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.
  */
 #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 (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++;
 		}
 		if (sindex > XT_STRING_MAX_PATTERN_SIZE)
 			xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
 		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));
 }
	/* 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 (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++;
	}
	if (sindex > XT_STRING_MAX_PATTERN_SIZE)
	xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
	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));
	}