1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
|
/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
* (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_limit.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
MODULE_DESCRIPTION("Xtables: rate-limit match");
MODULE_ALIAS("ipt_limit");
MODULE_ALIAS("ip6t_limit");
/* The algorithm used is the Simple Token Bucket Filter (TBF)
* see net/sched/sch_tbf.c in the linux source tree
*/
static DEFINE_SPINLOCK(limit_lock);
/* Rusty: This is my (non-mathematically-inclined) understanding of
this algorithm. The `average rate' in jiffies becomes your initial
amount of credit `credit' and the most credit you can ever have
`credit_cap'. The `peak rate' becomes the cost of passing the
test, `cost'.
`prev' tracks the last packet hit: you gain one credit per jiffy.
If you get credit balance more than this, the extra credit is
discarded. Every time the match passes, you lose `cost' credits;
if you don't have that many, the test fails.
See Alexey's formal explanation in net/sched/sch_tbf.c.
To get the maxmum range, we multiply by this factor (ie. you get N
credits per jiffy). We want to allow a rate as low as 1 per day
(slowest userspace tool allows), which means
CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
/* Repeated shift and or gives us all 1s, final shift and add 1 gives
* us the power of 2 below the theoretical max, so GCC simply does a
* shift. */
#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
static bool
limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
struct xt_rateinfo *r =
((const struct xt_rateinfo *)par->matchinfo)->master;
unsigned long now = jiffies;
spin_lock_bh(&limit_lock);
r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
if (r->credit > r->credit_cap)
r->credit = r->credit_cap;
if (r->credit >= r->cost) {
/* We're not limited. */
r->credit -= r->cost;
spin_unlock_bh(&limit_lock);
return true;
}
spin_unlock_bh(&limit_lock);
return false;
}
/* Precision saver. */
static u_int32_t
user2credits(u_int32_t user)
{
/* If multiplying would overflow... */
if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
/* Divide first. */
return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
}
static bool limit_mt_check(const struct xt_mtchk_param *par)
{
struct xt_rateinfo *r = par->matchinfo;
/* Check for overflow. */
if (r->burst == 0
|| user2credits(r->avg * r->burst) < user2credits(r->avg)) {
printk("Overflow in xt_limit, try lower: %u/%u\n",
r->avg, r->burst);
return false;
}
/* For SMP, we only want to use one set of counters. */
r->master = r;
if (r->cost == 0) {
/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
128. */
r->prev = jiffies;
r->credit = user2credits(r->avg * r->burst); /* Credits full. */
r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
r->cost = user2credits(r->avg);
}
return true;
}
#ifdef CONFIG_COMPAT
struct compat_xt_rateinfo {
u_int32_t avg;
u_int32_t burst;
compat_ulong_t prev;
u_int32_t credit;
u_int32_t credit_cap, cost;
u_int32_t master;
};
/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
* master pointer, which does not need to be preserved. */
static void limit_mt_compat_from_user(void *dst, void *src)
{
const struct compat_xt_rateinfo *cm = src;
struct xt_rateinfo m = {
.avg = cm->avg,
.burst = cm->burst,
.prev = cm->prev | (unsigned long)cm->master << 32,
.credit = cm->credit,
.credit_cap = cm->credit_cap,
.cost = cm->cost,
};
memcpy(dst, &m, sizeof(m));
}
static int limit_mt_compat_to_user(void __user *dst, void *src)
{
const struct xt_rateinfo *m = src;
struct compat_xt_rateinfo cm = {
.avg = m->avg,
.burst = m->burst,
.prev = m->prev,
.credit = m->credit,
.credit_cap = m->credit_cap,
.cost = m->cost,
.master = m->prev >> 32,
};
return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
}
#endif /* CONFIG_COMPAT */
static struct xt_match limit_mt_reg __read_mostly = {
.name = "limit",
.revision = 0,
.family = NFPROTO_UNSPEC,
.match = limit_mt,
.checkentry = limit_mt_check,
.matchsize = sizeof(struct xt_rateinfo),
#ifdef CONFIG_COMPAT
.compatsize = sizeof(struct compat_xt_rateinfo),
.compat_from_user = limit_mt_compat_from_user,
.compat_to_user = limit_mt_compat_to_user,
#endif
.me = THIS_MODULE,
};
static int __init limit_mt_init(void)
{
return xt_register_match(&limit_mt_reg);
}
static void __exit limit_mt_exit(void)
{
xt_unregister_match(&limit_mt_reg);
}
module_init(limit_mt_init);
module_exit(limit_mt_exit);
|
