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1 | // SPDX-License-Identifier: GPL-2.0-only | |
2 | /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr> | |
3 | * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> | |
4 | * (C) 2006-2012 Patrick McHardy <kaber@trash.net> | |
5 | */ | |
6 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
7 | ||
8 | #include <linux/slab.h> | |
9 | #include <linux/module.h> | |
10 | #include <linux/skbuff.h> | |
11 | #include <linux/interrupt.h> | |
12 | ||
13 | #include <linux/netfilter/x_tables.h> | |
14 | #include <linux/netfilter/xt_limit.h> | |
15 | ||
16 | struct xt_limit_priv { | |
17 | unsigned long prev; | |
18 | u32 credit; | |
19 | }; | |
20 | ||
21 | MODULE_LICENSE("GPL"); | |
22 | MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); | |
23 | MODULE_DESCRIPTION("Xtables: rate-limit match"); | |
24 | MODULE_ALIAS("ipt_limit"); | |
25 | MODULE_ALIAS("ip6t_limit"); | |
26 | ||
27 | /* The algorithm used is the Simple Token Bucket Filter (TBF) | |
28 | * see net/sched/sch_tbf.c in the linux source tree | |
29 | */ | |
30 | ||
31 | /* Rusty: This is my (non-mathematically-inclined) understanding of | |
32 | this algorithm. The `average rate' in jiffies becomes your initial | |
33 | amount of credit `credit' and the most credit you can ever have | |
34 | `credit_cap'. The `peak rate' becomes the cost of passing the | |
35 | test, `cost'. | |
36 | ||
37 | `prev' tracks the last packet hit: you gain one credit per jiffy. | |
38 | If you get credit balance more than this, the extra credit is | |
39 | discarded. Every time the match passes, you lose `cost' credits; | |
40 | if you don't have that many, the test fails. | |
41 | ||
42 | See Alexey's formal explanation in net/sched/sch_tbf.c. | |
43 | ||
44 | To get the maximum range, we multiply by this factor (ie. you get N | |
45 | credits per jiffy). We want to allow a rate as low as 1 per day | |
46 | (slowest userspace tool allows), which means | |
47 | CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ | |
48 | #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) | |
49 | ||
50 | /* Repeated shift and or gives us all 1s, final shift and add 1 gives | |
51 | * us the power of 2 below the theoretical max, so GCC simply does a | |
52 | * shift. */ | |
53 | #define _POW2_BELOW2(x) ((x)|((x)>>1)) | |
54 | #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) | |
55 | #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) | |
56 | #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) | |
57 | #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) | |
58 | #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) | |
59 | ||
60 | #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) | |
61 | ||
62 | static bool | |
63 | limit_mt(const struct sk_buff *skb, struct xt_action_param *par) | |
64 | { | |
65 | const struct xt_rateinfo *r = par->matchinfo; | |
66 | struct xt_limit_priv *priv = r->master; | |
67 | unsigned long now; | |
68 | u32 old_credit, new_credit, credit_increase = 0; | |
69 | bool ret; | |
70 | ||
71 | /* fastpath if there is nothing to update */ | |
72 | if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies)) | |
73 | return false; | |
74 | ||
75 | do { | |
76 | now = jiffies; | |
77 | credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; | |
78 | old_credit = READ_ONCE(priv->credit); | |
79 | new_credit = old_credit; | |
80 | new_credit += credit_increase; | |
81 | if (new_credit > r->credit_cap) | |
82 | new_credit = r->credit_cap; | |
83 | if (new_credit >= r->cost) { | |
84 | ret = true; | |
85 | new_credit -= r->cost; | |
86 | } else { | |
87 | ret = false; | |
88 | } | |
89 | } while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit); | |
90 | ||
91 | return ret; | |
92 | } | |
93 | ||
94 | /* Precision saver. */ | |
95 | static u32 user2credits(u32 user) | |
96 | { | |
97 | /* If multiplying would overflow... */ | |
98 | if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) | |
99 | /* Divide first. */ | |
100 | return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; | |
101 | ||
102 | return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; | |
103 | } | |
104 | ||
105 | static int limit_mt_check(const struct xt_mtchk_param *par) | |
106 | { | |
107 | struct xt_rateinfo *r = par->matchinfo; | |
108 | struct xt_limit_priv *priv; | |
109 | ||
110 | /* Check for overflow. */ | |
111 | if (r->burst == 0 | |
112 | || user2credits(r->avg * r->burst) < user2credits(r->avg)) { | |
113 | pr_info_ratelimited("Overflow, try lower: %u/%u\n", | |
114 | r->avg, r->burst); | |
115 | return -ERANGE; | |
116 | } | |
117 | ||
118 | priv = kmalloc(sizeof(*priv), GFP_KERNEL); | |
119 | if (priv == NULL) | |
120 | return -ENOMEM; | |
121 | ||
122 | /* For SMP, we only want to use one set of state. */ | |
123 | r->master = priv; | |
124 | /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * | |
125 | 128. */ | |
126 | priv->prev = jiffies; | |
127 | priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ | |
128 | if (r->cost == 0) { | |
129 | r->credit_cap = priv->credit; /* Credits full. */ | |
130 | r->cost = user2credits(r->avg); | |
131 | } | |
132 | ||
133 | return 0; | |
134 | } | |
135 | ||
136 | static void limit_mt_destroy(const struct xt_mtdtor_param *par) | |
137 | { | |
138 | const struct xt_rateinfo *info = par->matchinfo; | |
139 | ||
140 | kfree(info->master); | |
141 | } | |
142 | ||
143 | #ifdef CONFIG_NETFILTER_XTABLES_COMPAT | |
144 | struct compat_xt_rateinfo { | |
145 | u_int32_t avg; | |
146 | u_int32_t burst; | |
147 | ||
148 | compat_ulong_t prev; | |
149 | u_int32_t credit; | |
150 | u_int32_t credit_cap, cost; | |
151 | ||
152 | u_int32_t master; | |
153 | }; | |
154 | ||
155 | /* To keep the full "prev" timestamp, the upper 32 bits are stored in the | |
156 | * master pointer, which does not need to be preserved. */ | |
157 | static void limit_mt_compat_from_user(void *dst, const void *src) | |
158 | { | |
159 | const struct compat_xt_rateinfo *cm = src; | |
160 | struct xt_rateinfo m = { | |
161 | .avg = cm->avg, | |
162 | .burst = cm->burst, | |
163 | .prev = cm->prev | (unsigned long)cm->master << 32, | |
164 | .credit = cm->credit, | |
165 | .credit_cap = cm->credit_cap, | |
166 | .cost = cm->cost, | |
167 | }; | |
168 | memcpy(dst, &m, sizeof(m)); | |
169 | } | |
170 | ||
171 | static int limit_mt_compat_to_user(void __user *dst, const void *src) | |
172 | { | |
173 | const struct xt_rateinfo *m = src; | |
174 | struct compat_xt_rateinfo cm = { | |
175 | .avg = m->avg, | |
176 | .burst = m->burst, | |
177 | .prev = m->prev, | |
178 | .credit = m->credit, | |
179 | .credit_cap = m->credit_cap, | |
180 | .cost = m->cost, | |
181 | .master = m->prev >> 32, | |
182 | }; | |
183 | return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; | |
184 | } | |
185 | #endif /* CONFIG_NETFILTER_XTABLES_COMPAT */ | |
186 | ||
187 | static struct xt_match limit_mt_reg __read_mostly = { | |
188 | .name = "limit", | |
189 | .revision = 0, | |
190 | .family = NFPROTO_UNSPEC, | |
191 | .match = limit_mt, | |
192 | .checkentry = limit_mt_check, | |
193 | .destroy = limit_mt_destroy, | |
194 | .matchsize = sizeof(struct xt_rateinfo), | |
195 | #ifdef CONFIG_NETFILTER_XTABLES_COMPAT | |
196 | .compatsize = sizeof(struct compat_xt_rateinfo), | |
197 | .compat_from_user = limit_mt_compat_from_user, | |
198 | .compat_to_user = limit_mt_compat_to_user, | |
199 | #endif | |
200 | .usersize = offsetof(struct xt_rateinfo, prev), | |
201 | .me = THIS_MODULE, | |
202 | }; | |
203 | ||
204 | static int __init limit_mt_init(void) | |
205 | { | |
206 | return xt_register_match(&limit_mt_reg); | |
207 | } | |
208 | ||
209 | static void __exit limit_mt_exit(void) | |
210 | { | |
211 | xt_unregister_match(&limit_mt_reg); | |
212 | } | |
213 | ||
214 | module_init(limit_mt_init); | |
215 | module_exit(limit_mt_exit); |