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("$FreeBSD$"); 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 <net/vnet.h> 101 #include <netinet/in.h> 102 #include <netinet/ip6.h> 103 #include <netinet6/ip6_var.h> 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 which 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 which 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 which 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 static u_int32_t 160 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 161 { 162 u_int64_t s, t, u; 163 164 s = 1; 165 t = gen; 166 u = expo; 167 168 while (u) { 169 if (u & 1) 170 s = (s * t) % mod; 171 u >>= 1; 172 t = (t * t) % mod; 173 } 174 return (s); 175 } 176 177 /* 178 * Initalizes the seed and chooses a suitable generator. Also toggles 179 * the msb flag. The msb flag is used to generate two distinct 180 * cycles of random numbers and thus avoiding reuse of ids. 181 * 182 * This function is called from id_randomid() when needed, an 183 * application does not have to worry about it. 184 */ 185 static void 186 initid(struct randomtab *p) 187 { 188 u_int32_t j, i; 189 int noprime = 1; 190 191 p->ru_x = arc4random() % p->ru_m; 192 193 /* (bits - 1) bits of random seed */ 194 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 195 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 196 197 /* Determine the LCG we use */ 198 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 199 p->ru_a = pmod(p->ru_agen, 200 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 201 while (p->ru_b % 3 == 0) 202 p->ru_b += 2; 203 204 j = arc4random() % p->ru_n; 205 206 /* 207 * Do a fast gcd(j, RU_N - 1), so we can find a j with 208 * gcd(j, RU_N - 1) == 1, giving a new generator for 209 * RU_GEN^j mod RU_N 210 */ 211 while (noprime) { 212 for (i = 0; p->pfacts[i] > 0; i++) 213 if (j % p->pfacts[i] == 0) 214 break; 215 216 if (p->pfacts[i] == 0) 217 noprime = 0; 218 else 219 j = (j + 1) % p->ru_n; 220 } 221 222 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 223 p->ru_counter = 0; 224 225 p->ru_reseed = time_uptime + p->ru_out; 226 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 227 } 228 229 static u_int32_t 230 randomid(struct randomtab *p) 231 { 232 int i, n; 233 u_int32_t tmp; 234 235 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed) 236 initid(p); 237 238 tmp = arc4random(); 239 240 /* Skip a random number of ids */ 241 n = tmp & 0x3; tmp = tmp >> 2; 242 if (p->ru_counter + n >= p->ru_max) 243 initid(p); 244 245 for (i = 0; i <= n; i++) { 246 /* Linear Congruential Generator */ 247 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 248 } 249 250 p->ru_counter += i; 251 252 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 253 p->ru_msb; 254 } 255 256 u_int32_t 257 ip6_randomid(void) 258 { 259 260 return randomid(&randomtab_32); 261 } 262 263 u_int32_t 264 ip6_randomflowlabel(void) 265 { 266 267 return randomid(&randomtab_20) & 0xfffff; 268 } 269