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, 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 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 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 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 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
