1/* (C) 1999 J�r�me de Vivie <devivie@info.enserb.u-bordeaux.fr>
2 * (C) 1999 Herv� 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
17MODULE_LICENSE("GPL");
18MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
19MODULE_DESCRIPTION("iptables rate limit match");
20MODULE_ALIAS("ipt_limit");
21MODULE_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
27static 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
60static int
61ipt_limit_match(const struct sk_buff *skb,
62		const struct net_device *in,
63		const struct net_device *out,
64		const struct xt_match *match,
65		const void *matchinfo,
66		int offset,
67		unsigned int protoff,
68		int *hotdrop)
69{
70	struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master;
71	unsigned long now = jiffies;
72
73	spin_lock_bh(&limit_lock);
74	r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
75	if (r->credit > r->credit_cap)
76		r->credit = r->credit_cap;
77
78	if (r->credit >= r->cost) {
79		/* We're not limited. */
80		r->credit -= r->cost;
81		spin_unlock_bh(&limit_lock);
82		return 1;
83	}
84
85	spin_unlock_bh(&limit_lock);
86	return 0;
87}
88
89/* Precision saver. */
90static u_int32_t
91user2credits(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
101static int
102ipt_limit_checkentry(const char *tablename,
103		     const void *inf,
104		     const struct xt_match *match,
105		     void *matchinfo,
106		     unsigned int hook_mask)
107{
108	struct xt_rateinfo *r = matchinfo;
109
110	/* Check for overflow. */
111	if (r->burst == 0
112	    || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
113		printk("Overflow in xt_limit, try lower: %u/%u\n",
114		       r->avg, r->burst);
115		return 0;
116	}
117
118	/* For SMP, we only want to use one set of counters. */
119	r->master = r;
120	if (r->cost == 0) {
121		/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
122		   128. */
123		r->prev = jiffies;
124		r->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 1;
129}
130
131#ifdef CONFIG_COMPAT
132struct compat_xt_rateinfo {
133	u_int32_t avg;
134	u_int32_t burst;
135
136	compat_ulong_t prev;
137	u_int32_t credit;
138	u_int32_t credit_cap, cost;
139
140	u_int32_t master;
141};
142
143/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
144 * master pointer, which does not need to be preserved. */
145static void compat_from_user(void *dst, void *src)
146{
147	struct compat_xt_rateinfo *cm = src;
148	struct xt_rateinfo m = {
149		.avg		= cm->avg,
150		.burst		= cm->burst,
151		.prev		= cm->prev | (unsigned long)cm->master << 32,
152		.credit		= cm->credit,
153		.credit_cap	= cm->credit_cap,
154		.cost		= cm->cost,
155	};
156	memcpy(dst, &m, sizeof(m));
157}
158
159static int compat_to_user(void __user *dst, void *src)
160{
161	struct xt_rateinfo *m = src;
162	struct compat_xt_rateinfo cm = {
163		.avg		= m->avg,
164		.burst		= m->burst,
165		.prev		= m->prev,
166		.credit		= m->credit,
167		.credit_cap	= m->credit_cap,
168		.cost		= m->cost,
169		.master		= m->prev >> 32,
170	};
171	return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
172}
173#endif /* CONFIG_COMPAT */
174
175static struct xt_match xt_limit_match[] = {
176	{
177		.name		= "limit",
178		.family		= AF_INET,
179		.checkentry	= ipt_limit_checkentry,
180		.match		= ipt_limit_match,
181		.matchsize	= sizeof(struct xt_rateinfo),
182#ifdef CONFIG_COMPAT
183		.compatsize	= sizeof(struct compat_xt_rateinfo),
184		.compat_from_user = compat_from_user,
185		.compat_to_user	= compat_to_user,
186#endif
187		.me		= THIS_MODULE,
188	},
189	{
190		.name		= "limit",
191		.family		= AF_INET6,
192		.checkentry	= ipt_limit_checkentry,
193		.match		= ipt_limit_match,
194		.matchsize	= sizeof(struct xt_rateinfo),
195		.me		= THIS_MODULE,
196	},
197};
198
199static int __init xt_limit_init(void)
200{
201	return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
202}
203
204static void __exit xt_limit_fini(void)
205{
206	xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match));
207}
208
209module_init(xt_limit_init);
210module_exit(xt_limit_fini);
211