libxt_tcp.c revision 3dafef40228c372976eb714836ea097115d8fd03 
1/* Shared library add-on to iptables to add TCP support. */
2#include <stdbool.h>
3#include <stdio.h>
4#include <netdb.h>
5#include <string.h>
6#include <stdlib.h>
7#include <getopt.h>
8#include <netinet/in.h>
9#include <xtables.h>
10#include <linux/netfilter/xt_tcpudp.h>
11
12static void tcp_help(void)
13{
14	printf(
15"tcp match 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");
27}
28
29static const struct option tcp_opts[] = {
30	{.name = "source-port",      .has_arg = true,  .val = '1'},
31	{.name = "sport",            .has_arg = true,  .val = '1'}, /* synonym */
32	{.name = "destination-port", .has_arg = true,  .val = '2'},
33	{.name = "dport",            .has_arg = true,  .val = '2'}, /* synonym */
34	{.name = "syn",              .has_arg = false, .val = '3'},
35	{.name = "tcp-flags",        .has_arg = true,  .val = '4'},
36	{.name = "tcp-option",       .has_arg = true,  .val = '5'},
37	XT_GETOPT_TABLEEND,
38};
39
40static void
41parse_tcp_ports(const char *portstring, uint16_t *ports)
42{
43	char *buffer;
44	char *cp;
45
46	buffer = strdup(portstring);
47	if ((cp = strchr(buffer, ':')) == NULL)
48		ports[0] = ports[1] = xtables_parse_port(buffer, "tcp");
49	else {
50		*cp = '\0';
51		cp++;
52
53		ports[0] = buffer[0] ? xtables_parse_port(buffer, "tcp") : 0;
54		ports[1] = cp[0] ? xtables_parse_port(cp, "tcp") : 0xFFFF;
55
56		if (ports[0] > ports[1])
57			xtables_error(PARAMETER_PROBLEM,
58				   "invalid portrange (min > max)");
59	}
60	free(buffer);
61}
62
63struct tcp_flag_names {
64	const char *name;
65	unsigned int flag;
66};
67
68static const struct tcp_flag_names tcp_flag_names[]
69= { { "FIN", 0x01 },
70    { "SYN", 0x02 },
71    { "RST", 0x04 },
72    { "PSH", 0x08 },
73    { "ACK", 0x10 },
74    { "URG", 0x20 },
75    { "ALL", 0x3F },
76    { "NONE", 0 },
77};
78
79static unsigned int
80parse_tcp_flag(const char *flags)
81{
82	unsigned int ret = 0;
83	char *ptr;
84	char *buffer;
85
86	buffer = strdup(flags);
87
88	for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
89		unsigned int i;
90		for (i = 0; i < ARRAY_SIZE(tcp_flag_names); ++i)
91			if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
92				ret |= tcp_flag_names[i].flag;
93				break;
94			}
95		if (i == ARRAY_SIZE(tcp_flag_names))
96			xtables_error(PARAMETER_PROBLEM,
97				   "Unknown TCP flag `%s'", ptr);
98	}
99
100	free(buffer);
101	return ret;
102}
103
104static void
105parse_tcp_flags(struct xt_tcp *tcpinfo,
106		const char *mask,
107		const char *cmp,
108		int invert)
109{
110	tcpinfo->flg_mask = parse_tcp_flag(mask);
111	tcpinfo->flg_cmp = parse_tcp_flag(cmp);
112
113	if (invert)
114		tcpinfo->invflags |= XT_TCP_INV_FLAGS;
115}
116
117static void
118parse_tcp_option(const char *option, uint8_t *result)
119{
120	unsigned int ret;
121
122	if (!xtables_strtoui(option, NULL, &ret, 1, UINT8_MAX))
123		xtables_error(PARAMETER_PROBLEM, "Bad TCP option \"%s\"", option);
124
125	*result = ret;
126}
127
128static void tcp_init(struct xt_entry_match *m)
129{
130	struct xt_tcp *tcpinfo = (struct xt_tcp *)m->data;
131
132	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
133}
134
135#define TCP_SRC_PORTS 0x01
136#define TCP_DST_PORTS 0x02
137#define TCP_FLAGS 0x04
138#define TCP_OPTION	0x08
139
140static int
141tcp_parse(int c, char **argv, int invert, unsigned int *flags,
142          const void *entry, struct xt_entry_match **match)
143{
144	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;
145
146	switch (c) {
147	case '1':
148		if (*flags & TCP_SRC_PORTS)
149			xtables_error(PARAMETER_PROBLEM,
150				   "Only one `--source-port' allowed");
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		parse_tcp_ports(optarg, tcpinfo->dpts);
162		if (invert)
163			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
164		*flags |= TCP_DST_PORTS;
165		break;
166
167	case '3':
168		if (*flags & TCP_FLAGS)
169			xtables_error(PARAMETER_PROBLEM,
170				   "Only one of `--syn' or `--tcp-flags' "
171				   " allowed");
172		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
173		*flags |= TCP_FLAGS;
174		break;
175
176	case '4':
177		if (*flags & TCP_FLAGS)
178			xtables_error(PARAMETER_PROBLEM,
179				   "Only one of `--syn' or `--tcp-flags' "
180				   " allowed");
181		if (!argv[optind]
182		    || argv[optind][0] == '-' || argv[optind][0] == '!')
183			xtables_error(PARAMETER_PROBLEM,
184				   "--tcp-flags requires two args.");
185
186		parse_tcp_flags(tcpinfo, optarg, argv[optind],
187				invert);
188		optind++;
189		*flags |= TCP_FLAGS;
190		break;
191
192	case '5':
193		if (*flags & TCP_OPTION)
194			xtables_error(PARAMETER_PROBLEM,
195				   "Only one `--tcp-option' allowed");
196		parse_tcp_option(optarg, &tcpinfo->option);
197		if (invert)
198			tcpinfo->invflags |= XT_TCP_INV_OPTION;
199		*flags |= TCP_OPTION;
200		break;
201	}
202
203	return 1;
204}
205
206static const char *
207port_to_service(int port)
208{
209	const struct servent *service;
210
211	if ((service = getservbyport(htons(port), "tcp")))
212		return service->s_name;
213
214	return NULL;
215}
216
217static void
218print_port(uint16_t port, int numeric)
219{
220	const char *service;
221
222	if (numeric || (service = port_to_service(port)) == NULL)
223		printf("%u", port);
224	else
225		printf("%s", service);
226}
227
228static void
229print_ports(const char *name, uint16_t min, uint16_t max,
230	    int invert, int numeric)
231{
232	const char *inv = invert ? "!" : "";
233
234	if (min != 0 || max != 0xFFFF || invert) {
235		printf(" %s", name);
236		if (min == max) {
237			printf(":%s", inv);
238			print_port(min, numeric);
239		} else {
240			printf("s:%s", inv);
241			print_port(min, numeric);
242			printf(":");
243			print_port(max, numeric);
244		}
245	}
246}
247
248static void
249print_option(uint8_t option, int invert, int numeric)
250{
251	if (option || invert)
252		printf(" option=%s%u", invert ? "!" : "", option);
253}
254
255static void
256print_tcpf(uint8_t flags)
257{
258	int have_flag = 0;
259
260	while (flags) {
261		unsigned int i;
262
263		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
264
265		if (have_flag)
266			printf(",");
267		printf("%s", tcp_flag_names[i].name);
268		have_flag = 1;
269
270		flags &= ~tcp_flag_names[i].flag;
271	}
272
273	if (!have_flag)
274		printf("NONE");
275}
276
277static void
278print_flags(uint8_t mask, uint8_t cmp, int invert, int numeric)
279{
280	if (mask || invert) {
281		printf("flags:%s", invert ? "!" : "");
282		if (numeric)
283			printf(" 0x%02X/0x%02X", mask, cmp);
284		else {
285			printf(" ");
286			print_tcpf(mask);
287			printf("/");
288			print_tcpf(cmp);
289		}
290	}
291}
292
293static void
294tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
295{
296	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
297
298	printf(" tcp");
299	print_ports("spt", tcp->spts[0], tcp->spts[1],
300		    tcp->invflags & XT_TCP_INV_SRCPT,
301		    numeric);
302	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
303		    tcp->invflags & XT_TCP_INV_DSTPT,
304		    numeric);
305	print_option(tcp->option,
306		     tcp->invflags & XT_TCP_INV_OPTION,
307		     numeric);
308	print_flags(tcp->flg_mask, tcp->flg_cmp,
309		    tcp->invflags & XT_TCP_INV_FLAGS,
310		    numeric);
311	if (tcp->invflags & ~XT_TCP_INV_MASK)
312		printf(" Unknown invflags: 0x%X",
313		       tcp->invflags & ~XT_TCP_INV_MASK);
314}
315
316static void tcp_save(const void *ip, const struct xt_entry_match *match)
317{
318	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
319
320	if (tcpinfo->spts[0] != 0
321	    || tcpinfo->spts[1] != 0xFFFF) {
322		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
323			printf(" !");
324		if (tcpinfo->spts[0]
325		    != tcpinfo->spts[1])
326			printf(" --sport %u:%u",
327			       tcpinfo->spts[0],
328			       tcpinfo->spts[1]);
329		else
330			printf(" --sport %u",
331			       tcpinfo->spts[0]);
332	}
333
334	if (tcpinfo->dpts[0] != 0
335	    || tcpinfo->dpts[1] != 0xFFFF) {
336		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
337			printf(" !");
338		if (tcpinfo->dpts[0]
339		    != tcpinfo->dpts[1])
340			printf(" --dport %u:%u",
341			       tcpinfo->dpts[0],
342			       tcpinfo->dpts[1]);
343		else
344			printf(" --dport %u",
345			       tcpinfo->dpts[0]);
346	}
347
348	if (tcpinfo->option
349	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
350		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
351			printf(" !");
352		printf(" --tcp-option %u", tcpinfo->option);
353	}
354
355	if (tcpinfo->flg_mask
356	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
357		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
358			printf(" !");
359		printf(" --tcp-flags ");
360		print_tcpf(tcpinfo->flg_mask);
361		printf(" ");
362		print_tcpf(tcpinfo->flg_cmp);
363	}
364}
365
366static struct xtables_match tcp_match = {
367	.family		= NFPROTO_UNSPEC,
368	.name		= "tcp",
369	.version	= XTABLES_VERSION,
370	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
371	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
372	.help		= tcp_help,
373	.init		= tcp_init,
374	.parse		= tcp_parse,
375	.print		= tcp_print,
376	.save		= tcp_save,
377	.extra_opts	= tcp_opts,
378};
379
380void
381_init(void)
382{
383	xtables_register_match(&tcp_match);
384}
385