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/* Shared library add-on to iptables to add packet length matching support. */
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>
#include <iptables.h>
#include <linux/netfilter_ipv4/ipt_length.h>
/* Function which prints out usage message. */
static void
help(void)
{
printf(
"length v%s options:\n"
"[!] --length length[:length] Match packet length against value or range\n"
" of values (inclusive)\n",
NETFILTER_VERSION);
}
static struct option opts[] = {
{ "length", 1, 0, '1' },
{0}
};
/* Initialize the match. */
static void
init(struct ipt_entry_match *m, unsigned int *nfcache)
{
*nfcache |= NFC_UNKNOWN;
}
static u_int16_t
parse_length(const char *s)
{
unsigned int len;
if (string_to_number(s, 0, 0xFFFF, &len) == -1)
exit_error(PARAMETER_PROBLEM, "length invalid: `%s'\n", s);
else
return (u_int16_t )len;
}
/* If a single value is provided, min and max are both set to the value */
static void
parse_lengths(const char *s, struct ipt_length_info *info)
{
char *buffer;
char *cp;
buffer = strdup(s);
if ((cp = strchr(buffer, ':')) == NULL)
info->min = info->max = parse_length(buffer);
else {
*cp = '\0';
cp++;
info->min = buffer[0] ? parse_length(buffer) : 0;
info->max = cp[0] ? parse_length(cp) : 0xFFFF;
}
free(buffer);
if (info->min > info->max)
exit_error(PARAMETER_PROBLEM,
"length min. range value `%u' greater than max. "
"range value `%u'", info->min, info->max);
}
/* 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_length_info *info = (struct ipt_length_info *)(*match)->data;
switch (c) {
case '1':
if (*flags)
exit_error(PARAMETER_PROBLEM,
"length: `--length' may only be "
"specified once");
if (check_inverse(optarg, &invert))
optind++;
parse_lengths(argv[optind-1], info);
if (invert)
info->invert = 1;
*flags = 1;
break;
default:
return 0;
}
return 1;
}
/* Final check; must have specified --length. */
static void
final_check(unsigned int flags)
{
if (!flags)
exit_error(PARAMETER_PROBLEM,
"length: You must specify `--length'");
}
/* Common match printing code. */
static void
print_length(struct ipt_length_info *info)
{
if (info->invert)
fputc('!', stdout);
if (info->max == info->min)
printf("%u ", info->min);
else
printf("%u:%u ", info->min, info->max);
}
/* Prints out the matchinfo. */
static void
print(const struct ipt_ip *ip,
const struct ipt_entry_match *match,
int numeric)
{
printf("length ");
print_length((struct ipt_length_info *)match->data);
}
/* Saves the union ipt_matchinfo in parsable form to stdout. */
static void
save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
{
printf("--length ");
print_length((struct ipt_length_info *)match->data);
}
static
struct iptables_match length
= { NULL,
"length",
NETFILTER_VERSION,
IPT_ALIGN(sizeof(struct ipt_length_info)),
IPT_ALIGN(sizeof(struct ipt_length_info)),
&help,
&init,
&parse,
&final_check,
&print,
&save,
opts
};
void _init(void)
{
register_match(&length);
}
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