extensions/libipt_tcp.c

   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 <iptables.h>
   8 #include <linux/netfilter_ipv4/ip_tables.h>
   9
  10 /* Function which prints out usage message. */
  11 static void
  12 help(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 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",
  27 IPTABLES_VERSION);
  28 }
  29
  30 static struct option opts[] = {
  31         { "source-port", 1, 0, '1' },
  32         { "sport", 1, 0, '1' }, /* synonym */
  33         { "destination-port", 1, 0, '2' },
  34         { "dport", 1, 0, '2' }, /* synonym */
  35         { "syn", 0, 0, '3' },
  36         { "tcp-flags", 1, 0, '4' },
  37         { "tcp-option", 1, 0, '5' },
  38         {0}
  39 };
  40
  41 static int
  42 service_to_port(const char *name)
  43 {
  44         struct servent *service;
  45
  46         if ((service = getservbyname(name, "tcp")) != NULL)
  47                 return ntohs((unsigned short) service->s_port);
  48
  49         return -1;
  50 }
  51
  52 static u_int16_t
  53 parse_tcp_port(const char *port)
  54 {
  55         unsigned int portnum;
  56
  57         if (string_to_number(port, 0, 65535, &portnum) != -1 ||
  58             (portnum = service_to_port(port)) != -1)
  59                 return (u_int16_t)portnum;
  60
  61         exit_error(PARAMETER_PROBLEM,
  62                    "invalid TCP port/service `%s' specified", port);
  63 }
  64
  65 static void
  66 parse_tcp_ports(const char *portstring, u_int16_t *ports)
  67 {
  68         char *buffer;
  69         char *cp;
  70
  71         buffer = strdup(portstring);
  72         if ((cp = strchr(buffer, ':')) == NULL)
  73                 ports[0] = ports[1] = parse_tcp_port(buffer);
  74         else {
  75                 *cp = '\0';
  76                 cp++;
  77
  78                 ports[0] = buffer[0] ? parse_tcp_port(buffer) : 0;
  79                 ports[1] = cp[0] ? parse_tcp_port(cp) : 0xFFFF;
  80
  81                 if (ports[0] > ports[1])
  82                         exit_error(PARAMETER_PROBLEM,
  83                                    "invalid portrange (min > max)");
  84         }
  85         free(buffer);
  86 }
  87
  88 struct tcp_flag_names {
  89         const char *name;
  90         unsigned int flag;
  91 };
  92
  93 static struct tcp_flag_names tcp_flag_names[]
  94 = { { "FIN", 0x01 },
  95     { "SYN", 0x02 },
  96     { "RST", 0x04 },
  97     { "PSH", 0x08 },
  98     { "ACK", 0x10 },
  99     { "URG", 0x20 },
 100     { "ALL", 0x3F },
 101     { "NONE", 0 },
 102 };
 103
 104 static unsigned int
 105 parse_tcp_flag(const char *flags)
 106 {
 107         unsigned int ret = 0;
 108         char *ptr;
 109         char *buffer;
 110
 111         buffer = strdup(flags);
 112
 113         for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
 114                 unsigned int i;
 115                 for (i = 0;
 116                      i < sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names);
 117                      i++) {
 118                         if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
 119                                 ret |= tcp_flag_names[i].flag;
 120                                 break;
 121                         }
 122                 }
 123                 if (i == sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names))
 124                         exit_error(PARAMETER_PROBLEM,
 125                                    "Unknown TCP flag `%s'", ptr);
 126                 }
 127
 128         free(buffer);
 129         return ret;
 130 }
 131
 132 static void
 133 parse_tcp_flags(struct ipt_tcp *tcpinfo,
 134                 const char *mask,
 135                 const char *cmp,
 136                 int invert)
 137 {
 138         tcpinfo->flg_mask = parse_tcp_flag(mask);
 139         tcpinfo->flg_cmp = parse_tcp_flag(cmp);
 140
 141         if (invert)
 142                 tcpinfo->invflags |= IPT_TCP_INV_FLAGS;
 143 }
 144
 145 static void
 146 parse_tcp_option(const char *option, u_int8_t *result)
 147 {
 148         unsigned int ret;
 149
 150         if (string_to_number(option, 1, 255, &ret) == -1)
 151                 exit_error(PARAMETER_PROBLEM, "Bad TCP option `%s'", option);
 152
 153         *result = (u_int8_t)ret;
 154 }
 155
 156 /* Initialize the match. */
 157 static void
 158 init(struct ipt_entry_match *m, unsigned int *nfcache)
 159 {
 160         struct ipt_tcp *tcpinfo = (struct ipt_tcp *)m->data;
 161
 162         tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
 163 }
 164
 165 #define TCP_SRC_PORTS 0x01
 166 #define TCP_DST_PORTS 0x02
 167 #define TCP_FLAGS 0x04
 168 #define TCP_OPTION      0x08
 169
 170 /* Function which parses command options; returns true if it
 171    ate an option. */
 172 static int
 173 parse(int c, char **argv, int invert, unsigned int *flags,
 174       const struct ipt_entry *entry,
 175       unsigned int *nfcache,
 176       struct ipt_entry_match **match)
 177 {
 178         struct ipt_tcp *tcpinfo = (struct ipt_tcp *)(*match)->data;
 179
 180         switch (c) {
 181         case '1':
 182                 if (*flags & TCP_SRC_PORTS)
 183                         exit_error(PARAMETER_PROBLEM,
 184                                    "Only one `--source-port' allowed");
 185                 check_inverse(optarg, &invert, &optind, 0);
 186                 parse_tcp_ports(argv[optind-1], tcpinfo->spts);
 187                 if (invert)
 188                         tcpinfo->invflags |= IPT_TCP_INV_SRCPT;
 189                 *flags |= TCP_SRC_PORTS;
 190                 *nfcache |= NFC_IP_SRC_PT;
 191                 break;
 192
 193         case '2':
 194                 if (*flags & TCP_DST_PORTS)
 195                         exit_error(PARAMETER_PROBLEM,
 196                                    "Only one `--destination-port' allowed");
 197                 check_inverse(optarg, &invert, &optind, 0);
 198                 parse_tcp_ports(argv[optind-1], tcpinfo->dpts);
 199                 if (invert)
 200                         tcpinfo->invflags |= IPT_TCP_INV_DSTPT;
 201                 *flags |= TCP_DST_PORTS;
 202                 *nfcache |= NFC_IP_DST_PT;
 203                 break;
 204
 205         case '3':
 206                 if (*flags & TCP_FLAGS)
 207                         exit_error(PARAMETER_PROBLEM,
 208                                    "Only one of `--syn' or `--tcp-flags' "
 209                                    " allowed");
 210                 parse_tcp_flags(tcpinfo, "SYN,RST,ACK", "SYN", invert);
 211                 *flags |= TCP_FLAGS;
 212                 *nfcache |= NFC_IP_TCPFLAGS;
 213                 break;
 214
 215         case '4':
 216                 if (*flags & TCP_FLAGS)
 217                         exit_error(PARAMETER_PROBLEM,
 218                                    "Only one of `--syn' or `--tcp-flags' "
 219                                    " allowed");
 220                 check_inverse(optarg, &invert, &optind, 0);
 221
 222                 if (!argv[optind]
 223                     || argv[optind][0] == '-' || argv[optind][0] == '!')
 224                         exit_error(PARAMETER_PROBLEM,
 225                                    "--tcp-flags requires two args.");
 226
 227                 parse_tcp_flags(tcpinfo, argv[optind-1], argv[optind],
 228                                 invert);
 229                 optind++;
 230                 *flags |= TCP_FLAGS;
 231                 *nfcache |= NFC_IP_TCPFLAGS;
 232                 break;
 233
 234         case '5':
 235                 if (*flags & TCP_OPTION)
 236                         exit_error(PARAMETER_PROBLEM,
 237                                    "Only one `--tcp-option' allowed");
 238                 check_inverse(optarg, &invert, &optind, 0);
 239                 parse_tcp_option(argv[optind-1], &tcpinfo->option);
 240                 if (invert)
 241                         tcpinfo->invflags |= IPT_TCP_INV_OPTION;
 242                 *flags |= TCP_OPTION;
 243                 *nfcache |= NFC_IP_PROTO_UNKNOWN;
 244                 break;
 245
 246         default:
 247                 return 0;
 248         }
 249
 250         return 1;
 251 }
 252
 253 /* Final check; we don't care. */
 254 static void
 255 final_check(unsigned int flags)
 256 {
 257 }
 258
 259 static char *
 260 port_to_service(int port)
 261 {
 262         struct servent *service;
 263
 264         if ((service = getservbyport(htons(port), "tcp")))
 265                 return service->s_name;
 266
 267         return NULL;
 268 }
 269
 270 static void
 271 print_port(u_int16_t port, int numeric)
 272 {
 273         char *service;
 274
 275         if (numeric || (service = port_to_service(port)) == NULL)
 276                 printf("%u", port);
 277         else
 278                 printf("%s", service);
 279 }
 280
 281 static void
 282 print_ports(const char *name, u_int16_t min, u_int16_t max,
 283             int invert, int numeric)
 284 {
 285         const char *inv = invert ? "!" : "";
 286
 287         if (min != 0 || max != 0xFFFF || invert) {
 288                 printf("%s", name);
 289                 if (min == max) {
 290                         printf(":%s", inv);
 291                         print_port(min, numeric);
 292                 } else {
 293                         printf("s:%s", inv);
 294                         print_port(min, numeric);
 295                         printf(":");
 296                         print_port(max, numeric);
 297                 }
 298                 printf(" ");
 299         }
 300 }
 301
 302 static void
 303 print_option(u_int8_t option, int invert, int numeric)
 304 {
 305         if (option || invert)
 306                 printf("option=%s%u ", invert ? "!" : "", option);
 307 }
 308
 309 static void
 310 print_tcpf(u_int8_t flags)
 311 {
 312         int have_flag = 0;
 313
 314         while (flags) {
 315                 unsigned int i;
 316
 317                 for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
 318
 319                 if (have_flag)
 320                         printf(",");
 321                 printf("%s", tcp_flag_names[i].name);
 322                 have_flag = 1;
 323
 324                 flags &= ~tcp_flag_names[i].flag;
 325         }
 326
 327         if (!have_flag)
 328                 printf("NONE");
 329 }
 330
 331 static void
 332 print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
 333 {
 334         if (mask || invert) {
 335                 printf("flags:%s", invert ? "!" : "");
 336                 if (numeric)
 337                         printf("0x%02X/0x%02X ", mask, cmp);
 338                 else {
 339                         print_tcpf(mask);
 340                         printf("/");
 341                         print_tcpf(cmp);
 342                         printf(" ");
 343                 }
 344         }
 345 }
 346
 347 /* Prints out the union ipt_matchinfo. */
 348 static void
 349 print(const struct ipt_ip *ip,
 350       const struct ipt_entry_match *match, int numeric)
 351 {
 352         const struct ipt_tcp *tcp = (struct ipt_tcp *)match->data;
 353
 354         printf("tcp ");
 355         print_ports("spt", tcp->spts[0], tcp->spts[1],
 356                     tcp->invflags & IPT_TCP_INV_SRCPT,
 357                     numeric);
 358         print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
 359                     tcp->invflags & IPT_TCP_INV_DSTPT,
 360                     numeric);
 361         print_option(tcp->option,
 362                      tcp->invflags & IPT_TCP_INV_OPTION,
 363                      numeric);
 364         print_flags(tcp->flg_mask, tcp->flg_cmp,
 365                     tcp->invflags & IPT_TCP_INV_FLAGS,
 366                     numeric);
 367         if (tcp->invflags & ~IPT_TCP_INV_MASK)
 368                 printf("Unknown invflags: 0x%X ",
 369                        tcp->invflags & ~IPT_TCP_INV_MASK);
 370 }
 371
 372 /* Saves the union ipt_matchinfo in parsable form to stdout. */
 373 static void save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
 374 {
 375         const struct ipt_tcp *tcpinfo = (struct ipt_tcp *)match->data;
 376
 377         if (tcpinfo->spts[0] != 0
 378             || tcpinfo->spts[1] != 0xFFFF) {
 379                 if (tcpinfo->invflags & IPT_TCP_INV_SRCPT)
 380                         printf("! ");
 381                 if (tcpinfo->spts[0]
 382                     != tcpinfo->spts[1])
 383                         printf("--sport %u:%u ",
 384                                tcpinfo->spts[0],
 385                                tcpinfo->spts[1]);
 386                 else
 387                         printf("--sport %u ",
 388                                tcpinfo->spts[0]);
 389         }
 390
 391         if (tcpinfo->dpts[0] != 0
 392             || tcpinfo->dpts[1] != 0xFFFF) {
 393                 if (tcpinfo->invflags & IPT_TCP_INV_DSTPT)
 394                         printf("! ");
 395                 if (tcpinfo->dpts[0]
 396                     != tcpinfo->dpts[1])
 397                         printf("--dport %u:%u ",
 398                                tcpinfo->dpts[0],
 399                                tcpinfo->dpts[1]);
 400                 else
 401                         printf("--dport %u ",
 402                                tcpinfo->dpts[0]);
 403         }
 404
 405         if (tcpinfo->option
 406             || (tcpinfo->invflags & IPT_TCP_INV_OPTION)) {
 407                 if (tcpinfo->invflags & IPT_TCP_INV_OPTION)
 408                         printf("! ");
 409                 printf("--tcp-option %u ", tcpinfo->option);
 410         }
 411
 412         if (tcpinfo->flg_mask
 413             || (tcpinfo->invflags & IPT_TCP_INV_FLAGS)) {
 414                 if (tcpinfo->invflags & IPT_TCP_INV_FLAGS)
 415                         printf("! ");
 416                 printf("--tcp-flags ");
 417                 if (tcpinfo->flg_mask != 0xFF) {
 418                         print_tcpf(tcpinfo->flg_mask);
 419                 }
 420                 printf(" ");
 421                 print_tcpf(tcpinfo->flg_cmp);
 422                 printf(" ");
 423         }
 424 }
 425
 426 static
 427 struct iptables_match tcp
 428 = { NULL,
 429     "tcp",
 430     IPTABLES_VERSION,
 431     IPT_ALIGN(sizeof(struct ipt_tcp)),
 432     IPT_ALIGN(sizeof(struct ipt_tcp)),
 433     &help,
 434     &init,
 435     &parse,
 436     &final_check,
 437     &print,
 438     &save,
 439     opts };
 440
 441 void
 442 _init(void)
 443 {
 444         register_match(&tcp);
 445 }