| /* |
| Shared library add-on to iptables to add match support for every Nth packet |
| |
| This file is distributed under the terms of the GNU General Public |
| License (GPL). Copies of the GPL can be obtained from: |
| ftp://prep.ai.mit.edu/pub/gnu/GPL |
| |
| 2001-07-17 Fabrice MARIE <fabrice@celestix.com> : initial development. |
| */ |
| |
| #include <stdio.h> |
| #include <netdb.h> |
| #include <string.h> |
| #include <stdlib.h> |
| #include <syslog.h> |
| #include <getopt.h> |
| #include <iptables.h> |
| #include <linux/netfilter_ipv4/ip_tables.h> |
| #include <linux/netfilter_ipv4/ipt_nth.h> |
| |
| |
| /* Function which prints out usage message. */ |
| static void |
| help(void) |
| { |
| printf( |
| "nth v%s options:\n" |
| " --every Nth Match every Nth packet.\n\n", |
| " [--start] counter Initialize the counter at the number 'counter'\n" |
| " instead of 0. Must be of the form :\n" |
| " 0 <= counter <= (nth-1)" |
| " Example if nth=2 : 0 <= counter <= 1\n\n" |
| NETFILTER_VERSION); |
| } |
| |
| static struct option opts[] = { |
| { "every", 1, 0, '1' }, |
| { "start", 1, 0, '2' }, |
| { 0 } |
| }; |
| |
| /* Initialize the target. */ |
| static void |
| init(struct ipt_entry_match *m, unsigned int *nfcache) |
| { |
| *nfcache |= NFC_UNKNOWN; |
| } |
| |
| #define IPT_NTH_OPT_EVERY 0x01 |
| #define IPT_NTH_OPT_NOT_EVERY 0x02 |
| #define IPT_NTH_OPT_START 0x04 |
| |
| /* 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_nth_info *nthinfo = (struct ipt_nth_info *)(*match)->data; |
| unsigned int num; |
| |
| switch (c) { |
| case '1': |
| /* check for common mistakes... */ |
| if ((!invert) && (*flags & IPT_NTH_OPT_EVERY)) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify --every twice"); |
| if (invert && (*flags & IPT_NTH_OPT_NOT_EVERY)) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify ! --every twice"); |
| if ((!invert) && (*flags & IPT_NTH_OPT_NOT_EVERY)) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify --every with ! --every"); |
| if (invert && (*flags & IPT_NTH_OPT_EVERY)) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify ! --every with --every"); |
| |
| /* Remember, this function will interpret a leading 0 to be |
| Octal, a leading 0x to be hexdecimal... */ |
| if (string_to_number(optarg, 2, 100, &num) == -1 || num < 2) |
| exit_error(PARAMETER_PROBLEM, |
| "bad --every `%s', must be between 2 and 100", optarg); |
| |
| /* assign the values */ |
| nthinfo->every = num-1; |
| nthinfo->startat = 0; |
| if (invert) |
| { |
| *flags |= IPT_NTH_OPT_NOT_EVERY; |
| nthinfo->not = 1; |
| } |
| else |
| { |
| *flags |= IPT_NTH_OPT_EVERY; |
| nthinfo->not = 0; |
| } |
| break; |
| case '2': |
| /* check for common mistakes... */ |
| if (!((*flags & IPT_NTH_OPT_EVERY) || |
| (*flags & IPT_NTH_OPT_NOT_EVERY))) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify --start before --every"); |
| if (invert) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify with ! --start"); |
| if (*flags & IPT_NTH_OPT_START) |
| exit_error(PARAMETER_PROBLEM, |
| "Can't specify --start twice"); |
| if (string_to_number(optarg, 0, nthinfo->every, &num) == -1) |
| exit_error(PARAMETER_PROBLEM, |
| "bad --start `%s', must between 0 and %u", optarg, nthinfo->every); |
| *flags |= IPT_NTH_OPT_START; |
| nthinfo->startat = num; |
| break; |
| default: |
| return 0; |
| } |
| return 1; |
| } |
| |
| /* Final check; nothing. */ |
| static void final_check(unsigned int flags) |
| { |
| } |
| |
| /* Prints out the targinfo. */ |
| static void |
| print(const struct ipt_ip *ip, |
| const struct ipt_entry_match *match, |
| int numeric) |
| { |
| const struct ipt_nth_info *nthinfo |
| = (const struct ipt_nth_info *)match->data; |
| |
| if (nthinfo->not == 1) |
| printf(" !"); |
| printf("every %uth ", (nthinfo->every +1)); |
| if (nthinfo->startat != 0) |
| printf(" start at %u ", nthinfo->startat); |
| } |
| |
| /* Saves the union ipt_targinfo in parsable form to stdout. */ |
| static void |
| save(const struct ipt_ip *ip, const struct ipt_entry_match *match) |
| { |
| const struct ipt_nth_info *nthinfo |
| = (const struct ipt_nth_info *)match->data; |
| |
| if (nthinfo->not == 1) |
| printf("! "); |
| printf("--every %u ", (nthinfo->every +1)); |
| if (nthinfo->startat != 0) |
| printf(" --start %u", nthinfo->startat ); |
| } |
| |
| struct iptables_match nth |
| = { NULL, |
| "nth", |
| NETFILTER_VERSION, |
| IPT_ALIGN(sizeof(struct ipt_nth_info)), |
| IPT_ALIGN(sizeof(struct ipt_nth_info)), |
| &help, |
| &init, |
| &parse, |
| &final_check, |
| &print, |
| &save, |
| opts |
| }; |
| |
| void _init(void) |
| { |
| register_match(&nth); |
| } |