1 /*
2 * Copyright 2011 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * checksum.c - ipv4/ipv6 checksum calculation
17 */
18 #include <netinet/in.h>
19 #include <netinet/ip.h>
20 #include <netinet/ip_icmp.h>
21 #include <netinet/udp.h>
22 #include <netinet/tcp.h>
23 #include <netinet/ip6.h>
24 #include <netinet/icmp6.h>
25 #include <linux/icmp.h>
26
27 #include "checksum.h"
28
29 /* function: ip_checksum_add
30 * adds data to a checksum
31 * current - the current checksum (or 0 to start a new checksum)
32 * data - the data to add to the checksum
33 * len - length of data
34 */
ip_checksum_add(uint32_t current,const void * data,int len)35 uint32_t ip_checksum_add(uint32_t current, const void *data, int len) {
36 uint32_t checksum = current;
37 int left = len;
38 const uint16_t *data_16 = data;
39
40 while(left > 1) {
41 checksum += *data_16;
42 data_16++;
43 left -= 2;
44 }
45 if(left) {
46 checksum += *(uint8_t *)data_16;
47 }
48
49 return checksum;
50 }
51
52 /* function: ip_checksum_fold
53 * folds a 32-bit partial checksum into 16 bits
54 * temp_sum - sum from ip_checksum_add
55 * returns: the folded checksum in network byte order
56 */
ip_checksum_fold(uint32_t temp_sum)57 uint16_t ip_checksum_fold(uint32_t temp_sum) {
58 while(temp_sum > 0xffff)
59 temp_sum = (temp_sum >> 16) + (temp_sum & 0xFFFF);
60
61 return temp_sum;
62 }
63
64 /* function: ip_checksum_finish
65 * folds and closes the checksum
66 * temp_sum - sum from ip_checksum_add
67 * returns: a header checksum value in network byte order
68 */
ip_checksum_finish(uint32_t temp_sum)69 uint16_t ip_checksum_finish(uint32_t temp_sum) {
70 return ~ip_checksum_fold(temp_sum);
71 }
72
73 /* function: ip_checksum
74 * combined ip_checksum_add and ip_checksum_finish
75 * data - data to checksum
76 * len - length of data
77 */
ip_checksum(const void * data,int len)78 uint16_t ip_checksum(const void *data, int len) {
79 uint32_t temp_sum;
80
81 temp_sum = ip_checksum_add(0,data,len);
82 return ip_checksum_finish(temp_sum);
83 }
84
85 /* function: ipv6_pseudo_header_checksum
86 * calculate the pseudo header checksum for use in tcp/udp/icmp headers
87 * ip6 - the ipv6 header
88 * len - the transport length (transport header + payload)
89 * protocol - the transport layer protocol, can be different from ip6->ip6_nxt for fragments
90 */
ipv6_pseudo_header_checksum(const struct ip6_hdr * ip6,uint16_t len,uint8_t protocol)91 uint32_t ipv6_pseudo_header_checksum(const struct ip6_hdr *ip6, uint16_t len, uint8_t protocol) {
92 uint32_t checksum_len, checksum_next;
93 checksum_len = htonl((uint32_t) len);
94 checksum_next = htonl(protocol);
95
96 uint32_t current = 0;
97 current = ip_checksum_add(current, &(ip6->ip6_src), sizeof(struct in6_addr));
98 current = ip_checksum_add(current, &(ip6->ip6_dst), sizeof(struct in6_addr));
99 current = ip_checksum_add(current, &checksum_len, sizeof(checksum_len));
100 current = ip_checksum_add(current, &checksum_next, sizeof(checksum_next));
101
102 return current;
103 }
104
105 /* function: ipv4_pseudo_header_checksum
106 * calculate the pseudo header checksum for use in tcp/udp headers
107 * ip - the ipv4 header
108 * len - the transport length (transport header + payload)
109 */
ipv4_pseudo_header_checksum(const struct iphdr * ip,uint16_t len)110 uint32_t ipv4_pseudo_header_checksum(const struct iphdr *ip, uint16_t len) {
111 uint16_t temp_protocol, temp_length;
112
113 temp_protocol = htons(ip->protocol);
114 temp_length = htons(len);
115
116 uint32_t current = 0;
117 current = ip_checksum_add(current, &(ip->saddr), sizeof(uint32_t));
118 current = ip_checksum_add(current, &(ip->daddr), sizeof(uint32_t));
119 current = ip_checksum_add(current, &temp_protocol, sizeof(uint16_t));
120 current = ip_checksum_add(current, &temp_length, sizeof(uint16_t));
121
122 return current;
123 }
124
125 /* function: ip_checksum_adjust
126 * calculates a new checksum given a previous checksum and the old and new pseudo-header checksums
127 * checksum - the header checksum in the original packet in network byte order
128 * old_hdr_sum - the pseudo-header checksum of the original packet
129 * new_hdr_sum - the pseudo-header checksum of the translated packet
130 * returns: the new header checksum in network byte order
131 */
ip_checksum_adjust(uint16_t checksum,uint32_t old_hdr_sum,uint32_t new_hdr_sum)132 uint16_t ip_checksum_adjust(uint16_t checksum, uint32_t old_hdr_sum, uint32_t new_hdr_sum) {
133 // Algorithm suggested in RFC 1624.
134 // http://tools.ietf.org/html/rfc1624#section-3
135 checksum = ~checksum;
136 uint16_t folded_sum = ip_checksum_fold(checksum + new_hdr_sum);
137 uint16_t folded_old = ip_checksum_fold(old_hdr_sum);
138 if (folded_sum > folded_old) {
139 return ~(folded_sum - folded_old);
140 } else {
141 return ~(folded_sum - folded_old - 1); // end-around borrow
142 }
143 }
144