libxt_tcp.c revision d09b6d591ca7d7d7575cb6aa20384c9830f777ab 
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		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
152		parse_tcp_ports(optarg, tcpinfo->spts);
153		if (invert)
154			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
155		*flags |= TCP_SRC_PORTS;
156		break;
157
158	case '2':
159		if (*flags & TCP_DST_PORTS)
160			xtables_error(PARAMETER_PROBLEM,
161				   "Only one `--destination-port' allowed");
162		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
163		parse_tcp_ports(optarg, tcpinfo->dpts);
164		if (invert)
165			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
166		*flags |= TCP_DST_PORTS;
167		break;
168
169	case '3':
170		if (*flags & TCP_FLAGS)
171			xtables_error(PARAMETER_PROBLEM,
172				   "Only one of `--syn' or `--tcp-flags' "
173				   " allowed");
174		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
175		*flags |= TCP_FLAGS;
176		break;
177
178	case '4':
179		if (*flags & TCP_FLAGS)
180			xtables_error(PARAMETER_PROBLEM,
181				   "Only one of `--syn' or `--tcp-flags' "
182				   " allowed");
183		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
184
185		if (!argv[optind]
186		    || argv[optind][0] == '-' || argv[optind][0] == '!')
187			xtables_error(PARAMETER_PROBLEM,
188				   "--tcp-flags requires two args.");
189
190		parse_tcp_flags(tcpinfo, optarg, argv[optind],
191				invert);
192		optind++;
193		*flags |= TCP_FLAGS;
194		break;
195
196	case '5':
197		if (*flags & TCP_OPTION)
198			xtables_error(PARAMETER_PROBLEM,
199				   "Only one `--tcp-option' allowed");
200		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
201		parse_tcp_option(optarg, &tcpinfo->option);
202		if (invert)
203			tcpinfo->invflags |= XT_TCP_INV_OPTION;
204		*flags |= TCP_OPTION;
205		break;
206	}
207
208	return 1;
209}
210
211static char *
212port_to_service(int port)
213{
214	struct servent *service;
215
216	if ((service = getservbyport(htons(port), "tcp")))
217		return service->s_name;
218
219	return NULL;
220}
221
222static void
223print_port(uint16_t port, int numeric)
224{
225	char *service;
226
227	if (numeric || (service = port_to_service(port)) == NULL)
228		printf("%u", port);
229	else
230		printf("%s", service);
231}
232
233static void
234print_ports(const char *name, uint16_t min, uint16_t max,
235	    int invert, int numeric)
236{
237	const char *inv = invert ? "!" : "";
238
239	if (min != 0 || max != 0xFFFF || invert) {
240		printf("%s", name);
241		if (min == max) {
242			printf(":%s", inv);
243			print_port(min, numeric);
244		} else {
245			printf("s:%s", inv);
246			print_port(min, numeric);
247			printf(":");
248			print_port(max, numeric);
249		}
250		printf(" ");
251	}
252}
253
254static void
255print_option(uint8_t option, int invert, int numeric)
256{
257	if (option || invert)
258		printf("option=%s%u ", invert ? "!" : "", option);
259}
260
261static void
262print_tcpf(uint8_t flags)
263{
264	int have_flag = 0;
265
266	while (flags) {
267		unsigned int i;
268
269		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
270
271		if (have_flag)
272			printf(",");
273		printf("%s", tcp_flag_names[i].name);
274		have_flag = 1;
275
276		flags &= ~tcp_flag_names[i].flag;
277	}
278
279	if (!have_flag)
280		printf("NONE");
281}
282
283static void
284print_flags(uint8_t mask, uint8_t cmp, int invert, int numeric)
285{
286	if (mask || invert) {
287		printf("flags:%s", invert ? "!" : "");
288		if (numeric)
289			printf("0x%02X/0x%02X ", mask, cmp);
290		else {
291			print_tcpf(mask);
292			printf("/");
293			print_tcpf(cmp);
294			printf(" ");
295		}
296	}
297}
298
299static void
300tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
301{
302	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
303
304	printf("tcp ");
305	print_ports("spt", tcp->spts[0], tcp->spts[1],
306		    tcp->invflags & XT_TCP_INV_SRCPT,
307		    numeric);
308	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
309		    tcp->invflags & XT_TCP_INV_DSTPT,
310		    numeric);
311	print_option(tcp->option,
312		     tcp->invflags & XT_TCP_INV_OPTION,
313		     numeric);
314	print_flags(tcp->flg_mask, tcp->flg_cmp,
315		    tcp->invflags & XT_TCP_INV_FLAGS,
316		    numeric);
317	if (tcp->invflags & ~XT_TCP_INV_MASK)
318		printf("Unknown invflags: 0x%X ",
319		       tcp->invflags & ~XT_TCP_INV_MASK);
320}
321
322static void tcp_save(const void *ip, const struct xt_entry_match *match)
323{
324	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
325
326	if (tcpinfo->spts[0] != 0
327	    || tcpinfo->spts[1] != 0xFFFF) {
328		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
329			printf("! ");
330		if (tcpinfo->spts[0]
331		    != tcpinfo->spts[1])
332			printf("--sport %u:%u ",
333			       tcpinfo->spts[0],
334			       tcpinfo->spts[1]);
335		else
336			printf("--sport %u ",
337			       tcpinfo->spts[0]);
338	}
339
340	if (tcpinfo->dpts[0] != 0
341	    || tcpinfo->dpts[1] != 0xFFFF) {
342		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
343			printf("! ");
344		if (tcpinfo->dpts[0]
345		    != tcpinfo->dpts[1])
346			printf("--dport %u:%u ",
347			       tcpinfo->dpts[0],
348			       tcpinfo->dpts[1]);
349		else
350			printf("--dport %u ",
351			       tcpinfo->dpts[0]);
352	}
353
354	if (tcpinfo->option
355	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
356		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
357			printf("! ");
358		printf("--tcp-option %u ", tcpinfo->option);
359	}
360
361	if (tcpinfo->flg_mask
362	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
363		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
364			printf("! ");
365		printf("--tcp-flags ");
366		if (tcpinfo->flg_mask != 0xFF) {
367			print_tcpf(tcpinfo->flg_mask);
368		}
369		printf(" ");
370		print_tcpf(tcpinfo->flg_cmp);
371		printf(" ");
372	}
373}
374
375static struct xtables_match tcp_match = {
376	.family		= NFPROTO_UNSPEC,
377	.name		= "tcp",
378	.version	= XTABLES_VERSION,
379	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
380	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
381	.help		= tcp_help,
382	.init		= tcp_init,
383	.parse		= tcp_parse,
384	.print		= tcp_print,
385	.save		= tcp_save,
386	.extra_opts	= tcp_opts,
387};
388
389void
390_init(void)
391{
392	xtables_register_match(&tcp_match);
393}
394