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/*
* Copyright 2011 Daniel Drown
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* checksum.c - ipv4/ipv6 checksum calculation
*/
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include "checksum.h"
/* function: ip_checksum_add
* adds data to a checksum
* current - the current checksum (or 0 to start a new checksum)
* data - the data to add to the checksum
* len - length of data
*/
uint32_t ip_checksum_add(uint32_t current, const void *data, int len) {
uint32_t checksum = current;
int left = len;
const uint16_t *data_16 = data;
while(left > 1) {
checksum += *data_16;
data_16++;
left -= 2;
}
if(left) {
checksum += *(uint8_t *)data_16;
}
return checksum;
}
/* function: ip_checksum_fold
* folds a 32-bit partial checksum into 16 bits
* temp_sum - sum from ip_checksum_add
* returns: the folded checksum in network byte order
*/
uint16_t ip_checksum_fold(uint32_t temp_sum) {
while(temp_sum > 0xffff)
temp_sum = (temp_sum >> 16) + (temp_sum & 0xFFFF);
return temp_sum;
}
/* function: ip_checksum_finish
* folds and closes the checksum
* temp_sum - sum from ip_checksum_add
* returns: a header checksum value in network byte order
*/
uint16_t ip_checksum_finish(uint32_t temp_sum) {
return ~ip_checksum_fold(temp_sum);
}
/* function: ip_checksum
* combined ip_checksum_add and ip_checksum_finish
* data - data to checksum
* len - length of data
*/
uint16_t ip_checksum(const void *data, int len) {
uint32_t temp_sum;
temp_sum = ip_checksum_add(0,data,len);
return ip_checksum_finish(temp_sum);
}
/* function: ipv6_pseudo_header_checksum
* calculate the pseudo header checksum for use in tcp/udp/icmp headers
* ip6 - the ipv6 header
* len - the transport length (transport header + payload)
* protocol - the transport layer protocol, can be different from ip6->ip6_nxt for fragments
*/
uint32_t ipv6_pseudo_header_checksum(const struct ip6_hdr *ip6, uint16_t len, uint8_t protocol) {
uint32_t checksum_len, checksum_next;
checksum_len = htonl((uint32_t) len);
checksum_next = htonl(protocol);
uint32_t current = 0;
current = ip_checksum_add(current, &(ip6->ip6_src), sizeof(struct in6_addr));
current = ip_checksum_add(current, &(ip6->ip6_dst), sizeof(struct in6_addr));
current = ip_checksum_add(current, &checksum_len, sizeof(checksum_len));
current = ip_checksum_add(current, &checksum_next, sizeof(checksum_next));
return current;
}
/* function: ipv4_pseudo_header_checksum
* calculate the pseudo header checksum for use in tcp/udp headers
* ip - the ipv4 header
* len - the transport length (transport header + payload)
*/
uint32_t ipv4_pseudo_header_checksum(const struct iphdr *ip, uint16_t len) {
uint16_t temp_protocol, temp_length;
temp_protocol = htons(ip->protocol);
temp_length = htons(len);
uint32_t current = 0;
current = ip_checksum_add(current, &(ip->saddr), sizeof(uint32_t));
current = ip_checksum_add(current, &(ip->daddr), sizeof(uint32_t));
current = ip_checksum_add(current, &temp_protocol, sizeof(uint16_t));
current = ip_checksum_add(current, &temp_length, sizeof(uint16_t));
return current;
}
/* function: ip_checksum_adjust
* calculates a new checksum given a previous checksum and the old and new pseudo-header checksums
* checksum - the header checksum in the original packet in network byte order
* old_hdr_sum - the pseudo-header checksum of the original packet
* new_hdr_sum - the pseudo-header checksum of the translated packet
* returns: the new header checksum in network byte order
*/
uint16_t ip_checksum_adjust(uint16_t checksum, uint32_t old_hdr_sum, uint32_t new_hdr_sum) {
// Algorithm suggested in RFC 1624.
// http://tools.ietf.org/html/rfc1624#section-3
checksum = ~checksum;
uint16_t folded_sum = ip_checksum_fold(checksum + new_hdr_sum);
uint16_t folded_old = ip_checksum_fold(old_hdr_sum);
if (folded_sum > folded_old) {
return ~(folded_sum - folded_old);
} else {
return ~(folded_sum - folded_old - 1); // end-around borrow
}
}
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