Merge branch 'fixes' of git://git.linaro.org/people/rmk/linux-arm
[linux-2.6.git] / net / netfilter / xt_limit.c
blobbef85059655892982da73cc694183afc7399782c
1 /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
2 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
3 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 */
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11 #include <linux/slab.h>
12 #include <linux/module.h>
13 #include <linux/skbuff.h>
14 #include <linux/spinlock.h>
15 #include <linux/interrupt.h>
17 #include <linux/netfilter/x_tables.h>
18 #include <linux/netfilter/xt_limit.h>
20 struct xt_limit_priv {
21 unsigned long prev;
22 uint32_t credit;
25 MODULE_LICENSE("GPL");
26 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
27 MODULE_DESCRIPTION("Xtables: rate-limit match");
28 MODULE_ALIAS("ipt_limit");
29 MODULE_ALIAS("ip6t_limit");
31 /* The algorithm used is the Simple Token Bucket Filter (TBF)
32 * see net/sched/sch_tbf.c in the linux source tree
35 static DEFINE_SPINLOCK(limit_lock);
37 /* Rusty: This is my (non-mathematically-inclined) understanding of
38 this algorithm. The `average rate' in jiffies becomes your initial
39 amount of credit `credit' and the most credit you can ever have
40 `credit_cap'. The `peak rate' becomes the cost of passing the
41 test, `cost'.
43 `prev' tracks the last packet hit: you gain one credit per jiffy.
44 If you get credit balance more than this, the extra credit is
45 discarded. Every time the match passes, you lose `cost' credits;
46 if you don't have that many, the test fails.
48 See Alexey's formal explanation in net/sched/sch_tbf.c.
50 To get the maxmum range, we multiply by this factor (ie. you get N
51 credits per jiffy). We want to allow a rate as low as 1 per day
52 (slowest userspace tool allows), which means
53 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
54 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
56 /* Repeated shift and or gives us all 1s, final shift and add 1 gives
57 * us the power of 2 below the theoretical max, so GCC simply does a
58 * shift. */
59 #define _POW2_BELOW2(x) ((x)|((x)>>1))
60 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
61 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
62 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
63 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
64 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
66 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
68 static bool
69 limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
71 const struct xt_rateinfo *r = par->matchinfo;
72 struct xt_limit_priv *priv = r->master;
73 unsigned long now = jiffies;
75 spin_lock_bh(&limit_lock);
76 priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
77 if (priv->credit > r->credit_cap)
78 priv->credit = r->credit_cap;
80 if (priv->credit >= r->cost) {
81 /* We're not limited. */
82 priv->credit -= r->cost;
83 spin_unlock_bh(&limit_lock);
84 return true;
87 spin_unlock_bh(&limit_lock);
88 return false;
91 /* Precision saver. */
92 static u32 user2credits(u32 user)
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;
99 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
102 static int limit_mt_check(const struct xt_mtchk_param *par)
104 struct xt_rateinfo *r = par->matchinfo;
105 struct xt_limit_priv *priv;
107 /* Check for overflow. */
108 if (r->burst == 0
109 || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
110 pr_info("Overflow, try lower: %u/%u\n",
111 r->avg, r->burst);
112 return -ERANGE;
115 priv = kmalloc(sizeof(*priv), GFP_KERNEL);
116 if (priv == NULL)
117 return -ENOMEM;
119 /* For SMP, we only want to use one set of state. */
120 r->master = priv;
121 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
122 128. */
123 priv->prev = jiffies;
124 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
125 if (r->cost == 0) {
126 r->credit_cap = priv->credit; /* Credits full. */
127 r->cost = user2credits(r->avg);
129 return 0;
132 static void limit_mt_destroy(const struct xt_mtdtor_param *par)
134 const struct xt_rateinfo *info = par->matchinfo;
136 kfree(info->master);
139 #ifdef CONFIG_COMPAT
140 struct compat_xt_rateinfo {
141 u_int32_t avg;
142 u_int32_t burst;
144 compat_ulong_t prev;
145 u_int32_t credit;
146 u_int32_t credit_cap, cost;
148 u_int32_t master;
151 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
152 * master pointer, which does not need to be preserved. */
153 static void limit_mt_compat_from_user(void *dst, const void *src)
155 const struct compat_xt_rateinfo *cm = src;
156 struct xt_rateinfo m = {
157 .avg = cm->avg,
158 .burst = cm->burst,
159 .prev = cm->prev | (unsigned long)cm->master << 32,
160 .credit = cm->credit,
161 .credit_cap = cm->credit_cap,
162 .cost = cm->cost,
164 memcpy(dst, &m, sizeof(m));
167 static int limit_mt_compat_to_user(void __user *dst, const void *src)
169 const struct xt_rateinfo *m = src;
170 struct compat_xt_rateinfo cm = {
171 .avg = m->avg,
172 .burst = m->burst,
173 .prev = m->prev,
174 .credit = m->credit,
175 .credit_cap = m->credit_cap,
176 .cost = m->cost,
177 .master = m->prev >> 32,
179 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
181 #endif /* CONFIG_COMPAT */
183 static struct xt_match limit_mt_reg __read_mostly = {
184 .name = "limit",
185 .revision = 0,
186 .family = NFPROTO_UNSPEC,
187 .match = limit_mt,
188 .checkentry = limit_mt_check,
189 .destroy = limit_mt_destroy,
190 .matchsize = sizeof(struct xt_rateinfo),
191 #ifdef CONFIG_COMPAT
192 .compatsize = sizeof(struct compat_xt_rateinfo),
193 .compat_from_user = limit_mt_compat_from_user,
194 .compat_to_user = limit_mt_compat_to_user,
195 #endif
196 .me = THIS_MODULE,
199 static int __init limit_mt_init(void)
201 return xt_register_match(&limit_mt_reg);
204 static void __exit limit_mt_exit(void)
206 xt_unregister_match(&limit_mt_reg);
209 module_init(limit_mt_init);
210 module_exit(limit_mt_exit);