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("iptables 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 ipt_limit_match(const struct sk_buff *skb,
  62                 const struct net_device *in,
  63                 const struct net_device *out,
  64                 const struct xt_match *match,
  65                 const void *matchinfo,
  66                 int offset,
  67                 unsigned int protoff,
  68                 bool *hotdrop)
  69 {
  70         struct xt_rateinfo *r =
  71                 ((const struct xt_rateinfo *)matchinfo)->master;
  72         unsigned long now = jiffies;
  73
  74         spin_lock_bh(&limit_lock);
  75         r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
  76         if (r->credit > r->credit_cap)
  77                 r->credit = r->credit_cap;
  78
  79         if (r->credit >= r->cost) {
  80                 /* We're not limited. */
  81                 r->credit -= r->cost;
  82                 spin_unlock_bh(&limit_lock);
  83                 return true;
  84         }
  85
  86         spin_unlock_bh(&limit_lock);
  87         return false;
  88 }
  89
  90 /* Precision saver. */
  91 static u_int32_t
  92 user2credits(u_int32_t user)
  93 {
  94         /* If multiplying would overflow... */
  95         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  96                 /* Divide first. */
  97                 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  98
  99         return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
 100 }
 101
 102 static bool
 103 ipt_limit_checkentry(const char *tablename,
 104                      const void *inf,
 105                      const struct xt_match *match,
 106                      void *matchinfo,
 107                      unsigned int hook_mask)
 108 {
 109         struct xt_rateinfo *r = matchinfo;
 110
 111         /* Check for overflow. */
 112         if (r->burst == 0
 113             || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
 114                 printk("Overflow in xt_limit, try lower: %u/%u\n",
 115                        r->avg, r->burst);
 116                 return false;
 117         }
 118
 119         /* For SMP, we only want to use one set of counters. */
 120         r->master = r;
 121         if (r->cost == 0) {
 122                 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 123                    128. */
 124                 r->prev = jiffies;
 125                 r->credit = user2credits(r->avg * r->burst);     /* Credits full. */
 126                 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
 127                 r->cost = user2credits(r->avg);
 128         }
 129         return true;
 130 }
 131
 132 #ifdef CONFIG_COMPAT
 133 struct compat_xt_rateinfo {
 134         u_int32_t avg;
 135         u_int32_t burst;
 136
 137         compat_ulong_t prev;
 138         u_int32_t credit;
 139         u_int32_t credit_cap, cost;
 140
 141         u_int32_t master;
 142 };
 143
 144 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
 145  * master pointer, which does not need to be preserved. */
 146 static void compat_from_user(void *dst, void *src)
 147 {
 148         const struct compat_xt_rateinfo *cm = src;
 149         struct xt_rateinfo m = {
 150                 .avg            = cm->avg,
 151                 .burst          = cm->burst,
 152                 .prev           = cm->prev | (unsigned long)cm->master << 32,
 153                 .credit         = cm->credit,
 154                 .credit_cap     = cm->credit_cap,
 155                 .cost           = cm->cost,
 156         };
 157         memcpy(dst, &m, sizeof(m));
 158 }
 159
 160 static int compat_to_user(void __user *dst, void *src)
 161 {
 162         const struct xt_rateinfo *m = src;
 163         struct compat_xt_rateinfo cm = {
 164                 .avg            = m->avg,
 165                 .burst          = m->burst,
 166                 .prev           = m->prev,
 167                 .credit         = m->credit,
 168                 .credit_cap     = m->credit_cap,
 169                 .cost           = m->cost,
 170                 .master         = m->prev >> 32,
 171         };
 172         return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
 173 }
 174 #endif /* CONFIG_COMPAT */
 175
 176 static struct xt_match xt_limit_match[] __read_mostly = {
 177         {
 178                 .name           = "limit",
 179                 .family         = AF_INET,
 180                 .checkentry     = ipt_limit_checkentry,
 181                 .match          = ipt_limit_match,
 182                 .matchsize      = sizeof(struct xt_rateinfo),
 183 #ifdef CONFIG_COMPAT
 184                 .compatsize     = sizeof(struct compat_xt_rateinfo),
 185                 .compat_from_user = compat_from_user,
 186                 .compat_to_user = compat_to_user,
 187 #endif
 188                 .me             = THIS_MODULE,
 189         },
 190         {
 191                 .name           = "limit",
 192                 .family         = AF_INET6,
 193                 .checkentry     = ipt_limit_checkentry,
 194                 .match          = ipt_limit_match,
 195                 .matchsize      = sizeof(struct xt_rateinfo),
 196                 .me             = THIS_MODULE,
 197         },
 198 };
 199
 200 static int __init xt_limit_init(void)
 201 {
 202         return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 203 }
 204
 205 static void __exit xt_limit_fini(void)
 206 {
 207         xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 208 }
 209
 210 module_init(xt_limit_init);
 211 module_exit(xt_limit_fini);