问自定义ebtables模块&& skb操作&&内核死机

EN

// code for adding vlan tag based on skb->mark value
if (!skb_make_writable(skb, 0))
  return EBT_DROP;

if(skb->mark > 0){
  // maybe we should always seek VLAN_HLEN+ETH_HLEN instead of using condition?
  if (skb_headroom(skb) < (skb->mac_len == 0 ? VLAN_HLEN + ETH_HLEN : VLAN_HLEN ) ) {
    struct sk_buff *sk_tmp = skb;
    skb = skb_realloc_headroom(sk_tmp, VLAN_HLEN );
    kfree_skb(sk_tmp);

    if (skb == NULL) {
      return EBT_DROP;
    }
  }

  // we need 4 more bytes for 802.1q header, so push!...I can almost see the head(er)
  skb_push(skb, VLAN_HLEN);

  skb->mac_header-=VLAN_HLEN;
  skb->network_header-=VLAN_HLEN;
  skb->transport_header-=VLAN_HLEN;
  veth = (struct vlan_ethhdr *) eth_hdr(skb);

  // move dst/src mac addresses (12b of header) 4 bytes back to make room for
  // 802.1q header
  memmove( skb->head + skb->mac_header, skb->head + skb->mac_header + VLAN_HLEN, 12);

  // fill 802.1q header
  veth->h_vlan_proto = __constant_htons(ETH_P_8021Q);
  veth_TCI = skb->mark & 0xfff;
  veth->h_vlan_TCI = htons(veth_TCI);      
}

// code for stripping vlan tag and putting it into skb->mark value
veth = (struct vlan_ethhdr *)eth_hdr(skb);
if(veth->h_vlan_proto == __constant_htons(ETH_P_8021Q)){

  if (!skb_make_writable(skb, 0))
    return EBT_DROP;

  // determine vlan id
  vid=(ntohs(veth->h_vlan_TCI) & 0xfff);
  mark = vid;

  // copy dst/src mac addresses (12b) 4 bytes fwd, so it covers 802.1q header
  memmove(skb->head + skb->mac_header + VLAN_HLEN, skb->head + skb->mac_header, 12);

  // adapt header pointers
  skb->mac_header+=VLAN_HLEN;
  skb->mac_len = ETH_HLEN;
  skb->network_header+=VLAN_HLEN;
  skb->transport_header+=VLAN_HLEN;
  skb->data += VLAN_HLEN;
  skb->len -= VLAN_HLEN;

  eth = eth_hdr(skb);
  skb->protocol=eth->h_proto;
}
skb->mark=mark;