libxt_tcp.c revision bbe83862a5e1baf15f7c923352d4afdf59bc70e2 
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] = xtables_parse_port(buffer, "tcp");
48	else {
49		*cp = '\0';
50		cp++;
51
52		ports[0] = buffer[0] ? xtables_parse_port(buffer, "tcp") : 0;
53		ports[1] = cp[0] ? xtables_parse_port(cp, "tcp") : 0xFFFF;
54
55		if (ports[0] > ports[1])
56			xtables_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; i < ARRAY_SIZE(tcp_flag_names); ++i)
90			if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
91				ret |= tcp_flag_names[i].flag;
92				break;
93			}
94		if (i == ARRAY_SIZE(tcp_flag_names))
95			xtables_error(PARAMETER_PROBLEM,
96				   "Unknown TCP flag `%s'", ptr);
97	}
98
99	free(buffer);
100	return ret;
101}
102
103static void
104parse_tcp_flags(struct xt_tcp *tcpinfo,
105		const char *mask,
106		const char *cmp,
107		int invert)
108{
109	tcpinfo->flg_mask = parse_tcp_flag(mask);
110	tcpinfo->flg_cmp = parse_tcp_flag(cmp);
111
112	if (invert)
113		tcpinfo->invflags |= XT_TCP_INV_FLAGS;
114}
115
116static void
117parse_tcp_option(const char *option, u_int8_t *result)
118{
119	unsigned int ret;
120
121	if (!xtables_strtoui(option, NULL, &ret, 1, UINT8_MAX))
122		xtables_error(PARAMETER_PROBLEM, "Bad TCP option \"%s\"", option);
123
124	*result = ret;
125}
126
127static void tcp_init(struct xt_entry_match *m)
128{
129	struct xt_tcp *tcpinfo = (struct xt_tcp *)m->data;
130
131	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
132}
133
134#define TCP_SRC_PORTS 0x01
135#define TCP_DST_PORTS 0x02
136#define TCP_FLAGS 0x04
137#define TCP_OPTION	0x08
138
139static int
140tcp_parse(int c, char **argv, int invert, unsigned int *flags,
141          const void *entry, struct xt_entry_match **match)
142{
143	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;
144
145	switch (c) {
146	case '1':
147		if (*flags & TCP_SRC_PORTS)
148			xtables_error(PARAMETER_PROBLEM,
149				   "Only one `--source-port' allowed");
150		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
151		parse_tcp_ports(optarg, tcpinfo->spts);
152		if (invert)
153			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
154		*flags |= TCP_SRC_PORTS;
155		break;
156
157	case '2':
158		if (*flags & TCP_DST_PORTS)
159			xtables_error(PARAMETER_PROBLEM,
160				   "Only one `--destination-port' allowed");
161		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
162		parse_tcp_ports(optarg, tcpinfo->dpts);
163		if (invert)
164			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
165		*flags |= TCP_DST_PORTS;
166		break;
167
168	case '3':
169		if (*flags & TCP_FLAGS)
170			xtables_error(PARAMETER_PROBLEM,
171				   "Only one of `--syn' or `--tcp-flags' "
172				   " allowed");
173		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
174		*flags |= TCP_FLAGS;
175		break;
176
177	case '4':
178		if (*flags & TCP_FLAGS)
179			xtables_error(PARAMETER_PROBLEM,
180				   "Only one of `--syn' or `--tcp-flags' "
181				   " allowed");
182		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
183
184		if (!argv[optind]
185		    || argv[optind][0] == '-' || argv[optind][0] == '!')
186			xtables_error(PARAMETER_PROBLEM,
187				   "--tcp-flags requires two args.");
188
189		parse_tcp_flags(tcpinfo, optarg, argv[optind],
190				invert);
191		optind++;
192		*flags |= TCP_FLAGS;
193		break;
194
195	case '5':
196		if (*flags & TCP_OPTION)
197			xtables_error(PARAMETER_PROBLEM,
198				   "Only one `--tcp-option' allowed");
199		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
200		parse_tcp_option(optarg, &tcpinfo->option);
201		if (invert)
202			tcpinfo->invflags |= XT_TCP_INV_OPTION;
203		*flags |= TCP_OPTION;
204		break;
205
206	default:
207		return 0;
208	}
209
210	return 1;
211}
212
213static char *
214port_to_service(int port)
215{
216	struct servent *service;
217
218	if ((service = getservbyport(htons(port), "tcp")))
219		return service->s_name;
220
221	return NULL;
222}
223
224static void
225print_port(u_int16_t port, int numeric)
226{
227	char *service;
228
229	if (numeric || (service = port_to_service(port)) == NULL)
230		printf("%u", port);
231	else
232		printf("%s", service);
233}
234
235static void
236print_ports(const char *name, u_int16_t min, u_int16_t max,
237	    int invert, int numeric)
238{
239	const char *inv = invert ? "!" : "";
240
241	if (min != 0 || max != 0xFFFF || invert) {
242		printf("%s", name);
243		if (min == max) {
244			printf(":%s", inv);
245			print_port(min, numeric);
246		} else {
247			printf("s:%s", inv);
248			print_port(min, numeric);
249			printf(":");
250			print_port(max, numeric);
251		}
252		printf(" ");
253	}
254}
255
256static void
257print_option(u_int8_t option, int invert, int numeric)
258{
259	if (option || invert)
260		printf("option=%s%u ", invert ? "!" : "", option);
261}
262
263static void
264print_tcpf(u_int8_t flags)
265{
266	int have_flag = 0;
267
268	while (flags) {
269		unsigned int i;
270
271		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
272
273		if (have_flag)
274			printf(",");
275		printf("%s", tcp_flag_names[i].name);
276		have_flag = 1;
277
278		flags &= ~tcp_flag_names[i].flag;
279	}
280
281	if (!have_flag)
282		printf("NONE");
283}
284
285static void
286print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
287{
288	if (mask || invert) {
289		printf("flags:%s", invert ? "!" : "");
290		if (numeric)
291			printf("0x%02X/0x%02X ", mask, cmp);
292		else {
293			print_tcpf(mask);
294			printf("/");
295			print_tcpf(cmp);
296			printf(" ");
297		}
298	}
299}
300
301static void
302tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
303{
304	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
305
306	printf("tcp ");
307	print_ports("spt", tcp->spts[0], tcp->spts[1],
308		    tcp->invflags & XT_TCP_INV_SRCPT,
309		    numeric);
310	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
311		    tcp->invflags & XT_TCP_INV_DSTPT,
312		    numeric);
313	print_option(tcp->option,
314		     tcp->invflags & XT_TCP_INV_OPTION,
315		     numeric);
316	print_flags(tcp->flg_mask, tcp->flg_cmp,
317		    tcp->invflags & XT_TCP_INV_FLAGS,
318		    numeric);
319	if (tcp->invflags & ~XT_TCP_INV_MASK)
320		printf("Unknown invflags: 0x%X ",
321		       tcp->invflags & ~XT_TCP_INV_MASK);
322}
323
324static void tcp_save(const void *ip, const struct xt_entry_match *match)
325{
326	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
327
328	if (tcpinfo->spts[0] != 0
329	    || tcpinfo->spts[1] != 0xFFFF) {
330		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
331			printf("! ");
332		if (tcpinfo->spts[0]
333		    != tcpinfo->spts[1])
334			printf("--sport %u:%u ",
335			       tcpinfo->spts[0],
336			       tcpinfo->spts[1]);
337		else
338			printf("--sport %u ",
339			       tcpinfo->spts[0]);
340	}
341
342	if (tcpinfo->dpts[0] != 0
343	    || tcpinfo->dpts[1] != 0xFFFF) {
344		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
345			printf("! ");
346		if (tcpinfo->dpts[0]
347		    != tcpinfo->dpts[1])
348			printf("--dport %u:%u ",
349			       tcpinfo->dpts[0],
350			       tcpinfo->dpts[1]);
351		else
352			printf("--dport %u ",
353			       tcpinfo->dpts[0]);
354	}
355
356	if (tcpinfo->option
357	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
358		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
359			printf("! ");
360		printf("--tcp-option %u ", tcpinfo->option);
361	}
362
363	if (tcpinfo->flg_mask
364	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
365		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
366			printf("! ");
367		printf("--tcp-flags ");
368		if (tcpinfo->flg_mask != 0xFF) {
369			print_tcpf(tcpinfo->flg_mask);
370		}
371		printf(" ");
372		print_tcpf(tcpinfo->flg_cmp);
373		printf(" ");
374	}
375}
376
377static struct xtables_match tcp_match = {
378	.family		= NFPROTO_UNSPEC,
379	.name		= "tcp",
380	.version	= XTABLES_VERSION,
381	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
382	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
383	.help		= tcp_help,
384	.init		= tcp_init,
385	.parse		= tcp_parse,
386	.print		= tcp_print,
387	.save		= tcp_save,
388	.extra_opts	= tcp_opts,
389};
390
391void
392_init(void)
393{
394	xtables_register_match(&tcp_match);
395}
396