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