/* 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.

 */

#define _GNU_SOURCE 1 /* strnlen for older glibcs */

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <ctype.h>

#include <xtables.h>

#include <linux/netfilter/xt_string.h>

enum {

	O_FROM = 0,

	O_TO,

	O_ALGO,

	O_ICASE,

	O_STRING,

	O_HEX_STRING,

	F_STRING     = 1 << O_STRING,

	F_HEX_STRING = 1 << O_HEX_STRING,

	F_OP_ANY     = F_STRING | F_HEX_STRING,

};

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");

}

#define s struct xt_string_info

static const struct xt_option_entry string_opts[] = {

	{.name = "from", .id = O_FROM, .type = XTTYPE_UINT16,

	 .flags = XTOPT_PUT, XTOPT_POINTER(s, from_offset)},

	{.name = "to", .id = O_TO, .type = XTTYPE_UINT16,

	 .flags = XTOPT_PUT, XTOPT_POINTER(s, to_offset)},

	{.name = "algo", .id = O_ALGO, .type = XTTYPE_STRING,

	 .flags = XTOPT_MAND | XTOPT_PUT, XTOPT_POINTER(s, algo)},

	{.name = "string", .id = O_STRING, .type = XTTYPE_STRING,

	 .flags = XTOPT_INVERT, .excl = F_HEX_STRING},

	{.name = "hex-string", .id = O_HEX_STRING, .type = XTTYPE_STRING,

	 .flags = XTOPT_INVERT, .excl = F_STRING},

	{.name = "icase", .id = O_ICASE, .type = XTTYPE_NONE},

	XTOPT_TABLEEND,

};

#undef s

static void string_init(struct xt_entry_match *m)

{

	struct xt_string_info *i = (struct xt_string_info *) m->data;

	i->to_offset = UINT16_MAX;

}

static void

parse_string(const char *s, struct xt_string_info *info)

{	

	/* xt_string does not need \0 at the end of the pattern */

	if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {

		strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);

		info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);

		return;

	}

	xtables_error(PARAMETER_PROBLEM, "STRING 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) {

		xtables_error(PARAMETER_PROBLEM,

			"STRING must contain at least one char");

	}

	while (i < slen) {

		if (sindex >= XT_STRING_MAX_PATTERN_SIZE)

			xtables_error(PARAMETER_PROBLEM,

				      "STRING too long \"%s\"", s);

		if (s[i] == '\\' && !hex_f) {

			literal_f = 1;

		} else if (s[i] == '\\') {

			xtables_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) {

				xtables_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) {

				xtables_error(PARAMETER_PROBLEM,

					"Odd number of hex digits");

			}

			if (i+2 >= slen) {

				/* must end with a "|" */

				xtables_error(PARAMETER_PROBLEM, "Invalid hex block");

			}

			if (! isxdigit(s[i])) /* check for valid hex char */

				xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i]);

			if (! isxdigit(s[i+1])) /* check for valid hex char */

				xtables_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))

				xtables_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++;

		}

		sindex++;

	}

	info->patlen = sindex;

}

static void string_parse(struct xt_option_call *cb)

{

	struct xt_string_info *stringinfo = cb->data;

	const unsigned int revision = (*cb->match)->u.user.revision;

	xtables_option_parse(cb);

	switch (cb->entry->id) {

	case O_STRING:

		parse_string(cb->arg, stringinfo);

		if (cb->invert) {

			if (revision == 0)

				stringinfo->u.v0.invert = 1;

			else

				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;

		}

		break;

	case O_HEX_STRING:

		parse_hex_string(cb->arg, stringinfo);  /* sets length */

		if (cb->invert) {

			if (revision == 0)

				stringinfo->u.v0.invert = 1;

			else

				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;

		}

		break;

	case O_ICASE:

		if (revision == 0)

			xtables_error(VERSION_PROBLEM,

				   "Kernel doesn't support --icase");

		stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;

		break;

	}

}

static void string_check(struct xt_fcheck_call *cb)

{

	if (!(cb->xflags & F_OP_ANY))

		xtables_error(PARAMETER_PROBLEM,

			   "STRING match: You must specify `--string' or "

			   "`--hex-string'");

}

/* 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 (str[len-1] == '\\')

		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++)

		printf("%02x", (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 (str[i] == '\"' || str[i] == '\\')

			putchar('\\');

		printf("%c", (unsigned char) str[i]);

	}

	printf("\"");  /* closing quote */

}

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");

}

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("%s --hex-string", (invert) ? " !" : "");

		print_hex_string(info->pattern, info->patlen);

	} else {

		printf("%s --string", (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_mt_reg[] = {

	{

		.name          = "string",

		.revision      = 0,

		.family        = NFPROTO_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,

		.print         = string_print,

		.save          = string_save,

		.x6_parse      = string_parse,

		.x6_fcheck     = string_check,

		.x6_options    = string_opts,

	},

	{

		.name          = "string",

		.revision      = 1,

		.family        = NFPROTO_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,

		.print         = string_print,

		.save          = string_save,

		.x6_parse      = string_parse,

		.x6_fcheck     = string_check,

		.x6_options    = string_opts,

	},

};

void _init(void)

{

	xtables_register_matches(string_mt_reg, ARRAY_SIZE(string_mt_reg));

}