Re: freeing LDAPMessage in CheckLDAPAuth

Michael Paquier <michael(at)paquier(dot)xyz> writes:
> On Sat, Sep 03, 2022 at 05:00:30PM -0700, Zhihong Yu wrote:
>> Please see the attached patch which frees the search_message in the above case.

> Yep, nice catch, I am reading the same thing as you do. I can see
> that we already do that after a failing ldap_search_st() call in
> fe-connect.c for libpq. Hence, similarly, we'd better call
> ldap_msgfree() on search_message when it is not NULL after a search
> failure, no? The patch you are proposing does not do that.

I can't get too excited about this. All of the error exit paths in
backend authentication code will lead immediately to process exit, so
the possibility of some memory being leaked really has no consequences
worth worrying about. If we *were* worried about it, sprinkling a few
more ldap_msgfree() calls into the existing code would hardly make it
more bulletproof. There's lots of psprintf() and other
Postgres-universe calls in that code that could potentially fail and
force an elog exit without reaching ldap_msgfree. So if you wanted to
make this completely clean you'd need to resort to doing the freeing
in PG_CATCH blocks ... and I don't see any value in hacking it to that
extent.

What might be worth inspecting is the code paths in frontend libpq
that call ldap_msgfree(), because on the client side we don't get to
assume that an error will lead to immediate process exit. If we've
missed any cleanups over there, that *would* be worth fixing.

regards, tom lane