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/icmp6.h>
19 #include <netinet/in.h>
20 #include <netinet/ip.h>
21 #include <netinet/ip6.h>
22 #include <netinet/ip_icmp.h>
23 #include <netinet/tcp.h>
24 #include <netinet/udp.h>
25
26 #include "checksum.h"
27
28 /* function: ip_checksum_add
29 * adds data to a checksum. only known to work on little-endian hosts
30 * current - the current checksum (or 0 to start a new checksum)
31 * data - the data to add to the checksum
32 * len - length of data
33 */
ip_checksum_add(uint32_t current,const void * data,int len)34 uint32_t ip_checksum_add(uint32_t current, const void* data, int len) {
35 const uint16_t* data_16 = data;
36
37 while (len >= 2) {
38 current += *data_16;
39 data_16++;
40 len -= 2;
41 }
42 if (len) current += *(uint8_t*)data_16; // assumes little endian!
43
44 return current;
45 }
46
47 /* function: ip_checksum_fold
48 * folds a 32-bit partial checksum into 16 bits
49 * temp_sum - sum from ip_checksum_add
50 * returns: the folded checksum in network byte order
51 */
ip_checksum_fold(uint32_t temp_sum)52 uint16_t ip_checksum_fold(uint32_t temp_sum) {
53 temp_sum = (temp_sum >> 16) + (temp_sum & 0xFFFF);
54 temp_sum = (temp_sum >> 16) + (temp_sum & 0xFFFF);
55 return temp_sum;
56 }
57
58 /* function: ip_checksum_finish
59 * folds and closes the checksum
60 * temp_sum - sum from ip_checksum_add
61 * returns: a header checksum value in network byte order
62 */
ip_checksum_finish(uint32_t temp_sum)63 uint16_t ip_checksum_finish(uint32_t temp_sum) {
64 return ~ip_checksum_fold(temp_sum);
65 }
66
67 /* function: ip_checksum
68 * combined ip_checksum_add and ip_checksum_finish
69 * data - data to checksum
70 * len - length of data
71 */
ip_checksum(const void * data,int len)72 uint16_t ip_checksum(const void* data, int len) {
73 return ip_checksum_finish(ip_checksum_add(0xFFFF, data, len));
74 }
75
76 /* function: ipv6_pseudo_header_checksum
77 * calculate the pseudo header checksum for use in tcp/udp/icmp headers
78 * ip6 - the ipv6 header
79 * len - the transport length (transport header + payload)
80 * protocol - the transport layer protocol, can be different from ip6->ip6_nxt for fragments
81 */
ipv6_pseudo_header_checksum(const struct ip6_hdr * ip6,uint32_t len,uint8_t protocol)82 uint32_t ipv6_pseudo_header_checksum(const struct ip6_hdr* ip6, uint32_t len, uint8_t protocol) {
83 uint32_t checksum_len = htonl(len);
84 uint32_t checksum_next = htonl(protocol);
85 uint32_t current = 0;
86
87 current = ip_checksum_add(current, &(ip6->ip6_src), sizeof(struct in6_addr));
88 current = ip_checksum_add(current, &(ip6->ip6_dst), sizeof(struct in6_addr));
89 current = ip_checksum_add(current, &checksum_len, sizeof(checksum_len));
90 current = ip_checksum_add(current, &checksum_next, sizeof(checksum_next));
91
92 return current;
93 }
94
95 /* function: ipv4_pseudo_header_checksum
96 * calculate the pseudo header checksum for use in tcp/udp headers
97 * ip - the ipv4 header
98 * len - the transport length (transport header + payload)
99 */
ipv4_pseudo_header_checksum(const struct iphdr * ip,uint16_t len)100 uint32_t ipv4_pseudo_header_checksum(const struct iphdr* ip, uint16_t len) {
101 uint16_t temp_protocol = htons(ip->protocol);
102 uint16_t temp_length = htons(len);
103 uint32_t current = 0;
104
105 current = ip_checksum_add(current, &(ip->saddr), sizeof(uint32_t));
106 current = ip_checksum_add(current, &(ip->daddr), sizeof(uint32_t));
107 current = ip_checksum_add(current, &temp_protocol, sizeof(uint16_t));
108 current = ip_checksum_add(current, &temp_length, sizeof(uint16_t));
109
110 return current;
111 }
112
113 /* function: ip_checksum_adjust
114 * calculates a new checksum given a previous checksum and the old and new pseudo-header checksums
115 * checksum - the header checksum in the original packet in network byte order
116 * old_hdr_sum - the pseudo-header checksum of the original packet
117 * new_hdr_sum - the pseudo-header checksum of the translated packet
118 * returns: the new header checksum in network byte order
119 */
ip_checksum_adjust(uint16_t checksum,uint32_t old_hdr_sum,uint32_t new_hdr_sum)120 uint16_t ip_checksum_adjust(uint16_t checksum, uint32_t old_hdr_sum, uint32_t new_hdr_sum) {
121 // Algorithm suggested in RFC 1624.
122 // http://tools.ietf.org/html/rfc1624#section-3
123 checksum = ~checksum;
124 uint16_t folded_sum = ip_checksum_fold(new_hdr_sum + checksum);
125 uint16_t folded_old = ip_checksum_fold(old_hdr_sum);
126 if (folded_sum > folded_old) {
127 return ~(folded_sum - folded_old);
128 } else {
129 return ~(folded_sum - folded_old - 1); // end-around borrow
130 }
131 }
132