extensions/libxt_string.c - maze/iptables - Git at Google

 /* Shared library add-on to iptables to add string matching support.
  *
  * Copyright (C) 2000 Emmanuel Roger  <winfield@freegates.be>
  *
  * 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
  * 	- reimplemented to use new string matching iptables match
  * 	- add functionality to match packets by using window offsets
  * 	- add functionality to select the string matching algorithm
  *
  * ChangeLog
  *     29.12.2003: Michael Rash <mbr@cipherdyne.org>
  *             Fixed iptables save/restore for ascii strings
  *             that contain space chars, and hex strings that
  *             contain embedded NULL chars.  Updated to print
  *             strings in hex mode if any non-printable char
  *             is contained within the string.
  *
  *     27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
  *             Changed --tos to --string in save(). Also
  *             updated to work with slightly modified
  *             ipt_string_info.
  */
 #include <stdio.h>
 #include <netdb.h>
 #include <string.h>
 #include <stdlib.h>
 #include <getopt.h>
 #include <ctype.h>
 #include <xtables.h>
 #include <stddef.h>
 #include <linux/netfilter/xt_string.h>

 /* Function which prints out usage message. */
 static void string_help(void)
 {
 	printf(
 "string match options:\n"
 "--from                       Offset to start searching from\n"
 "--to                         Offset to stop searching\n"
 "--algo                       Algorithm\n"
 "--icase                      Ignore case (default: 0)\n"
 "[!] --string string          Match a string in a packet\n"
 "[!] --hex-string string      Match a hex string in a packet\n");
 }

 static const struct option string_opts[] = {
 	{ "from", 1, NULL, '1' },
 	{ "to", 1, NULL, '2' },
 	{ "algo", 1, NULL, '3' },
 	{ "string", 1, NULL, '4' },
 	{ "hex-string", 1, NULL, '5' },
 	{ "icase", 0, NULL, '6' },
 	{ .name = NULL }
 };

 static void string_init(struct xt_entry_match *m)
 {
 	struct xt_string_info *i = (struct xt_string_info *) m->data;

 	if (i->to_offset == 0)
 		i->to_offset = (u_int16_t) ~0UL;
 }

 static void
 parse_string(const char *s, struct xt_string_info *info)
 {
 	if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
 		strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
 		info->patlen = strlen(s);
 		return;
 	}
 	exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
 }

 static void
 parse_algo(const char *s, struct xt_string_info *info)
 {
 	if (strlen(s) <= XT_STRING_MAX_ALGO_NAME_SIZE) {
 		strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
 		return;
 	}
 	exit_error(PARAMETER_PROBLEM, "ALGO too long `%s'", s);
 }

 static void
 parse_hex_string(const char *s, struct xt_string_info *info)
 {
 	int i=0, slen, sindex=0, schar;
 	short hex_f = 0, literal_f = 0;
 	char hextmp[3];

 	slen = strlen(s);

 	if (slen == 0) {
 		exit_error(PARAMETER_PROBLEM,
 			"STRING must contain at least one char");
 	}

 	while (i < slen) {
 		if (s[i] == '\\' && !hex_f) {
 			literal_f = 1;
 		} else if (s[i] == '\\') {
 			exit_error(PARAMETER_PROBLEM,
 				"Cannot include literals in hex data");
 		} else if (s[i] == '|') {
 			if (hex_f)
 				hex_f = 0;
 			else {
 				hex_f = 1;
 				/* get past any initial whitespace just after the '|' */
 				while (s[i+1] == ' ')
 					i++;
 			}
 			if (i+1 >= slen)
 				break;
 			else
 				i++;  /* advance to the next character */
 		}

 		if (literal_f) {
 			if (i+1 >= slen) {
 				exit_error(PARAMETER_PROBLEM,
 					"Bad literal placement at end of string");
 			}
 			info->pattern[sindex] = s[i+1];
 			i += 2;  /* skip over literal char */
 			literal_f = 0;
 		} else if (hex_f) {
 			if (i+1 >= slen) {
 				exit_error(PARAMETER_PROBLEM,
 					"Odd number of hex digits");
 			}
 			if (i+2 >= slen) {
 				/* must end with a "|" */
 				exit_error(PARAMETER_PROBLEM, "Invalid hex block");
 			}
 			if (! isxdigit(s[i])) /* check for valid hex char */
 				exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i]);
 			if (! isxdigit(s[i+1])) /* check for valid hex char */
 				exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i+1]);
 			hextmp[0] = s[i];
 			hextmp[1] = s[i+1];
 			hextmp[2] = '\0';
 			if (! sscanf(hextmp, "%x", &schar))
 				exit_error(PARAMETER_PROBLEM,
 					"Invalid hex char `%c'", s[i]);
 			info->pattern[sindex] = (char) schar;
 			if (s[i+2] == ' ')
 				i += 3;  /* spaces included in the hex block */
 			else
 				i += 2;
 		} else {  /* the char is not part of hex data, so just copy */
 			info->pattern[sindex] = s[i];
 			i++;
 		}
 		if (sindex > XT_STRING_MAX_PATTERN_SIZE)
 			exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
 		sindex++;
 	}
 	info->patlen = sindex;
 }

 #define STRING 0x1
 #define ALGO   0x2
 #define FROM   0x4
 #define TO     0x8
 #define ICASE  0x10

 /* Function which parses command options; returns true if it
    ate an option */
 static int
 string_parse(int c, char **argv, int invert, unsigned int *flags,
              const void *entry, struct xt_entry_match **match)
 {
 	struct xt_string_info *stringinfo =
 	    (struct xt_string_info *)(*match)->data;
 	const int revision = (*match)->u.user.revision;

 	switch (c) {
 	case '1':
 		if (*flags & FROM)
 			exit_error(PARAMETER_PROBLEM,
 				   "Can't specify multiple --from");
 		stringinfo->from_offset = atoi(optarg);
 		*flags |= FROM;
 		break;
 	case '2':
 		if (*flags & TO)
 			exit_error(PARAMETER_PROBLEM,
 				   "Can't specify multiple --to");
 		stringinfo->to_offset = atoi(optarg);
 		*flags |= TO;
 		break;
 	case '3':
 		if (*flags & ALGO)
 			exit_error(PARAMETER_PROBLEM,
 				   "Can't specify multiple --algo");
 		parse_algo(optarg, stringinfo);
 		*flags |= ALGO;
 		break;
 	case '4':
 		if (*flags & STRING)
 			exit_error(PARAMETER_PROBLEM,
 				   "Can't specify multiple --string");
 		check_inverse(optarg, &invert, &optind, 0);
 		parse_string(argv[optind-1], stringinfo);
 		if (invert) {
 			if (revision == 0)
 				stringinfo->u.v0.invert = 1;
 			else
 				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 		}
 		stringinfo->patlen=strlen((char *)&stringinfo->pattern);
 		*flags |= STRING;
 		break;

 	case '5':
 		if (*flags & STRING)
 			exit_error(PARAMETER_PROBLEM,
 				   "Can't specify multiple --hex-string");

 		check_inverse(optarg, &invert, &optind, 0);
 		parse_hex_string(argv[optind-1], stringinfo);  /* sets length */
 		if (invert) {
 			if (revision == 0)
 				stringinfo->u.v0.invert = 1;
 			else
 				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 		}
 		*flags |= STRING;
 		break;

 	case '6':
 		if (revision == 0)
 			exit_error(VERSION_PROBLEM,
 				   "Kernel doesn't support --icase");

 		stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;
 		*flags |= ICASE;
 		break;

 	default:
 		return 0;
 	}
 	return 1;
 }


 /* Final check; must have specified --string. */
 static void string_check(unsigned int flags)
 {
 	if (!(flags & STRING))
 		exit_error(PARAMETER_PROBLEM,
 			   "STRING match: You must specify `--string' or "
 			   "`--hex-string'");
 	if (!(flags & ALGO))
 		exit_error(PARAMETER_PROBLEM,
 			   "STRING match: You must specify `--algo'");
 }

 /* Test to see if the string contains non-printable chars or quotes */
 static unsigned short int
 is_hex_string(const char *str, const unsigned short int len)
 {
 	unsigned int i;
 	for (i=0; i < len; i++)
 		if (! isprint(str[i]))
 			return 1;  /* string contains at least one non-printable char */
 	/* use hex output if the last char is a "\" */
 	if ((unsigned char) str[len-1] == 0x5c)
 		return 1;
 	return 0;
 }

 /* Print string with "|" chars included as one would pass to --hex-string */
 static void
 print_hex_string(const char *str, const unsigned short int len)
 {
 	unsigned int i;
 	/* start hex block */
 	printf("\"|");
 	for (i=0; i < len; i++) {
 		/* see if we need to prepend a zero */
 		if ((unsigned char) str[i] <= 0x0F)
 			printf("0%x", (unsigned char) str[i]);
 		else
 			printf("%x", (unsigned char) str[i]);
 	}
 	/* close hex block */
 	printf("|\" ");
 }

 static void
 print_string(const char *str, const unsigned short int len)
 {
 	unsigned int i;
 	printf("\"");
 	for (i=0; i < len; i++) {
 		if ((unsigned char) str[i] == 0x22)  /* escape any embedded quotes */
 			printf("%c", 0x5c);
 		printf("%c", (unsigned char) str[i]);
 	}
 	printf("\" ");  /* closing space and quote */
 }

 /* Prints out the matchinfo. */
 static void
 string_print(const void *ip, const struct xt_entry_match *match, int numeric)
 {
 	const struct xt_string_info *info =
 	    (const struct xt_string_info*) match->data;
 	const int revision = match->u.user.revision;
 	int invert = (revision == 0 ? info->u.v0.invert :
 				    info->u.v1.flags & XT_STRING_FLAG_INVERT);

 	if (is_hex_string(info->pattern, info->patlen)) {
 		printf("STRING match %s", invert ? "!" : "");
 		print_hex_string(info->pattern, info->patlen);
 	} else {
 		printf("STRING match %s", invert ? "!" : "");
 		print_string(info->pattern, info->patlen);
 	}
 	printf("ALGO name %s ", info->algo);
 	if (info->from_offset != 0)
 		printf("FROM %u ", info->from_offset);
 	if (info->to_offset != 0)
 		printf("TO %u ", info->to_offset);
 	if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
 		printf("ICASE ");
 }


 /* Saves the union ipt_matchinfo in parseable form to stdout. */
 static void string_save(const void *ip, const struct xt_entry_match *match)
 {
 	const struct xt_string_info *info =
 	    (const struct xt_string_info*) match->data;
 	const int revision = match->u.user.revision;
 	int invert = (revision == 0 ? info->u.v0.invert :
 				    info->u.v1.flags & XT_STRING_FLAG_INVERT);

 	if (is_hex_string(info->pattern, info->patlen)) {
 		printf("--hex-string %s", (invert) ? "! ": "");
 		print_hex_string(info->pattern, info->patlen);
 	} else {
 		printf("--string %s", (invert) ? "! ": "");
 		print_string(info->pattern, info->patlen);
 	}
 	printf("--algo %s ", info->algo);
 	if (info->from_offset != 0)
 		printf("--from %u ", info->from_offset);
 	if (info->to_offset != 0)
 		printf("--to %u ", info->to_offset);
 	if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
 		printf("--icase ");
 }


 static struct xtables_match string_match = {
     .name		= "string",
     .revision		= 0,
     .family		= AF_UNSPEC,
     .version		= XTABLES_VERSION,
     .size		= XT_ALIGN(sizeof(struct xt_string_info)),
     .userspacesize	= offsetof(struct xt_string_info, config),
     .help		= string_help,
     .init		= string_init,
     .parse		= string_parse,
     .final_check	= string_check,
     .print		= string_print,
     .save		= string_save,
     .extra_opts		= string_opts,
 };

 static struct xtables_match string_match_v1 = {
     .name		= "string",
     .revision		= 1,
     .family		= AF_UNSPEC,
     .version		= XTABLES_VERSION,
     .size		= XT_ALIGN(sizeof(struct xt_string_info)),
     .userspacesize	= offsetof(struct xt_string_info, config),
     .help		= string_help,
     .init		= string_init,
     .parse		= string_parse,
     .final_check	= string_check,
     .print		= string_print,
     .save		= string_save,
     .extra_opts		= string_opts,
 };

 void _init(void)
 {
 	xtables_register_match(&string_match);
 	xtables_register_match(&string_match_v1);
 }
	/* Shared library add-on to iptables to add string matching support.
	*
	* Copyright (C) 2000 Emmanuel Roger <winfield@freegates.be>
	*
	* 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
	* - reimplemented to use new string matching iptables match
	* - add functionality to match packets by using window offsets
	* - add functionality to select the string matching algorithm
	*
	* ChangeLog
	* 29.12.2003: Michael Rash <mbr@cipherdyne.org>
	* Fixed iptables save/restore for ascii strings
	* that contain space chars, and hex strings that
	* contain embedded NULL chars. Updated to print
	* strings in hex mode if any non-printable char
	* is contained within the string.
	*
	* 27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
	* Changed --tos to --string in save(). Also
	* updated to work with slightly modified
	* ipt_string_info.
	*/
	#include <stdio.h>
	#include <netdb.h>
	#include <string.h>
	#include <stdlib.h>
	#include <getopt.h>
	#include <ctype.h>
	#include <xtables.h>
	#include <stddef.h>
	#include <linux/netfilter/xt_string.h>

	/* Function which prints out usage message. */
	static void string_help(void)
	{
	printf(
	"string match options:\n"
	"--from Offset to start searching from\n"
	"--to Offset to stop searching\n"
	"--algo Algorithm\n"
	"--icase Ignore case (default: 0)\n"
	"[!] --string string Match a string in a packet\n"
	"[!] --hex-string string Match a hex string in a packet\n");
	}

	static const struct option string_opts[] = {
	{ "from", 1, NULL, '1' },
	{ "to", 1, NULL, '2' },
	{ "algo", 1, NULL, '3' },
	{ "string", 1, NULL, '4' },
	{ "hex-string", 1, NULL, '5' },
	{ "icase", 0, NULL, '6' },
	{ .name = NULL }
	};

	static void string_init(struct xt_entry_match *m)
	{
	struct xt_string_info i = (struct xt_string_info ) m->data;

	if (i->to_offset == 0)
	i->to_offset = (u_int16_t) ~0UL;
	}

	static void
	parse_string(const char s, struct xt_string_info info)
	{
	if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
	strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
	info->patlen = strlen(s);
	return;
	}
	exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
	}

	static void
	parse_algo(const char s, struct xt_string_info info)
	{
	if (strlen(s) <= XT_STRING_MAX_ALGO_NAME_SIZE) {
	strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
	return;
	}
	exit_error(PARAMETER_PROBLEM, "ALGO too long `%s'", s);
	}

	static void
	parse_hex_string(const char s, struct xt_string_info info)
	{
	int i=0, slen, sindex=0, schar;
	short hex_f = 0, literal_f = 0;
	char hextmp[3];

	slen = strlen(s);

	if (slen == 0) {
	exit_error(PARAMETER_PROBLEM,
	"STRING must contain at least one char");
	}

	while (i < slen) {
	if (s[i] == '\\' && !hex_f) {
	literal_f = 1;
	} else if (s[i] == '\\') {
	exit_error(PARAMETER_PROBLEM,
	"Cannot include literals in hex data");
	} else if (s[i] == '\|') {
	if (hex_f)
	hex_f = 0;
	else {
	hex_f = 1;
	/* get past any initial whitespace just after the '\|' */
	while (s[i+1] == ' ')
	i++;
	}
	if (i+1 >= slen)
	break;
	else
	i++; /* advance to the next character */
	}

	if (literal_f) {
	if (i+1 >= slen) {
	exit_error(PARAMETER_PROBLEM,
	"Bad literal placement at end of string");
	}
	info->pattern[sindex] = s[i+1];
	i += 2; /* skip over literal char */
	literal_f = 0;
	} else if (hex_f) {
	if (i+1 >= slen) {
	exit_error(PARAMETER_PROBLEM,
	"Odd number of hex digits");
	}
	if (i+2 >= slen) {
	/* must end with a "\|" */
	exit_error(PARAMETER_PROBLEM, "Invalid hex block");
	}
	if (! isxdigit(s[i])) /* check for valid hex char */
	exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i]);
	if (! isxdigit(s[i+1])) /* check for valid hex char */
	exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i+1]);
	hextmp[0] = s[i];
	hextmp[1] = s[i+1];
	hextmp[2] = '\0';
	if (! sscanf(hextmp, "%x", &schar))
	exit_error(PARAMETER_PROBLEM,
	"Invalid hex char `%c'", s[i]);
	info->pattern[sindex] = (char) schar;
	if (s[i+2] == ' ')
	i += 3; /* spaces included in the hex block */
	else
	i += 2;
	} else { /* the char is not part of hex data, so just copy */
	info->pattern[sindex] = s[i];
	i++;
	}
	if (sindex > XT_STRING_MAX_PATTERN_SIZE)
	exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
	sindex++;
	}
	info->patlen = sindex;
	}

	#define STRING 0x1
	#define ALGO 0x2
	#define FROM 0x4
	#define TO 0x8
	#define ICASE 0x10

	/* Function which parses command options; returns true if it
	ate an option */
	static int
	string_parse(int c, char *argv, int invert, unsigned int flags,
	const void entry, struct xt_entry_match *match)
	{
	struct xt_string_info *stringinfo =
	(struct xt_string_info )(match)->data;
	const int revision = (*match)->u.user.revision;

	switch (c) {
	case '1':
	if (*flags & FROM)
	exit_error(PARAMETER_PROBLEM,
	"Can't specify multiple --from");
	stringinfo->from_offset = atoi(optarg);
	*flags \|= FROM;
	break;
	case '2':
	if (*flags & TO)
	exit_error(PARAMETER_PROBLEM,
	"Can't specify multiple --to");
	stringinfo->to_offset = atoi(optarg);
	*flags \|= TO;
	break;
	case '3':
	if (*flags & ALGO)
	exit_error(PARAMETER_PROBLEM,
	"Can't specify multiple --algo");
	parse_algo(optarg, stringinfo);
	*flags \|= ALGO;
	break;
	case '4':
	if (*flags & STRING)
	exit_error(PARAMETER_PROBLEM,
	"Can't specify multiple --string");
	check_inverse(optarg, &invert, &optind, 0);
	parse_string(argv[optind-1], stringinfo);
	if (invert) {
	if (revision == 0)
	stringinfo->u.v0.invert = 1;
	else
	stringinfo->u.v1.flags \|= XT_STRING_FLAG_INVERT;
	}
	stringinfo->patlen=strlen((char *)&stringinfo->pattern);
	*flags \|= STRING;
	break;

	case '5':
	if (*flags & STRING)
	exit_error(PARAMETER_PROBLEM,
	"Can't specify multiple --hex-string");

	check_inverse(optarg, &invert, &optind, 0);
	parse_hex_string(argv[optind-1], stringinfo); /* sets length */
	if (invert) {
	if (revision == 0)
	stringinfo->u.v0.invert = 1;
	else
	stringinfo->u.v1.flags \|= XT_STRING_FLAG_INVERT;
	}
	*flags \|= STRING;
	break;

	case '6':
	if (revision == 0)
	exit_error(VERSION_PROBLEM,
	"Kernel doesn't support --icase");

	stringinfo->u.v1.flags \|= XT_STRING_FLAG_IGNORECASE;
	*flags \|= ICASE;
	break;

	default:
	return 0;
	}
	return 1;
	}


	/* Final check; must have specified --string. */
	static void string_check(unsigned int flags)
	{
	if (!(flags & STRING))
	exit_error(PARAMETER_PROBLEM,
	"STRING match: You must specify `--string' or "
	"`--hex-string'");
	if (!(flags & ALGO))
	exit_error(PARAMETER_PROBLEM,
	"STRING match: You must specify `--algo'");
	}

	/* Test to see if the string contains non-printable chars or quotes */
	static unsigned short int
	is_hex_string(const char *str, const unsigned short int len)
	{
	unsigned int i;
	for (i=0; i < len; i++)
	if (! isprint(str[i]))
	return 1; /* string contains at least one non-printable char */
	/* use hex output if the last char is a "\" */
	if ((unsigned char) str[len-1] == 0x5c)
	return 1;
	return 0;
	}

	/* Print string with "\|" chars included as one would pass to --hex-string */
	static void
	print_hex_string(const char *str, const unsigned short int len)
	{
	unsigned int i;
	/* start hex block */
	printf("\"\|");
	for (i=0; i < len; i++) {
	/* see if we need to prepend a zero */
	if ((unsigned char) str[i] <= 0x0F)
	printf("0%x", (unsigned char) str[i]);
	else
	printf("%x", (unsigned char) str[i]);
	}
	/* close hex block */
	printf("\|\" ");
	}

	static void
	print_string(const char *str, const unsigned short int len)
	{
	unsigned int i;
	printf("\"");
	for (i=0; i < len; i++) {
	if ((unsigned char) str[i] == 0x22) /* escape any embedded quotes */
	printf("%c", 0x5c);
	printf("%c", (unsigned char) str[i]);
	}
	printf("\" "); /* closing space and quote */
	}

	/* Prints out the matchinfo. */
	static void
	string_print(const void ip, const struct xt_entry_match match, int numeric)
	{
	const struct xt_string_info *info =
	(const struct xt_string_info*) match->data;
	const int revision = match->u.user.revision;
	int invert = (revision == 0 ? info->u.v0.invert :
	info->u.v1.flags & XT_STRING_FLAG_INVERT);

	if (is_hex_string(info->pattern, info->patlen)) {
	printf("STRING match %s", invert ? "!" : "");
	print_hex_string(info->pattern, info->patlen);
	} else {
	printf("STRING match %s", invert ? "!" : "");
	print_string(info->pattern, info->patlen);
	}
	printf("ALGO name %s ", info->algo);
	if (info->from_offset != 0)
	printf("FROM %u ", info->from_offset);
	if (info->to_offset != 0)
	printf("TO %u ", info->to_offset);
	if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
	printf("ICASE ");
	}


	/* Saves the union ipt_matchinfo in parseable form to stdout. */
	static void string_save(const void ip, const struct xt_entry_match match)
	{
	const struct xt_string_info *info =
	(const struct xt_string_info*) match->data;
	const int revision = match->u.user.revision;
	int invert = (revision == 0 ? info->u.v0.invert :
	info->u.v1.flags & XT_STRING_FLAG_INVERT);

	if (is_hex_string(info->pattern, info->patlen)) {
	printf("--hex-string %s", (invert) ? "! ": "");
	print_hex_string(info->pattern, info->patlen);
	} else {
	printf("--string %s", (invert) ? "! ": "");
	print_string(info->pattern, info->patlen);
	}
	printf("--algo %s ", info->algo);
	if (info->from_offset != 0)
	printf("--from %u ", info->from_offset);
	if (info->to_offset != 0)
	printf("--to %u ", info->to_offset);
	if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
	printf("--icase ");
	}


	static struct xtables_match string_match = {
	.name = "string",
	.revision = 0,
	.family = AF_UNSPEC,
	.version = XTABLES_VERSION,
	.size = XT_ALIGN(sizeof(struct xt_string_info)),
	.userspacesize = offsetof(struct xt_string_info, config),
	.help = string_help,
	.init = string_init,
	.parse = string_parse,
	.final_check = string_check,
	.print = string_print,
	.save = string_save,
	.extra_opts = string_opts,
	};

	static struct xtables_match string_match_v1 = {
	.name = "string",
	.revision = 1,
	.family = AF_UNSPEC,
	.version = XTABLES_VERSION,
	.size = XT_ALIGN(sizeof(struct xt_string_info)),
	.userspacesize = offsetof(struct xt_string_info, config),
	.help = string_help,
	.init = string_init,
	.parse = string_parse,
	.final_check = string_check,
	.print = string_print,
	.save = string_save,
	.extra_opts = string_opts,
	};

	void _init(void)
	{
	xtables_register_match(&string_match);
	xtables_register_match(&string_match_v1);
	}