Plug RLS related information leak in pg_stats view.

The pg_stats view is supposed to be restricted to only show rows
about tables the user can read. However, it sometimes can leak
information which could not otherwise be seen when row level security
is enabled. Fix that by not showing pg_stats rows to users that would
be subject to RLS on the table the row is related to. This is done
by creating/using the newly introduced SQL visible function,
row_security_active().

Along the way, clean up three call sites of check_enable_rls(). The second
argument of that function should only be specified as other than
InvalidOid when we are checking as a different user than the current one,
as in when querying through a view. These sites were passing GetUserId()
instead of InvalidOid, which can cause the function to return incorrect
results if the current user has the BYPASSRLS privilege and row_security
has been set to OFF.

Additionally fix a bug causing RI Trigger error messages to unintentionally
leak information when RLS is enabled, and other minor cleanup and
improvements. Also add WITH (security_barrier) to the definition of pg_stats.

Bumped CATVERSION due to new SQL functions and pg_stats view definition.

Back-patch to 9.5 where RLS was introduced. Reported by Yaroslav.
Patch by Joe Conway and Dean Rasheed with review and input by
Michael Paquier and Stephen Frost.

Author: jconway

doc/src/sgml/func.sgml

@@ -15259,6 +15259,12 @@ SET search_path TO <replaceable>schema</> <optional>, <replaceable>schema</>, ..
        <entry><type>boolean</type></entry>
        <entry>does current user have privilege for role</entry>
       </row>
+      <row>
+       <entry><literal><function>row_security_active</function>(<parameter>table</parameter>)</literal>
+       </entry>
+       <entry><type>boolean</type></entry>
+       <entry>does current user have row level security active for table</entry>
+      </row>
      </tbody>
     </tgroup>
    </table>
@@ -15299,6 +15305,9 @@ SET search_path TO <replaceable>schema</> <optional>, <replaceable>schema</>, ..
    <indexterm>
     <primary>pg_has_role</primary>
    </indexterm>
+   <indexterm>
+    <primary>row_security_active</primary>
+   </indexterm>
 
    <para>
     <function>has_table_privilege</function> checks whether a user
@@ -15462,6 +15471,13 @@ SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');
     are immediately available without doing <command>SET ROLE</>.
    </para>
 
+   <para>
+    <function>row_security_active</function> checks whether row level
+    security is active for the specified table in the context of the
+    <function>current_user</function> and environment. The table can
+    be specified by name or by OID.
+   </para>
+
   <para>
    <xref linkend="functions-info-schema-table"> shows functions that
    determine whether a certain object is <firstterm>visible</> in the

src/backend/access/index/genam.c

@@ -204,7 +204,7 @@ BuildIndexValueDescription(Relation indexRelation,
 	Assert(indexrelid == idxrec->indexrelid);
 
 	/* RLS check- if RLS is enabled then we don't return anything. */
-	if (check_enable_rls(indrelid, GetUserId(), true) == RLS_ENABLED)
+	if (check_enable_rls(indrelid, InvalidOid, true) == RLS_ENABLED)
 	{
 		ReleaseSysCache(ht_idx);
 		return NULL;

src/backend/catalog/system_views.sql

@@ -150,7 +150,7 @@ CREATE VIEW pg_indexes AS
          LEFT JOIN pg_tablespace T ON (T.oid = I.reltablespace)
     WHERE C.relkind IN ('r', 'm') AND I.relkind = 'i';
 
-CREATE VIEW pg_stats AS
+CREATE VIEW pg_stats WITH (security_barrier) AS
     SELECT
         nspname AS schemaname,
         relname AS tablename,
@@ -211,7 +211,9 @@ CREATE VIEW pg_stats AS
     FROM pg_statistic s JOIN pg_class c ON (c.oid = s.starelid)
          JOIN pg_attribute a ON (c.oid = attrelid AND attnum = s.staattnum)
          LEFT JOIN pg_namespace n ON (n.oid = c.relnamespace)
-    WHERE NOT attisdropped AND has_column_privilege(c.oid, a.attnum, 'select');
+    WHERE NOT attisdropped
+    AND has_column_privilege(c.oid, a.attnum, 'select')
+    AND (c.relrowsecurity = false OR NOT row_security_active(c.oid));
 
 REVOKE ALL on pg_statistic FROM public;
 

src/backend/executor/execMain.c

@@ -1874,7 +1874,7 @@ ExecBuildSlotValueDescription(Oid reloid,
 	 * then don't return anything.  Otherwise, go through normal permission
 	 * checks.
 	 */
-	if (check_enable_rls(reloid, GetUserId(), true) == RLS_ENABLED)
+	if (check_enable_rls(reloid, InvalidOid, true) == RLS_ENABLED)
 		return NULL;
 
 	initStringInfo(&buf);

src/backend/rewrite/rowsecurity.c

@@ -107,7 +107,6 @@ get_row_security_policies(Query *root, CmdType commandType, RangeTblEntry *rte,
 
 	Relation	rel;
 	Oid			user_id;
-	int			sec_context;
 	int			rls_status;
 	bool		defaultDeny = false;
 
@@ -117,22 +116,13 @@ get_row_security_policies(Query *root, CmdType commandType, RangeTblEntry *rte,
 	*hasRowSecurity = false;
 	*hasSubLinks = false;
 
-	/* This is just to get the security context */
-	GetUserIdAndSecContext(&user_id, &sec_context);
+	/* If this is not a normal relation, just return immediately */
+	if (rte->relkind != RELKIND_RELATION)
+		return;
 
 	/* Switch to checkAsUser if it's set */
 	user_id = rte->checkAsUser ? rte->checkAsUser : GetUserId();
 
-	/*
-	 * If this is not a normal relation, or we have been told to explicitly
-	 * skip RLS (perhaps because this is an FK check) then just return
-	 * immediately.
-	 */
-	if (rte->relid < FirstNormalObjectId
-		|| rte->relkind != RELKIND_RELATION
-		|| (sec_context & SECURITY_ROW_LEVEL_DISABLED))
-		return;
-
 	/* Determine the state of RLS for this, pass checkAsUser explicitly */
 	rls_status = check_enable_rls(rte->relid, rte->checkAsUser, false);
 

src/backend/utils/adt/ri_triggers.c

@@ -3243,7 +3243,7 @@ ri_ReportViolation(const RI_ConstraintInfo *riinfo,
 	 * privileges.
 	 */
 
-	if (check_enable_rls(rel_oid, GetUserId(), true) != RLS_ENABLED)
+	if (check_enable_rls(rel_oid, InvalidOid, true) != RLS_ENABLED)
 	{
 		aclresult = pg_class_aclcheck(rel_oid, GetUserId(), ACL_SELECT);
 		if (aclresult != ACLCHECK_OK)
@@ -3264,6 +3264,8 @@ ri_ReportViolation(const RI_ConstraintInfo *riinfo,
 			}
 		}
 	}
+	else
+		has_perm = false;
 
 	if (has_perm)
 	{

src/backend/utils/cache/plancache.c

@@ -153,8 +153,6 @@ CreateCachedPlan(Node *raw_parse_tree,
 	CachedPlanSource *plansource;
 	MemoryContext source_context;
 	MemoryContext oldcxt;
-	Oid			user_id;
-	int			security_context;
 
 	Assert(query_string != NULL);		/* required as of 8.4 */
 
@@ -177,8 +175,6 @@ CreateCachedPlan(Node *raw_parse_tree,
 	 */
 	oldcxt = MemoryContextSwitchTo(source_context);
 
-	GetUserIdAndSecContext(&user_id, &security_context);
-
 	plansource = (CachedPlanSource *) palloc0(sizeof(CachedPlanSource));
 	plansource->magic = CACHEDPLANSOURCE_MAGIC;
 	plansource->raw_parse_tree = copyObject(raw_parse_tree);
@@ -208,8 +204,7 @@ CreateCachedPlan(Node *raw_parse_tree,
 	plansource->total_custom_cost = 0;
 	plansource->num_custom_plans = 0;
 	plansource->hasRowSecurity = false;
-	plansource->rowSecurityDisabled
-		= (security_context & SECURITY_ROW_LEVEL_DISABLED) != 0;
+	plansource->rowSecurityDisabled = InRowLevelSecurityDisabled();
 	plansource->row_security_env = row_security;
 	plansource->planUserId = InvalidOid;
 

src/backend/utils/init/miscinit.c

@@ -341,7 +341,7 @@ GetAuthenticatedUserId(void)
  * GetUserIdAndSecContext/SetUserIdAndSecContext - get/set the current user ID
  * and the SecurityRestrictionContext flags.
  *
- * Currently there are two valid bits in SecurityRestrictionContext:
+ * Currently there are three valid bits in SecurityRestrictionContext:
  *
  * SECURITY_LOCAL_USERID_CHANGE indicates that we are inside an operation
  * that is temporarily changing CurrentUserId via these functions.  This is
@@ -359,6 +359,9 @@ GetAuthenticatedUserId(void)
  * where the called functions are really supposed to be side-effect-free
  * anyway, such as VACUUM/ANALYZE/REINDEX.
  *
+ * SECURITY_ROW_LEVEL_DISABLED indicates that we are inside an operation that
+ * needs to bypass row level security checks, for example FK checks.
+ *
  * Unlike GetUserId, GetUserIdAndSecContext does *not* Assert that the current
  * value of CurrentUserId is valid; nor does SetUserIdAndSecContext require
  * the new value to be valid.  In fact, these routines had better not
@@ -401,6 +404,15 @@ InSecurityRestrictedOperation(void)
 	return (SecurityRestrictionContext & SECURITY_RESTRICTED_OPERATION) != 0;
 }
 
+/*
+ * InRowLevelSecurityDisabled - are we inside a RLS-disabled operation?
+ */
+bool
+InRowLevelSecurityDisabled(void)
+{
+	return (SecurityRestrictionContext & SECURITY_ROW_LEVEL_DISABLED) != 0;
+}
+
 
 /*
  * These are obsolete versions of Get/SetUserIdAndSecContext that are

src/backend/utils/misc/rls.c

@@ -16,9 +16,12 @@
 
 #include "access/htup.h"
 #include "access/htup_details.h"
+#include "access/transam.h"
 #include "catalog/pg_class.h"
+#include "catalog/namespace.h"
 #include "miscadmin.h"
 #include "utils/acl.h"
+#include "utils/builtins.h"
 #include "utils/elog.h"
 #include "utils/rls.h"
 #include "utils/syscache.h"
@@ -37,7 +40,10 @@ extern int	check_enable_rls(Oid relid, Oid checkAsUser, bool noError);
  * for the table and the plan cache needs to be invalidated if the environment
  * changes.
  *
- * Handle checking as another role via checkAsUser (for views, etc).
+ * Handle checking as another role via checkAsUser (for views, etc). Note that
+ * if *not* checking as another role, the caller should pass InvalidOid rather
+ * than GetUserId(). Otherwise the check for row_security = OFF is skipped, and
+ * so we may falsely report that RLS is active when the user has bypassed it.
  *
  * If noError is set to 'true' then we just return RLS_ENABLED instead of doing
  * an ereport() if the user has attempted to bypass RLS and they are not
@@ -53,6 +59,17 @@ check_enable_rls(Oid relid, Oid checkAsUser, bool noError)
 	bool		relrowsecurity;
 	Oid			user_id = checkAsUser ? checkAsUser : GetUserId();
 
+	/* Nothing to do for built-in relations */
+	if (relid < FirstNormalObjectId)
+		return RLS_NONE;
+
+	/*
+	 * Check if we have been told to explicitly skip RLS (perhaps because this
+	 * is a foreign key check)
+	 */
+	if (InRowLevelSecurityDisabled())
+		return RLS_NONE;
+
 	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
 	if (!HeapTupleIsValid(tuple))
 		return RLS_NONE;
@@ -111,3 +128,37 @@ check_enable_rls(Oid relid, Oid checkAsUser, bool noError)
 	/* RLS should be fully enabled for this relation. */
 	return RLS_ENABLED;
 }
+
+/*
+ * row_security_active
+ *
+ * check_enable_rls wrapped as a SQL callable function except
+ * RLS_NONE_ENV and RLS_NONE are the same for this purpose.
+ */
+Datum
+row_security_active(PG_FUNCTION_ARGS)
+{
+	/* By OID */
+	Oid			tableoid = PG_GETARG_OID(0);
+	int			rls_status;
+
+	rls_status = check_enable_rls(tableoid, InvalidOid, true);
+	PG_RETURN_BOOL(rls_status == RLS_ENABLED);
+}
+
+Datum
+row_security_active_name(PG_FUNCTION_ARGS)
+{
+	/* By qualified name */
+	text	   *tablename = PG_GETARG_TEXT_P(0);
+	RangeVar   *tablerel;
+	Oid			tableoid;
+	int			rls_status;
+
+	/* Look up table name.  Can't lock it - we might not have privileges. */
+	tablerel = makeRangeVarFromNameList(textToQualifiedNameList(tablename));
+	tableoid = RangeVarGetRelid(tablerel, NoLock, false);
+
+	rls_status = check_enable_rls(tableoid, InvalidOid, true);
+	PG_RETURN_BOOL(rls_status == RLS_ENABLED);
+}

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201507252
+#define CATALOG_VERSION_NO	201507281
 
 #endif

src/include/catalog/pg_proc.h

@@ -5343,6 +5343,12 @@ DESCR("get progress for all replication origins");
 #define PROVOLATILE_STABLE		's'		/* does not change within a scan */
 #define PROVOLATILE_VOLATILE	'v'		/* can change even within a scan */
 
+/* rls */
+DATA(insert OID = 3298 (  row_security_active	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 16 "26" _null_ _null_ _null_ _null_ _null_	row_security_active _null_ _null_ _null_ ));
+DESCR("row security for current context active on table by table oid");
+DATA(insert OID = 3299 (  row_security_active	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 16 "25" _null_ _null_ _null_ _null_ _null_	row_security_active_name _null_ _null_ _null_ ));
+DESCR("row security for current context active on table by table name");
+
 /*
  * Symbolic values for proargmodes column.  Note that these must agree with
  * the FunctionParameterMode enum in parsenodes.h; we declare them here to

src/include/miscadmin.h

@@ -305,6 +305,7 @@ extern void GetUserIdAndSecContext(Oid *userid, int *sec_context);
 extern void SetUserIdAndSecContext(Oid userid, int sec_context);
 extern bool InLocalUserIdChange(void);
 extern bool InSecurityRestrictedOperation(void);
+extern bool InRowLevelSecurityDisabled(void);
 extern void GetUserIdAndContext(Oid *userid, bool *sec_def_context);
 extern void SetUserIdAndContext(Oid userid, bool sec_def_context);
 extern void InitializeSessionUserId(const char *rolename, Oid useroid);

src/include/utils/builtins.h

@@ -1121,6 +1121,10 @@ extern Datum set_config_by_name(PG_FUNCTION_ARGS);
 extern Datum show_all_settings(PG_FUNCTION_ARGS);
 extern Datum show_all_file_settings(PG_FUNCTION_ARGS);
 
+/* rls.c */
+extern Datum row_security_active(PG_FUNCTION_ARGS);
+extern Datum row_security_active_name(PG_FUNCTION_ARGS);
+
 /* lockfuncs.c */
 extern Datum pg_lock_status(PG_FUNCTION_ARGS);
 extern Datum pg_advisory_lock_int8(PG_FUNCTION_ARGS);

src/test/regress/expected/rowsecurity.out

@@ -307,7 +307,7 @@ SELECT * FROM document d FULL OUTER JOIN category c on d.cid = c.cid;
 
 DELETE FROM category WHERE cid = 33;    -- fails with FK violation
 ERROR:  update or delete on table "category" violates foreign key constraint "document_cid_fkey" on table "document"
-DETAIL:  Key (cid)=(33) is still referenced from table "document".
+DETAIL:  Key is still referenced from table "document".
 -- can insert FK referencing invisible PK
 SET SESSION AUTHORIZATION rls_regress_user2;
 SELECT * FROM document d FULL OUTER JOIN category c on d.cid = c.cid;
@@ -2886,11 +2886,45 @@ SELECT * FROM current_check;
 (1 row)
 
 COMMIT;
+--
+-- check pg_stats view filtering
+--
+SET row_security TO ON;
+SET SESSION AUTHORIZATION rls_regress_user0;
+ANALYZE current_check;
+-- Stats visible
+SELECT row_security_active('current_check');
+ row_security_active 
+---------------------
+ f
+(1 row)
+
+SELECT most_common_vals FROM pg_stats where tablename = 'current_check';
+  most_common_vals   
+---------------------
+ 
+ 
+ {rls_regress_user1}
+(3 rows)
+
+SET SESSION AUTHORIZATION rls_regress_user1;
+-- Stats not visible
+SELECT row_security_active('current_check');
+ row_security_active 
+---------------------
+ t
+(1 row)
+
+SELECT most_common_vals FROM pg_stats where tablename = 'current_check';
+ most_common_vals 
+------------------
+(0 rows)
+
 --
 -- Collation support
 --
 BEGIN;
-SET row_security = force;
+SET row_security TO FORCE;
 CREATE TABLE coll_t (c) AS VALUES ('bar'::text);
 CREATE POLICY coll_p ON coll_t USING (c < ('foo'::text COLLATE "C"));
 ALTER TABLE coll_t ENABLE ROW LEVEL SECURITY;

src/test/regress/expected/rules.out

@@ -2061,7 +2061,7 @@ pg_stats| SELECT n.nspname AS schemaname,
      JOIN pg_class c ON ((c.oid = s.starelid)))
      JOIN pg_attribute a ON (((c.oid = a.attrelid) AND (a.attnum = s.staattnum))))
      LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace)))
-  WHERE ((NOT a.attisdropped) AND has_column_privilege(c.oid, a.attnum, 'select'::text));
+  WHERE ((NOT a.attisdropped) AND has_column_privilege(c.oid, a.attnum, 'select'::text) AND ((c.relrowsecurity = false) OR (NOT row_security_active(c.oid))));
 pg_tables| SELECT n.nspname AS schemaname,
     c.relname AS tablename,
     pg_get_userbyid(c.relowner) AS tableowner,