Re: MarkGUCPrefixReserved() doesn't check all options

On 06/07/2023 12:17, Karina Litskevich wrote:
> Hi hackers,
> 
> Ekaterina Sokolova and I have found a bug in PG 15. Since 88103567cb 
> MarkGUCPrefixReserved() is supposed not only reporting GUCs that
> haven't been defined by the extension, but also removing them.
> However, it removes them in a wrong way, so that a GUC that goes
> after the removed GUC is never checked.
> 
> To reproduce the bug add the following to the postgresql.conf
> 
> shared_preload_libraries = 'pg_stat_statements'
> pg_stat_statements.nonexisting_option_1 = on
> pg_stat_statements.nonexisting_option_2 = on
> pg_stat_statements.nonexisting_option_3 = on
> pg_stat_statements.nonexisting_option_4 = on
> 
> and start the server. In the logfile you'll see only first and third
> options reported invalid and removed.

Good catch!

> In master MarkGUCPrefixReserved() iterates a hash table, not an array
> as in PG 15. I'm not sure whether it is safe to remove an entry from
> this hash table while iterating it, but at least I can't reproduce
> the bug on master.
Yes, it's safe to remove the current element, while scanning a hash 
table with hash_seq_init/search. See comment on hash_seq_init.

> I attached a bugfix for PG 15.

Applied, thanks!

-- 
Heikki Linnakangas
Neon (https://neon.tech)