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