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/* Shared library add-on to iptables to add tcp MSS matching support. */
#include <stdbool.h>
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>
#include <xtables.h>
#include <linux/netfilter/xt_tcpmss.h>
static void tcpmss_help(void)
{
printf(
"tcpmss match options:\n"
"[!] --mss value[:value] Match TCP MSS range.\n"
" (only valid for TCP SYN or SYN/ACK packets)\n");
}
static const struct option tcpmss_opts[] = {
{.name = "mss", .has_arg = true, .val = '1'},
XT_GETOPT_TABLEEND,
};
static uint16_t
parse_tcp_mssvalue(const char *mssvalue)
{
unsigned int mssvaluenum;
if (xtables_strtoui(mssvalue, NULL, &mssvaluenum, 0, UINT16_MAX))
return mssvaluenum;
xtables_error(PARAMETER_PROBLEM,
"Invalid mss `%s' specified", mssvalue);
}
static void
parse_tcp_mssvalues(const char *mssvaluestring,
uint16_t *mss_min, uint16_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);
}
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)
xtables_error(PARAMETER_PROBLEM,
"Only one `--mss' allowed");
xtables_check_inverse(optarg, &invert, &optind, 0, argv);
parse_tcp_mssvalues(optarg,
&mssinfo->mss_min, &mssinfo->mss_max);
if (invert)
mssinfo->invert = 1;
*flags = 1;
break;
}
return 1;
}
static void tcpmss_check(unsigned int flags)
{
if (!flags)
xtables_error(PARAMETER_PROBLEM,
"tcpmss match: You must specify `--mss'");
}
static void
tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
{
const struct xt_tcpmss_match_info *info = (void *)match->data;
printf(" tcpmss match %s", info->invert ? "!" : "");
if (info->mss_min == info->mss_max)
printf("%u", info->mss_min);
else
printf("%u:%u", info->mss_min, info->mss_max);
}
static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
{
const struct xt_tcpmss_match_info *info = (void *)match->data;
printf("%s --mss ", info->invert ? " !" : "");
if (info->mss_min == info->mss_max)
printf("%u", info->mss_min);
else
printf("%u:%u", info->mss_min, info->mss_max);
}
static struct xtables_match tcpmss_match = {
.family = NFPROTO_UNSPEC,
.name = "tcpmss",
.version = XTABLES_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);
}
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