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("Xtables: 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
limit_mt(const struct sk_buff * skb,const struct xt_match_param * par)61 limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
62 {
63 struct xt_rateinfo *r =
64 ((const struct xt_rateinfo *)par->matchinfo)->master;
65 unsigned long now = jiffies;
66
67 spin_lock_bh(&limit_lock);
68 r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
69 if (r->credit > r->credit_cap)
70 r->credit = r->credit_cap;
71
72 if (r->credit >= r->cost) {
73 /* We're not limited. */
74 r->credit -= r->cost;
75 spin_unlock_bh(&limit_lock);
76 return true;
77 }
78
79 spin_unlock_bh(&limit_lock);
80 return false;
81 }
82
83 /* Precision saver. */
84 static u_int32_t
user2credits(u_int32_t user)85 user2credits(u_int32_t user)
86 {
87 /* If multiplying would overflow... */
88 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
89 /* Divide first. */
90 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
91
92 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
93 }
94
limit_mt_check(const struct xt_mtchk_param * par)95 static bool limit_mt_check(const struct xt_mtchk_param *par)
96 {
97 struct xt_rateinfo *r = par->matchinfo;
98
99 /* Check for overflow. */
100 if (r->burst == 0
101 || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
102 printk("Overflow in xt_limit, try lower: %u/%u\n",
103 r->avg, r->burst);
104 return false;
105 }
106
107 /* For SMP, we only want to use one set of counters. */
108 r->master = r;
109 if (r->cost == 0) {
110 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
111 128. */
112 r->prev = jiffies;
113 r->credit = user2credits(r->avg * r->burst); /* Credits full. */
114 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
115 r->cost = user2credits(r->avg);
116 }
117 return true;
118 }
119
120 #ifdef CONFIG_COMPAT
121 struct compat_xt_rateinfo {
122 u_int32_t avg;
123 u_int32_t burst;
124
125 compat_ulong_t prev;
126 u_int32_t credit;
127 u_int32_t credit_cap, cost;
128
129 u_int32_t master;
130 };
131
132 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
133 * master pointer, which does not need to be preserved. */
limit_mt_compat_from_user(void * dst,void * src)134 static void limit_mt_compat_from_user(void *dst, void *src)
135 {
136 const struct compat_xt_rateinfo *cm = src;
137 struct xt_rateinfo m = {
138 .avg = cm->avg,
139 .burst = cm->burst,
140 .prev = cm->prev | (unsigned long)cm->master << 32,
141 .credit = cm->credit,
142 .credit_cap = cm->credit_cap,
143 .cost = cm->cost,
144 };
145 memcpy(dst, &m, sizeof(m));
146 }
147
limit_mt_compat_to_user(void __user * dst,void * src)148 static int limit_mt_compat_to_user(void __user *dst, void *src)
149 {
150 const struct xt_rateinfo *m = src;
151 struct compat_xt_rateinfo cm = {
152 .avg = m->avg,
153 .burst = m->burst,
154 .prev = m->prev,
155 .credit = m->credit,
156 .credit_cap = m->credit_cap,
157 .cost = m->cost,
158 .master = m->prev >> 32,
159 };
160 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
161 }
162 #endif /* CONFIG_COMPAT */
163
164 static struct xt_match limit_mt_reg __read_mostly = {
165 .name = "limit",
166 .revision = 0,
167 .family = NFPROTO_UNSPEC,
168 .match = limit_mt,
169 .checkentry = limit_mt_check,
170 .matchsize = sizeof(struct xt_rateinfo),
171 #ifdef CONFIG_COMPAT
172 .compatsize = sizeof(struct compat_xt_rateinfo),
173 .compat_from_user = limit_mt_compat_from_user,
174 .compat_to_user = limit_mt_compat_to_user,
175 #endif
176 .me = THIS_MODULE,
177 };
178
limit_mt_init(void)179 static int __init limit_mt_init(void)
180 {
181 return xt_register_match(&limit_mt_reg);
182 }
183
limit_mt_exit(void)184 static void __exit limit_mt_exit(void)
185 {
186 xt_unregister_match(&limit_mt_reg);
187 }
188
189 module_init(limit_mt_init);
190 module_exit(limit_mt_exit);
191