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
tcp_help(void)12 static 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
29 static 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
40 static void
parse_tcp_ports(const char * portstring,uint16_t * ports)41 parse_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
63 struct tcp_flag_names {
64 const char *name;
65 unsigned int flag;
66 };
67
68 static 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
79 static unsigned int
parse_tcp_flag(const char * flags)80 parse_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
104 static void
parse_tcp_flags(struct xt_tcp * tcpinfo,const char * mask,const char * cmp,int invert)105 parse_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
117 static void
parse_tcp_option(const char * option,uint8_t * result)118 parse_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
tcp_init(struct xt_entry_match * m)128 static 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
140 static int
tcp_parse(int c,char ** argv,int invert,unsigned int * flags,const void * entry,struct xt_entry_match ** match)141 tcp_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
206 static const char *
port_to_service(int port)207 port_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
217 static void
print_port(uint16_t port,int numeric)218 print_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
228 static void
print_ports(const char * name,uint16_t min,uint16_t max,int invert,int numeric)229 print_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
248 static void
print_option(uint8_t option,int invert,int numeric)249 print_option(uint8_t option, int invert, int numeric)
250 {
251 if (option || invert)
252 printf(" option=%s%u", invert ? "!" : "", option);
253 }
254
255 static void
print_tcpf(uint8_t flags)256 print_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
277 static void
print_flags(uint8_t mask,uint8_t cmp,int invert,int numeric)278 print_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 print_tcpf(mask);
286 printf("/");
287 print_tcpf(cmp);
288 }
289 }
290 }
291
292 static void
tcp_print(const void * ip,const struct xt_entry_match * match,int numeric)293 tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
294 {
295 const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
296
297 printf(" tcp");
298 print_ports("spt", tcp->spts[0], tcp->spts[1],
299 tcp->invflags & XT_TCP_INV_SRCPT,
300 numeric);
301 print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
302 tcp->invflags & XT_TCP_INV_DSTPT,
303 numeric);
304 print_option(tcp->option,
305 tcp->invflags & XT_TCP_INV_OPTION,
306 numeric);
307 print_flags(tcp->flg_mask, tcp->flg_cmp,
308 tcp->invflags & XT_TCP_INV_FLAGS,
309 numeric);
310 if (tcp->invflags & ~XT_TCP_INV_MASK)
311 printf(" Unknown invflags: 0x%X",
312 tcp->invflags & ~XT_TCP_INV_MASK);
313 }
314
tcp_save(const void * ip,const struct xt_entry_match * match)315 static void tcp_save(const void *ip, const struct xt_entry_match *match)
316 {
317 const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
318
319 if (tcpinfo->spts[0] != 0
320 || tcpinfo->spts[1] != 0xFFFF) {
321 if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
322 printf(" !");
323 if (tcpinfo->spts[0]
324 != tcpinfo->spts[1])
325 printf(" --sport %u:%u",
326 tcpinfo->spts[0],
327 tcpinfo->spts[1]);
328 else
329 printf(" --sport %u",
330 tcpinfo->spts[0]);
331 }
332
333 if (tcpinfo->dpts[0] != 0
334 || tcpinfo->dpts[1] != 0xFFFF) {
335 if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
336 printf(" !");
337 if (tcpinfo->dpts[0]
338 != tcpinfo->dpts[1])
339 printf(" --dport %u:%u",
340 tcpinfo->dpts[0],
341 tcpinfo->dpts[1]);
342 else
343 printf(" --dport %u",
344 tcpinfo->dpts[0]);
345 }
346
347 if (tcpinfo->option
348 || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
349 if (tcpinfo->invflags & XT_TCP_INV_OPTION)
350 printf(" !");
351 printf(" --tcp-option %u", tcpinfo->option);
352 }
353
354 if (tcpinfo->flg_mask
355 || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
356 if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
357 printf(" !");
358 printf(" --tcp-flags ");
359 print_tcpf(tcpinfo->flg_mask);
360 printf(" ");
361 print_tcpf(tcpinfo->flg_cmp);
362 }
363 }
364
365 static struct xtables_match tcp_match = {
366 .family = NFPROTO_UNSPEC,
367 .name = "tcp",
368 .version = XTABLES_VERSION,
369 .size = XT_ALIGN(sizeof(struct xt_tcp)),
370 .userspacesize = XT_ALIGN(sizeof(struct xt_tcp)),
371 .help = tcp_help,
372 .init = tcp_init,
373 .parse = tcp_parse,
374 .print = tcp_print,
375 .save = tcp_save,
376 .extra_opts = tcp_opts,
377 };
378
379 void
_init(void)380 _init(void)
381 {
382 xtables_register_match(&tcp_match);
383 }
384