libxt_tcp.c revision e917bca09924435f3fca23c01042543b1826c81e 
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 <netinet/in.h>
8#include <xtables.h>
9#include <linux/netfilter/xt_tcpudp.h>
10
11static void tcp_help(void)
12{
13	printf(
14"tcp match options:\n"
15"[!] --tcp-flags mask comp	match when TCP flags & mask == comp\n"
16"				(Flags: SYN ACK FIN RST URG PSH ALL NONE)\n"
17"[!] --syn			match when only SYN flag set\n"
18"				(equivalent to --tcp-flags SYN,RST,ACK,FIN SYN)\n"
19"[!] --source-port port[:port]\n"
20" --sport ...\n"
21"				match source port(s)\n"
22"[!] --destination-port port[:port]\n"
23" --dport ...\n"
24"				match destination port(s)\n"
25"[!] --tcp-option number        match if TCP option set\n");
26}
27
28static const struct option tcp_opts[] = {
29	{ "source-port", 1, NULL, '1' },
30	{ "sport", 1, NULL, '1' }, /* synonym */
31	{ "destination-port", 1, NULL, '2' },
32	{ "dport", 1, NULL, '2' }, /* synonym */
33	{ "syn", 0, NULL, '3' },
34	{ "tcp-flags", 1, NULL, '4' },
35	{ "tcp-option", 1, NULL, '5' },
36	{ .name = NULL }
37};
38
39static void
40parse_tcp_ports(const char *portstring, u_int16_t *ports)
41{
42	char *buffer;
43	char *cp;
44
45	buffer = strdup(portstring);
46	if ((cp = strchr(buffer, ':')) == NULL)
47		ports[0] = ports[1] = parse_port(buffer, "tcp");
48	else {
49		*cp = '\0';
50		cp++;
51
52		ports[0] = buffer[0] ? parse_port(buffer, "tcp") : 0;
53		ports[1] = cp[0] ? parse_port(cp, "tcp") : 0xFFFF;
54
55		if (ports[0] > ports[1])
56			exit_error(PARAMETER_PROBLEM,
57				   "invalid portrange (min > max)");
58	}
59	free(buffer);
60}
61
62struct tcp_flag_names {
63	const char *name;
64	unsigned int flag;
65};
66
67static const struct tcp_flag_names tcp_flag_names[]
68= { { "FIN", 0x01 },
69    { "SYN", 0x02 },
70    { "RST", 0x04 },
71    { "PSH", 0x08 },
72    { "ACK", 0x10 },
73    { "URG", 0x20 },
74    { "ALL", 0x3F },
75    { "NONE", 0 },
76};
77
78static unsigned int
79parse_tcp_flag(const char *flags)
80{
81	unsigned int ret = 0;
82	char *ptr;
83	char *buffer;
84
85	buffer = strdup(flags);
86
87	for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
88		unsigned int i;
89		for (i = 0;
90		     i < sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names);
91		     i++) {
92			if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
93				ret |= tcp_flag_names[i].flag;
94				break;
95			}
96		}
97		if (i == sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names))
98			exit_error(PARAMETER_PROBLEM,
99				   "Unknown TCP flag `%s'", ptr);
100		}
101
102	free(buffer);
103	return ret;
104}
105
106static void
107parse_tcp_flags(struct xt_tcp *tcpinfo,
108		const char *mask,
109		const char *cmp,
110		int invert)
111{
112	tcpinfo->flg_mask = parse_tcp_flag(mask);
113	tcpinfo->flg_cmp = parse_tcp_flag(cmp);
114
115	if (invert)
116		tcpinfo->invflags |= XT_TCP_INV_FLAGS;
117}
118
119static void
120parse_tcp_option(const char *option, u_int8_t *result)
121{
122	unsigned int ret;
123
124	if (string_to_number(option, 1, UINT8_MAX, &ret) == -1)
125		exit_error(PARAMETER_PROBLEM, "Bad TCP option `%s'", option);
126
127	*result = ret;
128}
129
130static void tcp_init(struct xt_entry_match *m)
131{
132	struct xt_tcp *tcpinfo = (struct xt_tcp *)m->data;
133
134	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
135}
136
137#define TCP_SRC_PORTS 0x01
138#define TCP_DST_PORTS 0x02
139#define TCP_FLAGS 0x04
140#define TCP_OPTION	0x08
141
142static int
143tcp_parse(int c, char **argv, int invert, unsigned int *flags,
144          const void *entry, struct xt_entry_match **match)
145{
146	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;
147
148	switch (c) {
149	case '1':
150		if (*flags & TCP_SRC_PORTS)
151			exit_error(PARAMETER_PROBLEM,
152				   "Only one `--source-port' allowed");
153		check_inverse(optarg, &invert, &optind, 0);
154		parse_tcp_ports(argv[optind-1], tcpinfo->spts);
155		if (invert)
156			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
157		*flags |= TCP_SRC_PORTS;
158		break;
159
160	case '2':
161		if (*flags & TCP_DST_PORTS)
162			exit_error(PARAMETER_PROBLEM,
163				   "Only one `--destination-port' allowed");
164		check_inverse(optarg, &invert, &optind, 0);
165		parse_tcp_ports(argv[optind-1], tcpinfo->dpts);
166		if (invert)
167			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
168		*flags |= TCP_DST_PORTS;
169		break;
170
171	case '3':
172		if (*flags & TCP_FLAGS)
173			exit_error(PARAMETER_PROBLEM,
174				   "Only one of `--syn' or `--tcp-flags' "
175				   " allowed");
176		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
177		*flags |= TCP_FLAGS;
178		break;
179
180	case '4':
181		if (*flags & TCP_FLAGS)
182			exit_error(PARAMETER_PROBLEM,
183				   "Only one of `--syn' or `--tcp-flags' "
184				   " allowed");
185		check_inverse(optarg, &invert, &optind, 0);
186
187		if (!argv[optind]
188		    || argv[optind][0] == '-' || argv[optind][0] == '!')
189			exit_error(PARAMETER_PROBLEM,
190				   "--tcp-flags requires two args.");
191
192		parse_tcp_flags(tcpinfo, argv[optind-1], argv[optind],
193				invert);
194		optind++;
195		*flags |= TCP_FLAGS;
196		break;
197
198	case '5':
199		if (*flags & TCP_OPTION)
200			exit_error(PARAMETER_PROBLEM,
201				   "Only one `--tcp-option' allowed");
202		check_inverse(optarg, &invert, &optind, 0);
203		parse_tcp_option(argv[optind-1], &tcpinfo->option);
204		if (invert)
205			tcpinfo->invflags |= XT_TCP_INV_OPTION;
206		*flags |= TCP_OPTION;
207		break;
208
209	default:
210		return 0;
211	}
212
213	return 1;
214}
215
216static char *
217port_to_service(int port)
218{
219	struct servent *service;
220
221	if ((service = getservbyport(htons(port), "tcp")))
222		return service->s_name;
223
224	return NULL;
225}
226
227static void
228print_port(u_int16_t port, int numeric)
229{
230	char *service;
231
232	if (numeric || (service = port_to_service(port)) == NULL)
233		printf("%u", port);
234	else
235		printf("%s", service);
236}
237
238static void
239print_ports(const char *name, u_int16_t min, u_int16_t max,
240	    int invert, int numeric)
241{
242	const char *inv = invert ? "!" : "";
243
244	if (min != 0 || max != 0xFFFF || invert) {
245		printf("%s", name);
246		if (min == max) {
247			printf(":%s", inv);
248			print_port(min, numeric);
249		} else {
250			printf("s:%s", inv);
251			print_port(min, numeric);
252			printf(":");
253			print_port(max, numeric);
254		}
255		printf(" ");
256	}
257}
258
259static void
260print_option(u_int8_t option, int invert, int numeric)
261{
262	if (option || invert)
263		printf("option=%s%u ", invert ? "!" : "", option);
264}
265
266static void
267print_tcpf(u_int8_t flags)
268{
269	int have_flag = 0;
270
271	while (flags) {
272		unsigned int i;
273
274		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
275
276		if (have_flag)
277			printf(",");
278		printf("%s", tcp_flag_names[i].name);
279		have_flag = 1;
280
281		flags &= ~tcp_flag_names[i].flag;
282	}
283
284	if (!have_flag)
285		printf("NONE");
286}
287
288static void
289print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
290{
291	if (mask || invert) {
292		printf("flags:%s", invert ? "!" : "");
293		if (numeric)
294			printf("0x%02X/0x%02X ", mask, cmp);
295		else {
296			print_tcpf(mask);
297			printf("/");
298			print_tcpf(cmp);
299			printf(" ");
300		}
301	}
302}
303
304static void
305tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
306{
307	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
308
309	printf("tcp ");
310	print_ports("spt", tcp->spts[0], tcp->spts[1],
311		    tcp->invflags & XT_TCP_INV_SRCPT,
312		    numeric);
313	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
314		    tcp->invflags & XT_TCP_INV_DSTPT,
315		    numeric);
316	print_option(tcp->option,
317		     tcp->invflags & XT_TCP_INV_OPTION,
318		     numeric);
319	print_flags(tcp->flg_mask, tcp->flg_cmp,
320		    tcp->invflags & XT_TCP_INV_FLAGS,
321		    numeric);
322	if (tcp->invflags & ~XT_TCP_INV_MASK)
323		printf("Unknown invflags: 0x%X ",
324		       tcp->invflags & ~XT_TCP_INV_MASK);
325}
326
327static void tcp_save(const void *ip, const struct xt_entry_match *match)
328{
329	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
330
331	if (tcpinfo->spts[0] != 0
332	    || tcpinfo->spts[1] != 0xFFFF) {
333		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
334			printf("! ");
335		if (tcpinfo->spts[0]
336		    != tcpinfo->spts[1])
337			printf("--sport %u:%u ",
338			       tcpinfo->spts[0],
339			       tcpinfo->spts[1]);
340		else
341			printf("--sport %u ",
342			       tcpinfo->spts[0]);
343	}
344
345	if (tcpinfo->dpts[0] != 0
346	    || tcpinfo->dpts[1] != 0xFFFF) {
347		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
348			printf("! ");
349		if (tcpinfo->dpts[0]
350		    != tcpinfo->dpts[1])
351			printf("--dport %u:%u ",
352			       tcpinfo->dpts[0],
353			       tcpinfo->dpts[1]);
354		else
355			printf("--dport %u ",
356			       tcpinfo->dpts[0]);
357	}
358
359	if (tcpinfo->option
360	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
361		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
362			printf("! ");
363		printf("--tcp-option %u ", tcpinfo->option);
364	}
365
366	if (tcpinfo->flg_mask
367	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
368		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
369			printf("! ");
370		printf("--tcp-flags ");
371		if (tcpinfo->flg_mask != 0xFF) {
372			print_tcpf(tcpinfo->flg_mask);
373		}
374		printf(" ");
375		print_tcpf(tcpinfo->flg_cmp);
376		printf(" ");
377	}
378}
379
380static struct xtables_match tcp_match = {
381	.family		= NFPROTO_IPV4,
382	.name		= "tcp",
383	.version	= XTABLES_VERSION,
384	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
385	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
386	.help		= tcp_help,
387	.init		= tcp_init,
388	.parse		= tcp_parse,
389	.print		= tcp_print,
390	.save		= tcp_save,
391	.extra_opts	= tcp_opts,
392};
393
394static struct xtables_match tcp_match6 = {
395	.family		= NFPROTO_IPV6,
396	.name		= "tcp",
397	.version	= XTABLES_VERSION,
398	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
399	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
400	.help		= tcp_help,
401	.init		= tcp_init,
402	.parse		= tcp_parse,
403	.print		= tcp_print,
404	.save		= tcp_save,
405	.extra_opts	= tcp_opts,
406};
407
408void
409_init(void)
410{
411	xtables_register_match(&tcp_match);
412	xtables_register_match(&tcp_match6);
413}
414