In security-restricted operations, block enqueue of at-commit user code.

Specifically, this blocks DECLARE ... WITH HOLD and firing of deferred
triggers within index expressions and materialized view queries.  An
attacker having permission to create non-temp objects in at least one
schema could execute arbitrary SQL functions under the identity of the
bootstrap superuser.  One can work around the vulnerability by disabling
autovacuum and not manually running ANALYZE, CLUSTER, REINDEX, CREATE
INDEX, VACUUM FULL, or REFRESH MATERIALIZED VIEW.  (Don't restore from
pg_dump, since it runs some of those commands.)  Plain VACUUM (without
FULL) is safe, and all commands are fine when a trusted user owns the
target object.  Performance may degrade quickly under this workaround,
however.  Back-patch to 9.5 (all supported versions).

Reviewed by Robert Haas.  Reported by Etienne Stalmans.

Security: CVE-2020-25695

diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 296830bd81ba1d0b27b2a183bb8c0ddf29331fa5..fed14eb85d146c2ef166035179881bc2458baccd 100644 (file)
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -645,6 +645,10 @@ pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
 
 /*
  * pgfdw_xact_callback --- cleanup at main-transaction end.
+ *
+ * This runs just late enough that it must not enter user-defined code
+ * locally.  (Entering such code on the remote side is fine.  Its remote
+ * COMMIT TRANSACTION may run deferred triggers.)
  */
 static void
 pgfdw_xact_callback(XactEvent event, void *arg)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 3c823f56821cbd130b16f6f6d5c2f32a1f040bdd..7181718d6e26e5a9e7e93a36646a24a0a77b54a2 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1993,9 +1993,10 @@ CommitTransaction(void)
 
        /*
         * Do pre-commit processing that involves calling user-defined code, such
-        * as triggers.  Since closing cursors could queue trigger actions,
-        * triggers could open cursors, etc, we have to keep looping until there's
-        * nothing left to do.
+        * as triggers.  SECURITY_RESTRICTED_OPERATION contexts must not queue an
+        * action that would run here, because that would bypass the sandbox.
+        * Since closing cursors could queue trigger actions, triggers could open
+        * cursors, etc, we have to keep looping until there's nothing left to do.
         */
        for (;;)
        {
@@ -2013,9 +2014,6 @@ CommitTransaction(void)
                        break;
        }
 
-       CallXactCallbacks(is_parallel_worker ? XACT_EVENT_PARALLEL_PRE_COMMIT
-                                         : XACT_EVENT_PRE_COMMIT);
-
        /*
         * The remaining actions cannot call any user-defined code, so it's safe
         * to start shutting down within-transaction services.  But note that most
@@ -2023,6 +2021,9 @@ CommitTransaction(void)
         * the transaction-abort path.
         */
 
+       CallXactCallbacks(is_parallel_worker ? XACT_EVENT_PARALLEL_PRE_COMMIT
+                                         : XACT_EVENT_PRE_COMMIT);
+
        /* If we might have parallel workers, clean them up now. */
        if (IsInParallelMode())
                AtEOXact_Parallel(true);

diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c
index 568499761ffa74e6ddc8ab9bf541510f87565941..e00ca83f0d85f57aaba7517554a5deafd18f1675 100644 (file)
--- a/src/backend/commands/portalcmds.c
+++ b/src/backend/commands/portalcmds.c
@@ -27,6 +27,7 @@
 #include "commands/portalcmds.h"
 #include "executor/executor.h"
 #include "executor/tstoreReceiver.h"
+#include "miscadmin.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/pquery.h"
 #include "tcop/tcopprot.h"
@@ -64,6 +65,10 @@ PerformCursorOpen(DeclareCursorStmt *cstmt, ParamListInfo params,
         */
        if (!(cstmt->options & CURSOR_OPT_HOLD))
                RequireTransactionBlock(isTopLevel, "DECLARE CURSOR");
+       else if (InSecurityRestrictedOperation())
+               ereport(ERROR,
+                               (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+                                errmsg("cannot create a cursor WITH HOLD within security-restricted operation")));
 
        /*
         * Parse analysis was done already, but we still have to run the rule

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 2a1bf8bf462eee5550235c0ec241bbc7d3ae9223..acfb9b261408156ffd5638df1bf679e0a1d577a3 100644 (file)
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -4383,6 +4383,7 @@ afterTriggerMarkEvents(AfterTriggerEventList *events,
                                           bool immediate_only)
 {
        bool            found = false;
+       bool            deferred_found = false;
        AfterTriggerEvent event;
        AfterTriggerEventChunk *chunk;
 
@@ -4418,6 +4419,7 @@ afterTriggerMarkEvents(AfterTriggerEventList *events,
                 */
                if (defer_it && move_list != NULL)
                {
+                       deferred_found = true;
                        /* add it to move_list */
                        afterTriggerAddEvent(move_list, event, evtshared);
                        /* mark original copy "done" so we don't do it again */
@@ -4425,6 +4427,16 @@ afterTriggerMarkEvents(AfterTriggerEventList *events,
                }
        }
 
+       /*
+        * We could allow deferred triggers if, before the end of the
+        * security-restricted operation, we were to verify that a SET CONSTRAINTS
+        * ... IMMEDIATE has fired all such triggers.  For now, don't bother.
+        */
+       if (deferred_found && InSecurityRestrictedOperation())
+               ereport(ERROR,
+                               (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+                                errmsg("cannot fire deferred trigger within security-restricted operation")));
+
        return found;
 }
 

diff --git a/src/test/regress/expected/privileges.out b/src/test/regress/expected/privileges.out
index a8346e1717438d4cf630c0fe07f88f14a12f7e90..a8987c8cd527d1211d539d4a29799764eed90997 100644 (file)
--- a/src/test/regress/expected/privileges.out
+++ b/src/test/regress/expected/privileges.out
@@ -1287,6 +1287,48 @@ SELECT has_table_privilege('regress_priv_user1', 'atest4', 'SELECT WITH GRANT OP
  t
 (1 row)
 
+-- security-restricted operations
+\c -
+CREATE ROLE regress_sro_user;
+SET SESSION AUTHORIZATION regress_sro_user;
+CREATE FUNCTION unwanted_grant() RETURNS void LANGUAGE sql AS
+       'GRANT regress_priv_group2 TO regress_sro_user';
+CREATE FUNCTION mv_action() RETURNS bool LANGUAGE sql AS
+       'DECLARE c CURSOR WITH HOLD FOR SELECT unwanted_grant(); SELECT true';
+-- REFRESH of this MV will queue a GRANT at end of transaction
+CREATE MATERIALIZED VIEW sro_mv AS SELECT mv_action() WITH NO DATA;
+REFRESH MATERIALIZED VIEW sro_mv;
+ERROR:  cannot create a cursor WITH HOLD within security-restricted operation
+CONTEXT:  SQL function "mv_action" statement 1
+\c -
+REFRESH MATERIALIZED VIEW sro_mv;
+ERROR:  cannot create a cursor WITH HOLD within security-restricted operation
+CONTEXT:  SQL function "mv_action" statement 1
+SET SESSION AUTHORIZATION regress_sro_user;
+-- INSERT to this table will queue a GRANT at end of transaction
+CREATE TABLE sro_trojan_table ();
+CREATE FUNCTION sro_trojan() RETURNS trigger LANGUAGE plpgsql AS
+       'BEGIN PERFORM unwanted_grant(); RETURN NULL; END';
+CREATE CONSTRAINT TRIGGER t AFTER INSERT ON sro_trojan_table
+    INITIALLY DEFERRED FOR EACH ROW EXECUTE PROCEDURE sro_trojan();
+-- Now, REFRESH will issue such an INSERT, queueing the GRANT
+CREATE OR REPLACE FUNCTION mv_action() RETURNS bool LANGUAGE sql AS
+       'INSERT INTO sro_trojan_table DEFAULT VALUES; SELECT true';
+REFRESH MATERIALIZED VIEW sro_mv;
+ERROR:  cannot fire deferred trigger within security-restricted operation
+CONTEXT:  SQL function "mv_action" statement 1
+\c -
+REFRESH MATERIALIZED VIEW sro_mv;
+ERROR:  cannot fire deferred trigger within security-restricted operation
+CONTEXT:  SQL function "mv_action" statement 1
+BEGIN; SET CONSTRAINTS ALL IMMEDIATE; REFRESH MATERIALIZED VIEW sro_mv; COMMIT;
+ERROR:  must have admin option on role "regress_priv_group2"
+CONTEXT:  SQL function "unwanted_grant" statement 1
+SQL statement "SELECT unwanted_grant()"
+PL/pgSQL function sro_trojan() line 1 at PERFORM
+SQL function "mv_action" statement 1
+DROP OWNED BY regress_sro_user;
+DROP ROLE regress_sro_user;
 -- Admin options
 SET SESSION AUTHORIZATION regress_priv_user4;
 CREATE FUNCTION dogrant_ok() RETURNS void LANGUAGE sql SECURITY DEFINER AS

diff --git a/src/test/regress/sql/privileges.sql b/src/test/regress/sql/privileges.sql
index c1e42d1be2fe6a7fd0d26389c8b1f50ab058f243..754daa5c0edd20dbac4fe55007f85d576ec9b040 100644 (file)
--- a/src/test/regress/sql/privileges.sql
+++ b/src/test/regress/sql/privileges.sql
@@ -778,6 +778,40 @@ SELECT has_table_privilege('regress_priv_user3', 'atest4', 'SELECT'); -- false
 SELECT has_table_privilege('regress_priv_user1', 'atest4', 'SELECT WITH GRANT OPTION'); -- true
 
 
+-- security-restricted operations
+\c -
+CREATE ROLE regress_sro_user;
+
+SET SESSION AUTHORIZATION regress_sro_user;
+CREATE FUNCTION unwanted_grant() RETURNS void LANGUAGE sql AS
+       'GRANT regress_priv_group2 TO regress_sro_user';
+CREATE FUNCTION mv_action() RETURNS bool LANGUAGE sql AS
+       'DECLARE c CURSOR WITH HOLD FOR SELECT unwanted_grant(); SELECT true';
+-- REFRESH of this MV will queue a GRANT at end of transaction
+CREATE MATERIALIZED VIEW sro_mv AS SELECT mv_action() WITH NO DATA;
+REFRESH MATERIALIZED VIEW sro_mv;
+\c -
+REFRESH MATERIALIZED VIEW sro_mv;
+
+SET SESSION AUTHORIZATION regress_sro_user;
+-- INSERT to this table will queue a GRANT at end of transaction
+CREATE TABLE sro_trojan_table ();
+CREATE FUNCTION sro_trojan() RETURNS trigger LANGUAGE plpgsql AS
+       'BEGIN PERFORM unwanted_grant(); RETURN NULL; END';
+CREATE CONSTRAINT TRIGGER t AFTER INSERT ON sro_trojan_table
+    INITIALLY DEFERRED FOR EACH ROW EXECUTE PROCEDURE sro_trojan();
+-- Now, REFRESH will issue such an INSERT, queueing the GRANT
+CREATE OR REPLACE FUNCTION mv_action() RETURNS bool LANGUAGE sql AS
+       'INSERT INTO sro_trojan_table DEFAULT VALUES; SELECT true';
+REFRESH MATERIALIZED VIEW sro_mv;
+\c -
+REFRESH MATERIALIZED VIEW sro_mv;
+BEGIN; SET CONSTRAINTS ALL IMMEDIATE; REFRESH MATERIALIZED VIEW sro_mv; COMMIT;
+
+DROP OWNED BY regress_sro_user;
+DROP ROLE regress_sro_user;
+
+
 -- Admin options
 
 SET SESSION AUTHORIZATION regress_priv_user4;