// SPDX-License-Identifier: GPL-2.0-only
/* (C) 1999 Jérôme de Vivie <[email protected]>
* (C) 1999 Hervé Eychenne <[email protected]>
* (C) 2006-2012 Patrick McHardy <[email protected]>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/interrupt.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_limit.h>
struct xt_limit_priv {
unsigned long prev;
u32 credit;
};
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Herve Eychenne <[email protected]>");
MODULE_DESCRIPTION("Xtables: 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
*/
/* 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 maximum 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 bool
limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_rateinfo *r = par->matchinfo;
struct xt_limit_priv *priv = r->master;
unsigned long now;
u32 old_credit, new_credit, credit_increase = 0;
bool ret;
/* fastpath if there is nothing to update */
if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies))
return false;
do {
now = jiffies;
credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
old_credit = READ_ONCE(priv->credit);
new_credit = old_credit;
new_credit += credit_increase;
if (new_credit > r->credit_cap)
new_credit = r->credit_cap;
if (new_credit >= r->cost) {
ret = true;
new_credit -= r->cost;
} else {
ret = false;
}
} while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit);
return ret;
}
/* Precision saver. */
static u32 user2credits(u32 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 limit_mt_check(const struct xt_mtchk_param *par)
{
struct xt_rateinfo *r = par->matchinfo;
struct xt_limit_priv *priv;
/* Check for overflow. */
if (r->burst == 0
|| user2credits(r->avg * r->burst) < user2credits(r->avg)) {
pr_info_ratelimited("Overflow, try lower: %u/%u\n",
r->avg, r->burst);
return -ERANGE;
}
priv = kmalloc(sizeof(*priv), GFP_KERNEL);
if (priv == NULL)
return -ENOMEM;
/* For SMP, we only want to use one set of state. */
r->master = priv;
/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
128. */
priv->prev = jiffies;
priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
if (r->cost == 0) {
r->credit_cap = priv->credit; /* Credits full. */
r->cost = user2credits(r->avg);
}
return 0;
}
static void limit_mt_destroy(const struct xt_mtdtor_param *par)
{
const struct xt_rateinfo *info = par->matchinfo;
kfree(info->master);
}
#ifdef CONFIG_NETFILTER_XTABLES_COMPAT
struct compat_xt_rateinfo {
u_int32_t avg;
u_int32_t burst;
compat_ulong_t prev;
u_int32_t credit;
u_int32_t credit_cap, cost;
u_int32_t master;
};
/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
* master pointer, which does not need to be preserved. */
static void limit_mt_compat_from_user(void *dst, const void *src)
{
const struct compat_xt_rateinfo *cm = src;
struct xt_rateinfo m = {
.avg = cm->avg,
.burst = cm->burst,
.prev = cm->prev | (unsigned long)cm->master << 32,
.credit = cm->credit,
.credit_cap = cm->credit_cap,
.cost = cm->cost,
};
memcpy(dst, &m, sizeof(m));
}
static int limit_mt_compat_to_user(void __user *dst, const void *src)
{
const struct xt_rateinfo *m = src;
struct compat_xt_rateinfo cm = {
.avg = m->avg,
.burst = m->burst,
.prev = m->prev,
.credit = m->credit,
.credit_cap = m->credit_cap,
.cost = m->cost,
.master = m->prev >> 32,
};
return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
}
#endif /* CONFIG_NETFILTER_XTABLES_COMPAT */
static struct xt_match limit_mt_reg __read_mostly = {
.name = "limit",
.revision = 0,
.family = NFPROTO_UNSPEC,
.match = limit_mt,
.checkentry = limit_mt_check,
.destroy = limit_mt_destroy,
.matchsize = sizeof(struct xt_rateinfo),
#ifdef CONFIG_NETFILTER_XTABLES_COMPAT
.compatsize = sizeof(struct compat_xt_rateinfo),
.compat_from_user = limit_mt_compat_from_user,
.compat_to_user = limit_mt_compat_to_user,
#endif
.usersize = offsetof(struct xt_rateinfo, prev),
.me = THIS_MODULE,
};
static int __init limit_mt_init(void)
{
return xt_register_match(&limit_mt_reg);
}
static void __exit limit_mt_exit(void)
{
xt_unregister_match(&limit_mt_reg);
}
module_init(limit_mt_init);
module_exit(limit_mt_exit);
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