-/* 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 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[] = {
- { "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 = 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,
-};
-
-static struct xtables_match tcpmss_match6 = {
- .family = AF_INET6,
- .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);
- xtables_register_match(&tcpmss_match6);
-}