JP Abgrall | 53f17a9 | 2014-02-12 14:02:41 -0800 | [diff] [blame] | 1 | /* in_cksum.c |
| 2 | * 4.4-Lite-2 Internet checksum routine, modified to take a vector of |
| 3 | * pointers/lengths giving the pieces to be checksummed. Also using |
| 4 | * Tahoe/CGI version of ADDCARRY(x) macro instead of from portable version. |
| 5 | */ |
| 6 | |
| 7 | /* |
| 8 | * Copyright (c) 1988, 1992, 1993 |
| 9 | * The Regents of the University of California. All rights reserved. |
| 10 | * |
| 11 | * Redistribution and use in source and binary forms, with or without |
| 12 | * modification, are permitted provided that the following conditions |
| 13 | * are met: |
| 14 | * 1. Redistributions of source code must retain the above copyright |
| 15 | * notice, this list of conditions and the following disclaimer. |
| 16 | * 2. Redistributions in binary form must reproduce the above copyright |
| 17 | * notice, this list of conditions and the following disclaimer in the |
| 18 | * documentation and/or other materials provided with the distribution. |
| 19 | * 3. Neither the name of the University nor the names of its contributors |
| 20 | * may be used to endorse or promote products derived from this software |
| 21 | * without specific prior written permission. |
| 22 | * |
| 23 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| 24 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 25 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 26 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| 27 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| 28 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| 29 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| 30 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 31 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| 32 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 33 | * SUCH DAMAGE. |
| 34 | * |
| 35 | * @(#)in_cksum.c 8.1 (Berkeley) 6/10/93 |
| 36 | */ |
| 37 | |
| 38 | #ifdef HAVE_CONFIG_H |
| 39 | # include "config.h" |
| 40 | #endif |
| 41 | |
| 42 | #include <tcpdump-stdinc.h> |
| 43 | |
| 44 | #include "interface.h" |
| 45 | |
| 46 | /* |
| 47 | * Checksum routine for Internet Protocol family headers (Portable Version). |
| 48 | * |
| 49 | * This routine is very heavily used in the network |
| 50 | * code and should be modified for each CPU to be as fast as possible. |
| 51 | */ |
| 52 | |
| 53 | #define ADDCARRY(x) {if ((x) > 65535) (x) -= 65535;} |
| 54 | #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);} |
| 55 | |
| 56 | u_int16_t |
| 57 | in_cksum(const struct cksum_vec *vec, int veclen) |
| 58 | { |
| 59 | register const u_int16_t *w; |
| 60 | register int sum = 0; |
| 61 | register int mlen = 0; |
| 62 | int byte_swapped = 0; |
| 63 | |
| 64 | union { |
| 65 | u_int8_t c[2]; |
| 66 | u_int16_t s; |
| 67 | } s_util; |
| 68 | union { |
| 69 | u_int16_t s[2]; |
| 70 | u_int32_t l; |
| 71 | } l_util; |
| 72 | |
| 73 | for (; veclen != 0; vec++, veclen--) { |
| 74 | if (vec->len == 0) |
| 75 | continue; |
| 76 | w = (const u_int16_t *)(void *)vec->ptr; |
| 77 | if (mlen == -1) { |
| 78 | /* |
| 79 | * The first byte of this chunk is the continuation |
| 80 | * of a word spanning between this chunk and the |
| 81 | * last chunk. |
| 82 | * |
| 83 | * s_util.c[0] is already saved when scanning previous |
| 84 | * chunk. |
| 85 | */ |
| 86 | s_util.c[1] = *(const u_int8_t *)w; |
| 87 | sum += s_util.s; |
| 88 | w = (const u_int16_t *)(void *)((const u_int8_t *)w + 1); |
| 89 | mlen = vec->len - 1; |
| 90 | } else |
| 91 | mlen = vec->len; |
| 92 | /* |
| 93 | * Force to even boundary. |
| 94 | */ |
| 95 | if ((1 & (unsigned long) w) && (mlen > 0)) { |
| 96 | REDUCE; |
| 97 | sum <<= 8; |
| 98 | s_util.c[0] = *(const u_int8_t *)w; |
| 99 | w = (const u_int16_t *)(void *)((const u_int8_t *)w + 1); |
| 100 | mlen--; |
| 101 | byte_swapped = 1; |
| 102 | } |
| 103 | /* |
| 104 | * Unroll the loop to make overhead from |
| 105 | * branches &c small. |
| 106 | */ |
| 107 | while ((mlen -= 32) >= 0) { |
| 108 | sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; |
| 109 | sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; |
| 110 | sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; |
| 111 | sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; |
| 112 | w += 16; |
| 113 | } |
| 114 | mlen += 32; |
| 115 | while ((mlen -= 8) >= 0) { |
| 116 | sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; |
| 117 | w += 4; |
| 118 | } |
| 119 | mlen += 8; |
| 120 | if (mlen == 0 && byte_swapped == 0) |
| 121 | continue; |
| 122 | REDUCE; |
| 123 | while ((mlen -= 2) >= 0) { |
| 124 | sum += *w++; |
| 125 | } |
| 126 | if (byte_swapped) { |
| 127 | REDUCE; |
| 128 | sum <<= 8; |
| 129 | byte_swapped = 0; |
| 130 | if (mlen == -1) { |
| 131 | s_util.c[1] = *(const u_int8_t *)w; |
| 132 | sum += s_util.s; |
| 133 | mlen = 0; |
| 134 | } else |
| 135 | mlen = -1; |
| 136 | } else if (mlen == -1) |
| 137 | s_util.c[0] = *(const u_int8_t *)w; |
| 138 | } |
| 139 | if (mlen == -1) { |
| 140 | /* The last mbuf has odd # of bytes. Follow the |
| 141 | standard (the odd byte may be shifted left by 8 bits |
| 142 | or not as determined by endian-ness of the machine) */ |
| 143 | s_util.c[1] = 0; |
| 144 | sum += s_util.s; |
| 145 | } |
| 146 | REDUCE; |
| 147 | return (~sum & 0xffff); |
| 148 | } |
| 149 | |
| 150 | /* |
| 151 | * Given the host-byte-order value of the checksum field in a packet |
| 152 | * header, and the network-byte-order computed checksum of the data |
| 153 | * that the checksum covers (including the checksum itself), compute |
| 154 | * what the checksum field *should* have been. |
| 155 | */ |
| 156 | u_int16_t |
| 157 | in_cksum_shouldbe(u_int16_t sum, u_int16_t computed_sum) |
| 158 | { |
| 159 | u_int32_t shouldbe; |
| 160 | |
| 161 | /* |
| 162 | * The value that should have gone into the checksum field |
| 163 | * is the negative of the value gotten by summing up everything |
| 164 | * *but* the checksum field. |
| 165 | * |
| 166 | * We can compute that by subtracting the value of the checksum |
| 167 | * field from the sum of all the data in the packet, and then |
| 168 | * computing the negative of that value. |
| 169 | * |
| 170 | * "sum" is the value of the checksum field, and "computed_sum" |
| 171 | * is the negative of the sum of all the data in the packets, |
| 172 | * so that's -(-computed_sum - sum), or (sum + computed_sum). |
| 173 | * |
| 174 | * All the arithmetic in question is one's complement, so the |
| 175 | * addition must include an end-around carry; we do this by |
| 176 | * doing the arithmetic in 32 bits (with no sign-extension), |
| 177 | * and then adding the upper 16 bits of the sum, which contain |
| 178 | * the carry, to the lower 16 bits of the sum, and then do it |
| 179 | * again in case *that* sum produced a carry. |
| 180 | * |
| 181 | * As RFC 1071 notes, the checksum can be computed without |
| 182 | * byte-swapping the 16-bit words; summing 16-bit words |
| 183 | * on a big-endian machine gives a big-endian checksum, which |
| 184 | * can be directly stuffed into the big-endian checksum fields |
| 185 | * in protocol headers, and summing words on a little-endian |
| 186 | * machine gives a little-endian checksum, which must be |
| 187 | * byte-swapped before being stuffed into a big-endian checksum |
| 188 | * field. |
| 189 | * |
| 190 | * "computed_sum" is a network-byte-order value, so we must put |
| 191 | * it in host byte order before subtracting it from the |
| 192 | * host-byte-order value from the header; the adjusted checksum |
| 193 | * will be in host byte order, which is what we'll return. |
| 194 | */ |
| 195 | shouldbe = sum; |
| 196 | shouldbe += ntohs(computed_sum); |
| 197 | shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); |
| 198 | shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); |
| 199 | return shouldbe; |
| 200 | } |