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