86 lines
2.2 KiB
C
86 lines
2.2 KiB
C
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/*
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* IP checksumming functions.
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* (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; under version 2 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "net/checksum.h"
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#define PROTO_TCP 6
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#define PROTO_UDP 17
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uint32_t net_checksum_add(int len, uint8_t *buf)
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{
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uint32_t sum = 0;
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int i;
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for (i = 0; i < len; i++) {
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if (i & 1)
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sum += (uint32_t)buf[i];
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else
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sum += (uint32_t)buf[i] << 8;
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}
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return sum;
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}
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uint16_t net_checksum_finish(uint32_t sum)
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{
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while (sum>>16)
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sum = (sum & 0xFFFF)+(sum >> 16);
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return ~sum;
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}
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uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
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uint8_t *addrs, uint8_t *buf)
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{
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uint32_t sum = 0;
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sum += net_checksum_add(length, buf); // payload
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sum += net_checksum_add(8, addrs); // src + dst address
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sum += proto + length; // protocol & length
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return net_checksum_finish(sum);
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}
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void net_checksum_calculate(uint8_t *data, int length)
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{
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int hlen, plen, proto, csum_offset;
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uint16_t csum;
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if ((data[14] & 0xf0) != 0x40)
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return; /* not IPv4 */
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hlen = (data[14] & 0x0f) * 4;
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plen = (data[16] << 8 | data[17]) - hlen;
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proto = data[23];
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switch (proto) {
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case PROTO_TCP:
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csum_offset = 16;
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break;
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case PROTO_UDP:
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csum_offset = 6;
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break;
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default:
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return;
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}
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if (plen < csum_offset+2)
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return;
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data[14+hlen+csum_offset] = 0;
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data[14+hlen+csum_offset+1] = 0;
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csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
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data[14+hlen+csum_offset] = csum >> 8;
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data[14+hlen+csum_offset+1] = csum & 0xff;
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}
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