Mark McLoughlin | 7200ac3 | 2009-10-22 17:49:03 +0100 | [diff] [blame] | 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 "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 | } |