Broken LibreSSL tls_conn_change_cert implementation

[sreimers]

Looks like there are some broken LibreSSL implementations #1127.

Let's start with test_tls_cli_conn_change_cert and tls_conn_change_cert, this does not work within libressl since SSL_certs_clear is not supported (There is usually a good reason why LibreSSL drops some APIs, mostly for security maintenance reasons).

tlstest: TEST_STRCMP: /home/sreimers/projekte/baresip/baresip-linux/re/test/tls.c:539: failed
expected string: (21 bytes)
"Mr Retest Client Cert"
actual string: (9 bytes)
"127.0.0.1"

re/src/tls/openssl/tls_tcp.c

Lines 331 to 333 in b41f503

	#if !defined(LIBRESSL_VERSION_NUMBER)
	SSL_certs_clear(tc->ssl);
	#endif

After studying the usage, I wonder why the ssl object is changed and not the ssl ctx before (or a new one used)? Since within tls_start_tcp a new ssl object is created from ctx. This way SSL_certs_clear can be avoided, I think.

re/src/sip/transp.c

Lines 827 to 843 in b41f503

	err = tls_start_tcp(&conn->sc, transp->tls, conn->tc, 0);
	if (err)
	goto out;
	hash = get_hash_of_fromhdr(mb);
	ccert = list_ledata(
	list_head(hash_list(transp->ht_ccert, hash)));
	if (ccert) {
	char *f;
	err = pl_strdup(&f, &ccert->file);
	if (err)
	goto out;
	err = tls_conn_change_cert(conn->sc, f);
	mem_deref(f);
	if (err)
	goto out;

We should keep all SSL implementations very generic.

@cHuberCoffee

[sreimers]

Maybe SSL_set_SSL_CTX can be used here too, will try after #1136 is merged.

[cHuberCoffee]

So the allocation of the tls struct containing an SSL_CTX is done by uag_transp_add.
Basically we only have one SSL_CTX where all SSL objects are inherited. This includes the loaded certificate which we need to replace. The SSL_certs_clear is for sure not a good implementation for doing so. The SSL_set_SSL_CTX would mean a new context for each certificate configured on user agent level.

It would be possible to create a new context for each such a configuration and saving these contexts as hash_list instead of the certificate path. Then using the SSL_set_SSL_CTX. For OpenSSL we have to find the same functionality. At least in the documentation i found nothing.

[sreimers]

SSL_set_SSL_CTX is supported and recommended by OpenSSL but not very documented:

#1136

[cHuberCoffee]

"not very documented" points it out.
But you are right, following down the implementation in OpenSSL for the function does look a lot like its exactly what we want to archive here.

[cspiel1]

Is v3.14.0 okay for this issue? Today we planned to release v3.13.0.