release/src-rt-6.x/linux/linux-2.6/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 int
  66 ipt_limit_match(const struct sk_buff *skb,
  67                 const struct net_device *in,
  68                 const struct net_device *out,
  69                 const struct xt_match *match,
  70                 const void *matchinfo,
  71                 int offset,
  72                 unsigned int protoff,
  73                 int *hotdrop)
  74 {
  75         const struct xt_rateinfo *r = (struct xt_rateinfo *)matchinfo;
  76         struct xt_limit_priv *priv = r->master;
  77         unsigned long now = jiffies;
  78
  79         spin_lock_bh(&limit_lock);
  80         priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
  81         if (priv->credit > r->credit_cap)
  82                 priv->credit = r->credit_cap;
  83
  84         if (priv->credit >= r->cost) {
  85                 /* We're not limited. */
  86                 priv->credit -= r->cost;
  87                 spin_unlock_bh(&limit_lock);
  88                 return 1;
  89         }
  90
  91         spin_unlock_bh(&limit_lock);
  92         return 0;
  93 }
  94
  95 /* Precision saver. */
  96 static u_int32_t
  97 user2credits(u_int32_t user)
  98 {
  99         /* If multiplying would overflow... */
 100         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
 101                 /* Divide first. */
 102                 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
 103
 104         return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
 105 }
 106
 107 static int
 108 ipt_limit_checkentry(const char *tablename,
 109                      const void *inf,
 110                      const struct xt_match *match,
 111                      void *matchinfo,
 112                      unsigned int hook_mask)
 113 {
 114         struct xt_rateinfo *r = matchinfo;
 115         struct xt_limit_priv *priv;
 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         priv = kmalloc(sizeof(*priv), GFP_KERNEL);
 126         if (priv == NULL)
 127                 return 0;
 128
 129         /* For SMP, we only want to use one set of state. */
 130         r->master = priv;
 131         if (r->cost == 0) {
 132                 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 133                    128. */
 134                 priv->prev = jiffies;
 135                 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
 136                 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
 137                 r->cost = user2credits(r->avg);
 138         }
 139         return 1;
 140 }
 141
 142 static void limit_mt_destroy(const struct xt_match *match, void *matchinfo)
 143 {
 144         const struct xt_rateinfo *info = matchinfo;
 145
 146         kfree(info->master);
 147 }
 148
 149 #ifdef CONFIG_COMPAT
 150 struct compat_xt_rateinfo {
 151         u_int32_t avg;
 152         u_int32_t burst;
 153
 154         compat_ulong_t prev;
 155         u_int32_t credit;
 156         u_int32_t credit_cap, cost;
 157
 158         u_int32_t master;
 159 };
 160
 161 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
 162  * master pointer, which does not need to be preserved. */
 163 static void compat_from_user(void *dst, void *src)
 164 {
 165         struct compat_xt_rateinfo *cm = src;
 166         struct xt_rateinfo m = {
 167                 .avg            = cm->avg,
 168                 .burst          = cm->burst,
 169                 .prev           = cm->prev | (unsigned long)cm->master << 32,
 170                 .credit         = cm->credit,
 171                 .credit_cap     = cm->credit_cap,
 172                 .cost           = cm->cost,
 173         };
 174         memcpy(dst, &m, sizeof(m));
 175 }
 176
 177 static int compat_to_user(void __user *dst, void *src)
 178 {
 179         struct xt_rateinfo *m = src;
 180         struct compat_xt_rateinfo cm = {
 181                 .avg            = m->avg,
 182                 .burst          = m->burst,
 183                 .prev           = m->prev,
 184                 .credit         = m->credit,
 185                 .credit_cap     = m->credit_cap,
 186                 .cost           = m->cost,
 187                 .master         = m->prev >> 32,
 188         };
 189         return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
 190 }
 191 #endif /* CONFIG_COMPAT */
 192
 193 static struct xt_match xt_limit_match[] = {
 194         {
 195                 .name           = "limit",
 196                 .family         = AF_INET,
 197                 .checkentry     = ipt_limit_checkentry,
 198                 .match          = ipt_limit_match,
 199                 .destroy        = limit_mt_destroy,
 200                 .matchsize      = sizeof(struct xt_rateinfo),
 201 #ifdef CONFIG_COMPAT
 202                 .compatsize     = sizeof(struct compat_xt_rateinfo),
 203                 .compat_from_user = compat_from_user,
 204                 .compat_to_user = compat_to_user,
 205 #endif
 206                 .me             = THIS_MODULE,
 207         },
 208         {
 209                 .name           = "limit",
 210                 .family         = AF_INET6,
 211                 .checkentry     = ipt_limit_checkentry,
 212                 .match          = ipt_limit_match,
 213                 .destroy        = limit_mt_destroy,
 214                 .matchsize      = sizeof(struct xt_rateinfo),
 215                 .me             = THIS_MODULE,
 216         },
 217 };
 218
 219 static int __init xt_limit_init(void)
 220 {
 221         return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 222 }
 223
 224 static void __exit xt_limit_fini(void)
 225 {
 226         xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
 227 }
 228
 229 module_init(xt_limit_init);
 230 module_exit(xt_limit_fini);