net-checksum.c

   1 /*
   2  *  IP checksumming functions.
   3  *  (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; under version 2 of the License.
   8  *
   9  *  This program is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *  GNU General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU General Public License
  15  *  along with this program; if not, write to the Free Software
  16  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA  02110-1301 USA
  17  */
  18
  19 #include "hw/hw.h"
  20 #include "net.h"
  21
  22 #define PROTO_TCP  6
  23 #define PROTO_UDP 17
  24
  25 uint32_t net_checksum_add(int len, uint8_t *buf)
  26 {
  27     uint32_t sum = 0;
  28     int i;
  29
  30     for (i = 0; i < len; i++) {
  31         if (i & 1)
  32             sum += (uint32_t)buf[i];
  33         else
  34             sum += (uint32_t)buf[i] << 8;
  35     }
  36     return sum;
  37 }
  38
  39 uint16_t net_checksum_finish(uint32_t sum)
  40 {
  41     while (sum>>16)
  42         sum = (sum & 0xFFFF)+(sum >> 16);
  43     return ~sum;
  44 }
  45
  46 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
  47                              uint8_t *addrs, uint8_t *buf)
  48 {
  49     uint32_t sum = 0;
  50
  51     sum += net_checksum_add(length, buf);         // payload
  52     sum += net_checksum_add(8, addrs);            // src + dst address
  53     sum += proto + length;                        // protocol & length
  54     return net_checksum_finish(sum);
  55 }
  56
  57 void net_checksum_calculate(uint8_t *data, int length)
  58 {
  59     int hlen, plen, proto, csum_offset;
  60     uint16_t csum;
  61
  62     if ((data[14] & 0xf0) != 0x40)
  63         return; /* not IPv4 */
  64     hlen  = (data[14] & 0x0f) * 4;
  65     plen  = (data[16] << 8 | data[17]) - hlen;
  66     proto = data[23];
  67
  68     switch (proto) {
  69     case PROTO_TCP:
  70         csum_offset = 16;
  71         break;
  72     case PROTO_UDP:
  73         csum_offset = 6;
  74         break;
  75     default:
  76         return;
  77     }
  78
  79     if (plen < csum_offset+2)
  80         return;
  81
  82     data[14+hlen+csum_offset]   = 0;
  83     data[14+hlen+csum_offset+1] = 0;
  84     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
  85     data[14+hlen+csum_offset]   = csum >> 8;
  86     data[14+hlen+csum_offset+1] = csum & 0xff;
  87 }