c9cf08e905
functions should now be used. The old 2.1 stuff is there for backwards compatability. Submitted by: Charles Mott <cmott@snake.srv.net>
138 lines
2.9 KiB
C
138 lines
2.9 KiB
C
/*
|
|
Alias_util.h 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 workd 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) = *(u_char *) ptr;
|
|
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) = *(u_char *) ptr;
|
|
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;
|
|
}
|
|
}
|
|
|