libxt_u32.c revision bc3aeaafcf33e3e6a51948568f4f7a16304f619b 
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 <ctype.h>
14#include <errno.h>
15#include <stdint.h>
16#include <stdlib.h>
17#include <stdio.h>
18#include <xtables.h>
19#include <linux/netfilter/xt_u32.h>
20
21enum {
22	O_U32 = 0,
23};
24
25static const struct xt_option_entry u32_opts[] = {
26	{.name = "u32", .id = O_U32, .type = XTTYPE_STRING,
27	 .flags = XTOPT_MAND | XTOPT_INVERT},
28	XTOPT_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(const 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 void u32_parse(struct xt_option_call *cb)
107{
108	struct xt_u32 *data = cb->data;
109	unsigned int testind = 0, locind = 0, valind = 0;
110	struct xt_u32_test *ct = &data->tests[testind]; /* current test */
111	const char *arg = cb->arg; /* the argument string */
112	const char *start = cb->arg;
113	int state = 0;
114
115	xtables_option_parse(cb);
116	data->invert = cb->invert;
117
118	/*
119	 * states:
120	 * 0 = looking for numbers and operations,
121	 * 1 = looking for ranges
122	 */
123	while (1) {
124		/* read next operand/number or range */
125		while (isspace(*arg))
126			++arg;
127
128		if (*arg == '\0') {
129			/* end of argument found */
130			if (state == 0)
131				xtables_error(PARAMETER_PROBLEM,
132					   "u32: abrupt end of input after location specifier");
133			if (valind == 0)
134				xtables_error(PARAMETER_PROBLEM,
135					   "u32: test ended with no value specified");
136
137			ct->nnums    = locind;
138			ct->nvalues  = valind;
139			data->ntests = ++testind;
140
141			if (testind > XT_U32_MAXSIZE)
142				xtables_error(PARAMETER_PROBLEM,
143				           "u32: at char %u: too many \"&&\"s",
144				           (unsigned int)(arg - start));
145			return;
146		}
147
148		if (state == 0) {
149			/*
150			 * reading location: read a number if nothing read yet,
151			 * otherwise either op number or = to end location spec
152			 */
153			if (*arg == '=') {
154				if (locind == 0) {
155					xtables_error(PARAMETER_PROBLEM,
156					           "u32: at char %u: "
157					           "location spec missing",
158					           (unsigned int)(arg - start));
159				} else {
160					++arg;
161					state = 1;
162				}
163			} else {
164				if (locind != 0) {
165					/* need op before number */
166					if (*arg == '&') {
167						ct->location[locind].nextop = XT_U32_AND;
168					} else if (*arg == '<') {
169						if (*++arg != '<')
170							xtables_error(PARAMETER_PROBLEM,
171								   "u32: at char %u: a second '<' was expected", (unsigned int)(arg - start));
172						ct->location[locind].nextop = XT_U32_LEFTSH;
173					} else if (*arg == '>') {
174						if (*++arg != '>')
175							xtables_error(PARAMETER_PROBLEM,
176								   "u32: at char %u: a second '>' was expected", (unsigned int)(arg - start));
177						ct->location[locind].nextop = XT_U32_RIGHTSH;
178					} else if (*arg == '@') {
179						ct->location[locind].nextop = XT_U32_AT;
180					} else {
181						xtables_error(PARAMETER_PROBLEM,
182							"u32: at char %u: operator expected", (unsigned int)(arg - start));
183					}
184					++arg;
185				}
186				/* now a number; string_to_number skips white space? */
187				ct->location[locind].number =
188					parse_number(&arg, arg - start);
189				if (++locind > XT_U32_MAXSIZE)
190					xtables_error(PARAMETER_PROBLEM,
191						   "u32: at char %u: too many operators", (unsigned int)(arg - start));
192			}
193		} else {
194			/*
195			 * state 1 - reading values: read a range if nothing
196			 * read yet, otherwise either ,range or && to end
197			 * test spec
198			 */
199			if (*arg == '&') {
200				if (*++arg != '&')
201					xtables_error(PARAMETER_PROBLEM,
202						   "u32: at char %u: a second '&' was expected", (unsigned int)(arg - start));
203				if (valind == 0) {
204					xtables_error(PARAMETER_PROBLEM,
205						   "u32: at char %u: value spec missing", (unsigned int)(arg - start));
206				} else {
207					ct->nnums   = locind;
208					ct->nvalues = valind;
209					ct = &data->tests[++testind];
210					if (testind > XT_U32_MAXSIZE)
211						xtables_error(PARAMETER_PROBLEM,
212							   "u32: at char %u: too many \"&&\"s", (unsigned int)(arg - start));
213					++arg;
214					state  = 0;
215					locind = 0;
216					valind = 0;
217				}
218			} else { /* read value range */
219				if (valind > 0) { /* need , before number */
220					if (*arg != ',')
221						xtables_error(PARAMETER_PROBLEM,
222							   "u32: at char %u: expected \",\" or \"&&\"", (unsigned int)(arg - start));
223					++arg;
224				}
225				ct->value[valind].min =
226					parse_number(&arg, arg - start);
227
228				while (isspace(*arg))
229					++arg;
230
231				if (*arg == ':') {
232					++arg;
233					ct->value[valind].max =
234						parse_number(&arg, arg-start);
235				} else {
236					ct->value[valind].max =
237						ct->value[valind].min;
238				}
239
240				if (++valind > XT_U32_MAXSIZE)
241					xtables_error(PARAMETER_PROBLEM,
242						   "u32: at char %u: too many \",\"s", (unsigned int)(arg - start));
243			}
244		}
245	}
246}
247
248static void u32_print(const void *ip, const struct xt_entry_match *match,
249                      int numeric)
250{
251	const struct xt_u32 *data = (const void *)match->data;
252	printf(" u32");
253	if (data->invert)
254		printf(" !");
255	u32_dump(data);
256}
257
258static void u32_save(const void *ip, const struct xt_entry_match *match)
259{
260	const struct xt_u32 *data = (const void *)match->data;
261	if (data->invert)
262		printf(" !");
263	printf(" --u32");
264	u32_dump(data);
265}
266
267static struct xtables_match u32_match = {
268	.name          = "u32",
269	.family        = NFPROTO_UNSPEC,
270	.version       = XTABLES_VERSION,
271	.size          = XT_ALIGN(sizeof(struct xt_u32)),
272	.userspacesize = XT_ALIGN(sizeof(struct xt_u32)),
273	.help          = u32_help,
274	.print         = u32_print,
275	.save          = u32_save,
276	.x6_parse      = u32_parse,
277	.x6_options    = u32_opts,
278};
279
280void _init(void)
281{
282	xtables_register_match(&u32_match);
283}
284