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 MODULE_LICENSE("GPL");
  18 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
  19 MODULE_DESCRIPTION("Xtables: rate-limit match");
  20 MODULE_ALIAS("ipt_limit");
  21 MODULE_ALIAS("ip6t_limit");
  22
  23 /* The algorithm used is the Simple Token Bucket Filter (TBF)
  24  * see net/sched/sch_tbf.c in the linux source tree
  25  */
  26
  27 static DEFINE_SPINLOCK(limit_lock);
  28
  29 /* Rusty: This is my (non-mathematically-inclined) understanding of
  30    this algorithm.  The `average rate' in jiffies becomes your initial
  31    amount of credit `credit' and the most credit you can ever have
  32    `credit_cap'.  The `peak rate' becomes the cost of passing the
  33    test, `cost'.
  34
  35    `prev' tracks the last packet hit: you gain one credit per jiffy.
  36    If you get credit balance more than this, the extra credit is
  37    discarded.  Every time the match passes, you lose `cost' credits;
  38    if you don't have that many, the test fails.
  39
  40    See Alexey's formal explanation in net/sched/sch_tbf.c.
  41
  42    To get the maxmum range, we multiply by this factor (ie. you get N
  43    credits per jiffy).  We want to allow a rate as low as 1 per day
  44    (slowest userspace tool allows), which means
  45    CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
  46 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
  47
  48 /* Repeated shift and or gives us all 1s, final shift and add 1 gives
  49  * us the power of 2 below the theoretical max, so GCC simply does a
  50  * shift. */
  51 #define _POW2_BELOW2(x) ((x)|((x)>>1))
  52 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
  53 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
  54 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
  55 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
  56 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
  57
  58 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
  59
  60 static bool
  61 limit_mt(const struct sk_buff *skb, const struct net_device *in,
  62          const struct net_device *out, const struct xt_match *match,
  63          const void *matchinfo, int offset, unsigned int protoff,
  64          bool *hotdrop)
  65 {
  66         struct xt_rateinfo *r =
  67                 ((const struct xt_rateinfo *)matchinfo)->master;
  68         unsigned long now = jiffies;
  69
  70         spin_lock_bh(&limit_lock);
  71         r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
  72         if (r->credit > r->credit_cap)
  73                 r->credit = r->credit_cap;
  74
  75         if (r->credit >= r->cost) {
  76                 /* We're not limited. */
  77                 r->credit -= r->cost;
  78                 spin_unlock_bh(&limit_lock);
  79                 return true;
  80         }
  81
  82         spin_unlock_bh(&limit_lock);
  83         return false;
  84 }
  85
  86 /* Precision saver. */
  87 static u_int32_t
  88 user2credits(u_int32_t user)
  89 {
  90         /* If multiplying would overflow... */
  91         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  92                 /* Divide first. */
  93                 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  94
  95         return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
  96 }
  97
  98 static bool
  99 limit_mt_check(const char *tablename, const void *inf,
 100                const struct xt_match *match, void *matchinfo,
 101                unsigned int hook_mask)
 102 {
 103         struct xt_rateinfo *r = matchinfo;
 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         /* For SMP, we only want to use one set of counters. */
 114         r->master = r;
 115         if (r->cost == 0) {
 116                 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 117                    128. */
 118                 r->prev = jiffies;
 119                 r->credit = user2credits(r->avg * r->burst);     /* Credits full. */
 120                 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
 121                 r->cost = user2credits(r->avg);
 122         }
 123         return true;
 124 }
 125
 126 #ifdef CONFIG_COMPAT
 127 struct compat_xt_rateinfo {
 128         u_int32_t avg;
 129         u_int32_t burst;
 130
 131         compat_ulong_t prev;
 132         u_int32_t credit;
 133         u_int32_t credit_cap, cost;
 134
 135         u_int32_t master;
 136 };
 137
 138 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
 139  * master pointer, which does not need to be preserved. */
 140 static void limit_mt_compat_from_user(void *dst, void *src)
 141 {
 142         const struct compat_xt_rateinfo *cm = src;
 143         struct xt_rateinfo m = {
 144                 .avg            = cm->avg,
 145                 .burst          = cm->burst,
 146                 .prev           = cm->prev | (unsigned long)cm->master << 32,
 147                 .credit         = cm->credit,
 148                 .credit_cap     = cm->credit_cap,
 149                 .cost           = cm->cost,
 150         };
 151         memcpy(dst, &m, sizeof(m));
 152 }
 153
 154 static int limit_mt_compat_to_user(void __user *dst, void *src)
 155 {
 156         const struct xt_rateinfo *m = src;
 157         struct compat_xt_rateinfo cm = {
 158                 .avg            = m->avg,
 159                 .burst          = m->burst,
 160                 .prev           = m->prev,
 161                 .credit         = m->credit,
 162                 .credit_cap     = m->credit_cap,
 163                 .cost           = m->cost,
 164                 .master         = m->prev >> 32,
 165         };
 166         return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
 167 }
 168 #endif /* CONFIG_COMPAT */
 169
 170 static struct xt_match limit_mt_reg[] __read_mostly = {
 171         {
 172                 .name           = "limit",
 173                 .family         = AF_INET,
 174                 .checkentry     = limit_mt_check,
 175                 .match          = limit_mt,
 176                 .matchsize      = sizeof(struct xt_rateinfo),
 177 #ifdef CONFIG_COMPAT
 178                 .compatsize     = sizeof(struct compat_xt_rateinfo),
 179                 .compat_from_user = limit_mt_compat_from_user,
 180                 .compat_to_user = limit_mt_compat_to_user,
 181 #endif
 182                 .me             = THIS_MODULE,
 183         },
 184         {
 185                 .name           = "limit",
 186                 .family         = AF_INET6,
 187                 .checkentry     = limit_mt_check,
 188                 .match          = limit_mt,
 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
 199 static int __init limit_mt_init(void)
 200 {
 201         return xt_register_matches(limit_mt_reg, ARRAY_SIZE(limit_mt_reg));
 202 }
 203
 204 static void __exit limit_mt_exit(void)
 205 {
 206         xt_unregister_matches(limit_mt_reg, ARRAY_SIZE(limit_mt_reg));
 207 }
 208
 209 module_init(limit_mt_init);
 210 module_exit(limit_mt_exit);