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/* Shared library add-on to iptables to add tcp MSS matching support. */
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>
#include <xtables.h>
#include <linux/netfilter/xt_tcpmss.h>
/* Function which prints out usage message. */
static void tcpmss_help(void)
{
printf(
"tcpmss match v%s options:\n"
"[!] --mss value[:value] Match TCP MSS range.\n"
" (only valid for TCP SYN or SYN/ACK packets)\n",
IPTABLES_VERSION);
}
static const struct option tcpmss_opts[] = {
{ "mss", 1, NULL, '1' },
{ .name = NULL }
};
static u_int16_t
parse_tcp_mssvalue(const char *mssvalue)
{
unsigned int mssvaluenum;
if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
return (u_int16_t)mssvaluenum;
exit_error(PARAMETER_PROBLEM,
"Invalid mss `%s' specified", mssvalue);
}
static void
parse_tcp_mssvalues(const char *mssvaluestring,
u_int16_t *mss_min, u_int16_t *mss_max)
{
char *buffer;
char *cp;
buffer = strdup(mssvaluestring);
if ((cp = strchr(buffer, ':')) == NULL)
*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
else {
*cp = '\0';
cp++;
*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
}
free(buffer);
}
/* Function which parses command options; returns true if it
ate an option */
static int
tcpmss_parse(int c, char **argv, int invert, unsigned int *flags,
const void *entry, struct xt_entry_match **match)
{
struct xt_tcpmss_match_info *mssinfo =
(struct xt_tcpmss_match_info *)(*match)->data;
switch (c) {
case '1':
if (*flags)
exit_error(PARAMETER_PROBLEM,
"Only one `--mss' allowed");
check_inverse(optarg, &invert, &optind, 0);
parse_tcp_mssvalues(argv[optind-1],
&mssinfo->mss_min, &mssinfo->mss_max);
if (invert)
mssinfo->invert = 1;
*flags = 1;
break;
default:
return 0;
}
return 1;
}
static void
print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
{
if (invert)
printf("! ");
if (mss_min == mss_max)
printf("%u ", mss_min);
else
printf("%u:%u ", mss_min, mss_max);
}
/* Final check; must have specified --mss. */
static void tcpmss_check(unsigned int flags)
{
if (!flags)
exit_error(PARAMETER_PROBLEM,
"tcpmss match: You must specify `--mss'");
}
/* Prints out the matchinfo. */
static void
tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
{
const struct xt_tcpmss_match_info *mssinfo =
(const struct xt_tcpmss_match_info *)match->data;
printf("tcpmss match ");
print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
mssinfo->invert, numeric);
}
/* Saves the union ipt_matchinfo in parsable form to stdout. */
static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
{
const struct xt_tcpmss_match_info *mssinfo =
(const struct xt_tcpmss_match_info *)match->data;
printf("--mss ");
print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
mssinfo->invert, 0);
}
static struct xtables_match tcpmss_match = {
.family = AF_INET,
.name = "tcpmss",
.version = IPTABLES_VERSION,
.size = XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
.userspacesize = XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
.help = tcpmss_help,
.parse = tcpmss_parse,
.final_check = tcpmss_check,
.print = tcpmss_print,
.save = tcpmss_save,
.extra_opts = tcpmss_opts,
};
static struct xtables_match tcpmss_match6 = {
.family = AF_INET6,
.name = "tcpmss",
.version = IPTABLES_VERSION,
.size = XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
.userspacesize = XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
.help = tcpmss_help,
.parse = tcpmss_parse,
.final_check = tcpmss_check,
.print = tcpmss_print,
.save = tcpmss_save,
.extra_opts = tcpmss_opts,
};
void _init(void)
{
xtables_register_match(&tcpmss_match);
xtables_register_match(&tcpmss_match6);
}
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