Hi!
> - If the user's permissions are later revoked, the subscription is unaffected.
Now it work the same, if we revoke superuser, subscription is unaffected and 
replication still work

Don't check grants in target database is very dangerous, i create publication 
with system tables(it's not difficult)

select * from pg_publication_tables ;
 pubname | schemaname |     tablename
---------+------------+--------------------
 pub     | pg_catalog | pg_authid
(1 row)

After that i create subscription, in log i see that
2019-03-21 11:19:50.863 MSK [58599] LOG:  logical replication table 
synchronization worker for subscription "sub_nosuper", table "pg_authid" has 
started
2019-03-21 11:19:51.039 MSK [58599] ERROR:  null value in column "oid" violates 
not-null constraint
2019-03-21 11:19:51.039 MSK [58599] DETAIL:  Failing row contains (null, 
pg_monitor, f, t, f, f, f, f, f, -1, null, null).
2019-03-21 11:19:51.039 MSK [58599] CONTEXT:  COPY pg_authid, line 1: 
"pg_monitor   f   t   f   f   f   f   f   -1  \N  \N"

I think it's no problem use it to attack target server after some hack on 
publication side.

-------- 
Efimkin Evgeny


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