| 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 | |