FreeBSD/Linux Kernel Cross Reference
sys/netinet6/ip6_id.c
1 /* $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $ */
2 /* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */
3 /* $FreeBSD: releng/5.2/sys/netinet6/ip6_id.c 120652 2003-10-01 21:45:57Z ume $ */
4
5 /*
6 * Copyright (C) 2003 WIDE Project.
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the project nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 /*
35 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
36 * All rights reserved.
37 *
38 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
39 * such a mathematical system to generate more random (yet non-repeating)
40 * ids to solve the resolver/named problem. But Niels designed the
41 * actual system based on the constraints.
42 *
43 * Redistribution and use in source and binary forms, with or without
44 * modification, are permitted provided that the following conditions
45 * are met:
46 * 1. Redistributions of source code must retain the above copyright
47 * notice, this list of conditions and the following disclaimer.
48 * 2. Redistributions in binary form must reproduce the above copyright
49 * notice, this list of conditions and the following disclaimer in the
50 * documentation and/or other materials provided with the distribution.
51 * 3. All advertising materials mentioning features or use of this software
52 * must display the following acknowledgement:
53 * This product includes software developed by Niels Provos.
54 * 4. The name of the author may not be used to endorse or promote products
55 * derived from this software without specific prior written permission.
56 *
57 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
58 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
59 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
60 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
61 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
62 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
63 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
64 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
65 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
66 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
67 */
68
69 /*
70 * seed = random (bits - 1) bit
71 * n = prime, g0 = generator to n,
72 * j = random so that gcd(j,n-1) == 1
73 * g = g0^j mod n will be a generator again.
74 *
75 * X[0] = random seed.
76 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
77 * with a = 7^(even random) mod m,
78 * b = random with gcd(b,m) == 1
79 * m = constant and a maximal period of m-1.
80 *
81 * The transaction id is determined by:
82 * id[n] = seed xor (g^X[n] mod n)
83 *
84 * Effectivly the id is restricted to the lower (bits - 1) bits, thus
85 * yielding two different cycles by toggling the msb on and off.
86 * This avoids reuse issues caused by reseeding.
87 */
88
89 #include "opt_random_ip_id.h"
90
91 #include <sys/types.h>
92 #include <sys/param.h>
93 #include <sys/kernel.h>
94 #include <sys/socket.h>
95 #include <sys/libkern.h>
96
97 #include <net/if.h>
98 #include <net/route.h>
99 #include <netinet/in.h>
100 #include <netinet/ip6.h>
101 #include <netinet6/ip6_var.h>
102
103 #ifdef RANDOM_IP_ID
104
105 #ifndef INT32_MAX
106 #define INT32_MAX 0x7fffffffU
107 #endif
108
109 struct randomtab {
110 const int ru_bits; /* resulting bits */
111 const long ru_out; /* Time after wich will be reseeded */
112 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
113 const u_int32_t ru_gen; /* Starting generator */
114 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
115 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
116 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
117 const u_int32_t pfacts[4]; /* factors of ru_n */
118
119 u_int32_t ru_counter;
120 u_int32_t ru_msb;
121
122 u_int32_t ru_x;
123 u_int32_t ru_seed, ru_seed2;
124 u_int32_t ru_a, ru_b;
125 u_int32_t ru_g;
126 long ru_reseed;
127 };
128
129 static struct randomtab randomtab_32 = {
130 32, /* resulting bits */
131 180, /* Time after wich will be reseeded */
132 1000000000, /* Uniq cycle, avoid blackjack prediction */
133 2, /* Starting generator */
134 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
135 7, /* determine ru_a as RU_AGEN^(2*rand) */
136 1836660096, /* RU_M = 2^7*3^15 - don't change */
137 { 2, 3, 59652323, 0 }, /* factors of ru_n */
138 };
139
140 static struct randomtab randomtab_20 = {
141 20, /* resulting bits */
142 180, /* Time after wich will be reseeded */
143 200000, /* Uniq cycle, avoid blackjack prediction */
144 2, /* Starting generator */
145 524269, /* RU_N-1 = 2^2*3^2*14563 */
146 7, /* determine ru_a as RU_AGEN^(2*rand) */
147 279936, /* RU_M = 2^7*3^7 - don't change */
148 { 2, 3, 14563, 0 }, /* factors of ru_n */
149 };
150
151 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
152 static void initid(struct randomtab *);
153 static u_int32_t randomid(struct randomtab *);
154
155 /*
156 * Do a fast modular exponation, returned value will be in the range
157 * of 0 - (mod-1)
158 */
159
160 static u_int32_t
161 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
162 {
163 u_int64_t s, t, u;
164
165 s = 1;
166 t = gen;
167 u = expo;
168
169 while (u) {
170 if (u & 1)
171 s = (s * t) % mod;
172 u >>= 1;
173 t = (t * t) % mod;
174 }
175 return (s);
176 }
177
178 /*
179 * Initalizes the seed and chooses a suitable generator. Also toggles
180 * the msb flag. The msb flag is used to generate two distinct
181 * cycles of random numbers and thus avoiding reuse of ids.
182 *
183 * This function is called from id_randomid() when needed, an
184 * application does not have to worry about it.
185 */
186 static void
187 initid(struct randomtab *p)
188 {
189 u_int32_t j, i;
190 int noprime = 1;
191
192 p->ru_x = arc4random() % p->ru_m;
193
194 /* (bits - 1) bits of random seed */
195 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
196 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
197
198 /* Determine the LCG we use */
199 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
200 p->ru_a = pmod(p->ru_agen,
201 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
202 while (p->ru_b % 3 == 0)
203 p->ru_b += 2;
204
205 j = arc4random() % p->ru_n;
206
207 /*
208 * Do a fast gcd(j, RU_N - 1), so we can find a j with
209 * gcd(j, RU_N - 1) == 1, giving a new generator for
210 * RU_GEN^j mod RU_N
211 */
212 while (noprime) {
213 for (i = 0; p->pfacts[i] > 0; i++)
214 if (j % p->pfacts[i] == 0)
215 break;
216
217 if (p->pfacts[i] == 0)
218 noprime = 0;
219 else
220 j = (j + 1) % p->ru_n;
221 }
222
223 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
224 p->ru_counter = 0;
225
226 p->ru_reseed = time_second + p->ru_out;
227 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
228 }
229
230 static u_int32_t
231 randomid(struct randomtab *p)
232 {
233 int i, n;
234 u_int32_t tmp;
235
236 if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
237 initid(p);
238
239 tmp = arc4random();
240
241 /* Skip a random number of ids */
242 n = tmp & 0x3; tmp = tmp >> 2;
243 if (p->ru_counter + n >= p->ru_max)
244 initid(p);
245
246 for (i = 0; i <= n; i++) {
247 /* Linear Congruential Generator */
248 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
249 }
250
251 p->ru_counter += i;
252
253 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) |
254 p->ru_msb;
255 }
256
257 u_int32_t
258 ip6_randomid(void)
259 {
260
261 return randomid(&randomtab_32);
262 }
263
264 u_int32_t
265 ip6_randomflowlabel(void)
266 {
267
268 return randomid(&randomtab_20) & 0xfffff;
269 }
270
271 #endif /* RANDOM_IP_ID */
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