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142 lines
4.6 KiB
142 lines
4.6 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/in.h> |
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#include <netinet/ip.h> |
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#include <netinet/ip_icmp.h> |
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#include <netinet/udp.h> |
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#include <netinet/tcp.h> |
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#include <netinet/ip6.h> |
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#include <netinet/icmp6.h> |
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#include "checksum.h" |
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/* function: ip_checksum_add |
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* adds data to a checksum |
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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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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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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, uint16_t len, uint8_t protocol) { |
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uint32_t checksum_len, checksum_next; |
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checksum_len = htonl((uint32_t) len); |
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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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