extensions/libipt_random.c

/* 
   Shared library add-on to iptables to add match support for random match.
   
   This file is distributed under the terms of the GNU General Public
   License (GPL). Copies of the GPL can be obtained from:
   ftp://prep.ai.mit.edu/pub/gnu/GPL

   2001-10-14 Fabrice MARIE <fabrice@netfilter.org> : initial development.
*/

#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <syslog.h>
#include <getopt.h>
#include <iptables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_random.h>

/**
 * The kernel random routing returns numbers between 0 and 255.
 * To ease the task of the user in choosing the probability
 * of matching, we want him to be able to use percentages.
 * Therefore we have to accept numbers in percentage here,
 * turn them into number between 0 and 255 for the kernel module,
 * and turn them back to percentages when we print/save
 * the rule.
 */


/* Function which prints out usage message. */
static void
help(void)
{
	printf(
"random v%s options:\n"
"  [--average      percent ]    The probability in percentage of the match\n"
"                               If ommited, a probability of 50%% percent is set.\n"
"                               Percentage must be within : 1 <= percent <= 99.\n\n",
IPTABLES_VERSION);
}

static struct option opts[] = {
	{ "average", 1, 0, '1' },
	{ 0 }
};

/* Initialize the target. */
static void
init(struct ipt_entry_match *m, unsigned int *nfcache)
{
	struct ipt_rand_info *randinfo = (struct ipt_rand_info *)(m)->data;

	/* We assign the average to be 50 which is our default value */
	/* 50 * 2.55 = 128 */
	randinfo->average = 128;
}

#define IPT_RAND_OPT_AVERAGE	0x01

/* Function which parses command options; returns true if it
   ate an option */
static int
parse(int c, char **argv, int invert, unsigned int *flags,
      const struct ipt_entry *entry,
      unsigned int *nfcache,
      struct ipt_entry_match **match)
{
	struct ipt_rand_info *randinfo = (struct ipt_rand_info *)(*match)->data;
	unsigned int num;

	switch (c) {
	case '1':
		/* check for common mistakes... */
		if (invert)
			exit_error(PARAMETER_PROBLEM,
				   "Can't specify ! --average");
		if (*flags & IPT_RAND_OPT_AVERAGE)
			exit_error(PARAMETER_PROBLEM,
				   "Can't specify --average twice");

		/* Remember, this function will interpret a leading 0 to be 
		   Octal, a leading 0x to be hexdecimal... */
                if (string_to_number(optarg, 1, 99, &num) == -1 || num < 1)
                        exit_error(PARAMETER_PROBLEM,
                                   "bad --average `%s', must be between 1 and 99", optarg);

		/* assign the values */
		randinfo->average = (int)(num * 2.55);
		*flags |= IPT_RAND_OPT_AVERAGE;
		break;
	default:
		return 0;
	}
	return 1;
}

/* Final check; nothing. */
static void final_check(unsigned int flags)
{
}

/* Prints out the targinfo. */
static void
print(const struct ipt_ip *ip,
      const struct ipt_entry_match *match,
      int numeric)
{
	const struct ipt_rand_info *randinfo
		= (const struct ipt_rand_info *)match->data;
	div_t result = div((randinfo->average*100), 255);
	if (result.rem > 127)  /* round up... */
		++result.quot;

	printf(" random %u%% ", result.quot);
}

/* Saves the union ipt_targinfo in parsable form to stdout. */
static void
save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
{
	const struct ipt_rand_info *randinfo
		= (const struct ipt_rand_info *)match->data;
	div_t result = div((randinfo->average *100), 255);
	if (result.rem > 127)  /* round up... */
		++result.quot;

	printf("--average %u ", result.quot);
}

struct iptables_match rand_match = { 
	.next		= NULL,
	.name		= "random",
	.version	= IPTABLES_VERSION,
	.size		= IPT_ALIGN(sizeof(struct ipt_rand_info)),
	.userspacesize	= IPT_ALIGN(sizeof(struct ipt_rand_info)),
	.help		= &help,
	.init		= &init,
	.parse		= &parse,
	.final_check	= &final_check,
	.print		= &print,
	.save		= &save,
	.extra_opts	= opts
};

void _init(void)
{
	register_match(&rand_match);
}