OpenSSL: Force RSA 3072-bit DH prime size limit for Suite B

Reject a DHE handshake if the server uses a DH prime that does not have
sufficient length to meet the Suite B 192-bit level requirement (<= 3k
(3072) bits).

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
This commit is contained in:
Jouni Malinen 2017-09-17 22:50:02 +03:00 committed by Jouni Malinen
parent 2ed70c7586
commit 1c9663cf6b

View file

@ -242,6 +242,9 @@ struct tls_connection {
unsigned char client_random[SSL3_RANDOM_SIZE];
unsigned char server_random[SSL3_RANDOM_SIZE];
u16 cipher_suite;
int server_dh_prime_len;
};
@ -1313,6 +1316,95 @@ static const char * openssl_handshake_type(int content_type, const u8 *buf,
}
#ifdef CONFIG_SUITEB
static void check_server_hello(struct tls_connection *conn,
const u8 *pos, const u8 *end)
{
size_t payload_len, id_len;
/*
* Parse ServerHello to get the selected cipher suite since OpenSSL does
* not make it cleanly available during handshake and we need to know
* whether DHE was selected.
*/
if (end - pos < 3)
return;
payload_len = WPA_GET_BE24(pos);
pos += 3;
if ((size_t) (end - pos) < payload_len)
return;
end = pos + payload_len;
/* Skip Version and Random */
if (end - pos < 2 + SSL3_RANDOM_SIZE)
return;
pos += 2 + SSL3_RANDOM_SIZE;
/* Skip Session ID */
if (end - pos < 1)
return;
id_len = *pos++;
if ((size_t) (end - pos) < id_len)
return;
pos += id_len;
if (end - pos < 2)
return;
conn->cipher_suite = WPA_GET_BE16(pos);
wpa_printf(MSG_DEBUG, "OpenSSL: Server selected cipher suite 0x%x",
conn->cipher_suite);
}
static void check_server_key_exchange(SSL *ssl, struct tls_connection *conn,
const u8 *pos, const u8 *end)
{
size_t payload_len;
u16 dh_len;
BIGNUM *p;
int bits;
if (!(conn->flags & TLS_CONN_SUITEB))
return;
/* DHE is enabled only with DHE-RSA-AES256-GCM-SHA384 */
if (conn->cipher_suite != 0x9f)
return;
if (end - pos < 3)
return;
payload_len = WPA_GET_BE24(pos);
pos += 3;
if ((size_t) (end - pos) < payload_len)
return;
end = pos + payload_len;
if (end - pos < 2)
return;
dh_len = WPA_GET_BE16(pos);
pos += 2;
if ((size_t) (end - pos) < dh_len)
return;
p = BN_bin2bn(pos, dh_len, NULL);
if (!p)
return;
bits = BN_num_bits(p);
BN_free(p);
conn->server_dh_prime_len = bits;
wpa_printf(MSG_DEBUG, "OpenSSL: Server DH prime length: %d bits",
conn->server_dh_prime_len);
}
#endif /* CONFIG_SUITEB */
static void tls_msg_cb(int write_p, int version, int content_type,
const void *buf, size_t len, SSL *ssl, void *arg)
{
@ -1339,6 +1431,18 @@ static void tls_msg_cb(int write_p, int version, int content_type,
conn->invalid_hb_used = 1;
}
}
#ifdef CONFIG_SUITEB
/*
* Need to parse these handshake messages to be able to check DH prime
* length since OpenSSL does not expose the new cipher suite and DH
* parameters during handshake (e.g., for cert_cb() callback).
*/
if (content_type == 22 && pos && len > 0 && pos[0] == 2)
check_server_hello(conn, pos + 1, pos + len);
if (content_type == 22 && pos && len > 0 && pos[0] == 12)
check_server_key_exchange(ssl, conn, pos + 1, pos + len);
#endif /* CONFIG_SUITEB */
}
@ -2297,8 +2401,42 @@ static int tls_connection_set_subject_match(struct tls_connection *conn,
}
static int tls_set_conn_flags(SSL *ssl, unsigned int flags)
#ifdef CONFIG_SUITEB
#if OPENSSL_VERSION_NUMBER >= 0x10002000L
static int suiteb_cert_cb(SSL *ssl, void *arg)
{
struct tls_connection *conn = arg;
/*
* This cert_cb() is not really the best location for doing a
* constraint check for the ServerKeyExchange message, but this seems to
* be the only place where the current OpenSSL sequence can be
* terminated cleanly with an TLS alert going out to the server.
*/
if (!(conn->flags & TLS_CONN_SUITEB))
return 1;
/* DHE is enabled only with DHE-RSA-AES256-GCM-SHA384 */
if (conn->cipher_suite != 0x9f)
return 1;
if (conn->server_dh_prime_len >= 3072)
return 1;
wpa_printf(MSG_DEBUG,
"OpenSSL: Server DH prime length (%d bits) not sufficient for Suite B RSA - reject handshake",
conn->server_dh_prime_len);
return 0;
}
#endif /* OPENSSL_VERSION_NUMBER */
#endif /* CONFIG_SUITEB */
static int tls_set_conn_flags(struct tls_connection *conn, unsigned int flags)
{
SSL *ssl = conn->ssl;
#ifdef SSL_OP_NO_TICKET
if (flags & TLS_CONN_DISABLE_SESSION_TICKET)
SSL_set_options(ssl, SSL_OP_NO_TICKET);
@ -2325,6 +2463,7 @@ static int tls_set_conn_flags(SSL *ssl, unsigned int flags)
SSL_clear_options(ssl, SSL_OP_NO_TLSv1_2);
#endif /* SSL_OP_NO_TLSv1_2 */
#ifdef CONFIG_SUITEB
#if OPENSSL_VERSION_NUMBER >= 0x10002000L
if (flags & TLS_CONN_SUITEB_NO_ECDH) {
const char *ciphers = "DHE-RSA-AES256-GCM-SHA384";
@ -2369,7 +2508,15 @@ static int tls_set_conn_flags(SSL *ssl, unsigned int flags)
SSL_set_options(ssl, SSL_OP_NO_TLSv1);
SSL_set_options(ssl, SSL_OP_NO_TLSv1_1);
SSL_set_cert_cb(ssl, suiteb_cert_cb, conn);
}
#else /* OPENSSL_VERSION_NUMBER < 0x10002000L */
if (flags & (TLS_CONN_SUITEB | TLS_CONN_SUITEB_NO_ECDH)) {
wpa_printf(MSG_ERROR,
"OpenSSL: Suite B RSA case not supported with this OpenSSL version");
return -1;
}
#endif /* OPENSSL_VERSION_NUMBER */
#endif /* CONFIG_SUITEB */
return 0;
@ -2396,7 +2543,7 @@ int tls_connection_set_verify(void *ssl_ctx, struct tls_connection *conn,
SSL_set_verify(conn->ssl, SSL_VERIFY_NONE, NULL);
}
if (tls_set_conn_flags(conn->ssl, flags) < 0)
if (tls_set_conn_flags(conn, flags) < 0)
return -1;
conn->flags = flags;
@ -3420,6 +3567,41 @@ openssl_handshake(struct tls_connection *conn, const struct wpabuf *in_data,
}
}
#ifdef CONFIG_SUITEB
if ((conn->flags & TLS_CONN_SUITEB) && !server &&
os_strncmp(SSL_get_cipher(conn->ssl), "DHE-", 4) == 0 &&
conn->server_dh_prime_len < 3072) {
struct tls_context *context = conn->context;
/*
* This should not be reached since earlier cert_cb should have
* terminated the handshake. Keep this check here for extra
* protection if anything goes wrong with the more low-level
* checks based on having to parse the TLS handshake messages.
*/
wpa_printf(MSG_DEBUG,
"OpenSSL: Server DH prime length: %d bits",
conn->server_dh_prime_len);
if (context->event_cb) {
union tls_event_data ev;
os_memset(&ev, 0, sizeof(ev));
ev.alert.is_local = 1;
ev.alert.type = "fatal";
ev.alert.description = "insufficient security";
context->event_cb(context->cb_ctx, TLS_ALERT, &ev);
}
/*
* Could send a TLS Alert to the server, but for now, simply
* terminate handshake.
*/
conn->failed++;
conn->write_alerts++;
return NULL;
}
#endif /* CONFIG_SUITEB */
/* Get the TLS handshake data to be sent to the server */
res = BIO_ctrl_pending(conn->ssl_out);
wpa_printf(MSG_DEBUG, "SSL: %d bytes pending from ssl_out", res);
@ -4201,7 +4383,7 @@ int tls_connection_set_params(void *tls_ctx, struct tls_connection *conn,
return -1;
}
if (tls_set_conn_flags(conn->ssl, params->flags) < 0)
if (tls_set_conn_flags(conn, params->flags) < 0)
return -1;
#ifdef OPENSSL_IS_BORINGSSL