Row-Level Security Policies (RLS)

Building on the updatable security-barrier views work, add the
ability to define policies on tables to limit the set of rows
which are returned from a query and which are allowed to be added
to a table.  Expressions defined by the policy for filtering are
added to the security barrier quals of the query, while expressions
defined to check records being added to a table are added to the
with-check options of the query.

New top-level commands are CREATE/ALTER/DROP POLICY and are
controlled by the table owner.  Row Security is able to be enabled
and disabled by the owner on a per-table basis using
ALTER TABLE .. ENABLE/DISABLE ROW SECURITY.

Per discussion, ROW SECURITY is disabled on tables by default and
must be enabled for policies on the table to be used.  If no
policies exist on a table with ROW SECURITY enabled, a default-deny
policy is used and no records will be visible.

By default, row security is applied at all times except for the
table owner and the superuser.  A new GUC, row_security, is added
which can be set to ON, OFF, or FORCE.  When set to FORCE, row
security will be applied even for the table owner and superusers.
When set to OFF, row security will be disabled when allowed and an
error will be thrown if the user does not have rights to bypass row
security.

Per discussion, pg_dump sets row_security = OFF by default to ensure
that exports and backups will have all data in the table or will
error if there are insufficient privileges to bypass row security.
A new option has been added to pg_dump, --enable-row-security, to
ask pg_dump to export with row security enabled.

A new role capability, BYPASSRLS, which can only be set by the
superuser, is added to allow other users to be able to bypass row
security using row_security = OFF.

Many thanks to the various individuals who have helped with the
design, particularly Robert Haas for his feedback.

Authors include Craig Ringer, KaiGai Kohei, Adam Brightwell, Dean
Rasheed, with additional changes and rework by me.

Reviewers have included all of the above, Greg Smith,
Jeff McCormick, and Robert Haas.

src/include/rewrite/rowsecurity.h

@@ -0,0 +1,80 @@
+/* -------------------------------------------------------------------------
+ *
+ * rowsecurity.h
+ *    prototypes for optimizer/rowsecurity.c
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * -------------------------------------------------------------------------
+ */
+#ifndef ROWSECURITY_H
+#define ROWSECURITY_H
+
+#include "nodes/execnodes.h"
+#include "nodes/parsenodes.h"
+#include "nodes/relation.h"
+#include "utils/array.h"
+
+typedef struct RowSecurityPolicy
+{
+	Oid					rsecid;
+	char			   *policy_name;
+	char				cmd;
+	ArrayType		   *roles;
+	Expr			   *qual;
+	Expr			   *with_check_qual;
+	bool				hassublinks;
+} RowSecurityPolicy;
+
+typedef struct RowSecurityDesc
+{
+	MemoryContext		rscxt;		/* row-security memory context */
+	List			   *policies;	/* list of row-security policies */
+} RowSecurityDesc;
+
+/* GUC variable */
+extern int row_security;
+
+/* Possible values for row_security GUC */
+typedef enum RowSecurityConfigType
+{
+	ROW_SECURITY_OFF,
+	ROW_SECURITY_ON,
+	ROW_SECURITY_FORCE
+} RowSecurityConfigType;
+
+/*
+ * Used by callers of check_enable_rls.
+ *
+ * RLS could be completely disabled on the tables involved in the query,
+ * which is the simple case, or it may depend on the current environment
+ * (the role which is running the query or the value of the row_security
+ * GUC- on, off, or force), or it might be simply enabled as usual.
+ *
+ * If RLS isn't on the table involved then RLS_NONE is returned to indicate
+ * that we don't need to worry about invalidating the query plan for RLS
+ * reasons.  If RLS is on the table, but we are bypassing it for now, then
+ * we return RLS_NONE_ENV to indicate that, if the environment changes,
+ * we need to invalidate and replan.  Finally, if RLS should be turned on
+ * for the query, then we return RLS_ENABLED, which means we also need to
+ * invalidate if the environment changes.
+ */
+enum CheckEnableRlsResult
+{
+	RLS_NONE,
+	RLS_NONE_ENV,
+	RLS_ENABLED
+};
+
+typedef List *(*row_security_policy_hook_type)(CmdType cmdtype,
+											   Relation relation);
+
+extern PGDLLIMPORT row_security_policy_hook_type row_security_policy_hook;
+
+extern bool prepend_row_security_policies(Query* root, RangeTblEntry* rte,
+									   int rt_index);
+
+extern int check_enable_rls(Oid relid, Oid checkAsUser);
+
+#endif	/* ROWSECURITY_H */