net/ipv6/netfilter/ip6t_limit.c

   1 /* Kernel module to control the rate
   2  *
   3  * 2 September 1999: Changed from the target RATE to the match
   4  *                   `limit', removed logging.  Did I mention that
   5  *                   Alexey is a fucking genius?
   6  *                   Rusty Russell (rusty@rustcorp.com.au).  */
   7
   8 /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
   9  * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License version 2 as
  13  * published by the Free Software Foundation.
  14  */
  15
  16 #include <linux/module.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/interrupt.h>
  20
  21 #include <linux/netfilter_ipv6/ip6_tables.h>
  22 #include <linux/netfilter_ipv6/ip6t_limit.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
  26 MODULE_DESCRIPTION("rate limiting within ip6tables");
  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 avoid underflow, we multiply by 128 (ie. you get 128 credits per
  48    jiffy).  Hence a cost of 2^32-1, means one pass per 32768 seconds
  49    at 1024HZ (or one every 9 hours).  A cost of 1 means 12800 passes
  50    per second at 100HZ.  */
  51
  52 #define CREDITS_PER_JIFFY 128
  53
  54 static int
  55 ip6t_limit_match(const struct sk_buff *skb,
  56                 const struct net_device *in,
  57                 const struct net_device *out,
  58                 const void *matchinfo,
  59                 int offset,
  60                 unsigned int protoff,
  61                 int *hotdrop)
  62 {
  63         struct ip6t_rateinfo *r = ((struct ip6t_rateinfo *)matchinfo)->master;
  64         unsigned long now = jiffies;
  65
  66         spin_lock_bh(&limit_lock);
  67         r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
  68         if (r->credit > r->credit_cap)
  69                 r->credit = r->credit_cap;
  70
  71         if (r->credit >= r->cost) {
  72                 /* We're not limited. */
  73                 r->credit -= r->cost;
  74                 spin_unlock_bh(&limit_lock);
  75                 return 1;
  76         }
  77
  78         spin_unlock_bh(&limit_lock);
  79         return 0;
  80 }
  81
  82 /* Precision saver. */
  83 static u_int32_t
  84 user2credits(u_int32_t user)
  85 {
  86         /* If multiplying would overflow... */
  87         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  88                 /* Divide first. */
  89                 return (user / IP6T_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  90
  91         return (user * HZ * CREDITS_PER_JIFFY) / IP6T_LIMIT_SCALE;
  92 }
  93
  94 static int
  95 ip6t_limit_checkentry(const char *tablename,
  96                      const struct ip6t_ip6 *ip,
  97                      void *matchinfo,
  98                      unsigned int matchsize,
  99                      unsigned int hook_mask)
 100 {
 101         struct ip6t_rateinfo *r = matchinfo;
 102
 103         if (matchsize != IP6T_ALIGN(sizeof(struct ip6t_rateinfo)))
 104                 return 0;
 105
 106         /* Check for overflow. */
 107         if (r->burst == 0
 108             || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
 109                 printk("Call rusty: overflow in ip6t_limit: %u/%u\n",
 110                        r->avg, r->burst);
 111                 return 0;
 112         }
 113
 114         /* User avg in seconds * IP6T_LIMIT_SCALE: convert to jiffies *
 115            128. */
 116         r->prev = jiffies;
 117         r->credit = user2credits(r->avg * r->burst);     /* Credits full. */
 118         r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
 119         r->cost = user2credits(r->avg);
 120
 121         /* For SMP, we only want to use one set of counters. */
 122         r->master = r;
 123
 124         return 1;
 125 }
 126
 127 static struct ip6t_match ip6t_limit_reg = {
 128         .name           = "limit",
 129         .match          = ip6t_limit_match,
 130         .checkentry     = ip6t_limit_checkentry,
 131         .me             = THIS_MODULE,
 132 };
 133
 134 static int __init init(void)
 135 {
 136         if (ip6t_register_match(&ip6t_limit_reg))
 137                 return -EINVAL;
 138         return 0;
 139 }
 140
 141 static void __exit fini(void)
 142 {
 143         ip6t_unregister_match(&ip6t_limit_reg);
 144 }
 145
 146 module_init(init);
 147 module_exit(fini);