libxt_string.c revision 500f483fff529dcd88ec96b9d5054be6cd6363a0 
1/* Shared library add-on to iptables to add string matching support.
2 *
3 * Copyright (C) 2000 Emmanuel Roger  <winfield@freegates.be>
4 *
5 * 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
6 * 	- reimplemented to use new string matching iptables match
7 * 	- add functionality to match packets by using window offsets
8 * 	- add functionality to select the string matching algorithm
9 *
10 * ChangeLog
11 *     29.12.2003: Michael Rash <mbr@cipherdyne.org>
12 *             Fixed iptables save/restore for ascii strings
13 *             that contain space chars, and hex strings that
14 *             contain embedded NULL chars.  Updated to print
15 *             strings in hex mode if any non-printable char
16 *             is contained within the string.
17 *
18 *     27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
19 *             Changed --tos to --string in save(). Also
20 *             updated to work with slightly modified
21 *             ipt_string_info.
22 */
23#include <stdio.h>
24#include <netdb.h>
25#include <string.h>
26#include <stdlib.h>
27#include <getopt.h>
28#include <ctype.h>
29#include <xtables.h>
30#include <stddef.h>
31#include <linux/netfilter/xt_string.h>
32
33/* Function which prints out usage message. */
34static void
35help(void)
36{
37	printf(
38"STRING match v%s options:\n"
39"--from                       Offset to start searching from\n"
40"--to                         Offset to stop searching\n"
41"--algo	                      Algorithm\n"
42"--string [!] string          Match a string in a packet\n"
43"--hex-string [!] string      Match a hex string in a packet\n",
44IPTABLES_VERSION);
45}
46
47static const struct option opts[] = {
48	{ "from", 1, NULL, '1' },
49	{ "to", 1, NULL, '2' },
50	{ "algo", 1, NULL, '3' },
51	{ "string", 1, NULL, '4' },
52	{ "hex-string", 1, NULL, '5' },
53	{ }
54};
55
56static void
57init(struct xt_entry_match *m)
58{
59	struct xt_string_info *i = (struct xt_string_info *) m->data;
60
61	if (i->to_offset == 0)
62		i->to_offset = (u_int16_t) ~0UL;
63}
64
65static void
66parse_string(const char *s, struct xt_string_info *info)
67{
68	if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
69		strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
70		info->patlen = strlen(s);
71		return;
72	}
73	exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
74}
75
76static void
77parse_algo(const char *s, struct xt_string_info *info)
78{
79	if (strlen(s) <= XT_STRING_MAX_ALGO_NAME_SIZE) {
80		strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
81		return;
82	}
83	exit_error(PARAMETER_PROBLEM, "ALGO too long `%s'", s);
84}
85
86static void
87parse_hex_string(const char *s, struct xt_string_info *info)
88{
89	int i=0, slen, sindex=0, schar;
90	short hex_f = 0, literal_f = 0;
91	char hextmp[3];
92
93	slen = strlen(s);
94
95	if (slen == 0) {
96		exit_error(PARAMETER_PROBLEM,
97			"STRING must contain at least one char");
98	}
99
100	while (i < slen) {
101		if (s[i] == '\\' && !hex_f) {
102			literal_f = 1;
103		} else if (s[i] == '\\') {
104			exit_error(PARAMETER_PROBLEM,
105				"Cannot include literals in hex data");
106		} else if (s[i] == '|') {
107			if (hex_f)
108				hex_f = 0;
109			else {
110				hex_f = 1;
111				/* get past any initial whitespace just after the '|' */
112				while (s[i+1] == ' ')
113					i++;
114			}
115			if (i+1 >= slen)
116				break;
117			else
118				i++;  /* advance to the next character */
119		}
120
121		if (literal_f) {
122			if (i+1 >= slen) {
123				exit_error(PARAMETER_PROBLEM,
124					"Bad literal placement at end of string");
125			}
126			info->pattern[sindex] = s[i+1];
127			i += 2;  /* skip over literal char */
128			literal_f = 0;
129		} else if (hex_f) {
130			if (i+1 >= slen) {
131				exit_error(PARAMETER_PROBLEM,
132					"Odd number of hex digits");
133			}
134			if (i+2 >= slen) {
135				/* must end with a "|" */
136				exit_error(PARAMETER_PROBLEM, "Invalid hex block");
137			}
138			if (! isxdigit(s[i])) /* check for valid hex char */
139				exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i]);
140			if (! isxdigit(s[i+1])) /* check for valid hex char */
141				exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i+1]);
142			hextmp[0] = s[i];
143			hextmp[1] = s[i+1];
144			hextmp[2] = '\0';
145			if (! sscanf(hextmp, "%x", &schar))
146				exit_error(PARAMETER_PROBLEM,
147					"Invalid hex char `%c'", s[i]);
148			info->pattern[sindex] = (char) schar;
149			if (s[i+2] == ' ')
150				i += 3;  /* spaces included in the hex block */
151			else
152				i += 2;
153		} else {  /* the char is not part of hex data, so just copy */
154			info->pattern[sindex] = s[i];
155			i++;
156		}
157		if (sindex > XT_STRING_MAX_PATTERN_SIZE)
158			exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
159		sindex++;
160	}
161	info->patlen = sindex;
162}
163
164#define STRING 0x1
165#define ALGO   0x2
166#define FROM   0x4
167#define TO     0x8
168
169/* Function which parses command options; returns true if it
170   ate an option */
171static int
172parse(int c, char **argv, int invert, unsigned int *flags,
173      const void *entry,
174      struct xt_entry_match **match)
175{
176	struct xt_string_info *stringinfo = (struct xt_string_info *)(*match)->data;
177
178	switch (c) {
179	case '1':
180		if (*flags & FROM)
181			exit_error(PARAMETER_PROBLEM,
182				   "Can't specify multiple --from");
183		stringinfo->from_offset = atoi(optarg);
184		*flags |= FROM;
185		break;
186	case '2':
187		if (*flags & TO)
188			exit_error(PARAMETER_PROBLEM,
189				   "Can't specify multiple --to");
190		stringinfo->to_offset = atoi(optarg);
191		*flags |= TO;
192		break;
193	case '3':
194		if (*flags & ALGO)
195			exit_error(PARAMETER_PROBLEM,
196				   "Can't specify multiple --algo");
197		parse_algo(optarg, stringinfo);
198		*flags |= ALGO;
199		break;
200	case '4':
201		if (*flags & STRING)
202			exit_error(PARAMETER_PROBLEM,
203				   "Can't specify multiple --string");
204		check_inverse(optarg, &invert, &optind, 0);
205		parse_string(argv[optind-1], stringinfo);
206		if (invert)
207			stringinfo->invert = 1;
208		stringinfo->patlen=strlen((char *)&stringinfo->pattern);
209		*flags |= STRING;
210		break;
211
212	case '5':
213		if (*flags & STRING)
214			exit_error(PARAMETER_PROBLEM,
215				   "Can't specify multiple --hex-string");
216
217		check_inverse(optarg, &invert, &optind, 0);
218		parse_hex_string(argv[optind-1], stringinfo);  /* sets length */
219		if (invert)
220			stringinfo->invert = 1;
221		*flags |= STRING;
222		break;
223
224	default:
225		return 0;
226	}
227	return 1;
228}
229
230
231/* Final check; must have specified --string. */
232static void
233final_check(unsigned int flags)
234{
235	if (!(flags & STRING))
236		exit_error(PARAMETER_PROBLEM,
237			   "STRING match: You must specify `--string' or "
238			   "`--hex-string'");
239	if (!(flags & ALGO))
240		exit_error(PARAMETER_PROBLEM,
241			   "STRING match: You must specify `--algo'");
242}
243
244/* Test to see if the string contains non-printable chars or quotes */
245static unsigned short int
246is_hex_string(const char *str, const unsigned short int len)
247{
248	unsigned int i;
249	for (i=0; i < len; i++)
250		if (! isprint(str[i]))
251			return 1;  /* string contains at least one non-printable char */
252	/* use hex output if the last char is a "\" */
253	if ((unsigned char) str[len-1] == 0x5c)
254		return 1;
255	return 0;
256}
257
258/* Print string with "|" chars included as one would pass to --hex-string */
259static void
260print_hex_string(const char *str, const unsigned short int len)
261{
262	unsigned int i;
263	/* start hex block */
264	printf("\"|");
265	for (i=0; i < len; i++) {
266		/* see if we need to prepend a zero */
267		if ((unsigned char) str[i] <= 0x0F)
268			printf("0%x", (unsigned char) str[i]);
269		else
270			printf("%x", (unsigned char) str[i]);
271	}
272	/* close hex block */
273	printf("|\" ");
274}
275
276static void
277print_string(const char *str, const unsigned short int len)
278{
279	unsigned int i;
280	printf("\"");
281	for (i=0; i < len; i++) {
282		if ((unsigned char) str[i] == 0x22)  /* escape any embedded quotes */
283			printf("%c", 0x5c);
284		printf("%c", (unsigned char) str[i]);
285	}
286	printf("\" ");  /* closing space and quote */
287}
288
289/* Prints out the matchinfo. */
290static void
291print(const void *ip,
292      const struct xt_entry_match *match,
293      int numeric)
294{
295	const struct xt_string_info *info =
296	    (const struct xt_string_info*) match->data;
297
298	if (is_hex_string(info->pattern, info->patlen)) {
299		printf("STRING match %s", (info->invert) ? "!" : "");
300		print_hex_string(info->pattern, info->patlen);
301	} else {
302		printf("STRING match %s", (info->invert) ? "!" : "");
303		print_string(info->pattern, info->patlen);
304	}
305	printf("ALGO name %s ", info->algo);
306	if (info->from_offset != 0)
307		printf("FROM %u ", info->from_offset);
308	if (info->to_offset != 0)
309		printf("TO %u ", info->to_offset);
310}
311
312
313/* Saves the union ipt_matchinfo in parseable form to stdout. */
314static void
315save(const void *ip, const struct xt_entry_match *match)
316{
317	const struct xt_string_info *info =
318	    (const struct xt_string_info*) match->data;
319
320	if (is_hex_string(info->pattern, info->patlen)) {
321		printf("--hex-string %s", (info->invert) ? "! ": "");
322		print_hex_string(info->pattern, info->patlen);
323	} else {
324		printf("--string %s", (info->invert) ? "! ": "");
325		print_string(info->pattern, info->patlen);
326	}
327	printf("--algo %s ", info->algo);
328	if (info->from_offset != 0)
329		printf("--from %u ", info->from_offset);
330	if (info->to_offset != 0)
331		printf("--to %u ", info->to_offset);
332}
333
334
335static struct xtables_match string = {
336    .name		= "string",
337    .family			= AF_INET,
338    .version		= IPTABLES_VERSION,
339    .size		= XT_ALIGN(sizeof(struct xt_string_info)),
340    .userspacesize	= offsetof(struct xt_string_info, config),
341    .help		= help,
342    .init		= init,
343    .parse		= parse,
344    .final_check	= final_check,
345    .print		= print,
346    .save		= save,
347    .extra_opts		= opts
348};
349
350
351static struct xtables_match string6 = {
352    .name		= "string",
353    .family			= AF_INET6,
354    .version		= IPTABLES_VERSION,
355    .size		= XT_ALIGN(sizeof(struct xt_string_info)),
356    .userspacesize	= offsetof(struct xt_string_info, config),
357    .help		= help,
358    .init		= init,
359    .parse		= parse,
360    .final_check	= final_check,
361    .print		= print,
362    .save		= save,
363    .extra_opts		= opts
364};
365
366void _init(void)
367{
368	xtables_register_match(&string);
369	xtables_register_match(&string6);
370}
371