IABSD.fr/src/sys/netinet/ip_id.c

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• Author : bluhm
  Date : 2025-01-01 13:44:22
  Hash : 66570633
  Message : Fix whitespace.

• sys/netinet/ip_id.c

• /*	$OpenBSD: ip_id.c,v 1.26 2025/01/01 13:44:22 bluhm Exp $ */
  
  /*
   * Copyright (c) 2008 Theo de Raadt, Ryan McBride
   *
   * Slightly different algorithm from the one designed by
   * Matthew Dillon <dillon@backplane.com> for The DragonFly Project
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  
  /*
   * Random ip sequence number generator.  Use the system PRNG to shuffle
   * the 65536 entry ID space.  We reshuffle the ID we pick out of the array
   * into the previous 32767 cells, providing an guarantee that an ID will not
   * be reused for at least 32768 calls.
   */
  #include <sys/param.h>
  #include <sys/systm.h>
  
  static u_int16_t ip_shuffle[65536];
  static int isindex = 0;
  
  u_int16_t ip_randomid(void);
  
  /*
   * Return a random IP id.  Shuffle the new value we get into the previous half
   * of the ip_shuffle ring (-32767 or swap with ourself), to avoid duplicates
   * occurring too quickly but also still be random.
   *
   * 0 is a special IP ID -- don't return it.
   */
  u_int16_t
  ip_randomid(void)
  {
  	static int ipid_initialized;
  	u_int16_t si, r;
  	int i, i2;
  
  	if (!ipid_initialized) {
  		ipid_initialized = 1;
  
  		/*
  		 * Initialize with a random permutation. Do so using Knuth
  		 * which avoids the exchange in the Durstenfeld shuffle.
  		 * (See "The Art of Computer Programming, Vol 2" 3rd ed, pg. 145).
  		 *
  		 * Even if our PRNG is imperfect at boot time, we have deferred
  		 * doing this until the first packet being sent and now must
  		 * generate an ID.
  		 */
  		for (i = 0; i < nitems(ip_shuffle); ++i) {
  			i2 = arc4random_uniform(i + 1);
  			ip_shuffle[i] = ip_shuffle[i2];
  			ip_shuffle[i2] = i;
  		}
  	}
  
  	do {
  		arc4random_buf(&si, sizeof(si));
  		i = isindex & 0xFFFF;
  		i2 = (isindex - (si & 0x7FFF)) & 0xFFFF;
  		r = ip_shuffle[i];
  		ip_shuffle[i] = ip_shuffle[i2];
  		ip_shuffle[i2] = r;
  		isindex++;
  	} while (r == 0);
  
  	return (r);
  }