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 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 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 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 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 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 } 127 128 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 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 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 } 210 211 static const char * 212 port_to_service(int port) 213 { 214 const struct servent *service; 215 216 if ((service = getservbyport(htons(port), "tcp"))) 217 return service->s_name; 218 219 return NULL; 220 } 221 222 static void 223 print_port(uint16_t port, int numeric) 224 { 225 const char *service; 226 227 if (numeric || (service = port_to_service(port)) == NULL) 228 printf("%u", port); 229 else 230 printf("%s", service); 231 } 232 233 static void 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 (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 } 251 } 252 253 static void 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 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 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 printf(" "); 291 print_tcpf(mask); 292 printf("/"); 293 print_tcpf(cmp); 294 } 295 } 296 } 297 298 static void 299 tcp_print(const void *ip, const struct xt_entry_match *match, int numeric) 300 { 301 const struct xt_tcp *tcp = (struct xt_tcp *)match->data; 302 303 printf(" tcp"); 304 print_ports("spt", tcp->spts[0], tcp->spts[1], 305 tcp->invflags & XT_TCP_INV_SRCPT, 306 numeric); 307 print_ports("dpt", tcp->dpts[0], tcp->dpts[1], 308 tcp->invflags & XT_TCP_INV_DSTPT, 309 numeric); 310 print_option(tcp->option, 311 tcp->invflags & XT_TCP_INV_OPTION, 312 numeric); 313 print_flags(tcp->flg_mask, tcp->flg_cmp, 314 tcp->invflags & XT_TCP_INV_FLAGS, 315 numeric); 316 if (tcp->invflags & ~XT_TCP_INV_MASK) 317 printf(" Unknown invflags: 0x%X", 318 tcp->invflags & ~XT_TCP_INV_MASK); 319 } 320 321 static void tcp_save(const void *ip, const struct xt_entry_match *match) 322 { 323 const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data; 324 325 if (tcpinfo->spts[0] != 0 326 || tcpinfo->spts[1] != 0xFFFF) { 327 if (tcpinfo->invflags & XT_TCP_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 (tcpinfo->dpts[0] != 0 340 || tcpinfo->dpts[1] != 0xFFFF) { 341 if (tcpinfo->invflags & XT_TCP_INV_DSTPT) 342 printf(" !"); 343 if (tcpinfo->dpts[0] 344 != tcpinfo->dpts[1]) 345 printf(" --dport %u:%u", 346 tcpinfo->dpts[0], 347 tcpinfo->dpts[1]); 348 else 349 printf(" --dport %u", 350 tcpinfo->dpts[0]); 351 } 352 353 if (tcpinfo->option 354 || (tcpinfo->invflags & XT_TCP_INV_OPTION)) { 355 if (tcpinfo->invflags & XT_TCP_INV_OPTION) 356 printf(" !"); 357 printf(" --tcp-option %u", tcpinfo->option); 358 } 359 360 if (tcpinfo->flg_mask 361 || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) { 362 if (tcpinfo->invflags & XT_TCP_INV_FLAGS) 363 printf(" !"); 364 printf(" --tcp-flags "); 365 if (tcpinfo->flg_mask != 0xFF) { 366 print_tcpf(tcpinfo->flg_mask); 367 } 368 printf(" "); 369 print_tcpf(tcpinfo->flg_cmp); 370 } 371 } 372 373 static struct xtables_match tcp_match = { 374 .family = NFPROTO_UNSPEC, 375 .name = "tcp", 376 .version = XTABLES_VERSION, 377 .size = XT_ALIGN(sizeof(struct xt_tcp)), 378 .userspacesize = XT_ALIGN(sizeof(struct xt_tcp)), 379 .help = tcp_help, 380 .init = tcp_init, 381 .parse = tcp_parse, 382 .print = tcp_print, 383 .save = tcp_save, 384 .extra_opts = tcp_opts, 385 }; 386 387 void 388 _init(void) 389 { 390 xtables_register_match(&tcp_match); 391 } 392
