net/netfilter/xt_limit.c

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