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
net_checksum_add(int len,uint8_t * buf)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
net_checksum_finish(uint32_t sum)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
net_checksum_tcpudp(uint16_t length,uint16_t proto,uint8_t * addrs,uint8_t * buf)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
net_checksum_calculate(uint8_t * data,int length)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 }
88