libtls: Enforce client/server identity when looking for public key

The client already enforces that the server identity is contained in the
received certificate.  But on the server, the referenced commit changed
the lookup from the configured (or adopted if %any was configured) client
identity to the subject DN of the received client certificate.  So any
client with a trusted certificate was accepted.

Fixes: d2fc9b0 ("tls-server: Mutual authentication support for TLS 1.3")
Closes strongswan#873

src/libtls/tls_peer.c

@@ -165,7 +165,7 @@ struct private_tls_peer_t {
 
 /* Implemented in tls_server.c */
 bool tls_write_key_share(bio_writer_t **key_share, diffie_hellman_t *dh);
-public_key_t *tls_find_public_key(auth_cfg_t *peer_auth);
+public_key_t *tls_find_public_key(auth_cfg_t *peer_auth, identification_t *id);
 
 /**
  * Verify the DH group/key type requested by the server is valid.
@@ -641,7 +641,7 @@ static status_t process_cert_verify(private_tls_peer_t *this,
 	public_key_t *public;
 	chunk_t msg;
 
-	public = tls_find_public_key(this->server_auth);
+	public = tls_find_public_key(this->server_auth, this->server);
 	if (!public)
 	{
 		DBG1(DBG_TLS, "no trusted certificate found for '%Y' to verify TLS server",
@@ -690,7 +690,7 @@ static status_t process_modp_key_exchange(private_tls_peer_t *this,
 		this->alert->add(this->alert, TLS_FATAL, TLS_INTERNAL_ERROR);
 		return NEED_MORE;
 	}
-	public = tls_find_public_key(this->server_auth);
+	public = tls_find_public_key(this->server_auth, this->server);
 	if (!public)
 	{
 		DBG1(DBG_TLS, "no TLS public key found for server '%Y'", this->server);
@@ -797,7 +797,7 @@ static status_t process_ec_key_exchange(private_tls_peer_t *this,
 		return NEED_MORE;
 	}
 
-	public = tls_find_public_key(this->server_auth);
+	public = tls_find_public_key(this->server_auth, this->server);
 	if (!public)
 	{
 		DBG1(DBG_TLS, "no TLS public key found for server '%Y'", this->server);
@@ -1621,7 +1621,7 @@ static status_t send_key_exchange_encrypt(private_tls_peer_t *this,
 		return NEED_MORE;
 	}
 
-	public = tls_find_public_key(this->server_auth);
+	public = tls_find_public_key(this->server_auth, this->server);
 	if (!public)
 	{
 		DBG1(DBG_TLS, "no TLS public key found for server '%Y'", this->server);

src/libtls/tls_server.c

@@ -173,7 +173,7 @@ struct private_tls_server_t {
 /**
  * Find a trusted public key to encrypt/verify key exchange data
  */
-public_key_t *tls_find_public_key(auth_cfg_t *peer_auth)
+public_key_t *tls_find_public_key(auth_cfg_t *peer_auth, identification_t *id)
 {
 	public_key_t *public = NULL, *current;
 	certificate_t *cert, *found;
@@ -184,8 +184,7 @@ public_key_t *tls_find_public_key(auth_cfg_t *peer_auth)
 	if (cert)
 	{
 		enumerator = lib->credmgr->create_public_enumerator(lib->credmgr,
-											KEY_ANY, cert->get_subject(cert),
-											peer_auth, TRUE);
+												KEY_ANY, id, peer_auth, TRUE);
 		while (enumerator->enumerate(enumerator, &current, &auth))
 		{
 			found = auth->get(auth, AUTH_RULE_SUBJECT_CERT);
@@ -923,7 +922,7 @@ static status_t process_cert_verify(private_tls_server_t *this,
 	public_key_t *public;
 	chunk_t msg;
 
-	public = tls_find_public_key(this->peer_auth);
+	public = tls_find_public_key(this->peer_auth, this->peer);
 	if (!public)
 	{
 		DBG1(DBG_TLS, "no trusted certificate found for '%Y' to verify TLS peer",