From: Arne Schwabe Date: Mon, 8 Apr 2024 12:49:33 +0000 (+0200) Subject: Allow the TLS session to send out TLS alerts X-Git-Tag: v2.7_alpha1~253 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fbe3b49b373ea8e81aaa31a383258403a3bfcd07;p=thirdparty%2Fopenvpn.git Allow the TLS session to send out TLS alerts Previous OpenVPN versions shut down the TLS control channel immediately when encountering an error. This also meant that we would not send out TLS alerts to notify a client about potential problems like mismatching TLS versions or having no common cipher. This commit adds a new key_state S_ERROR_PRE which still allows to send out the remaining TLS packets of the control session which are typically the alert message and then going to S_ERROR. We do not wait for retries. So this is more a one-shot notify but that is acceptable in this situation. Sending out alerts is a slight compromise in security as alerts give out a bit of information that otherwise is not given out. But since all other consumers TLS implementations are already doing this and TLS implementations (nowadays) are very careful not to leak (sensitive) information by alerts and since the user experience is much better with alerts, this compromise is worth it. Change-Id: I0ad48915004ddee587e97c8ed190ba8ee989e48d Signed-off-by: Arne Schwabe Acked-by: Frank Lichtenheld Message-Id: <20240408124933.243991-1-frank@lichtenheld.com> URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28540.html Signed-off-by: Gert Doering --- diff --git a/Changes.rst b/Changes.rst index 4bc3bb3c..439352ab 100644 --- a/Changes.rst +++ b/Changes.rst @@ -1,5 +1,14 @@ Overview of changes in 2.7 ========================== +New features +------------ +TLS alerts + OpenVPN 2.7 will send out TLS alerts to peers informing them if the TLS + session shuts down or when the TLS implementation informs the peer about + an error in the TLS session (e.g. mismatching TLS versions). This improves + the user experience as the client shows an error instead of running into + a timeout when the server just stops responding completely. + Deprecated features ------------------- ``secret`` support has been removed by default. diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index 7c494519..2054eb47 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -690,6 +690,9 @@ state_name(int state) case S_ERROR: return "S_ERROR"; + case S_ERROR_PRE: + return "S_ERROR_PRE"; + case S_GENERATED_KEYS: return "S_GENERATED_KEYS"; @@ -2682,6 +2685,25 @@ write_outgoing_tls_ciphertext(struct tls_session *session, bool *continue_tls_pr return true; } +static bool +check_outgoing_ciphertext(struct key_state *ks, struct tls_session *session, + bool *continue_tls_process) +{ + /* Outgoing Ciphertext to reliable buffer */ + if (ks->state >= S_START) + { + struct buffer *buf = reliable_get_buf_output_sequenced(ks->send_reliable); + if (buf) + { + if (!write_outgoing_tls_ciphertext(session, continue_tls_process)) + { + return false; + } + } + } + return true; +} + static bool tls_process_state(struct tls_multi *multi, struct tls_session *session, @@ -2706,7 +2728,7 @@ tls_process_state(struct tls_multi *multi, } /* Are we timed out on receive? */ - if (now >= ks->must_negotiate && ks->state < S_ACTIVE) + if (now >= ks->must_negotiate && ks->state >= S_UNDEF && ks->state < S_ACTIVE) { msg(D_TLS_ERRORS, "TLS Error: TLS key negotiation failed to occur within %d seconds (check your network connectivity)", @@ -2760,6 +2782,16 @@ tls_process_state(struct tls_multi *multi, return false; } + if (ks->state == S_ERROR_PRE) + { + /* When we end up here, we had one last chance to send an outstanding + * packet that contained an alert. We do not ensure that this packet + * has been successfully delivered (ie wait for the ACK etc) + * but rather stop processing now */ + ks->state = S_ERROR; + return false; + } + /* Write incoming ciphertext to TLS object */ struct reliable_entry *entry = reliable_get_entry_sequenced(ks->rec_reliable); if (entry) @@ -2840,29 +2872,31 @@ tls_process_state(struct tls_multi *multi, dmsg(D_TLS_DEBUG, "Outgoing Plaintext -> TLS"); } } - - /* Outgoing Ciphertext to reliable buffer */ - if (ks->state >= S_START) + if (!check_outgoing_ciphertext(ks, session, &continue_tls_process)) { - buf = reliable_get_buf_output_sequenced(ks->send_reliable); - if (buf) - { - if (!write_outgoing_tls_ciphertext(session, &continue_tls_process)) - { - goto error; - } - } + goto error; } return continue_tls_process; error: tls_clear_error(); - ks->state = S_ERROR; + + /* Shut down the TLS session but do a last read from the TLS + * object to be able to read potential TLS alerts */ + key_state_ssl_shutdown(&ks->ks_ssl); + check_outgoing_ciphertext(ks, session, &continue_tls_process); + + /* Put ourselves in the pre error state that will only send out the + * control channel packets but nothing else */ + ks->state = S_ERROR_PRE; + msg(D_TLS_ERRORS, "TLS Error: TLS handshake failed"); INCR_ERROR; - return false; - + return true; } + + + /* * This is the primary routine for processing TLS stuff inside the * the main event loop. When this routine exits @@ -2970,7 +3004,7 @@ tls_process(struct tls_multi *multi, } /* When should we wake up again? */ - if (ks->state >= S_INITIAL) + if (ks->state >= S_INITIAL || ks->state == S_ERROR_PRE) { compute_earliest_wakeup(wakeup, reliable_send_timeout(ks->send_reliable)); @@ -3123,7 +3157,7 @@ tls_multi_process(struct tls_multi *multi, session_id_print(&ks->session_id_remote, &gc), print_link_socket_actual(&ks->remote_addr, &gc)); - if (ks->state >= S_INITIAL && link_socket_actual_defined(&ks->remote_addr)) + if ((ks->state >= S_INITIAL || ks->state == S_ERROR_PRE) && link_socket_actual_defined(&ks->remote_addr)) { struct link_socket_actual *tla = NULL; @@ -3201,7 +3235,8 @@ tls_multi_process(struct tls_multi *multi, { msg(D_TLS_ERRORS, "TLS Error: generate_key_expansion failed"); ks->authenticated = KS_AUTH_FALSE; - ks->state = S_ERROR; + key_state_ssl_shutdown(&ks->ks_ssl); + ks->state = S_ERROR_PRE; } /* Update auth token on the client if needed on renegotiation diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h index 8c3403ca..285705f7 100644 --- a/src/openvpn/ssl_backend.h +++ b/src/openvpn/ssl_backend.h @@ -362,6 +362,13 @@ void tls_ctx_personalise_random(struct tls_root_ctx *ctx); void key_state_ssl_init(struct key_state_ssl *ks_ssl, const struct tls_root_ctx *ssl_ctx, bool is_server, struct tls_session *session); +/** + * Sets a TLS session to be shutdown state, so the TLS library will generate + * a shutdown alert. + */ +void +key_state_ssl_shutdown(struct key_state_ssl *ks_ssl); + /** * Free the SSL channel part of the given key state. * diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h index 5a7dd605..5bc2f2aa 100644 --- a/src/openvpn/ssl_common.h +++ b/src/openvpn/ssl_common.h @@ -74,7 +74,10 @@ * * @{ */ -#define S_ERROR -1 /**< Error state. */ +#define S_ERROR (-2) /**< Error state. */ +#define S_ERROR_PRE (-1) /**< Error state but try to send out alerts + * before killing the keystore and moving + * it to S_ERROR */ #define S_UNDEF 0 /**< Undefined state, used after a \c * key_state is cleaned up. */ #define S_INITIAL 1 /**< Initial \c key_state state after diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c index b0303b60..a68588e8 100644 --- a/src/openvpn/ssl_mbedtls.c +++ b/src/openvpn/ssl_mbedtls.c @@ -1276,6 +1276,14 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl, ssl_bio_read, NULL); } + +void +key_state_ssl_shutdown(struct key_state_ssl *ks_ssl) +{ + mbedtls_ssl_send_alert_message(ks_ssl->ctx, MBEDTLS_SSL_ALERT_LEVEL_FATAL, + MBEDTLS_SSL_ALERT_MSG_CLOSE_NOTIFY); +} + void key_state_ssl_free(struct key_state_ssl *ks_ssl) { diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c index 7e74f2f5..e8a30a31 100644 --- a/src/openvpn/ssl_openssl.c +++ b/src/openvpn/ssl_openssl.c @@ -1940,6 +1940,12 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl, const struct tls_root_ctx *ssl_ BIO_set_ssl(ks_ssl->ssl_bio, ks_ssl->ssl, BIO_NOCLOSE); } +void +key_state_ssl_shutdown(struct key_state_ssl *ks_ssl) +{ + SSL_set_shutdown(ks_ssl->ssl, SSL_SENT_SHUTDOWN | SSL_RECEIVED_SHUTDOWN); +} + void key_state_ssl_free(struct key_state_ssl *ks_ssl) {