libxt_u32.c revision 73866357e4a7a0fdc1b293bf8863fee2bd56da9e 
1/* Shared library add-on to iptables to add u32 matching,
2 * generalized matching on values found at packet offsets
3 *
4 * Detailed doc is in the kernel module source
5 * net/netfilter/xt_u32.c
6 *
7 * (C) 2002 by Don Cohen <don-netf@isis.cs3-inc.com>
8 * Released under the terms of GNU GPL v2
9 *
10 * Copyright © CC Computer Consultants GmbH, 2007
11 * Contact: <jengelh@computergmbh.de>
12 */
13#include <sys/types.h>
14#include <ctype.h>
15#include <errno.h>
16#include <getopt.h>
17#include <netdb.h>
18#include <stdbool.h>
19#include <stdlib.h>
20#include <stdio.h>
21#include <string.h>
22
23#include <xtables.h>
24#include <linux/netfilter/xt_u32.h>
25
26static const struct option u32_opts[] = {
27	{.name = "u32", .has_arg = true, .val = 'u'},
28	XT_GETOPT_TABLEEND,
29};
30
31static void u32_help(void)
32{
33	printf(
34		"u32 match options:\n"
35		"[!] --u32 tests\n"
36		"\t\t""tests := location \"=\" value | tests \"&&\" location \"=\" value\n"
37		"\t\t""value := range | value \",\" range\n"
38		"\t\t""range := number | number \":\" number\n"
39		"\t\t""location := number | location operator number\n"
40		"\t\t""operator := \"&\" | \"<<\" | \">>\" | \"@\"\n");
41}
42
43static void u32_dump(const struct xt_u32 *data)
44{
45	const struct xt_u32_test *ct;
46	unsigned int testind, i;
47
48	printf(" \"");
49	for (testind = 0; testind < data->ntests; ++testind) {
50		ct = &data->tests[testind];
51
52		if (testind > 0)
53			printf("&&");
54
55		printf("0x%x", ct->location[0].number);
56		for (i = 1; i < ct->nnums; ++i) {
57			switch (ct->location[i].nextop) {
58			case XT_U32_AND:
59				printf("&");
60				break;
61			case XT_U32_LEFTSH:
62				printf("<<");
63				break;
64			case XT_U32_RIGHTSH:
65				printf(">>");
66				break;
67			case XT_U32_AT:
68				printf("@");
69				break;
70			}
71			printf("0x%x", ct->location[i].number);
72		}
73
74		printf("=");
75		for (i = 0; i < ct->nvalues; ++i) {
76			if (i > 0)
77				printf(",");
78			if (ct->value[i].min == ct->value[i].max)
79				printf("0x%x", ct->value[i].min);
80			else
81				printf("0x%x:0x%x", ct->value[i].min,
82				       ct->value[i].max);
83		}
84	}
85	putchar('\"');
86}
87
88/* string_to_number() is not quite what we need here ... */
89static uint32_t parse_number(char **s, int pos)
90{
91	uint32_t number;
92	char *end;
93
94	errno  = 0;
95	number = strtoul(*s, &end, 0);
96	if (end == *s)
97		xtables_error(PARAMETER_PROBLEM,
98			   "u32: at char %d: expected number", pos);
99	if (errno != 0)
100		xtables_error(PARAMETER_PROBLEM,
101			   "u32: at char %d: error reading number", pos);
102	*s = end;
103	return number;
104}
105
106static int u32_parse(int c, char **argv, int invert, unsigned int *flags,
107		     const void *entry, struct xt_entry_match **match)
108{
109	struct xt_u32 *data = (void *)(*match)->data;
110	unsigned int testind = 0, locind = 0, valind = 0;
111	struct xt_u32_test *ct = &data->tests[testind]; /* current test */
112	char *arg = optarg; /* the argument string */
113	char *start = arg;
114	int state = 0;
115
116	if (c != 'u')
117		return 0;
118
119	data->invert = invert;
120
121	/*
122	 * states:
123	 * 0 = looking for numbers and operations,
124	 * 1 = looking for ranges
125	 */
126	while (1) {
127		/* read next operand/number or range */
128		while (isspace(*arg))
129			++arg;
130
131		if (*arg == '\0') {
132			/* end of argument found */
133			if (state == 0)
134				xtables_error(PARAMETER_PROBLEM,
135					   "u32: abrupt end of input after location specifier");
136			if (valind == 0)
137				xtables_error(PARAMETER_PROBLEM,
138					   "u32: test ended with no value specified");
139
140			ct->nnums    = locind;
141			ct->nvalues  = valind;
142			data->ntests = ++testind;
143
144			if (testind > XT_U32_MAXSIZE)
145				xtables_error(PARAMETER_PROBLEM,
146				           "u32: at char %u: too many \"&&\"s",
147				           (unsigned int)(arg - start));
148			return 1;
149		}
150
151		if (state == 0) {
152			/*
153			 * reading location: read a number if nothing read yet,
154			 * otherwise either op number or = to end location spec
155			 */
156			if (*arg == '=') {
157				if (locind == 0) {
158					xtables_error(PARAMETER_PROBLEM,
159					           "u32: at char %u: "
160					           "location spec missing",
161					           (unsigned int)(arg - start));
162				} else {
163					++arg;
164					state = 1;
165				}
166			} else {
167				if (locind != 0) {
168					/* need op before number */
169					if (*arg == '&') {
170						ct->location[locind].nextop = XT_U32_AND;
171					} else if (*arg == '<') {
172						if (*++arg != '<')
173							xtables_error(PARAMETER_PROBLEM,
174								   "u32: at char %u: a second '<' was expected", (unsigned int)(arg - start));
175						ct->location[locind].nextop = XT_U32_LEFTSH;
176					} else if (*arg == '>') {
177						if (*++arg != '>')
178							xtables_error(PARAMETER_PROBLEM,
179								   "u32: at char %u: a second '>' was expected", (unsigned int)(arg - start));
180						ct->location[locind].nextop = XT_U32_RIGHTSH;
181					} else if (*arg == '@') {
182						ct->location[locind].nextop = XT_U32_AT;
183					} else {
184						xtables_error(PARAMETER_PROBLEM,
185							"u32: at char %u: operator expected", (unsigned int)(arg - start));
186					}
187					++arg;
188				}
189				/* now a number; string_to_number skips white space? */
190				ct->location[locind].number =
191					parse_number(&arg, arg - start);
192				if (++locind > XT_U32_MAXSIZE)
193					xtables_error(PARAMETER_PROBLEM,
194						   "u32: at char %u: too many operators", (unsigned int)(arg - start));
195			}
196		} else {
197			/*
198			 * state 1 - reading values: read a range if nothing
199			 * read yet, otherwise either ,range or && to end
200			 * test spec
201			 */
202			if (*arg == '&') {
203				if (*++arg != '&')
204					xtables_error(PARAMETER_PROBLEM,
205						   "u32: at char %u: a second '&' was expected", (unsigned int)(arg - start));
206				if (valind == 0) {
207					xtables_error(PARAMETER_PROBLEM,
208						   "u32: at char %u: value spec missing", (unsigned int)(arg - start));
209				} else {
210					ct->nnums   = locind;
211					ct->nvalues = valind;
212					ct = &data->tests[++testind];
213					if (testind > XT_U32_MAXSIZE)
214						xtables_error(PARAMETER_PROBLEM,
215							   "u32: at char %u: too many \"&&\"s", (unsigned int)(arg - start));
216					++arg;
217					state  = 0;
218					locind = 0;
219					valind = 0;
220				}
221			} else { /* read value range */
222				if (valind > 0) { /* need , before number */
223					if (*arg != ',')
224						xtables_error(PARAMETER_PROBLEM,
225							   "u32: at char %u: expected \",\" or \"&&\"", (unsigned int)(arg - start));
226					++arg;
227				}
228				ct->value[valind].min =
229					parse_number(&arg, arg - start);
230
231				while (isspace(*arg))
232					++arg;
233
234				if (*arg == ':') {
235					++arg;
236					ct->value[valind].max =
237						parse_number(&arg, arg-start);
238				} else {
239					ct->value[valind].max =
240						ct->value[valind].min;
241				}
242
243				if (++valind > XT_U32_MAXSIZE)
244					xtables_error(PARAMETER_PROBLEM,
245						   "u32: at char %u: too many \",\"s", (unsigned int)(arg - start));
246			}
247		}
248	}
249}
250
251static void u32_print(const void *ip, const struct xt_entry_match *match,
252                      int numeric)
253{
254	const struct xt_u32 *data = (const void *)match->data;
255	printf(" u32");
256	if (data->invert)
257		printf(" !");
258	u32_dump(data);
259}
260
261static void u32_save(const void *ip, const struct xt_entry_match *match)
262{
263	const struct xt_u32 *data = (const void *)match->data;
264	if (data->invert)
265		printf(" !");
266	printf(" --u32");
267	u32_dump(data);
268}
269
270static struct xtables_match u32_match = {
271	.name          = "u32",
272	.family        = NFPROTO_UNSPEC,
273	.version       = XTABLES_VERSION,
274	.size          = XT_ALIGN(sizeof(struct xt_u32)),
275	.userspacesize = XT_ALIGN(sizeof(struct xt_u32)),
276	.help          = u32_help,
277	.parse         = u32_parse,
278	.print         = u32_print,
279	.save          = u32_save,
280	.extra_opts    = u32_opts,
281};
282
283void _init(void)
284{
285	xtables_register_match(&u32_match);
286}
287