Match pg_user_mappings limits to information_schema.user_mapping_options.

Both views replace the umoptions field with NULL when the user does not
meet qualifications to see it.  They used different qualifications, and
pg_user_mappings documented qualifications did not match its implemented
qualifications.  Make its documentation and implementation match those
of user_mapping_options.  One might argue for stronger qualifications,
but these have long, documented tenure.  pg_user_mappings has always
exhibited this problem, so back-patch to 9.2 (all supported versions).

Michael Paquier and Feike Steenbergen.  Reviewed by Jeff Janes.
Reported by Andrew Wheelwright.

Security: CVE-2017-7486

Author: nmisch

doc/src/sgml/catalogs.sgml

@@ -8769,8 +8769,11 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
       <entry></entry>
       <entry>
        User mapping specific options, as <quote>keyword=value</>
-       strings, if the current user is the owner of the foreign
-       server, else null
+       strings.  This column will show as null unless the current user
+       is the user being mapped, or the mapping is for
+       <literal>PUBLIC</literal> and the current user is the server
+       owner, or the current user is a superuser.  The intent is
+       to protect password information stored as user mapping option.
       </entry>
      </row>
     </tbody>

src/backend/catalog/system_views.sql

@@ -669,11 +669,11 @@ CREATE VIEW pg_user_mappings AS
         ELSE
             A.rolname
         END AS usename,
-        CASE WHEN pg_has_role(S.srvowner, 'USAGE') OR has_server_privilege(S.oid, 'USAGE') THEN
-            U.umoptions
-        ELSE
-            NULL
-        END AS umoptions
+        CASE WHEN (U.umuser <> 0 AND A.rolname = current_user)
+                    OR (U.umuser = 0 AND pg_has_role(S.srvowner, 'USAGE'))
+                    OR (SELECT rolsuper FROM pg_authid WHERE rolname = current_user)
+                    THEN U.umoptions
+                 ELSE NULL END AS umoptions
     FROM pg_user_mapping U
          LEFT JOIN pg_authid A ON (A.oid = U.umuser) JOIN
         pg_foreign_server S ON (U.umserver = S.oid);

src/test/regress/expected/foreign_data.out

@@ -1159,7 +1159,61 @@ WARNING:  no privileges were granted for "s9"
 CREATE USER MAPPING FOR current_user SERVER s9;
 DROP SERVER s9 CASCADE;                                         -- ERROR
 ERROR:  must be owner of foreign server s9
+-- Check visibility of user mapping data
+SET ROLE regress_test_role;
+CREATE SERVER s10 FOREIGN DATA WRAPPER foo;
+CREATE USER MAPPING FOR public SERVER s10 OPTIONS (user 'secret');
+GRANT USAGE ON FOREIGN SERVER s10 TO unprivileged_role;
+-- owner of server can see option fields
+\deu+
+             List of user mappings
+ Server |     User name     |    FDW Options    
+--------+-------------------+-------------------
+ s10    | public            | ("user" 'secret')
+ s4     | foreign_data_user | 
+ s5     | regress_test_role | (modified '1')
+ s6     | regress_test_role | 
+ s8     | foreign_data_user | 
+ s8     | public            | 
+ s9     | unprivileged_role | 
+ t1     | public            | (modified '1')
+(8 rows)
+
+RESET ROLE;
+-- superuser can see option fields
+\deu+
+              List of user mappings
+ Server |     User name     |     FDW Options     
+--------+-------------------+---------------------
+ s10    | public            | ("user" 'secret')
+ s4     | foreign_data_user | 
+ s5     | regress_test_role | (modified '1')
+ s6     | regress_test_role | 
+ s8     | foreign_data_user | (password 'public')
+ s8     | public            | 
+ s9     | unprivileged_role | 
+ t1     | public            | (modified '1')
+(8 rows)
+
+-- unprivileged user cannot see option fields
+SET ROLE unprivileged_role;
+\deu+
+          List of user mappings
+ Server |     User name     | FDW Options 
+--------+-------------------+-------------
+ s10    | public            | 
+ s4     | foreign_data_user | 
+ s5     | regress_test_role | 
+ s6     | regress_test_role | 
+ s8     | foreign_data_user | 
+ s8     | public            | 
+ s9     | unprivileged_role | 
+ t1     | public            | 
+(8 rows)
+
 RESET ROLE;
+DROP SERVER s10 CASCADE;
+NOTICE:  drop cascades to user mapping for public on server s10
 -- DROP FOREIGN TABLE
 DROP FOREIGN TABLE no_table;                                    -- ERROR
 ERROR:  foreign table "no_table" does not exist

src/test/regress/expected/rules.out

@@ -1322,7 +1322,7 @@ SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schem
  pg_timezone_abbrevs             | SELECT pg_timezone_abbrevs.abbrev, pg_timezone_abbrevs.utc_offset, pg_timezone_abbrevs.is_dst FROM pg_timezone_abbrevs() pg_timezone_abbrevs(abbrev, utc_offset, is_dst);
  pg_timezone_names               | SELECT pg_timezone_names.name, pg_timezone_names.abbrev, pg_timezone_names.utc_offset, pg_timezone_names.is_dst FROM pg_timezone_names() pg_timezone_names(name, abbrev, utc_offset, is_dst);
  pg_user                         | SELECT pg_shadow.usename, pg_shadow.usesysid, pg_shadow.usecreatedb, pg_shadow.usesuper, pg_shadow.usecatupd, pg_shadow.userepl, '********'::text AS passwd, pg_shadow.valuntil, pg_shadow.useconfig FROM pg_shadow;
- pg_user_mappings                | SELECT u.oid AS umid, s.oid AS srvid, s.srvname, u.umuser, CASE WHEN (u.umuser = (0)::oid) THEN 'public'::name ELSE a.rolname END AS usename, CASE WHEN (pg_has_role(s.srvowner, 'USAGE'::text) OR has_server_privilege(s.oid, 'USAGE'::text)) THEN u.umoptions ELSE NULL::text[] END AS umoptions FROM ((pg_user_mapping u LEFT JOIN pg_authid a ON ((a.oid = u.umuser))) JOIN pg_foreign_server s ON ((u.umserver = s.oid)));
+ pg_user_mappings                | SELECT u.oid AS umid, s.oid AS srvid, s.srvname, u.umuser, CASE WHEN (u.umuser = (0)::oid) THEN 'public'::name ELSE a.rolname END AS usename, CASE WHEN ((((u.umuser <> (0)::oid) AND (a.rolname = "current_user"())) OR ((u.umuser = (0)::oid) AND pg_has_role(s.srvowner, 'USAGE'::text))) OR (SELECT pg_authid.rolsuper FROM pg_authid WHERE (pg_authid.rolname = "current_user"()))) THEN u.umoptions ELSE NULL::text[] END AS umoptions FROM ((pg_user_mapping u LEFT JOIN pg_authid a ON ((a.oid = u.umuser))) JOIN pg_foreign_server s ON ((u.umserver = s.oid)));
  pg_views                        | SELECT n.nspname AS schemaname, c.relname AS viewname, pg_get_userbyid(c.relowner) AS viewowner, pg_get_viewdef(c.oid) AS definition FROM (pg_class c LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'v'::"char");
  rtest_v1                        | SELECT rtest_t1.a, rtest_t1.b FROM rtest_t1;
  rtest_vcomp                     | SELECT x.part, (x.size * y.factor) AS size_in_cm FROM rtest_comp x, rtest_unitfact y WHERE (x.unit = y.unit);

src/test/regress/sql/foreign_data.sql

@@ -469,7 +469,22 @@ ALTER SERVER s9 VERSION '1.2';                                  -- ERROR
 GRANT USAGE ON FOREIGN SERVER s9 TO regress_test_role;          -- WARNING
 CREATE USER MAPPING FOR current_user SERVER s9;
 DROP SERVER s9 CASCADE;                                         -- ERROR
+
+-- Check visibility of user mapping data
+SET ROLE regress_test_role;
+CREATE SERVER s10 FOREIGN DATA WRAPPER foo;
+CREATE USER MAPPING FOR public SERVER s10 OPTIONS (user 'secret');
+GRANT USAGE ON FOREIGN SERVER s10 TO unprivileged_role;
+-- owner of server can see option fields
+\deu+
+RESET ROLE;
+-- superuser can see option fields
+\deu+
+-- unprivileged user cannot see option fields
+SET ROLE unprivileged_role;
+\deu+
 RESET ROLE;
+DROP SERVER s10 CASCADE;
 
 -- DROP FOREIGN TABLE
 DROP FOREIGN TABLE no_table;                                    -- ERROR