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 } 101 102