FreeBSD/Linux Kernel Cross Reference
sys/netinet6/ip6_id.c
1 /*-
2 * Copyright (C) 2003 WIDE Project.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the project nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $
30 */
31
32 /*-
33 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
34 * All rights reserved.
35 *
36 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
37 * such a mathematical system to generate more random (yet non-repeating)
38 * ids to solve the resolver/named problem. But Niels designed the
39 * actual system based on the constraints.
40 *
41 * Redistribution and use in source and binary forms, with or without
42 * modification, are permitted provided that the following conditions
43 * are met:
44 * 1. Redistributions of source code must retain the above copyright
45 * notice, this list of conditions and the following disclaimer.
46 * 2. Redistributions in binary form must reproduce the above copyright
47 * notice, this list of conditions and the following disclaimer in the
48 * documentation and/or other materials provided with the distribution.
49 * 3. All advertising materials mentioning features or use of this software
50 * must display the following acknowledgement:
51 * This product includes software developed by Niels Provos.
52 * 4. The name of the author may not be used to endorse or promote products
53 * derived from this software without specific prior written permission.
54 *
55 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
56 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
57 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
58 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
59 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
60 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
61 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
62 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
63 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
64 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
65 *
66 * $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $
67 */
68
69 #include <sys/cdefs.h>
70 __FBSDID("$FreeBSD: src/sys/netinet6/ip6_id.c,v 1.9 2007/12/10 16:03:38 obrien Exp $");
71
72 /*
73 * seed = random (bits - 1) bit
74 * n = prime, g0 = generator to n,
75 * j = random so that gcd(j,n-1) == 1
76 * g = g0^j mod n will be a generator again.
77 *
78 * X[0] = random seed.
79 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
80 * with a = 7^(even random) mod m,
81 * b = random with gcd(b,m) == 1
82 * m = constant and a maximal period of m-1.
83 *
84 * The transaction id is determined by:
85 * id[n] = seed xor (g^X[n] mod n)
86 *
87 * Effectivly the id is restricted to the lower (bits - 1) bits, thus
88 * yielding two different cycles by toggling the msb on and off.
89 * This avoids reuse issues caused by reseeding.
90 */
91
92 #include <sys/types.h>
93 #include <sys/param.h>
94 #include <sys/kernel.h>
95 #include <sys/socket.h>
96 #include <sys/libkern.h>
97
98 #include <net/if.h>
99 #include <net/route.h>
100 #include <netinet/in.h>
101 #include <netinet/ip6.h>
102 #include <netinet6/ip6_var.h>
103
104 #ifndef INT32_MAX
105 #define INT32_MAX 0x7fffffffU
106 #endif
107
108 struct randomtab {
109 const int ru_bits; /* resulting bits */
110 const long ru_out; /* Time after wich will be reseeded */
111 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
112 const u_int32_t ru_gen; /* Starting generator */
113 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
114 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
115 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
116 const u_int32_t pfacts[4]; /* factors of ru_n */
117
118 u_int32_t ru_counter;
119 u_int32_t ru_msb;
120
121 u_int32_t ru_x;
122 u_int32_t ru_seed, ru_seed2;
123 u_int32_t ru_a, ru_b;
124 u_int32_t ru_g;
125 long ru_reseed;
126 };
127
128 static struct randomtab randomtab_32 = {
129 32, /* resulting bits */
130 180, /* Time after wich will be reseeded */
131 1000000000, /* Uniq cycle, avoid blackjack prediction */
132 2, /* Starting generator */
133 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
134 7, /* determine ru_a as RU_AGEN^(2*rand) */
135 1836660096, /* RU_M = 2^7*3^15 - don't change */
136 { 2, 3, 59652323, 0 }, /* factors of ru_n */
137 };
138
139 static struct randomtab randomtab_20 = {
140 20, /* resulting bits */
141 180, /* Time after wich will be reseeded */
142 200000, /* Uniq cycle, avoid blackjack prediction */
143 2, /* Starting generator */
144 524269, /* RU_N-1 = 2^2*3^2*14563 */
145 7, /* determine ru_a as RU_AGEN^(2*rand) */
146 279936, /* RU_M = 2^7*3^7 - don't change */
147 { 2, 3, 14563, 0 }, /* factors of ru_n */
148 };
149
150 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
151 static void initid(struct randomtab *);
152 static u_int32_t randomid(struct randomtab *);
153
154 /*
155 * Do a fast modular exponation, returned value will be in the range
156 * of 0 - (mod-1)
157 */
158 static u_int32_t
159 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
160 {
161 u_int64_t s, t, u;
162
163 s = 1;
164 t = gen;
165 u = expo;
166
167 while (u) {
168 if (u & 1)
169 s = (s * t) % mod;
170 u >>= 1;
171 t = (t * t) % mod;
172 }
173 return (s);
174 }
175
176 /*
177 * Initalizes the seed and chooses a suitable generator. Also toggles
178 * the msb flag. The msb flag is used to generate two distinct
179 * cycles of random numbers and thus avoiding reuse of ids.
180 *
181 * This function is called from id_randomid() when needed, an
182 * application does not have to worry about it.
183 */
184 static void
185 initid(struct randomtab *p)
186 {
187 u_int32_t j, i;
188 int noprime = 1;
189
190 p->ru_x = arc4random() % p->ru_m;
191
192 /* (bits - 1) bits of random seed */
193 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
194 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
195
196 /* Determine the LCG we use */
197 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
198 p->ru_a = pmod(p->ru_agen,
199 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
200 while (p->ru_b % 3 == 0)
201 p->ru_b += 2;
202
203 j = arc4random() % p->ru_n;
204
205 /*
206 * Do a fast gcd(j, RU_N - 1), so we can find a j with
207 * gcd(j, RU_N - 1) == 1, giving a new generator for
208 * RU_GEN^j mod RU_N
209 */
210 while (noprime) {
211 for (i = 0; p->pfacts[i] > 0; i++)
212 if (j % p->pfacts[i] == 0)
213 break;
214
215 if (p->pfacts[i] == 0)
216 noprime = 0;
217 else
218 j = (j + 1) % p->ru_n;
219 }
220
221 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
222 p->ru_counter = 0;
223
224 p->ru_reseed = time_second + p->ru_out;
225 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
226 }
227
228 static u_int32_t
229 randomid(struct randomtab *p)
230 {
231 int i, n;
232 u_int32_t tmp;
233
234 if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
235 initid(p);
236
237 tmp = arc4random();
238
239 /* Skip a random number of ids */
240 n = tmp & 0x3; tmp = tmp >> 2;
241 if (p->ru_counter + n >= p->ru_max)
242 initid(p);
243
244 for (i = 0; i <= n; i++) {
245 /* Linear Congruential Generator */
246 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
247 }
248
249 p->ru_counter += i;
250
251 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) |
252 p->ru_msb;
253 }
254
255 u_int32_t
256 ip6_randomid(void)
257 {
258
259 return randomid(&randomtab_32);
260 }
261
262 u_int32_t
263 ip6_randomflowlabel(void)
264 {
265
266 return randomid(&randomtab_20) & 0xfffff;
267 }
268
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