/*
 * snmp.c
 *
 * Copyright (C) 2009-2011 by ipoque GmbH
 * Copyright (C) 2011-18 - ntop.org
 *
 * 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_SNMP

#include "ndpi_api.h"

static void ndpi_int_snmp_add_connection(struct ndpi_detection_module_struct
        *ndpi_struct, struct ndpi_flow_struct *flow)
{
    ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SNMP);
}

void ndpi_search_snmp(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
    struct ndpi_packet_struct *packet = &flow->packet;

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

    if (packet->payload_packet_len > 32 && packet->payload[0] == 0x30) {
        int offset;
        u_int16_t u16;

        switch (packet->payload[1]) {
            case 0x81:
                offset = 3;
                break;
            case 0x82:
                offset = 4;
                break;
            default:
                if (packet->payload[1] > 0x82) {
                    NDPI_LOG_DBG2(ndpi_struct, "SNMP excluded, second byte is > 0x82\n");
                    goto excl;
                }
                offset = 2;
        }

        u16 = ntohs(get_u_int16_t(packet->payload, offset));

        if((u16 != 0x0201) && (u16 != 0x0204)) {
            NDPI_LOG_DBG2(ndpi_struct, "SNMP excluded, 0x0201/0x0204 pattern not found\n");
            goto excl;
        }

        if (packet->payload[offset + 2] >= 0x04) {
            NDPI_LOG_DBG2(ndpi_struct, "SNMP excluded, version > 3\n");
            goto excl;
        }

        if (flow->l4.udp.snmp_stage == 0) {
            if (packet->udp->dest == htons(161) || packet->udp->dest == htons(162)) {
                NDPI_LOG_INFO(ndpi_struct, "found SNMP by port\n");
                ndpi_int_snmp_add_connection(ndpi_struct, flow);
                return;
            }
            NDPI_LOG_DBG2(ndpi_struct, "SNMP stage 0\n");
            if (packet->payload[offset + 2] == 3) {
                flow->l4.udp.snmp_msg_id = ntohs(get_u_int32_t(packet->payload, offset + 8));
            } else if (packet->payload[offset + 2] == 0) {
                flow->l4.udp.snmp_msg_id = get_u_int8_t(packet->payload, offset + 15);
            } else {
                flow->l4.udp.snmp_msg_id = ntohs(get_u_int16_t(packet->payload, offset + 15));
            }
            flow->l4.udp.snmp_stage = 1 + packet->packet_direction;
            return;
        } else if (flow->l4.udp.snmp_stage == 1 + packet->packet_direction) {
            if (packet->payload[offset + 2] == 0) {
                if (flow->l4.udp.snmp_msg_id != get_u_int8_t(packet->payload, offset + 15) - 1) {
                    NDPI_LOG_DBG2(ndpi_struct,
                            "SNMP v1 excluded, message ID doesn't match\n");
                    goto excl;
                }
            }
        } else if (flow->l4.udp.snmp_stage == 2 - packet->packet_direction) {
            NDPI_LOG_DBG2(ndpi_struct, "SNMP stage 1-2\n");
            if (packet->payload[offset + 2] == 3) {
                if (flow->l4.udp.snmp_msg_id != ntohs(get_u_int32_t(packet->payload, offset + 8))) {
                    NDPI_LOG_DBG2(ndpi_struct,
                            "SNMP v3 excluded, message ID doesn't match\n");
                    goto excl;
                }
            } else if (packet->payload[offset + 2] == 0) {
                if (flow->l4.udp.snmp_msg_id != get_u_int8_t(packet->payload, offset + 15)) {
                    NDPI_LOG_DBG2(ndpi_struct,
                            "SNMP v1 excluded, message ID doesn't match\n");
                    goto excl;
                }
            } else {
                if (flow->l4.udp.snmp_msg_id != ntohs(get_u_int16_t(packet->payload, offset + 15))) {
                    NDPI_LOG_DBG2(ndpi_struct,
                            "SNMP v2 excluded, message ID doesn't match\n");
                    goto excl;
                }
            }
            NDPI_LOG_INFO(ndpi_struct, "found SNMP\n");
            ndpi_int_snmp_add_connection(ndpi_struct, flow);
            return;
        }
    }
excl:
    NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}


void init_snmp_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
    ndpi_set_bitmask_protocol_detection("SNMP", ndpi_struct, detection_bitmask, *id,
            NDPI_PROTOCOL_SNMP,
            ndpi_search_snmp,
            NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
            SAVE_DETECTION_BITMASK_AS_UNKNOWN,
            ADD_TO_DETECTION_BITMASK);

    *id += 1;
}

