sockets - 如何在内核模块开发下将Mac地址解析为IP地址？

Question

我想在内核模块中构建一个 tcp 包，并使用函数 dev_queue_xmit(skb) 通过 IP 地址将其发送到另一台主机。但我不想手动填写Mac地址。以下是包生成的代码。
一些内核函数调用 eth_rebuild_header(skb) 来重建 Mac 头文件。但是，就我而言，它在被调用后会挂起我的计算机。 Google 结果回答说，如果 arp 缓存不包含该 IP 地址的条目，arp_find 将使操作系统崩溃。但我确定它存在于由 shell 命令“arp -v”打印的 arp 缓存中。

static int build_and_xmit_tcp(char * eth, u_char * smac, u_char * dmac,
             u_long sip, u_long dip,
             u_short sport, u_short dport,
             u_char * pkt, int pkt_len,
             int syn, int ack, int fin,
             __be32 seq, __be32 seq_ack)
{
  struct sk_buff * skb = NULL;
  struct net_device * dev = NULL;
  struct ethhdr * ethdr = NULL;
  struct iphdr * iph = NULL;
  struct tcphdr * tcph = NULL;
  u_char * pdata = NULL;
  if(NULL == smac || NULL == dmac)
      goto out;

  if(NULL == (dev= dev_get_by_name(&init_net, eth)))
        goto out;
  skb = alloc_skb(pkt_len + sizeof(struct iphdr) + sizeof(struct tcphdr) + LL_RESERVED_SPACE(dev), GFP_ATOMIC);

  if(NULL == skb)
      goto out;
  skb_reserve(skb, LL_RESERVED_SPACE(dev));

  skb->dev = dev;
  skb->pkt_type = PACKET_OTHERHOST;
  skb->protocol = __constant_htons(ETH_P_IP);
  skb->ip_summed = CHECKSUM_NONE;
  skb->priority = 0;
    skb_set_network_header(skb, 0);
  skb_put(skb, sizeof(struct iphdr));
 skb_set_transport_header(skb, sizeof(struct iphdr));
  skb_put(skb, sizeof(struct tcphdr));

  pdata = skb_put(skb, pkt_len); 
  {
     if(NULL != pkt)
        memcpy(pdata, pkt, pkt_len);
  }

  tcph = tcp_hdr(skb);
  memset(tcph, 0, sizeof(struct tcphdr));
  tcph->source = sport;
  tcph->dest = dport;
  tcph->doff=5;
  tcph->seq = htonl(seq);
  tcph-> ack_seq= htonl( seq_ack);
  tcph->psh = pkt_len>0? 1:0;
  tcph ->fin = fin;
  tcph->ack = ack;
  tcph->syn=syn;
  tcph->window=__constant_htons (65535);
  skb->csum = 0;
  tcph->check = 0;
  iph = ip_hdr(skb);
  iph->version = 4;
  iph->ihl = sizeof(struct iphdr)>>2;
  iph->frag_off = 0;
  iph->protocol = IPPROTO_TCP;
  iph->tos = 0;
  iph->daddr = dip;
  iph->saddr = sip;
  iph->ttl = 0x40;
  iph->tot_len = __constant_htons(skb->len);
  iph->check = 0;
  iph->check = ip_fast_csum((unsigned char *)iph,iph->ihl);

  skb->csum = skb_checksum(skb, iph->ihl*4, skb->len - iph->ihl * 4, 0);
  tcph->check = csum_tcpudp_magic(sip, dip, skb->len - iph->ihl * 4, IPPROTO_TCP, skb->csum);
  skb_push(skb, 14);
  skb_set_mac_header(skb, 0);
  ethdr = (struct ethhdr *)eth_hdr(skb);
//  memcpy(ethdr->h_dest, dmac, ETH_ALEN);
 // memcpy(ethdr->h_source, smac, ETH_ALEN);
  ethdr->h_proto = __constant_htons(ETH_P_IP);

//  arp_send(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr,
//       dst_ha, dev->dev_addr, NULL);
    eth_rebuild_header(skb);      // kernel hang....
  if(0 > dev_queue_xmit(skb)) {
        dev_put (dev);
        kfree_skb (skb);
  }
   return(NF_ACCEPT);

 out:
        dev_put (dev);
        kfree_skb (skb);
   return(NF_ACCEPT);
}


static int __init myhook_init(void)
{
   printk("=========insert module......\n");
   build_and_xmit_tcp(ETH_O, GWMAC_O, DMAC, in_aton(GWIP_O), in_aton(DIP), htons(8888), htons(DPORT), 
                    "", 0,
                    1, 0, 0, 0, 0);
}

static void __exit myhook_fini(void)
{
   printk("=========rmmod ......\n");
}

module_init(myhook_init);
module_exit(myhook_fini);

谷歌给了我一些其他的解决方案。他们说 arp_ioctl 可以解析 Mac 地址。然而，事实是，arp_ioctl 被静态编译成 vmlinuz，它不会作为符号导出到其他模块。

int arp_get(char *ifname, char *ipStr)
{
    struct arpreq req;  
    struct sockaddr_in *sin;  
    int ret = 0;  
    int sock_fd = 0;
    struct net_device * dev = NULL;
    printk("arp  ----  \n");
    if(NULL == (dev= dev_get_by_name(&init_net, ifname))){
        dev_put (dev);
        printk("error dev get \n");
        return -1;
    }
    struct net *net_arp = dev_net(dev);
    memset(&req, 0, sizeof(struct arpreq));  

    sin = (struct sockaddr_in *)&req.arp_pa;  
    sin->sin_family = AF_INET;  
    sin->sin_addr.s_addr = in_aton(ipStr);  


    strncpy(req.arp_dev, ifname, 15);
    ret = arp_ioctl(net_arp, SIOCGARP, &req);     // can't be called
    unsigned char *hw = (unsigned char *)req.arp_ha.sa_data;  
    printk("%#x-%#x-%#x-%#x-%#x-%#x\n", hw[0], hw[1], hw[2], hw[3], hw[4], hw[5]);
    return 0;
}

也许我需要做一个套接字结构，并尝试一些基于套接字的上层功能。但是该怎么做...

内核版本:2.6.32
操作系统版本:ubuntu 9.10
gcc 版本:4.41

Answer 1

int ip_xmit(struct sk_buff *skb) 
{
    struct iphdr *iph = ip_hdr(skb);
    struct tcphdr *tcph = tcp_hdr(skb);
    printk("dst is %d\n", skb->_skb_dst);
    int err;
//    err = ip_route_input(skb, iph->daddr, iph->saddr, 0, skb->dev);

    struct rtalbe *rt;

    {
        struct flowi fl = { .oif = 0,
                    .nl_u = { .ip4_u =
                          { .daddr = iph->daddr,
                        .saddr = iph->saddr,
                        .tos = 0 } },
                    .proto = IPPROTO_TCP,
                    .flags = 0,
                    .uli_u = { .ports =
                           { .sport = tcph->source,
                         .dport = tcph->dest } } };

        if (err = ip_route_output_key(&init_net, &rt, &fl))
            return err;
            printk("err is %d\n", err);
    }
    skb_dst_set(skb, rt);
    if(0 > ip_local_out(skb)) {
        printk("dev error\n");
        kfree_skb (skb);
        return -1;
    }
    return 0;
}

函数 ip_route_output_key 可以获取路由目的地， ip_local_out 将 skb 传递出去。