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Diffstat (limited to 'lib/libalias/alias_util.c')
| -rw-r--r-- | lib/libalias/alias_util.c | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/lib/libalias/alias_util.c b/lib/libalias/alias_util.c new file mode 100644 index 0000000..787c859 --- /dev/null +++ b/lib/libalias/alias_util.c @@ -0,0 +1,169 @@ +/*- + * Copyright (c) 2001 Charles Mott <cm@linktel.net> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + + +/* + Alias_util.c contains general utilities used by other functions + in the packet aliasing module. At the moment, there are functions + for computing IP header and TCP packet checksums. + + The checksum routines are based upon example code in a Unix networking + text written by Stevens (sorry, I can't remember the title -- but + at least this is a good author). + + Initial Version: August, 1996 (cjm) + + Version 1.7: January 9, 1997 + Added differential checksum update function. +*/ + +/* +Note: the checksum routines assume that the actual checksum word has +been zeroed out. If the checksum word is filled with the proper value, +then these routines will give a result of zero (useful for testing +purposes); +*/ + +#include <sys/types.h> +#include <netinet/in_systm.h> +#include <netinet/in.h> +#include <netinet/ip.h> +#include <netinet/tcp.h> + +#include "alias.h" +#include "alias_local.h" + +u_short +PacketAliasInternetChecksum(u_short *ptr, int nbytes) +{ + int sum, oddbyte; + + sum = 0; + while (nbytes > 1) + { + sum += *ptr++; + nbytes -= 2; + } + if (nbytes == 1) + { + oddbyte = 0; + ((u_char *) &oddbyte)[0] = *(u_char *) ptr; + ((u_char *) &oddbyte)[1] = 0; + sum += oddbyte; + } + sum = (sum >> 16) + (sum & 0xffff); + sum += (sum >> 16); + return(~sum); +} + +u_short +IpChecksum(struct ip *pip) +{ + return( PacketAliasInternetChecksum((u_short *) pip, + (pip->ip_hl << 2)) ); + +} + +u_short +TcpChecksum(struct ip *pip) +{ + u_short *ptr; + struct tcphdr *tc; + int nhdr, ntcp, nbytes; + int sum, oddbyte; + + nhdr = pip->ip_hl << 2; + ntcp = ntohs(pip->ip_len) - nhdr; + + tc = (struct tcphdr *) ((char *) pip + nhdr); + ptr = (u_short *) tc; + +/* Add up TCP header and data */ + nbytes = ntcp; + sum = 0; + while (nbytes > 1) + { + sum += *ptr++; + nbytes -= 2; + } + if (nbytes == 1) + { + oddbyte = 0; + ((u_char *) &oddbyte)[0] = *(u_char *) ptr; + ((u_char *) &oddbyte)[1] = 0; + sum += oddbyte; + } + +/* "Pseudo-header" data */ + ptr = (u_short *) &(pip->ip_dst); + sum += *ptr++; + sum += *ptr; + ptr = (u_short *) &(pip->ip_src); + sum += *ptr++; + sum += *ptr; + sum += htons((u_short) ntcp); + sum += htons((u_short) pip->ip_p); + +/* Roll over carry bits */ + sum = (sum >> 16) + (sum & 0xffff); + sum += (sum >> 16); + +/* Return checksum */ + return((u_short) ~sum); +} + + +void +DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n) +{ + int i; + int accumulate; + + accumulate = *cksum; + for (i=0; i<n; i++) + { + accumulate -= *new++; + accumulate += *old++; + } + + if (accumulate < 0) + { + accumulate = -accumulate; + accumulate = (accumulate >> 16) + (accumulate & 0xffff); + accumulate += accumulate >> 16; + *cksum = (u_short) ~accumulate; + } + else + { + accumulate = (accumulate >> 16) + (accumulate & 0xffff); + accumulate += accumulate >> 16; + *cksum = (u_short) accumulate; + } +} + |
