/*
 * wireguard.c
 *
 * Copyright (C) 2019 - ntop.org
 * Copyright (C) 2019 - Yağmur Oymak
 *
 * This file is part of nDPI, an open source deep packet inspection
 * library based on the OpenDPI and PACE technology by ipoque GmbH
 *
 * nDPI is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * nDPI is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with nDPI.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include "ndpi_protocol_ids.h"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_WIREGUARD

#include "ndpi_api.h"

/*
 * See https://www.wireguard.com/protocol/ for protocol reference.
 */

enum wg_message_type {
    WG_TYPE_HANDSHAKE_INITIATION = 1,
    WG_TYPE_HANDSHAKE_RESPONSE = 2,
    WG_TYPE_COOKIE_REPLY = 3,
    WG_TYPE_TRANSPORT_DATA = 4
};

void ndpi_search_wireguard(struct ndpi_detection_module_struct
        *ndpi_struct, struct ndpi_flow_struct *flow)
{
    struct ndpi_packet_struct *packet = &flow->packet;
    const u_int8_t *payload = packet->payload;
    u_int8_t message_type = payload[0];

    NDPI_LOG_DBG(ndpi_struct, "search WireGuard\n");

    /*
     * First, try some easy ways to rule out the protocol.
     * The packet size and the reserved bytes in the header are good candidates.
     */

    /*
     * A transport packet contains at minimum the following fields:
     *  u8 message_type
     *  u8 reserved_zero[3]
     *  u32 receiver_index
     *  u64 counter
     *  u8 encrypted_encapsulated_packet[]
     * In the case of a keepalive message, the encapsulated packet will have
     * zero length, but will still have a 16 byte poly1305 authentication tag.
     * Thus, packet->payload will be at least 32 bytes in size.
     * Note that handshake packets have a slightly different structure, but they are larger.
     */
    if (packet->payload_packet_len < 32) {
        NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
        return;
    }
    /*
     * The next three bytes after the message type are reserved and set to zero.
     */
    if (payload[1] != 0 || payload[2] != 0 || payload[3] != 0) {
        NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
        return;
    }

    /*
     * Below we make a deeper analysis; possibly inspecting multiple packets to
     * look for consistent sender/receiver index fields. We also exploit the fact
     * that handshake messages always have a fixed size.
     *
     * Stages 1-2 means we are processing a handshake sequence.
     * Stages 3-4 means we are processing a transport packet sequence.
     *
     * Message type can be one of the following:
     * 1) Handshake Initiation (148 bytes)
     * 2) Handshake Response (92 bytes)
     * 3) Cookie Reply (64 bytes)
     * 4) Transport Data (variable length, min 32 bytes)
     */
    if (message_type == WG_TYPE_HANDSHAKE_INITIATION && packet->payload_packet_len <= 190) {
        u_int32_t sender_index = get_u_int32_t(payload, 4);
        /*
         * We always start a new detection stage on a handshake initiation.
         */
        flow->l4.udp.wireguard_stage = 1 + packet->packet_direction;
        flow->l4.udp.wireguard_peer_index[packet->packet_direction] = sender_index;
        /* need more packets before deciding */
    } else if (message_type == WG_TYPE_HANDSHAKE_RESPONSE && packet->payload_packet_len >= 134) {
        if (flow->l4.udp.wireguard_stage == 2 - packet->packet_direction) {
            /*
             * This means we are probably processing a handshake response to a handshake
             * initiation that we've just processed, so we check if the receiver index
             * matches the index in the handshake initiation.
             */
            u_int32_t receiver_index = get_u_int32_t(payload, 8);
            if (receiver_index == flow->l4.udp.wireguard_peer_index[1 - packet->packet_direction]) {
                ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_WIREGUARD);
            } else {
                NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
            }
        }
        /* need more packets before deciding */
    } else if (message_type == WG_TYPE_COOKIE_REPLY && packet->payload_packet_len == 64) {
        /*
         * A cookie reply is sent as response to a handshake initiation when under load,
         * for DoS mitigation. If we have just seen a handshake initiation before
         * this cookie reply packet, we check if the receiver index in this packet
         * matches the sender index in that handshake initiation packet.
         */
        if (flow->l4.udp.wireguard_stage == 2 - packet->packet_direction) {
            u_int32_t receiver_index = get_u_int32_t(payload, 4);
            if (receiver_index == flow->l4.udp.wireguard_peer_index[1 - packet->packet_direction]) {
                ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_WIREGUARD);
            } else {
                NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
            }
        }
        /* need more packets before deciding */
    } else if (message_type == WG_TYPE_TRANSPORT_DATA) {
        /*
         * For detecting transport data packets, we save the peer
         * indices in both directions first. This requires at least one packet in each
         * direction (stages 3-4). The third packet that we process will be checked
         * against the appropriate index for a match (stage 5).
         */
        u_int32_t receiver_index = get_u_int32_t(payload, 4);
        if (flow->l4.udp.wireguard_stage == 0) {
            flow->l4.udp.wireguard_stage = 3 + packet->packet_direction;
            flow->l4.udp.wireguard_peer_index[packet->packet_direction] = receiver_index;
            /* need more packets before deciding */
        } else if (flow->l4.udp.wireguard_stage == 4 - packet->packet_direction) {
            flow->l4.udp.wireguard_peer_index[packet->packet_direction] = receiver_index;
            flow->l4.udp.wireguard_stage = 5;
            /* need more packets before deciding */
        } else if (flow->l4.udp.wireguard_stage == 5) {
            if (receiver_index == flow->l4.udp.wireguard_peer_index[packet->packet_direction]) {
                ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_WIREGUARD);
            } else {
                NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
            }
        }
        /* need more packets before deciding */
    } else {
        NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
    }
}

void init_wireguard_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("WireGuard", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_WIREGUARD,
            ndpi_search_wireguard,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);

    *id += 1;
}
