The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet6/ip6_id.c

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    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 <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 }

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