Fix privilege checks in pg_stats_ext and pg_stats_ext_exprs.

The catalog view pg_stats_ext fails to consider privileges for
expression statistics.  The catalog view pg_stats_ext_exprs fails
to consider privileges and row-level security policies.  To fix,
restrict the data in these views to table owners or roles that
inherit privileges of the table owner.  It may be possible to apply
less restrictive privilege checks in some cases, but that is left
as a future exercise.  Furthermore, for pg_stats_ext_exprs, do not
return data for tables with row-level security enabled, as is
already done for pg_stats_ext.

On the back-branches, a fix-CVE-2024-4317.sql script is provided
that will install into the "share" directory.  This file can be
used to apply the fix to existing clusters.

Bumps catversion on 'master' branch only.

Reported-by: Lukas Fittl
Reviewed-by: Noah Misch, Tomas Vondra, Tom Lane
Security: CVE-2024-4317
Backpatch-through: 14

Author: nathan-bossart

doc/src/sgml/catalogs.sgml

@@ -7788,8 +7788,7 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
    is a publicly readable view
    on <structname>pg_statistic_ext_data</structname> (after joining
    with <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>) that only exposes
-   information about those tables and columns that are readable by the
-   current user.
+   information about tables the current user owns.
   </para>
 
   <table>

doc/src/sgml/system-views.sgml

@@ -3944,7 +3944,7 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
    and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
    catalogs.  This view allows access only to rows of
    <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link> and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
-   that correspond to tables the user has permission to read, and therefore
+   that correspond to tables the user owns, and therefore
    it is safe to allow public read access to this view.
   </para>
 
@@ -4155,7 +4155,7 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
    and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
    catalogs.  This view allows access only to rows of
    <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link> and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
-   that correspond to tables the user has permission to read, and therefore
+   that correspond to tables the user owns, and therefore
    it is safe to allow public read access to this view.
   </para>
 

src/backend/catalog/system_views.sql

@@ -305,12 +305,7 @@ CREATE VIEW pg_stats_ext WITH (security_barrier) AS
                             array_agg(base_frequency) AS most_common_base_freqs
                      FROM pg_mcv_list_items(sd.stxdmcv)
                    ) m ON sd.stxdmcv IS NOT NULL
-    WHERE NOT EXISTS
-              ( SELECT 1
-                FROM unnest(stxkeys) k
-                     JOIN pg_attribute a
-                          ON (a.attrelid = s.stxrelid AND a.attnum = k)
-                WHERE NOT has_column_privilege(c.oid, a.attnum, 'select') )
+    WHERE pg_has_role(c.relowner, 'USAGE')
     AND (c.relrowsecurity = false OR NOT row_security_active(c.oid));
 
 CREATE VIEW pg_stats_ext_exprs WITH (security_barrier) AS
@@ -380,7 +375,9 @@ CREATE VIEW pg_stats_ext_exprs WITH (security_barrier) AS
          JOIN LATERAL (
              SELECT unnest(pg_get_statisticsobjdef_expressions(s.oid)) AS expr,
                     unnest(sd.stxdexpr)::pg_statistic AS a
-         ) stat ON (stat.expr IS NOT NULL);
+         ) stat ON (stat.expr IS NOT NULL)
+    WHERE pg_has_role(c.relowner, 'USAGE')
+    AND (c.relrowsecurity = false OR NOT row_security_active(c.oid));
 
 -- unprivileged users may read pg_statistic_ext but not pg_statistic_ext_data
 REVOKE ALL ON pg_statistic_ext_data FROM public;

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202405051
+#define CATALOG_VERSION_NO	202405061
 
 #endif

src/test/regress/expected/rules.out

@@ -2531,10 +2531,7 @@ pg_stats_ext| SELECT cn.nspname AS schemaname,
             array_agg(pg_mcv_list_items.frequency) AS most_common_freqs,
             array_agg(pg_mcv_list_items.base_frequency) AS most_common_base_freqs
            FROM pg_mcv_list_items(sd.stxdmcv) pg_mcv_list_items(index, "values", nulls, frequency, base_frequency)) m ON ((sd.stxdmcv IS NOT NULL)))
-  WHERE ((NOT (EXISTS ( SELECT 1
-           FROM (unnest(s.stxkeys) k(k)
-             JOIN pg_attribute a ON (((a.attrelid = s.stxrelid) AND (a.attnum = k.k))))
-          WHERE (NOT has_column_privilege(c.oid, a.attnum, 'select'::text))))) AND ((c.relrowsecurity = false) OR (NOT row_security_active(c.oid))));
+  WHERE (pg_has_role(c.relowner, 'USAGE'::text) AND ((c.relrowsecurity = false) OR (NOT row_security_active(c.oid))));
 pg_stats_ext_exprs| SELECT cn.nspname AS schemaname,
     c.relname AS tablename,
     sn.nspname AS statistics_schemaname,
@@ -2607,7 +2604,8 @@ pg_stats_ext_exprs| SELECT cn.nspname AS schemaname,
      LEFT JOIN pg_namespace cn ON ((cn.oid = c.relnamespace)))
      LEFT JOIN pg_namespace sn ON ((sn.oid = s.stxnamespace)))
      JOIN LATERAL ( SELECT unnest(pg_get_statisticsobjdef_expressions(s.oid)) AS expr,
-            unnest(sd.stxdexpr) AS a) stat ON ((stat.expr IS NOT NULL)));
+            unnest(sd.stxdexpr) AS a) stat ON ((stat.expr IS NOT NULL)))
+  WHERE (pg_has_role(c.relowner, 'USAGE'::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,

src/test/regress/expected/stats_ext.out

@@ -3281,10 +3281,53 @@ SELECT * FROM tststats.priv_test_tbl WHERE a <<< 0 AND b <<< 0; -- Should not le
 (0 rows)
 
 DELETE FROM tststats.priv_test_tbl WHERE a <<< 0 AND b <<< 0; -- Should not leak
+-- privilege checks for pg_stats_ext and pg_stats_ext_exprs
+RESET SESSION AUTHORIZATION;
+CREATE TABLE stats_ext_tbl (id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY, col TEXT);
+INSERT INTO stats_ext_tbl (col) VALUES ('secret'), ('secret'), ('very secret');
+CREATE STATISTICS s_col ON id, col FROM stats_ext_tbl;
+CREATE STATISTICS s_expr ON mod(id, 2), lower(col) FROM stats_ext_tbl;
+ANALYZE stats_ext_tbl;
+-- unprivileged role should not have access
+SET SESSION AUTHORIZATION regress_stats_user1;
+SELECT statistics_name, most_common_vals FROM pg_stats_ext x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+ statistics_name | most_common_vals 
+-----------------+------------------
+(0 rows)
+
+SELECT statistics_name, most_common_vals FROM pg_stats_ext_exprs x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+ statistics_name | most_common_vals 
+-----------------+------------------
+(0 rows)
+
+-- give unprivileged role ownership of table
+RESET SESSION AUTHORIZATION;
+ALTER TABLE stats_ext_tbl OWNER TO regress_stats_user1;
+-- unprivileged role should now have access
+SET SESSION AUTHORIZATION regress_stats_user1;
+SELECT statistics_name, most_common_vals FROM pg_stats_ext x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+ statistics_name |             most_common_vals              
+-----------------+-------------------------------------------
+ s_col           | {{1,secret},{2,secret},{3,"very secret"}}
+ s_expr          | {{0,secret},{1,secret},{1,"very secret"}}
+(2 rows)
+
+SELECT statistics_name, most_common_vals FROM pg_stats_ext_exprs x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+ statistics_name | most_common_vals 
+-----------------+------------------
+ s_expr          | {secret}
+ s_expr          | {1}
+(2 rows)
+
 -- Tidy up
 DROP OPERATOR <<< (int, int);
 DROP FUNCTION op_leak(int, int);
 RESET SESSION AUTHORIZATION;
+DROP TABLE stats_ext_tbl;
 DROP SCHEMA tststats CASCADE;
 NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to table tststats.priv_test_tbl

src/test/regress/sql/stats_ext.sql

@@ -1657,9 +1657,36 @@ SET SESSION AUTHORIZATION regress_stats_user1;
 SELECT * FROM tststats.priv_test_tbl WHERE a <<< 0 AND b <<< 0; -- Should not leak
 DELETE FROM tststats.priv_test_tbl WHERE a <<< 0 AND b <<< 0; -- Should not leak
 
+-- privilege checks for pg_stats_ext and pg_stats_ext_exprs
+RESET SESSION AUTHORIZATION;
+CREATE TABLE stats_ext_tbl (id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY, col TEXT);
+INSERT INTO stats_ext_tbl (col) VALUES ('secret'), ('secret'), ('very secret');
+CREATE STATISTICS s_col ON id, col FROM stats_ext_tbl;
+CREATE STATISTICS s_expr ON mod(id, 2), lower(col) FROM stats_ext_tbl;
+ANALYZE stats_ext_tbl;
+
+-- unprivileged role should not have access
+SET SESSION AUTHORIZATION regress_stats_user1;
+SELECT statistics_name, most_common_vals FROM pg_stats_ext x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+SELECT statistics_name, most_common_vals FROM pg_stats_ext_exprs x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+
+-- give unprivileged role ownership of table
+RESET SESSION AUTHORIZATION;
+ALTER TABLE stats_ext_tbl OWNER TO regress_stats_user1;
+
+-- unprivileged role should now have access
+SET SESSION AUTHORIZATION regress_stats_user1;
+SELECT statistics_name, most_common_vals FROM pg_stats_ext x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+SELECT statistics_name, most_common_vals FROM pg_stats_ext_exprs x
+    WHERE tablename = 'stats_ext_tbl' ORDER BY ROW(x.*);
+
 -- Tidy up
 DROP OPERATOR <<< (int, int);
 DROP FUNCTION op_leak(int, int);
 RESET SESSION AUTHORIZATION;
+DROP TABLE stats_ext_tbl;
 DROP SCHEMA tststats CASCADE;
 DROP USER regress_stats_user1;