ggsn/checksum.c

   1 /*
   2  *
   3  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4  *              operating system.  INET is implemented using the  BSD Socket
   5  *              interface as the means of communication with the user level.
   6  *
   7  *              IP/TCP/UDP checksumming routines
   8  *
   9  * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
  10  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  11  *              Tom May, <ftom@netcom.com>
  12  *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
  13  *              Lots of code moved from tcp.c and ip.c; see those files
  14  *              for more names.
  15  *
  16  * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
  17  *              Fixed some nasty bugs, causing some horrible crashes.
  18  *              A: At some points, the sum (%0) was used as
  19  *              length-counter instead of the length counter
  20  *              (%1). Thanks to Roman Hodek for pointing this out.
  21  *              B: GCC seems to mess up if one uses too many
  22  *              data-registers to hold input values and one tries to
  23  *              specify d0 and d1 as scratch registers. Letting gcc
  24  *              choose these registers itself solves the problem.
  25  *
  26  *              This program is free software; you can redistribute it and/or
  27  *              modify it under the terms of the GNU General Public License
  28  *              as published by the Free Software Foundation; either version
  29  *              2 of the License, or (at your option) any later version.
  30  */
  31
  32 /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
  33  kills, so most of the assembly has to go. */
  34
  35 #if defined(__FreeBSD__)
  36 #define _KERNEL /* needed on FreeBSD 10.x for s6_addr32 */
  37 #include <sys/types.h>
  38 #include <netinet/in.h>
  39 #include <sys/endian.h>
  40 #endif
  41
  42 #include "checksum.h"
  43 #include <arpa/inet.h>
  44
  45 static inline unsigned short from32to16(unsigned int x)
  46 {
  47         /* add up 16-bit and 16-bit for 16+c bit */
  48         x = (x & 0xffff) + (x >> 16);
  49         /* add up carry.. */
  50         x = (x & 0xffff) + (x >> 16);
  51         return x;
  52 }
  53
  54 static unsigned int do_csum(const unsigned char *buff, int len)
  55 {
  56         int odd;
  57         unsigned int result = 0;
  58
  59         if (len <= 0)
  60                 goto out;
  61         odd = 1 & (unsigned long) buff;
  62         if (odd) {
  63 #if BYTE_ORDER == LITTLE_ENDIAN
  64                 result += (*buff << 8);
  65 #else
  66                 result = *buff;
  67 #endif
  68                 len--;
  69                 buff++;
  70         }
  71         if (len >= 2) {
  72                 if (2 & (unsigned long) buff) {
  73                         result += *(unsigned short *) buff;
  74                         len -= 2;
  75                         buff += 2;
  76                 }
  77                 if (len >= 4) {
  78                         const unsigned char *end = buff + ((unsigned)len & ~3);
  79                         unsigned int carry = 0;
  80                         do {
  81                                 unsigned int w = *(unsigned int *) buff;
  82                                 buff += 4;
  83                                 result += carry;
  84                                 result += w;
  85                                 carry = (w > result);
  86                         } while (buff < end);
  87                         result += carry;
  88                         result = (result & 0xffff) + (result >> 16);
  89                 }
  90                 if (len & 2) {
  91                         result += *(unsigned short *) buff;
  92                         buff += 2;
  93                 }
  94         }
  95         if (len & 1)
  96 #if BYTE_ORDER == LITTLE_ENDIAN
  97                 result += *buff;
  98 #else
  99                 result += (*buff << 8);
 100 #endif
 101         result = from32to16(result);
 102         if (odd)
 103                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 104 out:
 105         return result;
 106 }
 107
 108 /*
 109  *      This is a version of ip_compute_csum() optimized for IP headers,
 110  *      which always checksum on 4 octet boundaries.
 111  */
 112 uint16_t ip_fast_csum(const void *iph, unsigned int ihl)
 113 {
 114         return (uint16_t)~do_csum(iph, ihl*4);
 115 }
 116
 117 /*
 118  * computes the checksum of a memory block at buff, length len,
 119  * and adds in "sum" (32-bit)
 120  *
 121  * returns a 32-bit number suitable for feeding into itself
 122  * or csum_tcpudp_magic
 123  *
 124  * this function must be called with even lengths, except
 125  * for the last fragment, which may be odd
 126  *
 127  * it's best to have buff aligned on a 32-bit boundary
 128  */
 129 uint32_t csum_partial(const void *buff, int len, uint32_t wsum)
 130 {
 131         unsigned int sum = (unsigned int)wsum;
 132         unsigned int result = do_csum(buff, len);
 133
 134         /* add in old sum, and carry.. */
 135         result += sum;
 136         if (sum > result)
 137                 result += 1;
 138         return (uint32_t)result;
 139 }
 140
 141 /*
 142  * this routine is used for miscellaneous IP-like checksums, mainly
 143  * in icmp.c
 144  */
 145 uint16_t ip_compute_csum(const void *buff, int len)
 146 {
 147         return (uint16_t)~do_csum(buff, len);
 148 }
 149
 150 uint16_t csum_ipv6_magic(const struct in6_addr *saddr,
 151                         const struct in6_addr *daddr,
 152                         uint32_t len, uint8_t proto, uint32_t csum)
 153 {
 154         int carry;
 155         uint32_t ulen;
 156         uint32_t uproto;
 157         uint32_t sum = (uint32_t)csum;
 158
 159         sum += (uint32_t)saddr->s6_addr32[0];
 160         carry = (sum < (uint32_t)saddr->s6_addr32[0]);
 161         sum += carry;
 162
 163         sum += (uint32_t)saddr->s6_addr32[1];
 164         carry = (sum < (uint32_t)saddr->s6_addr32[1]);
 165         sum += carry;
 166
 167         sum += (uint32_t)saddr->s6_addr32[2];
 168         carry = (sum < (uint32_t)saddr->s6_addr32[2]);
 169         sum += carry;
 170
 171         sum += (uint32_t)saddr->s6_addr32[3];
 172         carry = (sum < (uint32_t)saddr->s6_addr32[3]);
 173         sum += carry;
 174
 175         sum += (uint32_t)daddr->s6_addr32[0];
 176         carry = (sum < (uint32_t)daddr->s6_addr32[0]);
 177         sum += carry;
 178
 179         sum += (uint32_t)daddr->s6_addr32[1];
 180         carry = (sum < (uint32_t)daddr->s6_addr32[1]);
 181         sum += carry;
 182
 183         sum += (uint32_t)daddr->s6_addr32[2];
 184         carry = (sum < (uint32_t)daddr->s6_addr32[2]);
 185         sum += carry;
 186
 187         sum += (uint32_t)daddr->s6_addr32[3];
 188         carry = (sum < (uint32_t)daddr->s6_addr32[3]);
 189         sum += carry;
 190
 191         ulen = (uint32_t)htonl((uint32_t) len);
 192         sum += ulen;
 193         carry = (sum < ulen);
 194         sum += carry;
 195
 196         uproto = (uint32_t)htonl(proto);
 197         sum += uproto;
 198         carry = (sum < uproto);
 199         sum += carry;
 200
 201         return csum_fold((uint32_t)sum);
 202 }
 203
 204 /* fold a partial checksum */
 205 uint16_t csum_fold(uint32_t csum)
 206 {
 207         uint32_t sum = (uint32_t)csum;
 208         sum = (sum & 0xffff) + (sum >> 16);
 209         sum = (sum & 0xffff) + (sum >> 16);
 210         return (uint16_t)~sum;
 211 }