sys/netinet/ip_id.c

   1 /*
   2  * Copyright (c) 2007 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/sys/netinet/ip_id.c,v 1.8 2007/11/23 22:29:51 dillon Exp $
  35  */
  36
  37 /*
  38  * Random ip sequence number generator.  Use the system PRNG to shuffle the
  39  * 65536 entry ID space.  We reshuffle the front-side of the array as we
  40  * index through it, guarenteeing an id will not be reused for at least
  41  * 32768 calls.
  42  */
  43 #include <sys/param.h>
  44 #include <sys/systm.h>
  45 #include <sys/kernel.h>
  46 #include <sys/random.h>
  47 #include <sys/spinlock.h>
  48 #include <sys/globaldata.h>
  49 #include <netinet/ip_var.h>
  50
  51 #include <sys/spinlock2.h>
  52
  53 static struct spinlock ip_shuffle_spin = SPINLOCK_INITIALIZER(ip_shuffle_spin);
  54 static u_int16_t ip_shuffle[65536];
  55
  56 /*
  57  * Initialize the shuffle.  We assume that the system PRNG won't be all that
  58  * good this early in the boot sequence but use it anyway.  The ids will be
  59  * reshuffled as they are popped and the PRNG should be better then.
  60  */
  61 static void
  62 ip_initshuffle(void *dummy __unused)
  63 {
  64         int i;
  65
  66         for (i = 0; i < 65536; ++i)
  67                 ip_shuffle[i] = i;
  68         for (i = 0; i < 65536; ++i)
  69                 ip_randomid();
  70 }
  71
  72 SYSINIT(ipshuffle, SI_SUB_PSEUDO, SI_ORDER_ANY, ip_initshuffle, NULL);
  73
  74 /*
  75  * Return a random IP id.  Use a forward shuffle over half the index
  76  * space to avoid duplicates occuring too quickly.  Since the initial
  77  * shuffle may not have had a good random basis we returned the element
  78  * at the shuffle target instead of the current element.
  79  *
  80  * XXX make per-cpu so the spinlock can be removed?
  81  */
  82 u_int16_t
  83 ip_randomid(void)
  84 {
  85         static int isindex;
  86         u_int16_t si, r;
  87         int i1, i2;
  88
  89         read_random_unlimited(&si, sizeof(si));
  90         spin_lock_wr(&ip_shuffle_spin);
  91         i1 = isindex & 0xFFFF;
  92         i2 = (isindex + (si & 0x7FFF)) & 0xFFFF;
  93         r = ip_shuffle[i2];
  94         ip_shuffle[i2] = ip_shuffle[i1];
  95         ip_shuffle[i1] = r;
  96         ++isindex;
  97         spin_unlock_wr(&ip_shuffle_spin);
  98
  99         return(r);
 100 }
 101