xt_limit.c revision 601e68e100b6bf8ba13a32db8faf92d43acaa997 
1/* Kernel module to control the rate
2 *
3 * 2 September 1999: Changed from the target RATE to the match
4 *                   `limit', removed logging.  Did I mention that
5 *                   Alexey is a fucking genius?
6 *                   Rusty Russell (rusty@rustcorp.com.au).  */
7
8/* (C) 1999 J�r�me de Vivie <devivie@info.enserb.u-bordeaux.fr>
9 * (C) 1999 Herv� Eychenne <eychenne@info.enserb.u-bordeaux.fr>
10 *
11 * This program is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU General Public License version 2 as
13 * published by the Free Software Foundation.
14 */
15
16#include <linux/module.h>
17#include <linux/skbuff.h>
18#include <linux/spinlock.h>
19#include <linux/interrupt.h>
20
21#include <linux/netfilter/x_tables.h>
22#include <linux/netfilter/xt_limit.h>
23
24MODULE_LICENSE("GPL");
25MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
26MODULE_DESCRIPTION("iptables rate limit match");
27MODULE_ALIAS("ipt_limit");
28MODULE_ALIAS("ip6t_limit");
29
30/* The algorithm used is the Simple Token Bucket Filter (TBF)
31 * see net/sched/sch_tbf.c in the linux source tree
32 */
33
34static DEFINE_SPINLOCK(limit_lock);
35
36/* Rusty: This is my (non-mathematically-inclined) understanding of
37   this algorithm.  The `average rate' in jiffies becomes your initial
38   amount of credit `credit' and the most credit you can ever have
39   `credit_cap'.  The `peak rate' becomes the cost of passing the
40   test, `cost'.
41
42   `prev' tracks the last packet hit: you gain one credit per jiffy.
43   If you get credit balance more than this, the extra credit is
44   discarded.  Every time the match passes, you lose `cost' credits;
45   if you don't have that many, the test fails.
46
47   See Alexey's formal explanation in net/sched/sch_tbf.c.
48
49   To get the maxmum range, we multiply by this factor (ie. you get N
50   credits per jiffy).  We want to allow a rate as low as 1 per day
51   (slowest userspace tool allows), which means
52   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
53#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
54
55/* Repeated shift and or gives us all 1s, final shift and add 1 gives
56 * us the power of 2 below the theoretical max, so GCC simply does a
57 * shift. */
58#define _POW2_BELOW2(x) ((x)|((x)>>1))
59#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
60#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
61#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
62#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
63#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
64
65#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
66
67static int
68ipt_limit_match(const struct sk_buff *skb,
69		const struct net_device *in,
70		const struct net_device *out,
71		const struct xt_match *match,
72		const void *matchinfo,
73		int offset,
74		unsigned int protoff,
75		int *hotdrop)
76{
77	struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master;
78	unsigned long now = jiffies;
79
80	spin_lock_bh(&limit_lock);
81	r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
82	if (r->credit > r->credit_cap)
83		r->credit = r->credit_cap;
84
85	if (r->credit >= r->cost) {
86		/* We're not limited. */
87		r->credit -= r->cost;
88		spin_unlock_bh(&limit_lock);
89		return 1;
90	}
91
92	spin_unlock_bh(&limit_lock);
93	return 0;
94}
95
96/* Precision saver. */
97static u_int32_t
98user2credits(u_int32_t user)
99{
100	/* If multiplying would overflow... */
101	if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
102		/* Divide first. */
103		return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
104
105	return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
106}
107
108static int
109ipt_limit_checkentry(const char *tablename,
110		     const void *inf,
111		     const struct xt_match *match,
112		     void *matchinfo,
113		     unsigned int hook_mask)
114{
115	struct xt_rateinfo *r = matchinfo;
116
117	/* Check for overflow. */
118	if (r->burst == 0
119	    || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
120		printk("Overflow in xt_limit, try lower: %u/%u\n",
121		       r->avg, r->burst);
122		return 0;
123	}
124
125	/* For SMP, we only want to use one set of counters. */
126	r->master = r;
127	if (r->cost == 0) {
128		/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
129		   128. */
130		r->prev = jiffies;
131		r->credit = user2credits(r->avg * r->burst);	 /* Credits full. */
132		r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
133		r->cost = user2credits(r->avg);
134	}
135	return 1;
136}
137
138#ifdef CONFIG_COMPAT
139struct 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. */
152static void compat_from_user(void *dst, void *src)
153{
154	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
166static int compat_to_user(void __user *dst, void *src)
167{
168	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
182static struct xt_match xt_limit_match[] = {
183	{
184		.name		= "limit",
185		.family		= AF_INET,
186		.checkentry	= ipt_limit_checkentry,
187		.match		= ipt_limit_match,
188		.matchsize	= sizeof(struct xt_rateinfo),
189#ifdef CONFIG_COMPAT
190		.compatsize	= sizeof(struct compat_xt_rateinfo),
191		.compat_from_user = compat_from_user,
192		.compat_to_user	= compat_to_user,
193#endif
194		.me		= THIS_MODULE,
195	},
196	{
197		.name		= "limit",
198		.family		= AF_INET6,
199		.checkentry	= ipt_limit_checkentry,
200		.match		= ipt_limit_match,
201		.matchsize	= sizeof(struct xt_rateinfo),
202		.me		= THIS_MODULE,
203	},
204};
205
206static int __init xt_limit_init(void)
207{
208	return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
209}
210
211static void __exit xt_limit_fini(void)
212{
213	xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
214}
215
216module_init(xt_limit_init);
217module_exit(xt_limit_fini);
218