Re: BUG #19547: libpqrcv_create_slot dereferences NULL on a malformed CREATE_REPLICATION_SLOT reply

Hi Hayato,

Thanks for looking at this.

> Hmm, but IDENTIFY_SYSTEM requires that number returned attributes should be 3 or
> 4, nevertheless first and second columns are checked. If we follow, isn't it
> better to require that there are 4 attributes? I checked old versions and the
> command has returned 4 attributes from the beginning [1].

Agreed. IDENTIFY_SYSTEM tolerates 3 columns only because older servers (9.3
and earlier) actually returned 3, whereas CREATE_REPLICATION_SLOT has always
returned 4, so there is no reason to be lenient here. v2 attached requires 4
fields, and updates the comment and errdetail accordingly.

Best regards,
Kenny Chen

Hayato Kuroda (Fujitsu) <kuroda(dot)hayato(at)fujitsu(dot)com> 於 2026年7月15日週三 下午12:33寫道：
>
> Hi Kenny,
>
> > The patch validates the result shape (>= 3 fields, exactly 1 row) before
> > reading those fields and raises a protocol-violation error otherwise,
> > mirroring what libpqrcv_identify_system() and the other result-consuming
> > paths in this file already do. I used "< 3" rather than "< 4" because the
> > function only reads fields 1 and 2.
>
> Hmm, but IDENTIFY_SYSTEM requires that number returned attributes should be 3 or
> 4, nevertheless first and second columns are checked. If we follow, isn't it
> better to require that there are 4 attributes? I checked old versions and the
> command has returned 4 attributes from the beginning [1].
>
> [1]: https://github.com/postgres/postgres/blob/b1b8b8e6f141e378db21c609d8ee74d9125a4aca/src/backend/replication/walsender.c#L853
>
> Best regards,
> Hayato Kuroda
> FUJITSU LIMITED
>