xref: /illumos-kvm-cmd/net-checksum.c (revision 68396ea9)
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