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/*
* ebt_limit
*
* Authors:
* Tom Marshall <tommy@home.tig-grr.com>
*
* Mostly copied from netfilter's ipt_limit.c
*
* September, 2003
*
*/
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_limit.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/spinlock.h>
/* The algorithm used is the Simple Token Bucket Filter (TBF)
* see net/sched/sch_tbf.c in the linux source tree
*/
static spinlock_t limit_lock = SPIN_LOCK_UNLOCKED;
/* Rusty: This is my (non-mathematically-inclined) understanding of
this algorithm. The `average rate' in jiffies becomes your initial
amount of credit `credit' and the most credit you can ever have
`credit_cap'. The `peak rate' becomes the cost of passing the
test, `cost'.
`prev' tracks the last packet hit: you gain one credit per jiffy.
If you get credit balance more than this, the extra credit is
discarded. Every time the match passes, you lose `cost' credits;
if you don't have that many, the test fails.
See Alexey's formal explanation in net/sched/sch_tbf.c.
To avoid underflow, we multiply by 128 (ie. you get 128 credits per
jiffy). Hence a cost of 2^32-1, means one pass per 32768 seconds
at 1024HZ (or one every 9 hours). A cost of 1 means 12800 passes
per second at 100HZ. */
#define CREDITS_PER_JIFFY 128
static int ebt_limit_match(const struct sk_buff *skb, const struct net_device *in,
const struct net_device *out, const void *data, unsigned int datalen)
{
struct ebt_limit_info *info = (struct ebt_limit_info *)data;
unsigned long now = jiffies;
spin_lock_bh(&limit_lock);
info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
if (info->credit > info->credit_cap)
info->credit = info->credit_cap;
if (info->credit >= info->cost) {
/* We're not limited. */
info->credit -= info->cost;
spin_unlock_bh(&limit_lock);
return EBT_MATCH;
}
spin_unlock_bh(&limit_lock);
return EBT_NOMATCH;
}
/* Precision saver. */
static u_int32_t
user2credits(u_int32_t user)
{
/* If multiplying would overflow... */
if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
/* Divide first. */
return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
}
static int ebt_limit_check(const char *tablename, unsigned int hookmask,
const struct ebt_entry *e, void *data, unsigned int datalen)
{
struct ebt_limit_info *info = (struct ebt_limit_info *)data;
if (datalen != EBT_ALIGN(sizeof(struct ebt_limit_info)))
return -EINVAL;
/* Check for overflow. */
if (info->burst == 0
|| user2credits(info->avg * info->burst) < user2credits(info->avg)) {
printk("Overflow in ebt_limit: %u/%u\n",
info->avg, info->burst);
return -EINVAL;
}
/* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
info->prev = jiffies;
info->credit = user2credits(info->avg * info->burst);
info->credit_cap = user2credits(info->avg * info->burst);
info->cost = user2credits(info->avg);
return 0;
}
static struct ebt_match ebt_limit_reg =
{
{NULL, NULL}, EBT_LIMIT_MATCH, ebt_limit_match, ebt_limit_check, NULL,
THIS_MODULE
};
static int __init init(void)
{
return ebt_register_match(&ebt_limit_reg);
}
static void __exit fini(void)
{
ebt_unregister_match(&ebt_limit_reg);
}
module_init(init);
module_exit(fini);
EXPORT_NO_SYMBOLS;
MODULE_LICENSE("GPL");
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