net/netfilter/xt_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/x_tables.h>
  22 #include <linux/netfilter/xt_limit.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
  26 MODULE_DESCRIPTION("iptables rate limit match");
  27 MODULE_ALIAS("ipt_limit");
  28 MODULE_ALIAS("ip6t_limit");
  29
  30 /* The algorithm used is the Simple Token Bucket Filter (TBF)
  31  * see net/sched/sch_tbf.c in the linux source tree
  32  */
  33
  34 static DEFINE_SPINLOCK(limit_lock);
  35
  36 /* Rusty: This is my (non-mathematically-inclined) understanding of
  37    this algorithm.  The `average rate' in jiffies becomes your initial
  38    amount of credit `credit' and the most credit you can ever have
  39    `credit_cap'.  The `peak rate' becomes the cost of passing the
  40    test, `cost'.
  41
  42    `prev' tracks the last packet hit: you gain one credit per jiffy.
  43    If you get credit balance more than this, the extra credit is
  44    discarded.  Every time the match passes, you lose `cost' credits;
  45    if you don't have that many, the test fails.
  46
  47    See Alexey's formal explanation in net/sched/sch_tbf.c.
  48
  49    To get the maxmum range, we multiply by this factor (ie. you get N
  50    credits per jiffy).  We want to allow a rate as low as 1 per day
  51    (slowest userspace tool allows), which means
  52    CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
  53 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
  54
  55 /* Repeated shift and or gives us all 1s, final shift and add 1 gives
  56  * us the power of 2 below the theoretical max, so GCC simply does a
  57  * shift. */
  58 #define _POW2_BELOW2(x) ((x)|((x)>>1))
  59 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
  60 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
  61 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
  62 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
  63 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
  64
  65 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
  66
  67 static int
  68 ipt_limit_match(const struct sk_buff *skb,
  69                 const struct net_device *in,
  70                 const struct net_device *out,
  71                 const struct xt_match *match,
  72                 const void *matchinfo,
  73                 int offset,
  74                 unsigned int protoff,
  75                 int *hotdrop)
  76 {
  77         struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master;
  78         unsigned long now = jiffies;
  79
  80         spin_lock_bh(&limit_lock);
  81         r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
  82         if (r->credit > r->credit_cap)
  83                 r->credit = r->credit_cap;
  84
  85         if (r->credit >= r->cost) {
  86                 /* We're not limited. */
  87                 r->credit -= r->cost;
  88                 spin_unlock_bh(&limit_lock);
  89                 return 1;
  90         }
  91
  92         spin_unlock_bh(&limit_lock);
  93         return 0;
  94 }
  95
  96 /* Precision saver. */
  97 static u_int32_t
  98 user2credits(u_int32_t user)
  99 {
 100         /* If multiplying would overflow... */
 101         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
 102                 /* Divide first. */
 103                 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
 104
 105         return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
 106 }
 107
 108 static int
 109 ipt_limit_checkentry(const char *tablename,
 110                      const void *inf,
 111                      const struct xt_match *match,
 112                      void *matchinfo,
 113                      unsigned int hook_mask)
 114 {
 115         struct xt_rateinfo *r = matchinfo;
 116
 117         /* Check for overflow. */
 118         if (r->burst == 0
 119             || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
 120                 printk("Overflow in xt_limit, try lower: %u/%u\n",
 121                        r->avg, r->burst);
 122                 return 0;
 123         }
 124
 125         /* For SMP, we only want to use one set of counters. */
 126         r->master = r;
 127         if (r->cost == 0) {
 128                 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 129                    128. */
 130                 r->prev = jiffies;
 131                 r->credit = user2credits(r->avg * r->burst);     /* Credits full. */
 132                 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
 133                 r->cost = user2credits(r->avg);
 134         }
 135         return 1;
 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 compat_from_user(void *dst, void *src)
 153 {
 154         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 compat_to_user(void __user *dst, void *src)
 167 {
 168         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 xt_limit_match[] = {
 183         {
 184                 .name           = "limit",
 185                 .family         = AF_INET,
 186                 .checkentry     = ipt_limit_checkentry,
 187                 .match          = ipt_limit_match,
 188                 .matchsize      = sizeof(struct xt_rateinfo),
 189 #ifdef CONFIG_COMPAT
 190                 .compatsize     = sizeof(struct compat_xt_rateinfo),
 191                 .compat_from_user = compat_from_user,
 192                 .compat_to_user = compat_to_user,
 193 #endif
 194                 .me             = THIS_MODULE,
 195         },
 196         {
 197                 .name           = "limit",
 198                 .family         = AF_INET6,
 199                 .checkentry     = ipt_limit_checkentry,
 200                 .match          = ipt_limit_match,
 201                 .matchsize      = sizeof(struct xt_rateinfo),
 202                 .me             = THIS_MODULE,
 203         },
 204 };
 205
 206 static int __init xt_limit_init(void)
 207 {
 208         return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 209 }
 210
 211 static void __exit xt_limit_fini(void)
 212 {
 213         xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 214 }
 215
 216 module_init(xt_limit_init);
 217 module_exit(xt_limit_fini);