1 | /* $NetBSD: ip6_id.c,v 1.18 2015/08/07 08:11:33 ozaki-r Exp $ */ |
2 | /* $KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun Exp $ */ |
3 | /* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */ |
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 | * |
52 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
53 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
54 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
55 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
56 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
57 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
58 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
59 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
60 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
61 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
62 | */ |
63 | |
64 | /* |
65 | * seed = random (bits - 1) bit |
66 | * n = prime, g0 = generator to n, |
67 | * j = random so that gcd(j,n-1) == 1 |
68 | * g = g0^j mod n will be a generator again. |
69 | * |
70 | * X[0] = random seed. |
71 | * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator |
72 | * with a = 7^(even random) mod m, |
73 | * b = random with gcd(b,m) == 1 |
74 | * m = constant and a maximal period of m-1. |
75 | * |
76 | * The transaction id is determined by: |
77 | * id[n] = seed xor (g^X[n] mod n) |
78 | * |
79 | * Effectively the id is restricted to the lower (bits - 1) bits, thus |
80 | * yielding two different cycles by toggling the msb on and off. |
81 | * This avoids reuse issues caused by reseeding. |
82 | */ |
83 | |
84 | #include <sys/cdefs.h> |
85 | __KERNEL_RCSID(0, "$NetBSD: ip6_id.c,v 1.18 2015/08/07 08:11:33 ozaki-r Exp $" ); |
86 | |
87 | #include <sys/param.h> |
88 | #include <sys/cprng.h> |
89 | |
90 | #include <lib/libkern/libkern.h> |
91 | |
92 | #include <net/if.h> |
93 | #include <netinet/in.h> |
94 | #include <netinet/ip6.h> |
95 | #include <netinet6/ip6_var.h> |
96 | |
97 | struct randomtab { |
98 | const int ru_bits; /* resulting bits */ |
99 | const long ru_out; /* Time after wich will be reseeded */ |
100 | const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */ |
101 | const u_int32_t ru_gen; /* Starting generator */ |
102 | const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ |
103 | const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */ |
104 | const u_int32_t ru_m; /* ru_m = 2^x*3^y */ |
105 | const u_int32_t ru_pfacts[4]; /* factors of ru_n */ |
106 | |
107 | u_int32_t ru_counter; |
108 | u_int32_t ru_msb; |
109 | |
110 | u_int32_t ru_x; |
111 | u_int32_t ru_seed, ru_seed2; |
112 | u_int32_t ru_a, ru_b; |
113 | u_int32_t ru_g; |
114 | long ru_reseed; |
115 | }; |
116 | |
117 | static struct randomtab randomtab_32 = { |
118 | .ru_bits = 32, /* resulting bits */ |
119 | .ru_out = 180, /* Time after wich will be reseeded */ |
120 | .ru_max = 1000000000, /* Uniq cycle, avoid blackjack prediction */ |
121 | .ru_gen = 2, /* Starting generator */ |
122 | .ru_n = 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ |
123 | .ru_agen = 7, /* determine ru_a as RU_AGEN^(2*rand) */ |
124 | .ru_m = 1836660096, /* RU_M = 2^7*3^15 - don't change */ |
125 | .ru_pfacts = { 2, 3, 59652323, 0 }, /* factors of ru_n */ |
126 | }; |
127 | |
128 | static struct randomtab randomtab_20 = { |
129 | .ru_bits = 20, /* resulting bits */ |
130 | .ru_out = 180, /* Time after wich will be reseeded */ |
131 | .ru_max = 200000, /* Uniq cycle, avoid blackjack prediction */ |
132 | .ru_gen = 2, /* Starting generator */ |
133 | .ru_n = 524269, /* RU_N-1 = 2^2*3^2*14563 */ |
134 | .ru_agen = 7, /* determine ru_a as RU_AGEN^(2*rand) */ |
135 | .ru_m = 279936, /* RU_M = 2^7*3^7 - don't change */ |
136 | .ru_pfacts = { 2, 3, 14563, 0 }, /* factors of ru_n */ |
137 | }; |
138 | |
139 | static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); |
140 | static void initid(struct randomtab *); |
141 | static u_int32_t randomid(struct randomtab *); |
142 | |
143 | /* |
144 | * Do a fast modular exponation, returned value will be in the range |
145 | * of 0 - (mod-1) |
146 | */ |
147 | |
148 | static u_int32_t |
149 | pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) |
150 | { |
151 | u_int64_t s, t, u; |
152 | |
153 | s = 1; |
154 | t = gen; |
155 | u = expo; |
156 | |
157 | while (u) { |
158 | if (u & 1) |
159 | s = (s * t) % mod; |
160 | u >>= 1; |
161 | t = (t * t) % mod; |
162 | } |
163 | return (s); |
164 | } |
165 | |
166 | /* |
167 | * Initalizes the seed and chooses a suitable generator. Also toggles |
168 | * the msb flag. The msb flag is used to generate two distinct |
169 | * cycles of random numbers and thus avoiding reuse of ids. |
170 | * |
171 | * This function is called from id_randomid() when needed, an |
172 | * application does not have to worry about it. |
173 | */ |
174 | static void |
175 | initid(struct randomtab *p) |
176 | { |
177 | u_int32_t j, i; |
178 | int noprime = 1; |
179 | |
180 | p->ru_x = cprng_fast32() % p->ru_m; |
181 | |
182 | /* (bits - 1) bits of random seed */ |
183 | p->ru_seed = cprng_fast32() & (~0U >> (32 - p->ru_bits + 1)); |
184 | p->ru_seed2 = cprng_fast32() & (~0U >> (32 - p->ru_bits + 1)); |
185 | |
186 | /* Determine the LCG we use */ |
187 | p->ru_b = (cprng_fast32() & (~0U >> (32 - p->ru_bits))) | 1; |
188 | p->ru_a = pmod(p->ru_agen, |
189 | (cprng_fast32() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); |
190 | while (p->ru_b % 3 == 0) |
191 | p->ru_b += 2; |
192 | |
193 | j = cprng_fast32() % p->ru_n; |
194 | |
195 | /* |
196 | * Do a fast gcd(j, RU_N - 1), so we can find a j with |
197 | * gcd(j, RU_N - 1) == 1, giving a new generator for |
198 | * RU_GEN^j mod RU_N |
199 | */ |
200 | while (noprime) { |
201 | for (i = 0; p->ru_pfacts[i] > 0; i++) |
202 | if (j % p->ru_pfacts[i] == 0) |
203 | break; |
204 | |
205 | if (p->ru_pfacts[i] == 0) |
206 | noprime = 0; |
207 | else |
208 | j = (j + 1) % p->ru_n; |
209 | } |
210 | |
211 | p->ru_g = pmod(p->ru_gen, j, p->ru_n); |
212 | p->ru_counter = 0; |
213 | |
214 | p->ru_reseed = time_uptime + p->ru_out; |
215 | p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); |
216 | } |
217 | |
218 | static u_int32_t |
219 | randomid(struct randomtab *p) |
220 | { |
221 | int i, n; |
222 | |
223 | if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed) |
224 | initid(p); |
225 | |
226 | /* Skip a random number of ids */ |
227 | n = cprng_fast32() & 0x3; |
228 | if (p->ru_counter + n >= p->ru_max) |
229 | initid(p); |
230 | |
231 | for (i = 0; i <= n; i++) { |
232 | /* Linear Congruential Generator */ |
233 | p->ru_x = ((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; |
234 | } |
235 | |
236 | p->ru_counter += i; |
237 | |
238 | return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) | |
239 | p->ru_msb; |
240 | } |
241 | |
242 | u_int32_t |
243 | ip6_randomid(void) |
244 | { |
245 | |
246 | return randomid(&randomtab_32); |
247 | } |
248 | |
249 | u_int32_t |
250 | ip6_randomflowlabel(void) |
251 | { |
252 | |
253 | return randomid(&randomtab_20) & 0xfffff; |
254 | } |
255 | |