mdw@git.distorted.org.uk Git - userv-utils/blob - ipif/mech-sequence.c

   1 /*
   2  * Sequence number / nonce mechanism for udp tunnel
   3  *
   4  * mechanisms: nonce, sequence
   5  * arguments: none
   6  *
   7  * restrictions: none
   8  * encoding: prepend 4 bytes of sequence arithmetic serial number
   9  * decoding: check increasingness (sequence), or ignore (nonce)
  10  */
  11 /*
  12  * This file is part of ipif, part of userv-utils
  13  *
  14  * Copyright 1996-2013 Ian Jackson <ijackson@chiark.greenend.org.uk>
  15  * Copyright 1998 David Damerell <damerell@chiark.greenend.org.uk>
  16  * Copyright 1999,2003
  17  *    Chancellor Masters and Scholars of the University of Cambridge
  18  * Copyright 2010 Tony Finch <fanf@dotat.at>
  19  *
  20  * This is free software; you can redistribute it and/or modify it
  21  * under the terms of the GNU General Public License as published by
  22  * the Free Software Foundation; either version 3 of the License, or
  23  * (at your option) any later version.
  24  *
  25  * This program is distributed in the hope that it will be useful, but
  26  * WITHOUT ANY WARRANTY; without even the implied warranty of
  27  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  28  * General Public License for more details.
  29  *
  30  * You should have received a copy of the GNU General Public License
  31  * along with userv-utils; if not, see http://www.gnu.org/licenses/.
  32  */
  33
  34 #include <netinet/in.h>
  35
  36 #include "forwarder.h"
  37
  38 struct mechdata {
  39   uint32_t number;
  40   int anyseen; /* decode only */
  41 };
  42
  43 static void mes_sequence(struct mechdata **md_r, int *maxprefix_io, int *maxsuffix_io) {
  44   struct mechdata *md;
  45
  46   XMALLOC(md);
  47   get_random(&md->number,sizeof(md->number));
  48   *maxprefix_io += 4;
  49   *md_r= md;
  50 }
  51
  52 static void mds_sequence(struct mechdata **md_r) {
  53   struct mechdata *md;
  54   XMALLOC(md);
  55   md->anyseen= 0;
  56   *md_r= md;
  57 }
  58
  59 static void menc_sequence(struct mechdata *md, struct buffer *buf) {
  60   md->number++;
  61   *(uint32_t*)buf_prepend(buf,4)= htonl(md->number);
  62 }
  63
  64 static const char *mdec_check(struct mechdata *md, struct buffer *buf) {
  65   uint32_t *sp, sequence;
  66
  67   BUF_UNPREPEND(sp,buf,4);
  68   sequence= ntohl(*sp);
  69
  70   if (md->anyseen)
  71     if (sequence - md->number >= 0x800000UL) return "out of order packet";
  72
  73   md->number= sequence;
  74   md->anyseen= 1;
  75
  76   return 0;
  77 }
  78
  79 static const char *mdec_skip(struct mechdata *md, struct buffer *buf) {
  80   uint32_t *sp;
  81   BUF_UNPREPEND(sp,buf,4);
  82   return 0;
  83 }
  84
  85 const struct mechanism mechlist_sequence[]= {
  86  { "nonce",         mes_sequence, mds_sequence,  menc_sequence, mdec_skip    },
  87  { "sequence",      mes_sequence, mds_sequence,  menc_sequence, mdec_check   },
  88  { 0 }
  89 };