nf_register_hook() -->
int nf_register_hook(struct nf_hook_ops *reg)
{
struct list_head *i;
spin_lock_bh(&nf_hook_lock);
list_for_each(i, &nf_hooks[reg->pf][reg->hooknum]) {
if (reg->priority < ((struct nf_hook_ops *)i)->priority)
break;
}
list_add_rcu(®->list, i->prev);
spin_unlock_bh(&nf_hook_lock);
synchronize_net();
return 0;
}
struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];
#define NPROTO 32 /* should be enough for now.. */
/* Largest hook number + 1 */
#define NF_MAX_HOOKS 8
reg->hooknum
/* IP Hooks */
/* After promisc drops, checksum checks. */
#define NF_IP_PRE_ROUTING 0
/* If the packet is destined for this box. */
#define NF_IP_LOCAL_IN 1
/* If the packet is destined for another interface. */
#define NF_IP_FORWARD 2
/* Packets coming from a local process. */
#define NF_IP_LOCAL_OUT 3
/* Packets about to hit the wire. */
#define NF_IP_POST_ROUTING 4
#define NF_IP_NUMHOOKS 5
reg->priority
enum nf_ip_hook_priorities {
NF_IP_PRI_FIRST = INT_MIN,
NF_IP_PRI_CONNTRACK_DEFRAG = -400,
NF_IP_PRI_RAW = -300,
NF_IP_PRI_SELINUX_FIRST = -225,
NF_IP_PRI_CONNTRACK = -200,
NF_IP_PRI_BRIDGE_SABOTAGE_FORWARD = -175,
NF_IP_PRI_MANGLE = -150,
NF_IP_PRI_NAT_DST = -100,
NF_IP_PRI_BRIDGE_SABOTAGE_LOCAL_OUT = -50,
NF_IP_PRI_FILTER = 0,
NF_IP_PRI_NAT_SRC = 100,
NF_IP_PRI_SELINUX_LAST = 225,
NF_IP_PRI_LAST = INT_MAX,
};
在來看一下NF_HOOK宏
ip_forward() return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
ip_forward_finish);
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn) \
(list_empty(&nf_hooks[(pf)][(hook)]) \
? (okfn)(skb) \
: nf_hook_slow((pf), (hook), (skb), (indev), (outdev), (okfn), INT_MIN))
int nf_hook_slow(int pf, unsigned int hook, struct sk_buff *skb,
struct net_device *indev,
struct net_device *outdev,
int (*okfn)(struct sk_buff *),
int hook_thresh){
struct list_head *elem;
elem = &nf_hooks[pf][hook];
next_hook:
verdict = nf_iterate(&nf_hooks[pf][hook], &skb, hook, indev,
outdev, &elem, okfn, hook_thresh);
if (verdict == NF_QUEUE) {
NFDEBUG("nf_hook: Verdict = QUEUE.\n");
if (!nf_queue(skb, elem, pf, hook, indev, outdev, okfn))
goto next_hook;
}
switch (verdict) {
case NF_ACCEPT:
ret = okfn(skb);
break;
case NF_DROP:
kfree_skb(skb);
ret = -EPERM;
break;
}
rcu_read_unlock();
return ret;
}
static unsigned int nf_iterate(struct list_head *head,
struct sk_buff **skb,
int hook,
const struct net_device *indev,
const struct net_device *outdev,
struct list_head **i,
int (*okfn)(struct sk_buff *),
int hook_thresh)
{
/*
* The caller must not block between calls to this
* function because of risk of continuing from deleted element.
*/
list_for_each_continue_rcu(*i, head) {
struct nf_hook_ops *elem = (struct nf_hook_ops *)*i;
if (hook_thresh > elem->priority)
continue;
/* Optimization: we don't need to hold module
reference here, since function can't sleep. --RR */
switch (elem->hook(hook, skb, indev, outdev, okfn)) {
case NF_QUEUE:
return NF_QUEUE;
case NF_STOLEN:
return NF_STOLEN;
case NF_DROP:
return NF_DROP;
case NF_REPEAT:
*i = (*i)->prev;
break;
#ifdef CONFIG_NETFILTER_DEBUG
case NF_ACCEPT:
break;
default:
NFDEBUG("Evil return from %p(%u).\n",
elem->hook, hook);
#endif
}
}
return NF_ACCEPT;
}
源碼net\ipv4目錄下 grep NF_HOOK *.c 可以看到內核使用了如下HOOK點
arp.c: NF_HOOK(NF_ARP, NF_ARP_OUT, skb, NULL, skb->dev, dev_queue_xmit);
arp.c: return NF_HOOK(NF_ARP, NF_ARP_IN, skb, dev, NULL, arp_process);
igmp.c: return NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, skb->dev,
igmp.c: return NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, rt->u.dst.dev,
ip_forward.c: return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
ip_input.c: return NF_HOOK(PF_INET, NF_IP_LOCAL_IN, skb, skb->dev, NULL,
ip_input.c: return NF_HOOK(PF_INET, NF_IP_PRE_ROUTING, skb, dev, NULL,
ipmr.c: NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, dev,
ip_output.c: return NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, rt->u.dst.dev,
ip_output.c: return NF_HOOK(PF_INET, NF_IP_POST_ROUTING, skb, NULL, dev,
ip_output.c: NF_HOOK(PF_INET, NF_IP_POST_ROUTING, newskb, NULL,
ip_output.c: NF_HOOK(PF_INET, NF_IP_POST_ROUTING, newskb, NULL,
ip_output.c: return NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, rt->u.dst.dev,
ip_output.c: err = NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL,
raw.c: err = NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, rt->u.dst.dev,