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