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