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 885bd075798c2cf6dd297164aa30a57621769dc2..5dcff3d07624c3a380c9ceec1aa350c2f040b1be 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 37f31a2c31ead06cf6572ac493c48bdcd7555edf..00cec50e8402c679b9d1eb1e005196af34973bf9 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1994,9 +1994,10 @@ 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 (;;)
    {
@@ -2014,9 +2015,6 @@ 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
@@ -2024,6 +2022,9 @@ 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 46369cf3dbee8a9a6395c5658a52cc02cccab970..3d01a782da0619302d2f8e1f0e716b6305034a71 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))
        RequireTransactionChain(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 f8384062534862971904bd386967ac2f8513f50e..9c04eee48422a26dc3a1c6e814306953f1007bfe 100644 (file)
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -4144,6 +4144,7 @@ afterTriggerMarkEvents(AfterTriggerEventList *events,
                       bool immediate_only)
 {
    bool        found = false;
+   bool        deferred_found = false;
    AfterTriggerEvent event;
    AfterTriggerEventChunk *chunk;
 
@@ -4179,6 +4180,7 @@ 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 */
@@ -4186,6 +4188,16 @@ 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 dacc98450514a9b83f58eae2e476065432993c75..26ee16a0c370e13650f558ddbdd34969016fd0eb 100644 (file)
--- a/src/test/regress/expected/privileges.out
+++ b/src/test/regress/expected/privileges.out
@@ -1253,6 +1253,48 @@ SELECT has_table_privilege('regress_user1', 'atest4', 'SELECT WITH GRANT OPTION'
  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_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_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_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 4263315a2d8721ca6305e0b30ebb422e686e9f98..f979cccea03f973ecc273e3e75a8239c38bb8cf4 100644 (file)
--- a/src/test/regress/sql/privileges.sql
+++ b/src/test/regress/sql/privileges.sql
@@ -761,6 +761,40 @@ SELECT has_table_privilege('regress_user3', 'atest4', 'SELECT'); -- false
 SELECT has_table_privilege('regress_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_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_user4;