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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/slab.h> |
10 | #include <linux/module.h> |
11 | #include <linux/skbuff.h> |
12 | #include <linux/spinlock.h> |
13 | #include <linux/interrupt.h> |
14 | |
15 | #include <linux/netfilter/x_tables.h> |
16 | #include <linux/netfilter/xt_limit.h> |
17 | |
18 | struct xt_limit_priv { |
19 | unsigned long prev; |
20 | uint32_t credit; |
21 | }; |
22 | |
23 | MODULE_LICENSE("GPL"); |
24 | MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); |
25 | MODULE_DESCRIPTION("Xtables: rate-limit match"); |
26 | MODULE_ALIAS("ipt_limit"); |
27 | MODULE_ALIAS("ip6t_limit"); |
28 | |
29 | /* The algorithm used is the Simple Token Bucket Filter (TBF) |
30 | * see net/sched/sch_tbf.c in the linux source tree |
31 | */ |
32 | |
33 | static DEFINE_SPINLOCK(limit_lock); |
34 | |
35 | /* Rusty: This is my (non-mathematically-inclined) understanding of |
36 | this algorithm. The `average rate' in jiffies becomes your initial |
37 | amount of credit `credit' and the most credit you can ever have |
38 | `credit_cap'. The `peak rate' becomes the cost of passing the |
39 | test, `cost'. |
40 | |
41 | `prev' tracks the last packet hit: you gain one credit per jiffy. |
42 | If you get credit balance more than this, the extra credit is |
43 | discarded. Every time the match passes, you lose `cost' credits; |
44 | if you don't have that many, the test fails. |
45 | |
46 | See Alexey's formal explanation in net/sched/sch_tbf.c. |
47 | |
48 | To get the maxmum range, we multiply by this factor (ie. you get N |
49 | credits per jiffy). We want to allow a rate as low as 1 per day |
50 | (slowest userspace tool allows), which means |
51 | CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ |
52 | #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) |
53 | |
54 | /* Repeated shift and or gives us all 1s, final shift and add 1 gives |
55 | * us the power of 2 below the theoretical max, so GCC simply does a |
56 | * shift. */ |
57 | #define _POW2_BELOW2(x) ((x)|((x)>>1)) |
58 | #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) |
59 | #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) |
60 | #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) |
61 | #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) |
62 | #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) |
63 | |
64 | #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) |
65 | |
66 | static bool |
67 | limit_mt(const struct sk_buff *skb, const struct xt_match_param *par) |
68 | { |
69 | const struct xt_rateinfo *r = par->matchinfo; |
70 | struct xt_limit_priv *priv = r->master; |
71 | unsigned long now = jiffies; |
72 | |
73 | spin_lock_bh(&limit_lock); |
74 | priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; |
75 | if (priv->credit > r->credit_cap) |
76 | priv->credit = r->credit_cap; |
77 | |
78 | if (priv->credit >= r->cost) { |
79 | /* We're not limited. */ |
80 | priv->credit -= r->cost; |
81 | spin_unlock_bh(&limit_lock); |
82 | return true; |
83 | } |
84 | |
85 | spin_unlock_bh(&limit_lock); |
86 | return false; |
87 | } |
88 | |
89 | /* Precision saver. */ |
90 | static u_int32_t |
91 | user2credits(u_int32_t user) |
92 | { |
93 | /* If multiplying would overflow... */ |
94 | if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) |
95 | /* Divide first. */ |
96 | return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; |
97 | |
98 | return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; |
99 | } |
100 | |
101 | static bool limit_mt_check(const struct xt_mtchk_param *par) |
102 | { |
103 | struct xt_rateinfo *r = par->matchinfo; |
104 | struct xt_limit_priv *priv; |
105 | |
106 | /* Check for overflow. */ |
107 | if (r->burst == 0 |
108 | || user2credits(r->avg * r->burst) < user2credits(r->avg)) { |
109 | printk("Overflow in xt_limit, try lower: %u/%u\n", |
110 | r->avg, r->burst); |
111 | return false; |
112 | } |
113 | |
114 | priv = kmalloc(sizeof(*priv), GFP_KERNEL); |
115 | if (priv == NULL) |
116 | return false; |
117 | |
118 | /* For SMP, we only want to use one set of state. */ |
119 | r->master = priv; |
120 | if (r->cost == 0) { |
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 | r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ |
126 | r->cost = user2credits(r->avg); |
127 | } |
128 | return true; |
129 | } |
130 | |
131 | static void limit_mt_destroy(const struct xt_mtdtor_param *par) |
132 | { |
133 | const struct xt_rateinfo *info = par->matchinfo; |
134 | |
135 | kfree(info->master); |
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 limit_mt_compat_from_user(void *dst, const void *src) |
153 | { |
154 | const 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 limit_mt_compat_to_user(void __user *dst, const void *src) |
167 | { |
168 | const 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 limit_mt_reg __read_mostly = { |
183 | .name = "limit", |
184 | .revision = 0, |
185 | .family = NFPROTO_UNSPEC, |
186 | .match = limit_mt, |
187 | .checkentry = limit_mt_check, |
188 | .destroy = limit_mt_destroy, |
189 | .matchsize = sizeof(struct xt_rateinfo), |
190 | #ifdef CONFIG_COMPAT |
191 | .compatsize = sizeof(struct compat_xt_rateinfo), |
192 | .compat_from_user = limit_mt_compat_from_user, |
193 | .compat_to_user = limit_mt_compat_to_user, |
194 | #endif |
195 | .me = THIS_MODULE, |
196 | }; |
197 | |
198 | static int __init limit_mt_init(void) |
199 | { |
200 | return xt_register_match(&limit_mt_reg); |
201 | } |
202 | |
203 | static void __exit limit_mt_exit(void) |
204 | { |
205 | xt_unregister_match(&limit_mt_reg); |
206 | } |
207 | |
208 | module_init(limit_mt_init); |
209 | module_exit(limit_mt_exit); |
210 |
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