sys/netinet6/ip6_id.c

   1 /*      $NetBSD: ip6_id.c,v 1.15 2006/06/07 22:34:03 kardel 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 1.15 2006/06/07 22:34:03 kardel Exp $");
  86
  87 #include <sys/param.h>
  88 #include <lib/libkern/libkern.h>
  89
  90 #include <net/if.h>
  91 #include <netinet/in.h>
  92 #include <netinet/ip6.h>
  93 #include <netinet6/ip6_var.h>
  94
  95 struct randomtab {
  96         const int       ru_bits; /* resulting bits */
  97         const long      ru_out; /* Time after wich will be reseeded */
  98         const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
  99         const u_int32_t ru_gen; /* Starting generator */
 100         const u_int32_t ru_n;   /* ru_n: prime, ru_n - 1: product of pfacts[] */
 101         const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
 102         const u_int32_t ru_m;   /* ru_m = 2^x*3^y */
 103         const u_int32_t ru_pfacts[4];   /* factors of ru_n */
 104
 105         u_int32_t ru_counter;
 106         u_int32_t ru_msb;
 107
 108         u_int32_t ru_x;
 109         u_int32_t ru_seed, ru_seed2;
 110         u_int32_t ru_a, ru_b;
 111         u_int32_t ru_g;
 112         long ru_reseed;
 113 };
 114
 115 static struct randomtab randomtab_32 = {
 116         .ru_bits = 32,          /* resulting bits */
 117         .ru_out = 180,          /* Time after wich will be reseeded */
 118         .ru_max = 1000000000,   /* Uniq cycle, avoid blackjack prediction */
 119         .ru_gen = 2,            /* Starting generator */
 120         .ru_n = 2147483629,     /* RU_N-1 = 2^2*3^2*59652323 */
 121         .ru_agen = 7,           /* determine ru_a as RU_AGEN^(2*rand) */
 122         .ru_m = 1836660096,     /* RU_M = 2^7*3^15 - don't change */
 123         .ru_pfacts = { 2, 3, 59652323, 0 },     /* factors of ru_n */
 124 };
 125
 126 static struct randomtab randomtab_20 = {
 127         .ru_bits = 20,          /* resulting bits */
 128         .ru_out = 180,          /* Time after wich will be reseeded */
 129         .ru_max = 200000,       /* Uniq cycle, avoid blackjack prediction */
 130         .ru_gen = 2,            /* Starting generator */
 131         .ru_n = 524269,         /* RU_N-1 = 2^2*3^2*14563 */
 132         .ru_agen = 7,           /* determine ru_a as RU_AGEN^(2*rand) */
 133         .ru_m = 279936,         /* RU_M = 2^7*3^7 - don't change */
 134         .ru_pfacts = { 2, 3, 14563, 0 },        /* factors of ru_n */
 135 };
 136
 137 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
 138 static void initid(struct randomtab *);
 139 static u_int32_t randomid(struct randomtab *);
 140
 141 /*
 142  * Do a fast modular exponation, returned value will be in the range
 143  * of 0 - (mod-1)
 144  */
 145
 146 static u_int32_t
 147 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
 148 {
 149         u_int64_t s, t, u;
 150
 151         s = 1;
 152         t = gen;
 153         u = expo;
 154
 155         while (u) {
 156                 if (u & 1)
 157                         s = (s * t) % mod;
 158                 u >>= 1;
 159                 t = (t * t) % mod;
 160         }
 161         return (s);
 162 }
 163
 164 /*
 165  * Initalizes the seed and chooses a suitable generator. Also toggles
 166  * the msb flag. The msb flag is used to generate two distinct
 167  * cycles of random numbers and thus avoiding reuse of ids.
 168  *
 169  * This function is called from id_randomid() when needed, an
 170  * application does not have to worry about it.
 171  */
 172 static void
 173 initid(struct randomtab *p)
 174 {
 175         u_int32_t j, i;
 176         int noprime = 1;
 177
 178         p->ru_x = arc4random() % p->ru_m;
 179
 180         /* (bits - 1) bits of random seed */
 181         p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
 182         p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
 183
 184         /* Determine the LCG we use */
 185         p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
 186         p->ru_a = pmod(p->ru_agen,
 187             (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
 188         while (p->ru_b % 3 == 0)
 189                 p->ru_b += 2;
 190
 191         j = arc4random() % p->ru_n;
 192
 193         /*
 194          * Do a fast gcd(j, RU_N - 1), so we can find a j with
 195          * gcd(j, RU_N - 1) == 1, giving a new generator for
 196          * RU_GEN^j mod RU_N
 197          */
 198         while (noprime) {
 199                 for (i = 0; p->ru_pfacts[i] > 0; i++)
 200                         if (j % p->ru_pfacts[i] == 0)
 201                                 break;
 202
 203                 if (p->ru_pfacts[i] == 0)
 204                         noprime = 0;
 205                 else
 206                         j = (j + 1) % p->ru_n;
 207         }
 208
 209         p->ru_g = pmod(p->ru_gen, j, p->ru_n);
 210         p->ru_counter = 0;
 211
 212         p->ru_reseed = time_second + p->ru_out;
 213         p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
 214 }
 215
 216 static u_int32_t
 217 randomid(struct randomtab *p)
 218 {
 219         int i, n;
 220
 221         if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
 222                 initid(p);
 223
 224         /* Skip a random number of ids */
 225         n = arc4random() & 0x3;
 226         if (p->ru_counter + n >= p->ru_max)
 227                 initid(p);
 228
 229         for (i = 0; i <= n; i++) {
 230                 /* Linear Congruential Generator */
 231                 p->ru_x = ((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
 232         }
 233
 234         p->ru_counter += i;
 235
 236         return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
 237             p->ru_msb;
 238 }
 239
 240 u_int32_t
 241 ip6_randomid(void)
 242 {
 243
 244         return randomid(&randomtab_32);
 245 }
 246
 247 u_int32_t
 248 ip6_randomflowlabel(void)
 249 {
 250
 251         return randomid(&randomtab_20) & 0xfffff;
 252 }