skb中的端口信息与tcpdump的端口信息不匹配

我在功能的/net/core/dev.c文件中捕获了网络数据包__netif_receive_skb_core()。我解析数据包并提取src_port，dest_port等等。我在任何接口上都使用了tcpdump。但是tcpdump的端口信息与我获取的端口信息不匹配。我不明白为什么。

orig_dev = skb->dev;
eth = eth_hdr(skb);
__be16 src_port = 0, dest_port = 0; 

if (skb->protocol == htons(ETH_P_IP))
{
    ih = ip_hdr(skb);
    proto_num = ih->protocol;
    switch (ih->protocol)
    {
    case IPPROTO_TCP:
    {
        struct tcphdr *th = tcp_hdr(skb);
        src_port = th->source;
        dest_port = th->dest;
        break;
    }
    case IPPROTO_UDP:
    {
        struct udphdr *uh = udp_hdr(skb);
        src_port = uh->source;
        dest_port = uh->dest;
        break;
    }
    default:
        src_port = 0;
        dest_port = 0;
    }

    fast_node = NULL;
    fast_node = (struct fast_pktlist *)kzalloc(sizeof(*fast_node), GFP_KERNEL);

    if (fast_node)
    {

        fast_node->protocol_num = proto_num;
        strcpy(fast_node->in_interface, orig_dev->name);
        fast_node->orgsrc_ip = ih->saddr;
        fast_node->orgdest_ip = ih->daddr;
        memcpy(fast_node->orgsrc_mac, eth->h_source, 6);

        fast_node->org_srcport = src_port;
        fast_node->org_destport = dest_port;

        INIT_LIST_HEAD(&fast_node->_list);
        list_add_tail(&fast_node->_list, &FAST_HEAD);
    }
    else
    {
        printk("can not allocate memory at line number = %d\n", __LINE__);
    }
}