OpenSSL: Detect and prevent TLS heartbeat attack

Some OpenSSL versions have vulnerability in TLS heartbeat request
processing. Check the processed message to determine if the attack has
been used and if so, do not send the response to the peer. This does not
prevent the buffer read overflow within OpenSSL, but this prevents the
attacker from receiving the information.

This change is an additional layer of protection if some yet to be
identified paths were to expose this OpenSSL vulnerability. However, the
way OpenSSL is used for EAP-TLS/TTLS/PEAP/FAST in hostapd/wpa_supplicant
was already rejecting the messages before the response goes out and as
such, this additional change is unlikely to be needed to avoid the
issue.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/crypto/tls_openssl.c

@@ -105,6 +105,7 @@ struct tls_connection {
 	unsigned int ca_cert_verify:1;
 	unsigned int cert_probe:1;
 	unsigned int server_cert_only:1;
+	unsigned int invalid_hb_used:1;
 
 	u8 srv_cert_hash[32];
 
@@ -984,6 +985,26 @@ int tls_get_errors(void *ssl_ctx)
 	return count;
 }
 
+
+static void tls_msg_cb(int write_p, int version, int content_type,
+		       const void *buf, size_t len, SSL *ssl, void *arg)
+{
+	struct tls_connection *conn = arg;
+	const u8 *pos = buf;
+
+	wpa_printf(MSG_DEBUG, "OpenSSL: %s ver=0x%x content_type=%d",
+		   write_p ? "TX" : "RX", version, content_type);
+	wpa_hexdump_key(MSG_MSGDUMP, "OpenSSL: Message", buf, len);
+	if (content_type == 24 && len >= 3 && pos[0] == 1) {
+		size_t payload_len = WPA_GET_BE16(pos + 1);
+		if (payload_len + 3 > len) {
+			wpa_printf(MSG_ERROR, "OpenSSL: Heartbeat attack detected");
+			conn->invalid_hb_used = 1;
+		}
+	}
+}
+
+
 struct tls_connection * tls_connection_init(void *ssl_ctx)
 {
 	SSL_CTX *ssl = ssl_ctx;
@@ -1008,6 +1029,8 @@ struct tls_connection * tls_connection_init(void *ssl_ctx)
 
 	conn->context = context;
 	SSL_set_app_data(conn->ssl, conn);
+	SSL_set_msg_callback(conn->ssl, tls_msg_cb);
+	SSL_set_msg_callback_arg(conn->ssl, conn);
 	options = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 |
 		SSL_OP_SINGLE_DH_USE;
 #ifdef SSL_OP_NO_COMPRESSION
@@ -2642,10 +2665,25 @@ openssl_connection_handshake(struct tls_connection *conn,
 	out_data = openssl_handshake(conn, in_data, server);
 	if (out_data == NULL)
 		return NULL;
+	if (conn->invalid_hb_used) {
+		wpa_printf(MSG_INFO, "TLS: Heartbeat attack detected - do not send response");
+		wpabuf_free(out_data);
+		return NULL;
+	}
 
 	if (SSL_is_init_finished(conn->ssl) && appl_data && in_data)
 		*appl_data = openssl_get_appl_data(conn, wpabuf_len(in_data));
 
+	if (conn->invalid_hb_used) {
+		wpa_printf(MSG_INFO, "TLS: Heartbeat attack detected - do not send response");
+		if (appl_data) {
+			wpabuf_free(*appl_data);
+			*appl_data = NULL;
+		}
+		wpabuf_free(out_data);
+		return NULL;
+	}
+
 	return out_data;
 }
 
@@ -2747,6 +2785,12 @@ struct wpabuf * tls_connection_decrypt(void *tls_ctx,
 	}
 	wpabuf_put(buf, res);
 
+	if (conn->invalid_hb_used) {
+		wpa_printf(MSG_INFO, "TLS: Heartbeat attack detected - do not send response");
+		wpabuf_free(buf);
+		return NULL;
+	}
+
 	return buf;
 }