Home | History | Annotate | Download | only in net 
      1 /*
      2  *  IP checksumming functions.
      3  *  (c) 2008 Gerd Hoffmann <kraxel (at) 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/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 }
     87