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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 <xtables.h>
#include <linux/netfilter/xt_length.h>
static void length_help(void)
{
printf(
"length match options:\n"
"[!] --length length[:length] Match packet length against value or range\n"
" of values (inclusive)\n");
}
static const struct option length_opts[] = {
{ "length", 1, NULL, '1' },
{ .name = NULL }
};
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 xt_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);
}
static int
length_parse(int c, char **argv, int invert, unsigned int *flags,
const void *entry, struct xt_entry_match **match)
{
struct xt_length_info *info = (struct xt_length_info *)(*match)->data;
switch (c) {
case '1':
if (*flags)
exit_error(PARAMETER_PROBLEM,
"length: `--length' may only be "
"specified once");
check_inverse(optarg, &invert, &optind, 0);
parse_lengths(argv[optind-1], info);
if (invert)
info->invert = 1;
*flags = 1;
break;
default:
return 0;
}
return 1;
}
static void length_check(unsigned int flags)
{
if (!flags)
exit_error(PARAMETER_PROBLEM,
"length: You must specify `--length'");
}
static void
print_length(struct xt_length_info *info)
{
if (info->invert)
printf("! ");
if (info->max == info->min)
printf("%u ", info->min);
else
printf("%u:%u ", info->min, info->max);
}
static void
length_print(const void *ip, const struct xt_entry_match *match, int numeric)
{
printf("length ");
print_length((struct xt_length_info *)match->data);
}
static void length_save(const void *ip, const struct xt_entry_match *match)
{
printf("--length ");
print_length((struct xt_length_info *)match->data);
}
static struct xtables_match length_match = {
.family = AF_UNSPEC,
.name = "length",
.version = XTABLES_VERSION,
.size = XT_ALIGN(sizeof(struct xt_length_info)),
.userspacesize = XT_ALIGN(sizeof(struct xt_length_info)),
.help = length_help,
.parse = length_parse,
.final_check = length_check,
.print = length_print,
.save = length_save,
.extra_opts = length_opts,
};
void _init(void)
{
xtables_register_match(&length_match);
}
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