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, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "hw/hw.h"
  19 #include "net.h"
  20
  21 #define PROTO_TCP  6
  22 #define PROTO_UDP 17
  23
  24 uint32_t net_checksum_add(int len, uint8_t *buf)
  25 {
  26     uint32_t sum = 0;
  27     int i;
  28
  29     for (i = 0; i < len; i++) {
  30         if (i & 1)
  31             sum += (uint32_t)buf[i];
  32         else
  33             sum += (uint32_t)buf[i] << 8;
  34     }
  35     return sum;
  36 }
  37
  38 uint16_t net_checksum_finish(uint32_t sum)
  39 {
  40     while (sum>>16)
  41         sum = (sum & 0xFFFF)+(sum >> 16);
  42     return ~sum;
  43 }
  44
  45 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
  46                              uint8_t *addrs, uint8_t *buf)
  47 {
  48     uint32_t sum = 0;
  49
  50     sum += net_checksum_add(length, buf);         // payload
  51     sum += net_checksum_add(8, addrs);            // src + dst address
  52     sum += proto + length;                        // protocol & length
  53     return net_checksum_finish(sum);
  54 }
  55
  56 void net_checksum_calculate(uint8_t *data, int length)
  57 {
  58     int hlen, plen, proto, csum_offset;
  59     uint16_t csum;
  60
  61     if ((data[14] & 0xf0) != 0x40)
  62         return; /* not IPv4 */
  63     hlen  = (data[14] & 0x0f) * 4;
  64     plen  = (data[16] << 8 | data[17]) - hlen;
  65     proto = data[23];
  66
  67     switch (proto) {
  68     case PROTO_TCP:
  69         csum_offset = 16;
  70         break;
  71     case PROTO_UDP:
  72         csum_offset = 6;
  73         break;
  74     default:
  75         return;
  76     }
  77
  78     if (plen < csum_offset+2)
  79         return;
  80
  81     data[14+hlen+csum_offset]   = 0;
  82     data[14+hlen+csum_offset+1] = 0;
  83     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
  84     data[14+hlen+csum_offset]   = csum >> 8;
  85     data[14+hlen+csum_offset+1] = csum & 0xff;
  86 }