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/globaldata.h>
  48
  49 #include <net/netmsg2.h>
  50 #include <net/netisr2.h>
  51
  52 #include <netinet/ip_var.h>
  53
  54 #define IPRANDCOUNT     32
  55
  56 typedef struct iprandinfo {
  57         short   randdata[IPRANDCOUNT];
  58         int     randidx;
  59         int     isidx;
  60 } *iprandinfo_t __cachealign;
  61
  62 struct iprandinfo iprandcpu[MAXCPU];
  63
  64 static u_int16_t ip_shuffle[65536];
  65
  66 static void
  67 ip_idinit_handler(netmsg_t msg)
  68 {
  69         int i;
  70
  71         for (i = 0; i < 65536; ++i)
  72                 ip_randomid();
  73
  74         /* Done! */
  75         netisr_replymsg(&msg->base, 0);
  76 }
  77
  78 /*
  79  * Initialize the shuffle.  We assume that the system PRNG won't be all that
  80  * good this early in the boot sequence but use it anyway.  The ids will be
  81  * reshuffled as they are popped and the PRNG should be better then.
  82  */
  83 static void
  84 ip_idinit_shuffle(void *dummy __unused)
  85 {
  86         struct netmsg_base msg;
  87         int i;
  88
  89         for (i = 0; i < 65536; ++i)
  90                 ip_shuffle[i] = i;
  91         for (i = 0; i < ncpus; ++i) {
  92                 netmsg_init(&msg, NULL, &curthread->td_msgport, 0,
  93                     ip_idinit_handler);
  94                 netisr_domsg(&msg, i);
  95                 iprandcpu[i].isidx = i * (65536 / ncpus_fit);
  96         }
  97 }
  98
  99 SYSINIT(ipshuffle, SI_SUB_PSEUDO, SI_ORDER_ANY, ip_idinit_shuffle, NULL);
 100
 101 /*
 102  * Return a random IP id.  Use a forward shuffle over half the index
 103  * space to avoid duplicates occuring too quickly.  Since the initial
 104  * shuffle may not have had a good random basis we returned the element
 105  * at the shuffle target instead of the current element.
 106  */
 107 u_int16_t
 108 ip_randomid(void)
 109 {
 110         globaldata_t gd = mycpu;
 111         iprandinfo_t info;
 112         u_int16_t si, r;
 113         int i1, i2;
 114
 115         info = &iprandcpu[gd->gd_cpuid];
 116
 117         /*
 118          * Reload random array efficiently
 119          */
 120         if (info->randidx == 0) {
 121                 info->randidx = IPRANDCOUNT;
 122                 read_random(info->randdata, sizeof(info->randdata), 1);
 123         }
 124
 125         /*
 126          * Get random number (si) and calculate shuffle.  The shuffle
 127          * is calculated such that the cpus do not interfere with each
 128          * other.
 129          */
 130         si = info->randdata[--info->randidx];
 131         i1 = (info->isidx & 0xFFFF & ~ncpus_fit_mask) | gd->gd_cpuid;
 132         i2 = ((i1 + (si & 0x7FFF)) & 0xFFFF & ~ncpus_fit_mask) | gd->gd_cpuid;
 133
 134         /*
 135          * Do the shuffle, bump isidx taking into account the cpu
 136          * partitioning.
 137          */
 138         r = ip_shuffle[i2];
 139         ip_shuffle[i2] = ip_shuffle[i1];
 140         ip_shuffle[i1] = r;
 141         info->isidx += ncpus_fit;
 142
 143         return (r);
 144 }