Sending built-by-hand packet and kernel panic.

[Emmanuel Guiton]

Hi!

Can any experienced network programmer give a quick look at the 
following? I try to send a TCP packet built by hand. It works, but it 
also leads to a kernel panic if a second packet is to be sent. As I'm 
not an experienced kernel programmer, I guess I'm doing some stupid 
thing that can be easily solved.

Basically, my code just fills a sk_buff structure and sends it with NF_HOOK.

Thanks for any help,
          Emmanuel



       /* skb is allocated 56 bytes = TCP message with no data 
(detailed hereafter)
        * + 2 extra bytes before the ethernet header (see hereafter)
        */
   skb = alloc_skb(56, GFP_ATOMIC);
   skb_reserve(skb, 2); /* for 16-bit alignment*/
       /* ethernet header is 14 byte long */
   eth = (__u8 *) skb_put(skb, 14);
       /* ip header is 20 byte long */
   iph = (struct iphdr *)skb_put(skb, sizeof(struct iphdr));
       /* tcp header (no options) is 20 byte long */
   tcph = (struct tcphdr *)skb_put(skb, sizeof(struct tcphdr));

   /* skb->dst AND skb->dev (the latter is set by the former) */
   if (ip_route_output(&rt, ip_dst, 0, 0, 0) != 0)
   {
       printk("ip_route_output failed.\n");
       return -1;
   }
   skb->dst = (struct rt_entry *) rt; /* A trick from ip_route_input.c */
   skb->dev = skb->dst->dev;
  
   /* Socket allocation. */
   if (sock_create(PF_INET, SOCK_RAW, IPPROTO_RAW, &sending_socket) < 0)
   {   
       printk("Error socket creation.\n");
       sock_release(sending_socket);
       return -1;
   }
   sk = kmalloc(sizeof(struct sock), GFP_KERNEL);
   memcpy(&(sending_socket->sk), sk, sizeof(struct sock));
   sock_release(sending_socket);
   if (sk == NULL)
   {
       printk("Error: sk == NULL\n");
       return -1;
   }
       /* Now, set the sock field. */
   skb->sk = sk;
  
   /* TRANSPORT HEADER: TCP */
       /* here, TCP header data is filled in tcph. */
   skb->h.th = tcph;
   /* NETWORK HEADER: IP */
       /* here, IP header data is filled in iph*/
   skb->nh.iph = iph;
   /* LINK HEADER: ETHERNET */
       /* here, ethernet header data is filled in iph*/
   skb->mac.ethernet = ((u8 *)iph) - 14;

   /* Fix me:
    * Scheduling priority put at max, choose more correct value.
    */
   skb->priority = 15;
   /* To choose right pkt_type when receiving a packet.
    * We're not receivng anything, but I set the value like the guys
    * in pktgen.c did, there should be a reason for that.
    */
   skb->protocol = __constant_htons(ETH_P_IP);
   
   /* TIMESTAMP */
       /* last, so it's closest to sending time. */
   do_gettimeofday(&skb->stamp);
   
printk("Going to send initialized skb! ...\n");
//    if (NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, skb->dev, 
output_maybe_reroute) < 0)
   NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, skb->dev, 
ip_finish_output) < 0

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/