libxt_tcp.c revision 0e2abed11985e16215559cefd90625f99317b96c 
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, NULL, '1' },
32	{ "sport", 1, NULL, '1' }, /* synonym */
33	{ "destination-port", 1, NULL, '2' },
34	{ "dport", 1, NULL, '2' }, /* synonym */
35	{ "syn", 0, NULL, '3' },
36	{ "tcp-flags", 1, NULL, '4' },
37	{ "tcp-option", 1, NULL, '5' },
38	{ }
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 const 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)
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      struct xt_entry_match **match)
152{
153	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;
154
155	switch (c) {
156	case '1':
157		if (*flags & TCP_SRC_PORTS)
158			exit_error(PARAMETER_PROBLEM,
159				   "Only one `--source-port' allowed");
160		check_inverse(optarg, &invert, &optind, 0);
161		parse_tcp_ports(argv[optind-1], tcpinfo->spts);
162		if (invert)
163			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
164		*flags |= TCP_SRC_PORTS;
165		break;
166
167	case '2':
168		if (*flags & TCP_DST_PORTS)
169			exit_error(PARAMETER_PROBLEM,
170				   "Only one `--destination-port' allowed");
171		check_inverse(optarg, &invert, &optind, 0);
172		parse_tcp_ports(argv[optind-1], tcpinfo->dpts);
173		if (invert)
174			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
175		*flags |= TCP_DST_PORTS;
176		break;
177
178	case '3':
179		if (*flags & TCP_FLAGS)
180			exit_error(PARAMETER_PROBLEM,
181				   "Only one of `--syn' or `--tcp-flags' "
182				   " allowed");
183		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
184		*flags |= TCP_FLAGS;
185		break;
186
187	case '4':
188		if (*flags & TCP_FLAGS)
189			exit_error(PARAMETER_PROBLEM,
190				   "Only one of `--syn' or `--tcp-flags' "
191				   " allowed");
192		check_inverse(optarg, &invert, &optind, 0);
193
194		if (!argv[optind]
195		    || argv[optind][0] == '-' || argv[optind][0] == '!')
196			exit_error(PARAMETER_PROBLEM,
197				   "--tcp-flags requires two args.");
198
199		parse_tcp_flags(tcpinfo, argv[optind-1], argv[optind],
200				invert);
201		optind++;
202		*flags |= TCP_FLAGS;
203		break;
204
205	case '5':
206		if (*flags & TCP_OPTION)
207			exit_error(PARAMETER_PROBLEM,
208				   "Only one `--tcp-option' allowed");
209		check_inverse(optarg, &invert, &optind, 0);
210		parse_tcp_option(argv[optind-1], &tcpinfo->option);
211		if (invert)
212			tcpinfo->invflags |= XT_TCP_INV_OPTION;
213		*flags |= TCP_OPTION;
214		break;
215
216	default:
217		return 0;
218	}
219
220	return 1;
221}
222
223static char *
224port_to_service(int port)
225{
226	struct servent *service;
227
228	if ((service = getservbyport(htons(port), "tcp")))
229		return service->s_name;
230
231	return NULL;
232}
233
234static void
235print_port(u_int16_t port, int numeric)
236{
237	char *service;
238
239	if (numeric || (service = port_to_service(port)) == NULL)
240		printf("%u", port);
241	else
242		printf("%s", service);
243}
244
245static void
246print_ports(const char *name, u_int16_t min, u_int16_t max,
247	    int invert, int numeric)
248{
249	const char *inv = invert ? "!" : "";
250
251	if (min != 0 || max != 0xFFFF || invert) {
252		printf("%s", name);
253		if (min == max) {
254			printf(":%s", inv);
255			print_port(min, numeric);
256		} else {
257			printf("s:%s", inv);
258			print_port(min, numeric);
259			printf(":");
260			print_port(max, numeric);
261		}
262		printf(" ");
263	}
264}
265
266static void
267print_option(u_int8_t option, int invert, int numeric)
268{
269	if (option || invert)
270		printf("option=%s%u ", invert ? "!" : "", option);
271}
272
273static void
274print_tcpf(u_int8_t flags)
275{
276	int have_flag = 0;
277
278	while (flags) {
279		unsigned int i;
280
281		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
282
283		if (have_flag)
284			printf(",");
285		printf("%s", tcp_flag_names[i].name);
286		have_flag = 1;
287
288		flags &= ~tcp_flag_names[i].flag;
289	}
290
291	if (!have_flag)
292		printf("NONE");
293}
294
295static void
296print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
297{
298	if (mask || invert) {
299		printf("flags:%s", invert ? "!" : "");
300		if (numeric)
301			printf("0x%02X/0x%02X ", mask, cmp);
302		else {
303			print_tcpf(mask);
304			printf("/");
305			print_tcpf(cmp);
306			printf(" ");
307		}
308	}
309}
310
311/* Prints out the union ipt_matchinfo. */
312static void
313print(const void *ip,
314      const struct xt_entry_match *match, int numeric)
315{
316	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
317
318	printf("tcp ");
319	print_ports("spt", tcp->spts[0], tcp->spts[1],
320		    tcp->invflags & XT_TCP_INV_SRCPT,
321		    numeric);
322	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
323		    tcp->invflags & XT_TCP_INV_DSTPT,
324		    numeric);
325	print_option(tcp->option,
326		     tcp->invflags & XT_TCP_INV_OPTION,
327		     numeric);
328	print_flags(tcp->flg_mask, tcp->flg_cmp,
329		    tcp->invflags & XT_TCP_INV_FLAGS,
330		    numeric);
331	if (tcp->invflags & ~XT_TCP_INV_MASK)
332		printf("Unknown invflags: 0x%X ",
333		       tcp->invflags & ~XT_TCP_INV_MASK);
334}
335
336/* Saves the union ipt_matchinfo in parsable form to stdout. */
337static void save(const void *ip, const struct xt_entry_match *match)
338{
339	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
340
341	if (tcpinfo->spts[0] != 0
342	    || tcpinfo->spts[1] != 0xFFFF) {
343		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
344			printf("! ");
345		if (tcpinfo->spts[0]
346		    != tcpinfo->spts[1])
347			printf("--sport %u:%u ",
348			       tcpinfo->spts[0],
349			       tcpinfo->spts[1]);
350		else
351			printf("--sport %u ",
352			       tcpinfo->spts[0]);
353	}
354
355	if (tcpinfo->dpts[0] != 0
356	    || tcpinfo->dpts[1] != 0xFFFF) {
357		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
358			printf("! ");
359		if (tcpinfo->dpts[0]
360		    != tcpinfo->dpts[1])
361			printf("--dport %u:%u ",
362			       tcpinfo->dpts[0],
363			       tcpinfo->dpts[1]);
364		else
365			printf("--dport %u ",
366			       tcpinfo->dpts[0]);
367	}
368
369	if (tcpinfo->option
370	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
371		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
372			printf("! ");
373		printf("--tcp-option %u ", tcpinfo->option);
374	}
375
376	if (tcpinfo->flg_mask
377	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
378		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
379			printf("! ");
380		printf("--tcp-flags ");
381		if (tcpinfo->flg_mask != 0xFF) {
382			print_tcpf(tcpinfo->flg_mask);
383		}
384		printf(" ");
385		print_tcpf(tcpinfo->flg_cmp);
386		printf(" ");
387	}
388}
389
390static struct xtables_match tcp = {
391	.family		= AF_INET,
392	.name		= "tcp",
393	.version	= IPTABLES_VERSION,
394	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
395	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
396	.help		= &help,
397	.init		= &init,
398	.parse		= &parse,
399	.print		= &print,
400	.save		= &save,
401	.extra_opts	= opts,
402};
403
404static struct xtables_match tcp6 = {
405	.family		= AF_INET6,
406	.name		= "tcp",
407	.version	= IPTABLES_VERSION,
408	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
409	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
410	.help		= &help,
411	.init		= &init,
412	.parse		= &parse,
413	.print		= &print,
414	.save		= &save,
415	.extra_opts	= opts,
416};
417
418void
419_init(void)
420{
421	xtables_register_match(&tcp);
422	xtables_register_match(&tcp6);
423}
424