public inbox for [email protected]  

help / color / mirror / Atom feed

From: Jacob Champion <[email protected]>
To: Daniel Schreiber <[email protected]>
Cc: [email protected]
Subject: Re: PostgreSQL 17: Bug in libpq when libpq is dlopened/closed multiple times
Date: Fri, 17 Apr 2026 12:14:49 -0700
Message-ID: <CAOYmi+=e9bQQa1jgLqZ18m5w-7KA44VeL9FON6i2gd8bi=d5Jw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Fri, Apr 17, 2026 at 7:33 AM Daniel Schreiber
<[email protected]> wrote:
> my colleagues and I probably found a bug in libpq when libpq is dlopened
> and closed multiple times during the lifetime of a process. In our setup
> we use a PAM module which links to libpq. The process using PAM is
> linked against openssl, so openssl is loaded during the complete
> lifetime of the process whereas libpq is loaded only during PAM
> authentication (and unloaded when PAM has finished).
>
> [snip]
>
> According to our findings every time a connection is established after
> dlopening libpq one of the 127 available BIO_METHOD structures in
> OpenSSL is consumed:
> https://github.com/postgres/postgres/blob/REL_17_9/src/interfaces/libpq/fe-secure-openssl.c#L1987

Right. I think in this *particular* case, we should simply skip the
call to BIO_get_new_index(). We don't need it, IIUC.

But I think we may also need to set expectations on whether or not
infinite dlopen/dlclose loops are supported in general. If we ever
come across a situation in which a call to BIO_get_new_index() is
necessary, that leak just fundamentally can't be plugged. The same is
true for any third-party libraries (or their dependencies, or
theirs...) that require "one-time", irreversible calls which can't be
tracked after we're unloaded. And we can't push these concerns up to
the top level application developer, because they don't know we exist.

(I'd be surprised if this were the only such resource leak across all
supported versions and combinations of Kerberos, OpenSSL, OpenLDAP,
Curl, etc. etc. From a quick search, you're the first to report this
in the ten years since the leak was introduced, so there may be more
dragons where you're headed.)

--Jacob

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: PostgreSQL 17: Bug in libpq when libpq is dlopened/closed multiple times
  In-Reply-To: <CAOYmi+=e9bQQa1jgLqZ18m5w-7KA44VeL9FON6i2gd8bi=d5Jw@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox