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