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 or later 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 "qemu/osdep.h"
  19 #include "qemu-common.h"
  20 #include "net/checksum.h"
  21
  22 #define PROTO_TCP  6
  23 #define PROTO_UDP 17
  24
  25 uint32_t net_checksum_add_cont(int len, uint8_t *buf, int seq)
  26 {
  27     uint32_t sum = 0;
  28     int i;
  29
  30     for (i = seq; i < seq + len; i++) {
  31         if (i & 1) {
  32             sum += (uint32_t)buf[i - seq];
  33         } else {
  34             sum += (uint32_t)buf[i - seq] << 8;
  35         }
  36     }
  37     return sum;
  38 }
  39
  40 uint16_t net_checksum_finish(uint32_t sum)
  41 {
  42     while (sum>>16)
  43         sum = (sum & 0xFFFF)+(sum >> 16);
  44     return ~sum;
  45 }
  46
  47 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
  48                              uint8_t *addrs, uint8_t *buf)
  49 {
  50     uint32_t sum = 0;
  51
  52     sum += net_checksum_add(length, buf);         // payload
  53     sum += net_checksum_add(8, addrs);            // src + dst address
  54     sum += proto + length;                        // protocol & length
  55     return net_checksum_finish(sum);
  56 }
  57
  58 void net_checksum_calculate(uint8_t *data, int length)
  59 {
  60     int hlen, plen, proto, csum_offset;
  61     uint16_t csum;
  62
  63     /* Ensure data has complete L2 & L3 headers. */
  64     if (length < 14 + 20) {
  65         return;
  66     }
  67
  68     if ((data[14] & 0xf0) != 0x40)
  69         return; /* not IPv4 */
  70     hlen  = (data[14] & 0x0f) * 4;
  71     plen  = (data[16] << 8 | data[17]) - hlen;
  72     proto = data[23];
  73
  74     switch (proto) {
  75     case PROTO_TCP:
  76         csum_offset = 16;
  77         break;
  78     case PROTO_UDP:
  79         csum_offset = 6;
  80         break;
  81     default:
  82         return;
  83     }
  84
  85     if (plen < csum_offset + 2 || 14 + hlen + plen > length) {
  86         return;
  87     }
  88
  89     data[14+hlen+csum_offset]   = 0;
  90     data[14+hlen+csum_offset+1] = 0;
  91     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
  92     data[14+hlen+csum_offset]   = csum >> 8;
  93     data[14+hlen+csum_offset+1] = csum & 0xff;
  94 }
  95
  96 uint32_t
  97 net_checksum_add_iov(const struct iovec *iov, const unsigned int iov_cnt,
  98                      uint32_t iov_off, uint32_t size)
  99 {
 100     size_t iovec_off, buf_off;
 101     unsigned int i;
 102     uint32_t res = 0;
 103     uint32_t seq = 0;
 104
 105     iovec_off = 0;
 106     buf_off = 0;
 107     for (i = 0; i < iov_cnt && size; i++) {
 108         if (iov_off < (iovec_off + iov[i].iov_len)) {
 109             size_t len = MIN((iovec_off + iov[i].iov_len) - iov_off , size);
 110             void *chunk_buf = iov[i].iov_base + (iov_off - iovec_off);
 111
 112             res += net_checksum_add_cont(len, chunk_buf, seq);
 113             seq += len;
 114
 115             buf_off += len;
 116             iov_off += len;
 117             size -= len;
 118         }
 119         iovec_off += iov[i].iov_len;
 120     }
 121     return res;
 122 }