Sending built-by-hand packet and kernel panic.

[Emmanuel Guiton <emmanuel@netlab.hut.fi>]

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