linux/net/netfilter/xt_limit.c
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   1/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
   2 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
   3 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   4 *
   5 * This program is free software; you can redistribute it and/or modify
   6 * it under the terms of the GNU General Public License version 2 as
   7 * published by the Free Software Foundation.
   8 */
   9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  10
  11#include <linux/slab.h>
  12#include <linux/module.h>
  13#include <linux/skbuff.h>
  14#include <linux/spinlock.h>
  15#include <linux/interrupt.h>
  16
  17#include <linux/netfilter/x_tables.h>
  18#include <linux/netfilter/xt_limit.h>
  19
  20struct xt_limit_priv {
  21        unsigned long prev;
  22        uint32_t credit;
  23};
  24
  25MODULE_LICENSE("GPL");
  26MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
  27MODULE_DESCRIPTION("Xtables: rate-limit match");
  28MODULE_ALIAS("ipt_limit");
  29MODULE_ALIAS("ip6t_limit");
  30
  31/* The algorithm used is the Simple Token Bucket Filter (TBF)
  32 * see net/sched/sch_tbf.c in the linux source tree
  33 */
  34
  35static DEFINE_SPINLOCK(limit_lock);
  36
  37/* Rusty: This is my (non-mathematically-inclined) understanding of
  38   this algorithm.  The `average rate' in jiffies becomes your initial
  39   amount of credit `credit' and the most credit you can ever have
  40   `credit_cap'.  The `peak rate' becomes the cost of passing the
  41   test, `cost'.
  42
  43   `prev' tracks the last packet hit: you gain one credit per jiffy.
  44   If you get credit balance more than this, the extra credit is
  45   discarded.  Every time the match passes, you lose `cost' credits;
  46   if you don't have that many, the test fails.
  47
  48   See Alexey's formal explanation in net/sched/sch_tbf.c.
  49
  50   To get the maxmum range, we multiply by this factor (ie. you get N
  51   credits per jiffy).  We want to allow a rate as low as 1 per day
  52   (slowest userspace tool allows), which means
  53   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
  54#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
  55
  56/* Repeated shift and or gives us all 1s, final shift and add 1 gives
  57 * us the power of 2 below the theoretical max, so GCC simply does a
  58 * shift. */
  59#define _POW2_BELOW2(x) ((x)|((x)>>1))
  60#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
  61#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
  62#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
  63#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
  64#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
  65
  66#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
  67
  68static bool
  69limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
  70{
  71        const struct xt_rateinfo *r = par->matchinfo;
  72        struct xt_limit_priv *priv = r->master;
  73        unsigned long now = jiffies;
  74
  75        spin_lock_bh(&limit_lock);
  76        priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
  77        if (priv->credit > r->credit_cap)
  78                priv->credit = r->credit_cap;
  79
  80        if (priv->credit >= r->cost) {
  81                /* We're not limited. */
  82                priv->credit -= r->cost;
  83                spin_unlock_bh(&limit_lock);
  84                return true;
  85        }
  86
  87        spin_unlock_bh(&limit_lock);
  88        return false;
  89}
  90
  91/* Precision saver. */
  92static u32 user2credits(u32 user)
  93{
  94        /* If multiplying would overflow... */
  95        if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  96                /* Divide first. */
  97                return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  98
  99        return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
 100}
 101
 102static int limit_mt_check(const struct xt_mtchk_param *par)
 103{
 104        struct xt_rateinfo *r = par->matchinfo;
 105        struct xt_limit_priv *priv;
 106
 107        /* Check for overflow. */
 108        if (r->burst == 0
 109            || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
 110                pr_info("Overflow, try lower: %u/%u\n",
 111                        r->avg, r->burst);
 112                return -ERANGE;
 113        }
 114
 115        priv = kmalloc(sizeof(*priv), GFP_KERNEL);
 116        if (priv == NULL)
 117                return -ENOMEM;
 118
 119        /* For SMP, we only want to use one set of state. */
 120        r->master = priv;
 121        /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 122           128. */
 123        priv->prev = jiffies;
 124        priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
 125        if (r->cost == 0) {
 126                r->credit_cap = priv->credit; /* Credits full. */
 127                r->cost = user2credits(r->avg);
 128        }
 129        return 0;
 130}
 131
 132static void limit_mt_destroy(const struct xt_mtdtor_param *par)
 133{
 134        const struct xt_rateinfo *info = par->matchinfo;
 135
 136        kfree(info->master);
 137}
 138
 139#ifdef CONFIG_COMPAT
 140struct compat_xt_rateinfo {
 141        u_int32_t avg;
 142        u_int32_t burst;
 143
 144        compat_ulong_t prev;
 145        u_int32_t credit;
 146        u_int32_t credit_cap, cost;
 147
 148        u_int32_t master;
 149};
 150
 151/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
 152 * master pointer, which does not need to be preserved. */
 153static void limit_mt_compat_from_user(void *dst, const void *src)
 154{
 155        const struct compat_xt_rateinfo *cm = src;
 156        struct xt_rateinfo m = {
 157                .avg            = cm->avg,
 158                .burst          = cm->burst,
 159                .prev           = cm->prev | (unsigned long)cm->master << 32,
 160                .credit         = cm->credit,
 161                .credit_cap     = cm->credit_cap,
 162                .cost           = cm->cost,
 163        };
 164        memcpy(dst, &m, sizeof(m));
 165}
 166
 167static int limit_mt_compat_to_user(void __user *dst, const void *src)
 168{
 169        const struct xt_rateinfo *m = src;
 170        struct compat_xt_rateinfo cm = {
 171                .avg            = m->avg,
 172                .burst          = m->burst,
 173                .prev           = m->prev,
 174                .credit         = m->credit,
 175                .credit_cap     = m->credit_cap,
 176                .cost           = m->cost,
 177                .master         = m->prev >> 32,
 178        };
 179        return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
 180}
 181#endif /* CONFIG_COMPAT */
 182
 183static struct xt_match limit_mt_reg __read_mostly = {
 184        .name             = "limit",
 185        .revision         = 0,
 186        .family           = NFPROTO_UNSPEC,
 187        .match            = limit_mt,
 188        .checkentry       = limit_mt_check,
 189        .destroy          = limit_mt_destroy,
 190        .matchsize        = sizeof(struct xt_rateinfo),
 191#ifdef CONFIG_COMPAT
 192        .compatsize       = sizeof(struct compat_xt_rateinfo),
 193        .compat_from_user = limit_mt_compat_from_user,
 194        .compat_to_user   = limit_mt_compat_to_user,
 195#endif
 196        .me               = THIS_MODULE,
 197};
 198
 199static int __init limit_mt_init(void)
 200{
 201        return xt_register_match(&limit_mt_reg);
 202}
 203
 204static void __exit limit_mt_exit(void)
 205{
 206        xt_unregister_match(&limit_mt_reg);
 207}
 208
 209module_init(limit_mt_init);
 210module_exit(limit_mt_exit);
 211
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