suricata 3.1 源码分析26 （数据包VLAN解码）

╰+攻爆jí腚メ 2022-07-16 06:28 143阅读 0赞

由于VLAN可能嵌套，因此Packet结构体中使用以下相应字段进行记录：  
字段含义vlan\_idx当前的vlan层数，初始为0，最多为2，即最多只能嵌套一层VLAN，否则会报错。vlan\_id\[2\]记录每一层的VLAN ID（共12位，可表示4096个VLAN），通过GET\_VLAN\_ID获得。vlanh\[2\]记录每一层的VLAN头指针（VLANHdr \*类型）。

/** * \internal * \brief this function is used to decode IEEE802.1q packets * * \param tv pointer to the thread vars * \param dtv pointer code thread vars * \param p pointer to the packet struct * \param pkt pointer to the raw packet * \param len packet len * \param pq pointer to the packet queue * */
    int DecodeVLAN(ThreadVars *tv, DecodeThreadVars *dtv, Packet *p, uint8_t *pkt, uint16_t len, PacketQueue *pq)
    {
        uint32_t proto;
    
        if (p->vlan_idx == 0)
            StatsIncr(tv, dtv->counter_vlan);
        else if (p->vlan_idx == 1)
            StatsIncr(tv, dtv->counter_vlan_qinq);
    
        if(len < VLAN_HEADER_LEN)    {
            ENGINE_SET_INVALID_EVENT(p, VLAN_HEADER_TOO_SMALL);
            return TM_ECODE_FAILED;
    //若len小于VLAN_HEADER_LEN（4），则添加VLAN_HEADER_TOO_SMALL事件。
    
        }
        if (p->vlan_idx >= 2) {
            ENGINE_SET_EVENT(p,VLAN_HEADER_TOO_MANY_LAYERS);
            return TM_ECODE_FAILED;
    //vlan_idx是否大于或等于2，否则添加VLAN_HEADER_TOO_MANY_LAYERS事件。
    
        }
    
        p->vlanh[p->vlan_idx] = (VLANHdr *)pkt;
        if(p->vlanh[p->vlan_idx] == NULL)
            return TM_ECODE_FAILED;
    
        proto = GET_VLAN_PROTO(p->vlanh[p->vlan_idx]);
    
        SCLogDebug("p %p pkt %p VLAN protocol %04x VLAN PRI %d VLAN CFI %d VLAN ID %d Len: %" PRId32 "",
                p, pkt, proto, GET_VLAN_PRIORITY(p->vlanh[p->vlan_idx]),
                GET_VLAN_CFI(p->vlanh[p->vlan_idx]), GET_VLAN_ID(p->vlanh[p->vlan_idx]), len);
    
        /* only store the id for flow hashing if it's not disabled. */
        if (dtv->vlan_disabled == 0)
            p->vlan_id[p->vlan_idx] = (uint16_t)GET_VLAN_ID(p->vlanh[p->vlan_idx]);
    
        p->vlan_idx++;
    
        switch (proto)   {
            case ETHERNET_TYPE_IP:
                DecodeIPV4(tv, dtv, p, pkt + VLAN_HEADER_LEN,
                           len - VLAN_HEADER_LEN, pq);
                break;
            case ETHERNET_TYPE_IPV6:
                DecodeIPV6(tv, dtv, p, pkt + VLAN_HEADER_LEN,
                           len - VLAN_HEADER_LEN, pq);
                break;
            case ETHERNET_TYPE_PPPOE_SESS:
                DecodePPPOESession(tv, dtv, p, pkt + VLAN_HEADER_LEN,
                                   len - VLAN_HEADER_LEN, pq);
                break;
            case ETHERNET_TYPE_PPPOE_DISC:
                DecodePPPOEDiscovery(tv, dtv, p, pkt + VLAN_HEADER_LEN,
                                     len - VLAN_HEADER_LEN, pq);
                break;
            case ETHERNET_TYPE_VLAN:
            case ETHERNET_TYPE_8021AD:
                if (p->vlan_idx >= 2) {
                    ENGINE_SET_EVENT(p,VLAN_HEADER_TOO_MANY_LAYERS);
                    return TM_ECODE_OK;
                } else {
                    DecodeVLAN(tv, dtv, p, pkt + VLAN_HEADER_LEN,
                            len - VLAN_HEADER_LEN, pq);
                }
                break;
            default:
                SCLogDebug("unknown VLAN type: %" PRIx32 "", proto);
                ENGINE_SET_INVALID_EVENT(p, VLAN_UNKNOWN_TYPE);
                return TM_ECODE_OK;
        }
    
        return TM_ECODE_OK;
    }