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/* Kernel module to control the rate
*
* 2 September 1999: Changed from the target RATE to the match
* `limit', removed logging. Did I mention that
* Alexey is a fucking genius?
* Rusty Russell (rusty@rustcorp.com.au). */
/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
* (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_limit.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
MODULE_DESCRIPTION("iptables rate limit match");
MODULE_ALIAS("ipt_limit");
MODULE_ALIAS("ip6t_limit");
/* The algorithm used is the Simple Token Bucket Filter (TBF)
* see net/sched/sch_tbf.c in the linux source tree
*/
static DEFINE_SPINLOCK(limit_lock);
/* 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 get the maxmum range, we multiply by this factor (ie. you get N
credits per jiffy). We want to allow a rate as low as 1 per day
(slowest userspace tool allows), which means
CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
/* Repeated shift and or gives us all 1s, final shift and add 1 gives
* us the power of 2 below the theoretical max, so GCC simply does a
* shift. */
#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
static int
ipt_limit_match(const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const struct xt_match *match,
const void *matchinfo,
int offset,
unsigned int protoff,
int *hotdrop)
{
struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master;
unsigned long now = jiffies;
spin_lock_bh(&limit_lock);
r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
if (r->credit > r->credit_cap)
r->credit = r->credit_cap;
if (r->credit >= r->cost) {
/* We're not limited. */
r->credit -= r->cost;
spin_unlock_bh(&limit_lock);
return 1;
}
spin_unlock_bh(&limit_lock);
return 0;
}
/* 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 / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
}
static int
ipt_limit_checkentry(const char *tablename,
const void *inf,
const struct xt_match *match,
void *matchinfo,
unsigned int matchsize,
unsigned int hook_mask)
{
struct xt_rateinfo *r = matchinfo;
/* Check for overflow. */
if (r->burst == 0
|| user2credits(r->avg * r->burst) < user2credits(r->avg)) {
printk("Overflow in xt_limit, try lower: %u/%u\n",
r->avg, r->burst);
return 0;
}
/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
128. */
r->prev = jiffies;
r->credit = user2credits(r->avg * r->burst); /* Credits full. */
r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
r->cost = user2credits(r->avg);
/* For SMP, we only want to use one set of counters. */
r->master = r;
return 1;
}
static struct xt_match ipt_limit_reg = {
.name = "limit",
.match = ipt_limit_match,
.matchsize = sizeof(struct xt_rateinfo),
.checkentry = ipt_limit_checkentry,
.me = THIS_MODULE,
};
static struct xt_match limit6_reg = {
.name = "limit",
.match = ipt_limit_match,
.matchsize = sizeof(struct xt_rateinfo),
.checkentry = ipt_limit_checkentry,
.me = THIS_MODULE,
};
static int __init init(void)
{
int ret;
ret = xt_register_match(AF_INET, &ipt_limit_reg);
if (ret)
return ret;
ret = xt_register_match(AF_INET6, &limit6_reg);
if (ret)
xt_unregister_match(AF_INET, &ipt_limit_reg);
return ret;
}
static void __exit fini(void)
{
xt_unregister_match(AF_INET, &ipt_limit_reg);
xt_unregister_match(AF_INET6, &limit6_reg);
}
module_init(init);
module_exit(fini);
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