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

     /*      $NetBSD: ip6_id.c,v 1.13 2004/03/23 05:31:54 itojun Exp $       */
     /*      $KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun Exp $  */
     /*      $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $       */
     
     /*
      * Copyright (C) 2003 WIDE Project.
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the project nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * Copyright 1998 Niels Provos <provos@citi.umich.edu>
     * All rights reserved.
     *
     * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
     * such a mathematical system to generate more random (yet non-repeating)
     * ids to solve the resolver/named problem.  But Niels designed the
     * actual system based on the constraints.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     */
    
    /*
     * seed = random (bits - 1) bit
     * n = prime, g0 = generator to n,
     * j = random so that gcd(j,n-1) == 1
     * g = g0^j mod n will be a generator again.
     *
     * X[0] = random seed.
     * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
     * with a = 7^(even random) mod m,
     *      b = random with gcd(b,m) == 1
     *      m = constant and a maximal period of m-1.
     *
     * The transaction id is determined by:
     * id[n] = seed xor (g^X[n] mod n)
     *
     * Effectively the id is restricted to the lower (bits - 1) bits, thus
     * yielding two different cycles by toggling the msb on and off.
     * This avoids reuse issues caused by reseeding.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: ip6_id.c,v 1.13 2004/03/23 05:31:54 itojun Exp $");
    
    #include <sys/types.h>
    #include <sys/param.h>
    #include <sys/kernel.h>
    #include <lib/libkern/libkern.h>
    
    #include <net/if.h>
    #include <netinet/in.h>
    #include <netinet/ip6.h>
    #include <netinet6/ip6_var.h>
    
    struct randomtab {
            const int       ru_bits; /* resulting bits */
            const long      ru_out; /* Time after wich will be reseeded */
           const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
           const u_int32_t ru_gen; /* Starting generator */
           const u_int32_t ru_n;   /* ru_n: prime, ru_n - 1: product of pfacts[] */
           const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
           const u_int32_t ru_m;   /* ru_m = 2^x*3^y */
           const u_int32_t pfacts[4];      /* factors of ru_n */
   
           u_int32_t ru_counter;
           u_int32_t ru_msb;
   
           u_int32_t ru_x;
           u_int32_t ru_seed, ru_seed2;
           u_int32_t ru_a, ru_b;
           u_int32_t ru_g;
           long ru_reseed;
   };
   
   static struct randomtab randomtab_32 = {
           32,                     /* resulting bits */
           180,                    /* Time after wich will be reseeded */
           1000000000,             /* Uniq cycle, avoid blackjack prediction */
           2,                      /* Starting generator */
           2147483629,             /* RU_N-1 = 2^2*3^2*59652323 */
           7,                      /* determine ru_a as RU_AGEN^(2*rand) */
           1836660096,             /* RU_M = 2^7*3^15 - don't change */
           { 2, 3, 59652323, 0 },  /* factors of ru_n */
   };
   
   static struct randomtab randomtab_20 = {
           20,                     /* resulting bits */
           180,                    /* Time after wich will be reseeded */
           200000,                 /* Uniq cycle, avoid blackjack prediction */
           2,                      /* Starting generator */
           524269,                 /* RU_N-1 = 2^2*3^2*14563 */
           7,                      /* determine ru_a as RU_AGEN^(2*rand) */
           279936,                 /* RU_M = 2^7*3^7 - don't change */
           { 2, 3, 14563, 0 },     /* factors of ru_n */
   };
   
   static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
   static void initid(struct randomtab *);
   static u_int32_t randomid(struct randomtab *);
   
   /*
    * Do a fast modular exponation, returned value will be in the range
    * of 0 - (mod-1)
    */
   
   static u_int32_t
   pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
   {
           u_int64_t s, t, u;
   
           s = 1;
           t = gen;
           u = expo;
   
           while (u) {
                   if (u & 1)
                           s = (s * t) % mod;
                   u >>= 1;
                   t = (t * t) % mod;
           }
           return (s);
   }
   
   /*
    * Initalizes the seed and chooses a suitable generator. Also toggles
    * the msb flag. The msb flag is used to generate two distinct
    * cycles of random numbers and thus avoiding reuse of ids.
    *
    * This function is called from id_randomid() when needed, an
    * application does not have to worry about it.
    */
   static void
   initid(struct randomtab *p)
   {
           u_int32_t j, i;
           int noprime = 1;
   
           p->ru_x = arc4random() % p->ru_m;
   
           /* (bits - 1) bits of random seed */
           p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
           p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
   
           /* Determine the LCG we use */
           p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
           p->ru_a = pmod(p->ru_agen,
               (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
           while (p->ru_b % 3 == 0)
                   p->ru_b += 2;
   
           j = arc4random() % p->ru_n;
   
           /*
            * Do a fast gcd(j, RU_N - 1), so we can find a j with
            * gcd(j, RU_N - 1) == 1, giving a new generator for
            * RU_GEN^j mod RU_N
            */
           while (noprime) {
                   for (i = 0; p->pfacts[i] > 0; i++)
                           if (j % p->pfacts[i] == 0)
                                   break;
   
                   if (p->pfacts[i] == 0)
                           noprime = 0;
                   else
                           j = (j + 1) % p->ru_n;
           }
   
           p->ru_g = pmod(p->ru_gen, j, p->ru_n);
           p->ru_counter = 0;
   
           p->ru_reseed = time.tv_sec + p->ru_out;
           p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
   }
   
   static u_int32_t
   randomid(struct randomtab *p)
   {
           int i, n;
   
           if (p->ru_counter >= p->ru_max || time.tv_sec > p->ru_reseed)
                   initid(p);
   
           /* Skip a random number of ids */
           n = arc4random() & 0x3;
           if (p->ru_counter + n >= p->ru_max)
                   initid(p);
   
           for (i = 0; i <= n; i++) {
                   /* Linear Congruential Generator */
                   p->ru_x = ((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
           }
   
           p->ru_counter += i;
   
           return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
               p->ru_msb;
   }
   
   u_int32_t
   ip6_randomid(void)
   {
   
           return randomid(&randomtab_32);
   }
   
   u_int32_t
   ip6_randomflowlabel(void)
   {
   
           return randomid(&randomtab_20) & 0xfffff;
   }

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