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 = xtables_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 = xtables_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
skip_ports_match(uint16_t min,uint16_t max,bool inv)228 static bool skip_ports_match(uint16_t min, uint16_t max, bool inv)
229 {
230 return min == 0 && max == UINT16_MAX && !inv;
231 }
232
233 static void
print_ports(const char * name,uint16_t min,uint16_t max,int invert,int numeric)234 print_ports(const char *name, uint16_t min, uint16_t max,
235 int invert, int numeric)
236 {
237 const char *inv = invert ? "!" : "";
238
239 if (!skip_ports_match(min, max, 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 }
251 }
252
253 static void
print_option(uint8_t option,int invert,int numeric)254 print_option(uint8_t option, int invert, int numeric)
255 {
256 if (option || invert)
257 printf(" option=%s%u", invert ? "!" : "", option);
258 }
259
260 static void
print_tcpf(uint8_t flags)261 print_tcpf(uint8_t flags)
262 {
263 int have_flag = 0;
264
265 while (flags) {
266 unsigned int i;
267
268 for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
269
270 if (have_flag)
271 printf(",");
272 printf("%s", tcp_flag_names[i].name);
273 have_flag = 1;
274
275 flags &= ~tcp_flag_names[i].flag;
276 }
277
278 if (!have_flag)
279 printf("NONE");
280 }
281
282 static void
print_flags(uint8_t mask,uint8_t cmp,int invert,int numeric)283 print_flags(uint8_t mask, uint8_t cmp, int invert, int numeric)
284 {
285 if (mask || invert) {
286 printf(" flags:%s", invert ? "!" : "");
287 if (numeric)
288 printf("0x%02X/0x%02X", mask, cmp);
289 else {
290 print_tcpf(mask);
291 printf("/");
292 print_tcpf(cmp);
293 }
294 }
295 }
296
297 static void
tcp_print(const void * ip,const struct xt_entry_match * match,int numeric)298 tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
299 {
300 const struct xt_tcp *tcp = (struct xt_tcp *)match->data;
301
302 printf(" tcp");
303 print_ports("spt", tcp->spts[0], tcp->spts[1],
304 tcp->invflags & XT_TCP_INV_SRCPT,
305 numeric);
306 print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
307 tcp->invflags & XT_TCP_INV_DSTPT,
308 numeric);
309 print_option(tcp->option,
310 tcp->invflags & XT_TCP_INV_OPTION,
311 numeric);
312 print_flags(tcp->flg_mask, tcp->flg_cmp,
313 tcp->invflags & XT_TCP_INV_FLAGS,
314 numeric);
315 if (tcp->invflags & ~XT_TCP_INV_MASK)
316 printf(" Unknown invflags: 0x%X",
317 tcp->invflags & ~XT_TCP_INV_MASK);
318 }
319
tcp_save(const void * ip,const struct xt_entry_match * match)320 static void tcp_save(const void *ip, const struct xt_entry_match *match)
321 {
322 const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;
323 bool inv_srcpt = tcpinfo->invflags & XT_TCP_INV_SRCPT;
324 bool inv_dstpt = tcpinfo->invflags & XT_TCP_INV_DSTPT;
325
326 if (!skip_ports_match(tcpinfo->spts[0], tcpinfo->spts[1], inv_srcpt)) {
327 if (inv_srcpt)
328 printf(" !");
329 if (tcpinfo->spts[0]
330 != tcpinfo->spts[1])
331 printf(" --sport %u:%u",
332 tcpinfo->spts[0],
333 tcpinfo->spts[1]);
334 else
335 printf(" --sport %u",
336 tcpinfo->spts[0]);
337 }
338
339 if (!skip_ports_match(tcpinfo->dpts[0], tcpinfo->dpts[1], inv_dstpt)) {
340 if (inv_dstpt)
341 printf(" !");
342 if (tcpinfo->dpts[0]
343 != tcpinfo->dpts[1])
344 printf(" --dport %u:%u",
345 tcpinfo->dpts[0],
346 tcpinfo->dpts[1]);
347 else
348 printf(" --dport %u",
349 tcpinfo->dpts[0]);
350 }
351
352 if (tcpinfo->option
353 || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
354 if (tcpinfo->invflags & XT_TCP_INV_OPTION)
355 printf(" !");
356 printf(" --tcp-option %u", tcpinfo->option);
357 }
358
359 if (tcpinfo->flg_mask
360 || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
361 if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
362 printf(" !");
363 printf(" --tcp-flags ");
364 print_tcpf(tcpinfo->flg_mask);
365 printf(" ");
366 print_tcpf(tcpinfo->flg_cmp);
367 }
368 }
369
370 static const struct tcp_flag_names tcp_flag_names_xlate[] = {
371 { "fin", 0x01 },
372 { "syn", 0x02 },
373 { "rst", 0x04 },
374 { "psh", 0x08 },
375 { "ack", 0x10 },
376 { "urg", 0x20 },
377 };
378
print_tcp_xlate(struct xt_xlate * xl,uint8_t flags)379 static void print_tcp_xlate(struct xt_xlate *xl, uint8_t flags)
380 {
381 int have_flag = 0;
382
383 while (flags) {
384 unsigned int i;
385
386 for (i = 0; (flags & tcp_flag_names_xlate[i].flag) == 0; i++);
387
388 xt_xlate_add(xl, "%s%s",
389 have_flag ? "," : "",
390 tcp_flag_names_xlate[i].name);
391 have_flag = 1;
392
393 flags &= ~tcp_flag_names_xlate[i].flag;
394 }
395
396 if (!have_flag)
397 xt_xlate_add(xl, "0x0");
398 }
399
tcp_xlate(struct xt_xlate * xl,const struct xt_xlate_mt_params * params)400 static int tcp_xlate(struct xt_xlate *xl,
401 const struct xt_xlate_mt_params *params)
402 {
403 const struct xt_tcp *tcpinfo =
404 (const struct xt_tcp *)params->match->data;
405 bool inv_srcpt = tcpinfo->invflags & XT_TCP_INV_SRCPT;
406 bool inv_dstpt = tcpinfo->invflags & XT_TCP_INV_DSTPT;
407 bool xlated = false;
408
409 if (!skip_ports_match(tcpinfo->spts[0], tcpinfo->spts[1], inv_srcpt)) {
410 if (tcpinfo->spts[0] != tcpinfo->spts[1]) {
411 xt_xlate_add(xl, "tcp sport %s%u-%u",
412 inv_srcpt ? "!= " : "",
413 tcpinfo->spts[0], tcpinfo->spts[1]);
414 } else {
415 xt_xlate_add(xl, "tcp sport %s%u",
416 inv_srcpt ? "!= " : "",
417 tcpinfo->spts[0]);
418 }
419 xlated = true;
420 }
421
422 if (!skip_ports_match(tcpinfo->dpts[0], tcpinfo->dpts[1], inv_dstpt)) {
423 if (tcpinfo->dpts[0] != tcpinfo->dpts[1]) {
424 xt_xlate_add(xl, "tcp dport %s%u-%u",
425 inv_dstpt ? "!= " : "",
426 tcpinfo->dpts[0], tcpinfo->dpts[1]);
427 } else {
428 xt_xlate_add(xl, "tcp dport %s%u",
429 inv_dstpt ? "!= " : "",
430 tcpinfo->dpts[0]);
431 }
432 xlated = true;
433 }
434
435 if (tcpinfo->option) {
436 xt_xlate_add(xl, "tcp option %u %s", tcpinfo->option,
437 tcpinfo->invflags & XT_TCP_INV_OPTION ?
438 "missing" : "exists");
439 xlated = true;
440 }
441
442 if (tcpinfo->flg_mask || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
443 xt_xlate_add(xl, "tcp flags %s",
444 tcpinfo->invflags & XT_TCP_INV_FLAGS ? "!= ": "");
445 print_tcp_xlate(xl, tcpinfo->flg_cmp);
446 xt_xlate_add(xl, " / ");
447 print_tcp_xlate(xl, tcpinfo->flg_mask);
448 xlated = true;
449 }
450
451 if (!xlated)
452 xt_xlate_add(xl, "meta l4proto tcp");
453
454 return 1;
455 }
456
457 static struct xtables_match tcp_match = {
458 .family = NFPROTO_UNSPEC,
459 .name = "tcp",
460 .version = XTABLES_VERSION,
461 .size = XT_ALIGN(sizeof(struct xt_tcp)),
462 .userspacesize = XT_ALIGN(sizeof(struct xt_tcp)),
463 .help = tcp_help,
464 .init = tcp_init,
465 .parse = tcp_parse,
466 .print = tcp_print,
467 .save = tcp_save,
468 .extra_opts = tcp_opts,
469 .xlate = tcp_xlate,
470 };
471
472 void
_init(void)473 _init(void)
474 {
475 xtables_register_match(&tcp_match);
476 }
477