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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 <iptables.h>
#include <linux/netfilter_ipv4/ipt_tcpmss.h>
/* Function which prints out usage message. */
static void
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",
NETFILTER_VERSION);
}
static struct option opts[] = {
{ "mss", 1, 0, '1' },
{0}
};
/* Initialize the match. */
static void
init(struct ipt_entry_match *m, unsigned int *nfcache)
{
*nfcache |= NFC_IP_PROTO_UNKNOWN;
}
static u_int16_t
parse_tcp_mssvalue(const char *mssvalue)
{
int mssvaluenum;
if ((mssvaluenum = string_to_number(mssvalue, 0, 65535)) != -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
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_tcpmss_match_info *mssinfo =
(struct ipt_tcpmss_match_info *)(*match)->data;
switch (c) {
case '1':
if (*flags)
exit_error(PARAMETER_PROBLEM,
"Only one `--mss' allowed");
if (check_inverse(optarg, &invert))
optind++;
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
final_check(unsigned int flags)
{
if (!flags)
exit_error(PARAMETER_PROBLEM,
"tcpmss match: You must specify `--mss'");
}
/* Prints out the matchinfo. */
static void
print(const struct ipt_ip *ip,
const struct ipt_entry_match *match,
int numeric)
{
const struct ipt_tcpmss_match_info *mssinfo =
(const struct ipt_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
save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
{
const struct ipt_tcpmss_match_info *mssinfo =
(const struct ipt_tcpmss_match_info *)match->data;
printf("--mss ");
print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
mssinfo->invert, 0);
}
struct iptables_match tcpmss
= { NULL,
"tcpmss",
NETFILTER_VERSION,
IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
&help,
&init,
&parse,
&final_check,
&print,
&save,
opts
};
void _init(void)
{
register_match(&tcpmss);
}
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