src/mops_checksums.c

   1 /*
   2  * Mausezahn - A fast versatile traffic generator
   3  * Copyright (C) 2008-2010 Herbert Haas
   4  *
   5  * This program is free software; you can redistribute it and/or modify it under
   6  * the terms of the GNU General Public License version 2 as published by the
   7  * Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  11  * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
  12  * details.
  13  *
  14  * You should have received a copy of the GNU General Public License along with
  15  * this program; if not, see http://www.gnu.org/licenses/gpl-2.0.html
  16  *
  17 */
  18
  19 #include "mz.h"
  20 #include "mops.h"
  21
  22
  23
  24
  25 // -- TOC: --
  26 //
  27 // u_int16_t      mops_sum16                  (u_int16_t len, u_int8_t buff[])
  28 // int            mops_get_transport_sum      (struct mops *mp)
  29
  30
  31 //////////////////////////////////////////////////////////////////////////////////
  32 //
  33 //  See also:
  34 //
  35 //  RFC1071 - Computing the Internet checksum
  36 //
  37 //////////////////////////////////////////////////////////////////////////////////
  38
  39
  40
  41 // Generic 16-bit checksum code as required for IP and other headers.
  42 // The checksum is calculated over buff[] which is of length len.
  43 //
  44 // RETURN VALUE: The checksum! (Validated - correct!!!)
  45 //
  46 // Example:  t16 = mops_sum16 (20, &mp->frame[fp]);
  47 //
  48 u_int16_t mops_sum16 (u_int16_t len, u_int8_t buff[])
  49 {
  50
  51    u_int16_t word16;
  52    u_int32_t sum=0;
  53    u_int16_t i;
  54
  55    // make 16 bit words out of every two adjacent 8 bit words in the packet and add them up
  56    for (i=0; i<len; i=i+2)
  57      {
  58         word16 =((buff[i]<<8)&0xFF00)+buff[i+1];
  59         sum = sum + (u_int32_t) word16;
  60      }
  61
  62    // take only 16 bits out of the 32 bit sum and add up the carries
  63    while (sum>>16)
  64      sum = (sum & 0xFFFF)+(sum >> 16);
  65
  66    // one's complement the result
  67    sum = ~sum;
  68
  69    return ((u_int16_t) sum);
  70 }
  71
  72
  73
  74
  75
  76 // sets UDP or TCP checksum within mp[]->frame
  77 //   TODO: copying the whole segment is ugly and slow;
  78 //         make it more efficient and realize it in-place.
  79 //
  80 int mops_get_transport_sum(struct mops *mp)
  81 {
  82    u_int8_t buf[MAX_PAYLOAD_SIZE];
  83    u_int16_t len;
  84    int udp_used;
  85
  86    u_int16_t sum;
  87
  88    udp_used = mp->use_UDP; // 0 or 1, 0 means TCP
  89
  90    // IP Pseudoheader (12 Bytes)
  91    mops_hton4(&mp->ip_src, &buf[0]);
  92    mops_hton4(&mp->ip_dst, &buf[4]);
  93    buf[9]=0x00;
  94
  95
  96    // Copy segment
  97    if (udp_used)
  98      {
  99         buf[10]=0x11; // proto UDP (17 dec)
 100         len = mp->udp_len;
 101         mops_hton2(&len, &buf[11]);
 102         memcpy(&buf[13], &mp->frame[mp->begin_UDP], len);
 103         // reset checksum to zero
 104         buf[19] = 0x00;
 105         buf[20] = 0x00;
 106         sum = mops_sum16(len+12, buf);
 107         // insert checksum in UDP header (in frame)
 108         mops_hton2 (&sum, &mp->frame[(mp->begin_UDP)+7]);
 109
 110      }
 111    else
 112      {
 113         buf[10]=0x06; // proto TCP
 114         len = mp->ip_len - mp->ip_IHL;
 115         mops_hton2((u_int16_t*)&len, &buf[11]);
 116         memcpy(&buf[13], &mp->frame[mp->begin_TCP], len);
 117         // reset checksum to zero
 118         buf[29] = 0x00;
 119         buf[30] = 0x00;
 120         sum = mops_sum16(len+12, buf);
 121         // insert checksum in TCP header (in frame)
 122         mops_hton2 (&sum, &mp->frame[(mp->begin_TCP)+17]);
 123      }
 124
 125
 126    return 0;
 127 }
 128