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 * Contributions after 2012-01-13 are licensed under the terms of the 18 * GNU GPL, version 2 or (at your option) any later version. 19 */ 20 21 #include "net/checksum.h" 22 23 #define PROTO_TCP 6 24 #define PROTO_UDP 17 25 26 uint32_t net_checksum_add(int len, uint8_t *buf) 27 { 28 uint32_t sum = 0; 29 int i; 30 31 for (i = 0; i < len; i++) { 32 if (i & 1) 33 sum += (uint32_t)buf[i]; 34 else 35 sum += (uint32_t)buf[i] << 8; 36 } 37 return sum; 38 } 39 40 uint16_t net_checksum_finish(uint32_t sum) 41 { 42 while (sum>>16) 43 sum = (sum & 0xFFFF)+(sum >> 16); 44 return ~sum; 45 } 46 47 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto, 48 uint8_t *addrs, uint8_t *buf) 49 { 50 uint32_t sum = 0; 51 52 sum += net_checksum_add(length, buf); // payload 53 sum += net_checksum_add(8, addrs); // src + dst address 54 sum += proto + length; // protocol & length 55 return net_checksum_finish(sum); 56 } 57 58 void net_checksum_calculate(uint8_t *data, int length) 59 { 60 int hlen, plen, proto, csum_offset; 61 uint16_t csum; 62 63 if ((data[14] & 0xf0) != 0x40) 64 return; /* not IPv4 */ 65 hlen = (data[14] & 0x0f) * 4; 66 plen = (data[16] << 8 | data[17]) - hlen; 67 proto = data[23]; 68 69 switch (proto) { 70 case PROTO_TCP: 71 csum_offset = 16; 72 break; 73 case PROTO_UDP: 74 csum_offset = 6; 75 break; 76 default: 77 return; 78 } 79 80 if (plen < csum_offset+2) 81 return; 82 83 data[14+hlen+csum_offset] = 0; 84 data[14+hlen+csum_offset+1] = 0; 85 csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen); 86 data[14+hlen+csum_offset] = csum >> 8; 87 data[14+hlen+csum_offset+1] = csum & 0xff; 88 } 89