Re: PostgreSQL 17: Bug in libpq when libpq is dlopened/closed multiple times

On Fri, Apr 17, 2026 at 7:33 AM Daniel Schreiber
<daniel.schreiber@hrz.tu-chemnitz.de> 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