convert table "t" to a view because it has row security enabled
+ROLLBACK TO q;
+ALTER TABLE t DISABLE ROW LEVEL SECURITY;
+SAVEPOINT q;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- fails due to policy p on t
+ERROR:  could not convert table "t" to a view because it has row security policies
+ROLLBACK TO q;
+DROP POLICY p ON t;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- succeeds
+ROLLBACK;
+--
 -- Clean up objects
 --
 RESET SESSION AUTHORIZATION;

src/test/regress/sql/rowsecurity.sql

@@ -1260,6 +1260,31 @@ ROLLBACK TO q;
 
 ROLLBACK; -- cleanup
 
+--
+-- Converting table to view
+--
+BEGIN;
+SET ROW_SECURITY = FORCE;
+CREATE TABLE t (c int);
+CREATE POLICY p ON t USING (c % 2 = 1);
+ALTER TABLE t ENABLE ROW LEVEL SECURITY;
+
+SAVEPOINT q;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- fails due to row level security enabled
+ROLLBACK TO q;
+
+ALTER TABLE t DISABLE ROW LEVEL SECURITY;
+SAVEPOINT q;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- fails due to policy p on t
+ROLLBACK TO q;
+
+DROP POLICY p ON t;
+CREATE RULE "_RETURN" AS ON SELECT TO t DO INSTEAD
+  SELECT * FROM generate_series(1,5) t0(c); -- succeeds
+ROLLBACK;
+
 --
 -- Clean up objects
 --