Re: BUG #15367: Crash in pg_fe_scram_free when using foreign tables

I wrote:
> I tried setting up a scram-auth-based postgres_fdw connection on
> my RHEL6 box and forcing it through the questionable code path
> by issuing a dummy ALTER USER MAPPING command from another session.
> It worked fine, so the problem doesn't seem to be present on Linux.

Oh, I meant to show the test I used, for the benefit of anyone who
wants to test on other platforms. Do this (with adjustments to
taste) to set up:

set password_encryption = "scram-sha-256" ;
create user u1 password 'foobar';
create extension postgres_fdw;
create server loopback foreign data wrapper postgres_fdw
options (host 'localhost', dbname 'postgres');
create user mapping for u1 server loopback
options (user 'u1', password 'foobar');
grant usage on foreign server loopback to u1;
\c - u1
create table remote (f1 int);
insert into remote values(1),(2);
create foreign table localt (f1 int) server loopback
options (table_name 'remote');

At this point you should be able to do

select * from localt;

as u1; if not, adjust pg_hba.conf to require a password on localhost
connections. Once the select works, *leave that session open*, and
in another session do any no-op ALTER on the user mapping, such as

alter user mapping for u1 server loopback options (set user 'u1');

Now, in the first session, repeat

select * from localt;

It'll dump core with a backtrace similar to what Jeremy showed,
if the bug is present.

regards, tom lane