libxt_tcp.c revision 661f112072bc13a1625c4eb5983695e122ea97da 
1/* Shared library add-on to iptables to add TCP support. */
2#include <stdio.h>
3#include <netdb.h>
4#include <string.h>
5#include <stdlib.h>
6#include <getopt.h>
7#include <xtables.h>
8#include <linux/netfilter/xt_tcpudp.h>
9
10/* Function which prints out usage message. */
11static void
12help(void)
13{
14	printf(
15"TCP v%s options:\n"
16" --tcp-flags [!] mask comp	match when TCP flags & mask == comp\n"
17"				(Flags: SYN ACK FIN RST URG PSH ALL NONE)\n"
18"[!] --syn			match when only SYN flag set\n"
19"				(equivalent to --tcp-flags SYN,RST,ACK,FIN SYN)\n"
20" --source-port [!] port[:port]\n"
21" --sport ...\n"
22"				match source port(s)\n"
23" --destination-port [!] port[:port]\n"
24" --dport ...\n"
25"				match destination port(s)\n"
26" --tcp-option [!] number       match if TCP option set\n\n",
27IPTABLES_VERSION);
28}
29
30static const struct option opts[] = {
31	{ "source-port", 1, 0, '1' },
32	{ "sport", 1, 0, '1' }, /* synonym */
33	{ "destination-port", 1, 0, '2' },
34	{ "dport", 1, 0, '2' }, /* synonym */
35	{ "syn", 0, 0, '3' },
36	{ "tcp-flags", 1, 0, '4' },
37	{ "tcp-option", 1, 0, '5' },
38	{0}
39};
40
41static void
42parse_tcp_ports(const char *portstring, u_int16_t *ports)
43{
44	char *buffer;
45	char *cp;
46
47	buffer = strdup(portstring);
48	if ((cp = strchr(buffer, ':')) == NULL)
49		ports[0] = ports[1] = parse_port(buffer, "tcp");
50	else {
51		*cp = '\0';
52		cp++;
53
54		ports[0] = buffer[0] ? parse_port(buffer, "tcp") : 0;
55		ports[1] = cp[0] ? parse_port(cp, "tcp") : 0xFFFF;
56
57		if (ports[0] > ports[1])
58			exit_error(PARAMETER_PROBLEM,
59				   "invalid portrange (min > max)");
60	}
61	free(buffer);
62}
63
64struct tcp_flag_names {
65	const char *name;
66	unsigned int flag;
67};
68
69static struct tcp_flag_names tcp_flag_names[]
70= { { "FIN", 0x01 },
71    { "SYN", 0x02 },
72    { "RST", 0x04 },
73    { "PSH", 0x08 },
74    { "ACK", 0x10 },
75    { "URG", 0x20 },
76    { "ALL", 0x3F },
77    { "NONE", 0 },
78};
79
80static unsigned int
81parse_tcp_flag(const char *flags)
82{
83	unsigned int ret = 0;
84	char *ptr;
85	char *buffer;
86
87	buffer = strdup(flags);
88
89	for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
90		unsigned int i;
91		for (i = 0;
92		     i < sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names);
93		     i++) {
94			if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
95				ret |= tcp_flag_names[i].flag;
96				break;
97			}
98		}
99		if (i == sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names))
100			exit_error(PARAMETER_PROBLEM,
101				   "Unknown TCP flag `%s'", ptr);
102		}
103
104	free(buffer);
105	return ret;
106}
107
108static void
109parse_tcp_flags(struct xt_tcp *tcpinfo,
110		const char *mask,
111		const char *cmp,
112		int invert)
113{
114	tcpinfo->flg_mask = parse_tcp_flag(mask);
115	tcpinfo->flg_cmp = parse_tcp_flag(cmp);
116
117	if (invert)
118		tcpinfo->invflags |= XT_TCP_INV_FLAGS;
119}
120
121static void
122parse_tcp_option(const char *option, u_int8_t *result)
123{
124	unsigned int ret;
125
126	if (string_to_number(option, 1, 255, &ret) == -1)
127		exit_error(PARAMETER_PROBLEM, "Bad TCP option `%s'", option);
128
129	*result = (u_int8_t)ret;
130}
131
132/* Initialize the match. */
133static void
134init(struct xt_entry_match *m, unsigned int *nfcache)
135{
136	struct xt_tcp *tcpinfo = (struct xt_tcp *)m->data;
137
138	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
139}
140
141#define TCP_SRC_PORTS 0x01
142#define TCP_DST_PORTS 0x02
143#define TCP_FLAGS 0x04
144#define TCP_OPTION	0x08
145
146/* Function which parses command options; returns true if it
147   ate an option. */
148static int
149parse(int c, char **argv, int invert, unsigned int *flags,
150      const void *entry,
151      unsigned int *nfcache,
152      struct xt_entry_match **match)
153{
154	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;
155
156	switch (c) {
157	case '1':
158		if (*flags & TCP_SRC_PORTS)
159			exit_error(PARAMETER_PROBLEM,
160				   "Only one `--source-port' allowed");
161		check_inverse(optarg, &invert, &optind, 0);
162		parse_tcp_ports(argv[optind-1], tcpinfo->spts);
163		if (invert)
164			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
165		*flags |= TCP_SRC_PORTS;
166		break;
167
168	case '2':
169		if (*flags & TCP_DST_PORTS)
170			exit_error(PARAMETER_PROBLEM,
171				   "Only one `--destination-port' allowed");
172		check_inverse(optarg, &invert, &optind, 0);
173		parse_tcp_ports(argv[optind-1], tcpinfo->dpts);
174		if (invert)
175			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
176		*flags |= TCP_DST_PORTS;
177		break;
178
179	case '3':
180		if (*flags & TCP_FLAGS)
181			exit_error(PARAMETER_PROBLEM,
182				   "Only one of `--syn' or `--tcp-flags' "
183				   " allowed");
184		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
185		*flags |= TCP_FLAGS;
186		break;
187
188	case '4':
189		if (*flags & TCP_FLAGS)
190			exit_error(PARAMETER_PROBLEM,
191				   "Only one of `--syn' or `--tcp-flags' "
192				   " allowed");
193		check_inverse(optarg, &invert, &optind, 0);
194
195		if (!argv[optind]
196		    || argv[optind][0] == '-' || argv[optind][0] == '!')
197			exit_error(PARAMETER_PROBLEM,
198				   "--tcp-flags requires two args.");
199
200		parse_tcp_flags(tcpinfo, argv[optind-1], argv[optind],
201				invert);
202		optind++;
203		*flags |= TCP_FLAGS;
204		break;
205
206	case '5':
207		if (*flags & TCP_OPTION)
208			exit_error(PARAMETER_PROBLEM,
209				   "Only one `--tcp-option' allowed");
210		check_inverse(optarg, &invert, &optind, 0);
211		parse_tcp_option(argv[optind-1], &tcpinfo->option);
212		if (invert)
213			tcpinfo->invflags |= XT_TCP_INV_OPTION;
214		*flags |= TCP_OPTION;
215		break;
216
217	default:
218		return 0;
219	}
220
221	return 1;
222}
223
224/* Final check; we don't care. */
225static void
226final_check(unsigned int flags)
227{
228}
229
230static char *
231port_to_service(int port)
232{
233	struct servent *service;
234
235	if ((service = getservbyport(htons(port), "tcp")))
236		return service->s_name;
237
238	return NULL;
239}
240
241static void
242print_port(u_int16_t port, int numeric)
243{
244	char *service;
245
246	if (numeric || (service = port_to_service(port)) == NULL)
247		printf("%u", port);
248	else
249		printf("%s", service);
250}
251
252static void
253print_ports(const char *name, u_int16_t min, u_int16_t max,
254	    int invert, int numeric)
255{
256	const char *inv = invert ? "!" : "";
257
258	if (min != 0 || max != 0xFFFF || invert) {
259		printf("%s", name);
260		if (min == max) {
261			printf(":%s", inv);
262			print_port(min, numeric);
263		} else {
264			printf("s:%s", inv);
265			print_port(min, numeric);
266			printf(":");
267			print_port(max, numeric);
268		}
269		printf(" ");
270	}
271}
272
273static void
274print_option(u_int8_t option, int invert, int numeric)
275{
276	if (option || invert)
277		printf("option=%s%u ", invert ? "!" : "", option);
278}
279
280static void
281print_tcpf(u_int8_t flags)
282{
283	int have_flag = 0;
284
285	while (flags) {
286		unsigned int i;
287
288		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
289
290		if (have_flag)
291			printf(",");
292		printf("%s", tcp_flag_names[i].name);
293		have_flag = 1;
294
295		flags &= ~tcp_flag_names[i].flag;
296	}
297
298	if (!have_flag)
299		printf("NONE");
300}
301
302static void
303print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
304{
305	if (mask || invert) {
306		printf("flags:%s", invert ? "!" : "");
307		if (numeric)
308			printf("0x%02X/0x%02X ", mask, cmp);
309		else {
310			print_tcpf(mask);
311			printf("/");
312			print_tcpf(cmp);
313			printf(" ");
314		}
315	}
316}
317
318/* Prints out the union ipt_matchinfo. */
319static void
320print(const void *ip,
321      const struct xt_entry_match *match, int numeric)
322{
323	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
324
325	printf("tcp ");
326	print_ports("spt", tcp->spts[0], tcp->spts[1],
327		    tcp->invflags & XT_TCP_INV_SRCPT,
328		    numeric);
329	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
330		    tcp->invflags & XT_TCP_INV_DSTPT,
331		    numeric);
332	print_option(tcp->option,
333		     tcp->invflags & XT_TCP_INV_OPTION,
334		     numeric);
335	print_flags(tcp->flg_mask, tcp->flg_cmp,
336		    tcp->invflags & XT_TCP_INV_FLAGS,
337		    numeric);
338	if (tcp->invflags & ~XT_TCP_INV_MASK)
339		printf("Unknown invflags: 0x%X ",
340		       tcp->invflags & ~XT_TCP_INV_MASK);
341}
342
343/* Saves the union ipt_matchinfo in parsable form to stdout. */
344static void save(const void *ip, const struct xt_entry_match *match)
345{
346	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
347
348	if (tcpinfo->spts[0] != 0
349	    || tcpinfo->spts[1] != 0xFFFF) {
350		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
351			printf("! ");
352		if (tcpinfo->spts[0]
353		    != tcpinfo->spts[1])
354			printf("--sport %u:%u ",
355			       tcpinfo->spts[0],
356			       tcpinfo->spts[1]);
357		else
358			printf("--sport %u ",
359			       tcpinfo->spts[0]);
360	}
361
362	if (tcpinfo->dpts[0] != 0
363	    || tcpinfo->dpts[1] != 0xFFFF) {
364		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
365			printf("! ");
366		if (tcpinfo->dpts[0]
367		    != tcpinfo->dpts[1])
368			printf("--dport %u:%u ",
369			       tcpinfo->dpts[0],
370			       tcpinfo->dpts[1]);
371		else
372			printf("--dport %u ",
373			       tcpinfo->dpts[0]);
374	}
375
376	if (tcpinfo->option
377	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
378		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
379			printf("! ");
380		printf("--tcp-option %u ", tcpinfo->option);
381	}
382
383	if (tcpinfo->flg_mask
384	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
385		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
386			printf("! ");
387		printf("--tcp-flags ");
388		if (tcpinfo->flg_mask != 0xFF) {
389			print_tcpf(tcpinfo->flg_mask);
390		}
391		printf(" ");
392		print_tcpf(tcpinfo->flg_cmp);
393		printf(" ");
394	}
395}
396
397static struct xtables_match tcp = {
398	.family		= AF_INET,
399	.name		= "tcp",
400	.version	= IPTABLES_VERSION,
401	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
402	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
403	.help		= &help,
404	.init		= &init,
405	.parse		= &parse,
406	.final_check	= &final_check,
407	.print		= &print,
408	.save		= &save,
409	.extra_opts	= opts,
410};
411
412static struct xtables_match tcp6 = {
413	.family		= AF_INET6,
414	.name		= "tcp",
415	.version	= IPTABLES_VERSION,
416	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
417	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
418	.help		= &help,
419	.init		= &init,
420	.parse		= &parse,
421	.final_check	= &final_check,
422	.print		= &print,
423	.save		= &save,
424	.extra_opts	= opts,
425};
426
427void
428_init(void)
429{
430	xtables_register_match(&tcp);
431	xtables_register_match(&tcp6);
432}
433