// SPDX-License-Identifier: GPL-2.0-only
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/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
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* (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
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* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/slab.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/spinlock.h>
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#include <linux/interrupt.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter/xt_limit.h>
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struct xt_limit_priv {
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spinlock_t lock;
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unsigned long prev;
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uint32_t credit;
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};
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
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MODULE_DESCRIPTION("Xtables: rate-limit match");
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MODULE_ALIAS("ipt_limit");
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MODULE_ALIAS("ip6t_limit");
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/* The algorithm used is the Simple Token Bucket Filter (TBF)
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* see net/sched/sch_tbf.c in the linux source tree
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*/
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/* Rusty: This is my (non-mathematically-inclined) understanding of
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this algorithm. The `average rate' in jiffies becomes your initial
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amount of credit `credit' and the most credit you can ever have
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`credit_cap'. The `peak rate' becomes the cost of passing the
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test, `cost'.
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`prev' tracks the last packet hit: you gain one credit per jiffy.
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If you get credit balance more than this, the extra credit is
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discarded. Every time the match passes, you lose `cost' credits;
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if you don't have that many, the test fails.
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See Alexey's formal explanation in net/sched/sch_tbf.c.
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To get the maximum range, we multiply by this factor (ie. you get N
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credits per jiffy). We want to allow a rate as low as 1 per day
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(slowest userspace tool allows), which means
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CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
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#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
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/* Repeated shift and or gives us all 1s, final shift and add 1 gives
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* us the power of 2 below the theoretical max, so GCC simply does a
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* shift. */
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#define _POW2_BELOW2(x) ((x)|((x)>>1))
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#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
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#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
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#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
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#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
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#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
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#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
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static bool
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limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
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{
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const struct xt_rateinfo *r = par->matchinfo;
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struct xt_limit_priv *priv = r->master;
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unsigned long now = jiffies;
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spin_lock_bh(&priv->lock);
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priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
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if (priv->credit > r->credit_cap)
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priv->credit = r->credit_cap;
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if (priv->credit >= r->cost) {
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/* We're not limited. */
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priv->credit -= r->cost;
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spin_unlock_bh(&priv->lock);
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return true;
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}
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spin_unlock_bh(&priv->lock);
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return false;
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}
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/* Precision saver. */
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static u32 user2credits(u32 user)
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{
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/* If multiplying would overflow... */
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if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
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/* Divide first. */
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return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
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return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
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}
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static int limit_mt_check(const struct xt_mtchk_param *par)
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{
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struct xt_rateinfo *r = par->matchinfo;
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struct xt_limit_priv *priv;
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/* Check for overflow. */
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if (r->burst == 0
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|| user2credits(r->avg * r->burst) < user2credits(r->avg)) {
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pr_info_ratelimited("Overflow, try lower: %u/%u\n",
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r->avg, r->burst);
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return -ERANGE;
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}
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priv = kmalloc(sizeof(*priv), GFP_KERNEL);
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if (priv == NULL)
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return -ENOMEM;
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/* For SMP, we only want to use one set of state. */
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r->master = priv;
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/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
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128. */
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priv->prev = jiffies;
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priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
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if (r->cost == 0) {
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r->credit_cap = priv->credit; /* Credits full. */
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r->cost = user2credits(r->avg);
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}
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spin_lock_init(&priv->lock);
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return 0;
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}
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static void limit_mt_destroy(const struct xt_mtdtor_param *par)
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{
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const struct xt_rateinfo *info = par->matchinfo;
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kfree(info->master);
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}
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#ifdef CONFIG_COMPAT
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struct compat_xt_rateinfo {
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u_int32_t avg;
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u_int32_t burst;
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compat_ulong_t prev;
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u_int32_t credit;
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u_int32_t credit_cap, cost;
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u_int32_t master;
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};
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/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
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* master pointer, which does not need to be preserved. */
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static void limit_mt_compat_from_user(void *dst, const void *src)
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{
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const struct compat_xt_rateinfo *cm = src;
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struct xt_rateinfo m = {
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.avg = cm->avg,
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.burst = cm->burst,
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.prev = cm->prev | (unsigned long)cm->master << 32,
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.credit = cm->credit,
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.credit_cap = cm->credit_cap,
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.cost = cm->cost,
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};
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memcpy(dst, &m, sizeof(m));
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}
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static int limit_mt_compat_to_user(void __user *dst, const void *src)
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{
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const struct xt_rateinfo *m = src;
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struct compat_xt_rateinfo cm = {
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.avg = m->avg,
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.burst = m->burst,
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.prev = m->prev,
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.credit = m->credit,
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.credit_cap = m->credit_cap,
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.cost = m->cost,
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.master = m->prev >> 32,
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};
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return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
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}
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#endif /* CONFIG_COMPAT */
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static struct xt_match limit_mt_reg __read_mostly = {
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.name = "limit",
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.revision = 0,
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.family = NFPROTO_UNSPEC,
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.match = limit_mt,
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.checkentry = limit_mt_check,
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.destroy = limit_mt_destroy,
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.matchsize = sizeof(struct xt_rateinfo),
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#ifdef CONFIG_COMPAT
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.compatsize = sizeof(struct compat_xt_rateinfo),
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.compat_from_user = limit_mt_compat_from_user,
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.compat_to_user = limit_mt_compat_to_user,
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#endif
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.usersize = offsetof(struct xt_rateinfo, prev),
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.me = THIS_MODULE,
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};
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static int __init limit_mt_init(void)
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{
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return xt_register_match(&limit_mt_reg);
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}
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static void __exit limit_mt_exit(void)
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{
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xt_unregister_match(&limit_mt_reg);
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}
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module_init(limit_mt_init);
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module_exit(limit_mt_exit);
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