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 or later 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 "net/checksum.h" 19 20 #define PROTO_TCP 6 21 #define PROTO_UDP 17 22 23 uint32_t net_checksum_add(int len, uint8_t *buf) 24 { 25 uint32_t sum = 0; 26 int i; 27 28 for (i = 0; i < len; i++) { 29 if (i & 1) 30 sum += (uint32_t)buf[i]; 31 else 32 sum += (uint32_t)buf[i] << 8; 33 } 34 return sum; 35 } 36 37 uint16_t net_checksum_finish(uint32_t sum) 38 { 39 while (sum>>16) 40 sum = (sum & 0xFFFF)+(sum >> 16); 41 return ~sum; 42 } 43 44 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto, 45 uint8_t *addrs, uint8_t *buf) 46 { 47 uint32_t sum = 0; 48 49 sum += net_checksum_add(length, buf); // payload 50 sum += net_checksum_add(8, addrs); // src + dst address 51 sum += proto + length; // protocol & length 52 return net_checksum_finish(sum); 53 } 54 55 void net_checksum_calculate(uint8_t *data, int length) 56 { 57 int hlen, plen, proto, csum_offset; 58 uint16_t csum; 59 60 if ((data[14] & 0xf0) != 0x40) 61 return; /* not IPv4 */ 62 hlen = (data[14] & 0x0f) * 4; 63 plen = (data[16] << 8 | data[17]) - hlen; 64 proto = data[23]; 65 66 switch (proto) { 67 case PROTO_TCP: 68 csum_offset = 16; 69 break; 70 case PROTO_UDP: 71 csum_offset = 6; 72 break; 73 default: 74 return; 75 } 76 77 if (plen < csum_offset+2) 78 return; 79 80 data[14+hlen+csum_offset] = 0; 81 data[14+hlen+csum_offset+1] = 0; 82 csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen); 83 data[14+hlen+csum_offset] = csum >> 8; 84 data[14+hlen+csum_offset+1] = csum & 0xff; 85 } 86