networking/udhcp/dhcpd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * udhcp Server
   4  * Copyright (C) 1999 Matthew Ramsay <matthewr@moreton.com.au>
   5  *                      Chris Trew <ctrew@moreton.com.au>
   6  *
   7  * Rewrite by Russ Dill <Russ.Dill@asu.edu> July 2001
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License as published by
  11  * the Free Software Foundation; either version 2 of the License, or
  12  * (at your option) any later version.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, write to the Free Software
  21  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  22  */
  23
  24 #include <syslog.h>
  25 #include "common.h"
  26 #include "dhcpc.h"
  27 #include "dhcpd.h"
  28 #include "options.h"
  29
  30
  31 /* send a packet to gateway_nip using the kernel ip stack */
  32 static int send_packet_to_relay(struct dhcp_packet *dhcp_pkt)
  33 {
  34         log1("Forwarding packet to relay");
  35
  36         return udhcp_send_kernel_packet(dhcp_pkt,
  37                         server_config.server_nip, SERVER_PORT,
  38                         dhcp_pkt->gateway_nip, SERVER_PORT);
  39 }
  40
  41 /* send a packet to a specific mac address and ip address by creating our own ip packet */
  42 static int send_packet_to_client(struct dhcp_packet *dhcp_pkt, int force_broadcast)
  43 {
  44         const uint8_t *chaddr;
  45         uint32_t ciaddr;
  46
  47         // Was:
  48         //if (force_broadcast) { /* broadcast */ }
  49         //else if (dhcp_pkt->ciaddr) { /* unicast to dhcp_pkt->ciaddr */ }
  50         //else if (dhcp_pkt->flags & htons(BROADCAST_FLAG)) { /* broadcast */ }
  51         //else { /* unicast to dhcp_pkt->yiaddr */ }
  52         // But this is wrong: yiaddr is _our_ idea what client's IP is
  53         // (for example, from lease file). Client may not know that,
  54         // and may not have UDP socket listening on that IP!
  55         // We should never unicast to dhcp_pkt->yiaddr!
  56         // dhcp_pkt->ciaddr, OTOH, comes from client's request packet,
  57         // and can be used.
  58
  59         if (force_broadcast
  60          || (dhcp_pkt->flags & htons(BROADCAST_FLAG))
  61          || !dhcp_pkt->ciaddr
  62         ) {
  63                 log1("Broadcasting packet to client");
  64                 ciaddr = INADDR_BROADCAST;
  65                 chaddr = MAC_BCAST_ADDR;
  66         } else {
  67                 log1("Unicasting packet to client ciaddr");
  68                 ciaddr = dhcp_pkt->ciaddr;
  69                 chaddr = dhcp_pkt->chaddr;
  70         }
  71
  72         return udhcp_send_raw_packet(dhcp_pkt,
  73                 /*src*/ server_config.server_nip, SERVER_PORT,
  74                 /*dst*/ ciaddr, CLIENT_PORT, chaddr,
  75                 server_config.ifindex);
  76 }
  77
  78 /* Send the dhcp packet.
  79  * If force broadcast is set, the packet will be broadcast.
  80  */
  81 static int send_packet(struct dhcp_packet *dhcp_pkt, int force_broadcast)
  82 {
  83         if (dhcp_pkt->gateway_nip)
  84                 return send_packet_to_relay(dhcp_pkt);
  85         return send_packet_to_client(dhcp_pkt, force_broadcast);
  86 }
  87
  88 static void init_packet(struct dhcp_packet *packet, struct dhcp_packet *oldpacket, char type)
  89 {
  90         udhcp_init_header(packet, type);
  91         packet->xid = oldpacket->xid;
  92         memcpy(packet->chaddr, oldpacket->chaddr, sizeof(oldpacket->chaddr));
  93         packet->flags = oldpacket->flags;
  94         packet->gateway_nip = oldpacket->gateway_nip;
  95         packet->ciaddr = oldpacket->ciaddr;
  96         add_simple_option(packet->options, DHCP_SERVER_ID, server_config.server_nip);
  97 }
  98
  99 /* Fill options field, siaddr_nip, and sname and boot_file fields.
 100  * TODO: teach this code to use overload option.
 101  */
 102 static void add_server_options(struct dhcp_packet *packet)
 103 {
 104         struct option_set *curr = server_config.options;
 105
 106         while (curr) {
 107                 if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
 108                         add_option_string(packet->options, curr->data);
 109                 curr = curr->next;
 110         }
 111
 112         packet->siaddr_nip = server_config.siaddr_nip;
 113
 114         if (server_config.sname)
 115                 strncpy((char*)packet->sname, server_config.sname, sizeof(packet->sname) - 1);
 116         if (server_config.boot_file)
 117                 strncpy((char*)packet->file, server_config.boot_file, sizeof(packet->file) - 1);
 118 }
 119
 120 static uint32_t select_lease_time(struct dhcp_packet *packet)
 121 {
 122         uint32_t lease_time_sec = server_config.max_lease_sec;
 123         uint8_t *lease_time_opt = get_option(packet, DHCP_LEASE_TIME);
 124         if (lease_time_opt) {
 125                 move_from_unaligned32(lease_time_sec, lease_time_opt);
 126                 lease_time_sec = ntohl(lease_time_sec);
 127                 if (lease_time_sec > server_config.max_lease_sec)
 128                         lease_time_sec = server_config.max_lease_sec;
 129                 if (lease_time_sec < server_config.min_lease_sec)
 130                         lease_time_sec = server_config.min_lease_sec;
 131         }
 132         return lease_time_sec;
 133 }
 134
 135 /* send a DHCP OFFER to a DHCP DISCOVER */
 136 static int send_offer(struct dhcp_packet *oldpacket, uint32_t static_lease_nip, struct dyn_lease *lease)
 137 {
 138         struct dhcp_packet packet;
 139         uint32_t lease_time_sec = server_config.max_lease_sec;
 140         const char *p_host_name;
 141         struct in_addr addr;
 142
 143         init_packet(&packet, oldpacket, DHCPOFFER);
 144
 145         /* ADDME: if static, short circuit */
 146         if (!static_lease_nip) {
 147                 uint32_t req_nip;
 148                 uint8_t *req_ip_opt;
 149
 150                 /* The client is in our lease/offered table */
 151                 if (lease) {
 152                         packet.yiaddr = lease->lease_nip;
 153                 }
 154                 /* Or the client has requested an IP */
 155                 else if ((req_ip_opt = get_option(oldpacket, DHCP_REQUESTED_IP)) != NULL
 156                  /* (read IP) */
 157                  && (move_from_unaligned32(req_nip, req_ip_opt), 1)
 158                  /* and the IP is in the lease range */
 159                  && ntohl(req_nip) >= server_config.start_ip
 160                  && ntohl(req_nip) <= server_config.end_ip
 161                  /* and */
 162                  && (  !(lease = find_lease_by_nip(req_nip)) /* is not already taken */
 163                     || is_expired_lease(lease) /* or is taken, but expired */
 164                     )
 165                 ) {
 166                         packet.yiaddr = req_nip;
 167                 }
 168                 /* Otherwise, find a free IP */
 169                 else {
 170                         packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr);
 171                 }
 172
 173                 if (!packet.yiaddr) {
 174                         bb_error_msg("no IP addresses to give - OFFER abandoned");
 175                         return -1;
 176                 }
 177                 p_host_name = (const char*) get_option(oldpacket, DHCP_HOST_NAME);
 178                 if (add_lease(packet.chaddr, packet.yiaddr,
 179                                 server_config.offer_time,
 180                                 p_host_name,
 181                                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 182                         ) == 0
 183                 ) {
 184                         bb_error_msg("lease pool is full - OFFER abandoned");
 185                         return -1;
 186                 }
 187                 lease_time_sec = select_lease_time(oldpacket);
 188         } else {
 189                 /* It is a static lease... use it */
 190                 packet.yiaddr = static_lease_nip;
 191         }
 192
 193         add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
 194         add_server_options(&packet);
 195
 196         addr.s_addr = packet.yiaddr;
 197         bb_info_msg("Sending OFFER of %s", inet_ntoa(addr));
 198         return send_packet(&packet, /*force_bcast:*/ 0);
 199 }
 200
 201 static int send_NAK(struct dhcp_packet *oldpacket)
 202 {
 203         struct dhcp_packet packet;
 204
 205         init_packet(&packet, oldpacket, DHCPNAK);
 206
 207         log1("Sending NAK");
 208         return send_packet(&packet, /*force_bcast:*/ 1);
 209 }
 210
 211 static int send_ACK(struct dhcp_packet *oldpacket, uint32_t yiaddr)
 212 {
 213         struct dhcp_packet packet;
 214         uint32_t lease_time_sec;
 215         struct in_addr addr;
 216         const char *p_host_name;
 217
 218         init_packet(&packet, oldpacket, DHCPACK);
 219         packet.yiaddr = yiaddr;
 220
 221         lease_time_sec = select_lease_time(oldpacket);
 222
 223         add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
 224         add_server_options(&packet);
 225
 226         addr.s_addr = packet.yiaddr;
 227         bb_info_msg("Sending ACK to %s", inet_ntoa(addr));
 228
 229         if (send_packet(&packet, /*force_bcast:*/ 0) < 0)
 230                 return -1;
 231
 232         p_host_name = (const char*) get_option(oldpacket, DHCP_HOST_NAME);
 233         add_lease(packet.chaddr, packet.yiaddr,
 234                 lease_time_sec,
 235                 p_host_name,
 236                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 237         );
 238         if (ENABLE_FEATURE_UDHCPD_WRITE_LEASES_EARLY) {
 239                 /* rewrite the file with leases at every new acceptance */
 240                 write_leases();
 241         }
 242
 243         return 0;
 244 }
 245
 246 static int send_inform(struct dhcp_packet *oldpacket)
 247 {
 248         struct dhcp_packet packet;
 249
 250         init_packet(&packet, oldpacket, DHCPACK);
 251         add_server_options(&packet);
 252
 253         return send_packet(&packet, /*force_bcast:*/ 0);
 254 }
 255
 256
 257 /* globals */
 258 struct dyn_lease *g_leases;
 259 /* struct server_config_t server_config is in bb_common_bufsiz1 */
 260
 261
 262 int udhcpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 263 int udhcpd_main(int argc UNUSED_PARAM, char **argv)
 264 {
 265         fd_set rfds;
 266         int server_socket = -1, retval, max_sock;
 267         struct dhcp_packet packet;
 268         uint8_t *state;
 269         uint32_t static_lease_nip;
 270         unsigned timeout_end;
 271         unsigned num_ips;
 272         unsigned opt;
 273         struct option_set *option;
 274         struct dyn_lease *lease, fake_lease;
 275         IF_FEATURE_UDHCP_PORT(char *str_P;)
 276
 277 #if ENABLE_FEATURE_UDHCP_PORT
 278         SERVER_PORT = 67;
 279         CLIENT_PORT = 68;
 280 #endif
 281
 282 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 283         opt_complementary = "vv";
 284 #endif
 285         opt = getopt32(argv, "fSv"
 286                 IF_FEATURE_UDHCP_PORT("P:", &str_P)
 287 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 288                 , &dhcp_verbose
 289 #endif
 290                 );
 291         argv += optind;
 292         if (!(opt & 1)) { /* no -f */
 293                 bb_daemonize_or_rexec(0, argv);
 294                 logmode = LOGMODE_NONE;
 295         }
 296         if (opt & 2) { /* -S */
 297                 openlog(applet_name, LOG_PID, LOG_DAEMON);
 298                 logmode |= LOGMODE_SYSLOG;
 299         }
 300 #if ENABLE_FEATURE_UDHCP_PORT
 301         if (opt & 4) { /* -P */
 302                 SERVER_PORT = xatou16(str_P);
 303                 CLIENT_PORT = SERVER_PORT + 1;
 304         }
 305 #endif
 306         /* Would rather not do read_config before daemonization -
 307          * otherwise NOMMU machines will parse config twice */
 308         read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE);
 309
 310         /* Make sure fd 0,1,2 are open */
 311         bb_sanitize_stdio();
 312         /* Equivalent of doing a fflush after every \n */
 313         setlinebuf(stdout);
 314
 315         /* Create pidfile */
 316         write_pidfile(server_config.pidfile);
 317         /* if (!..) bb_perror_msg("can't create pidfile %s", pidfile); */
 318
 319         bb_info_msg("%s (v"BB_VER") started", applet_name);
 320
 321         option = find_option(server_config.options, DHCP_LEASE_TIME);
 322         server_config.max_lease_sec = LEASE_TIME;
 323         if (option) {
 324                 move_from_unaligned32(server_config.max_lease_sec, option->data + OPT_DATA);
 325                 server_config.max_lease_sec = ntohl(server_config.max_lease_sec);
 326         }
 327
 328         /* Sanity check */
 329         num_ips = server_config.end_ip - server_config.start_ip + 1;
 330         if (server_config.max_leases > num_ips) {
 331                 bb_error_msg("max_leases=%u is too big, setting to %u",
 332                         (unsigned)server_config.max_leases, num_ips);
 333                 server_config.max_leases = num_ips;
 334         }
 335
 336         g_leases = xzalloc(server_config.max_leases * sizeof(g_leases[0]));
 337         read_leases(server_config.lease_file);
 338
 339         if (udhcp_read_interface(server_config.interface,
 340                         &server_config.ifindex,
 341                         &server_config.server_nip,
 342                         server_config.server_mac)
 343         ) {
 344                 retval = 1;
 345                 goto ret;
 346         }
 347
 348         /* Setup the signal pipe */
 349         udhcp_sp_setup();
 350
 351         timeout_end = monotonic_sec() + server_config.auto_time;
 352         while (1) { /* loop until universe collapses */
 353                 int bytes;
 354                 struct timeval tv;
 355
 356                 if (server_socket < 0) {
 357                         server_socket = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT,
 358                                         server_config.interface);
 359                 }
 360
 361                 max_sock = udhcp_sp_fd_set(&rfds, server_socket);
 362                 if (server_config.auto_time) {
 363                         tv.tv_sec = timeout_end - monotonic_sec();
 364                         tv.tv_usec = 0;
 365                 }
 366                 retval = 0;
 367                 if (!server_config.auto_time || tv.tv_sec > 0) {
 368                         retval = select(max_sock + 1, &rfds, NULL, NULL,
 369                                         server_config.auto_time ? &tv : NULL);
 370                 }
 371                 if (retval == 0) {
 372                         write_leases();
 373                         timeout_end = monotonic_sec() + server_config.auto_time;
 374                         continue;
 375                 }
 376                 if (retval < 0 && errno != EINTR) {
 377                         log1("Error on select");
 378                         continue;
 379                 }
 380
 381                 switch (udhcp_sp_read(&rfds)) {
 382                 case SIGUSR1:
 383                         bb_info_msg("Received a SIGUSR1");
 384                         write_leases();
 385                         /* why not just reset the timeout, eh */
 386                         timeout_end = monotonic_sec() + server_config.auto_time;
 387                         continue;
 388                 case SIGTERM:
 389                         bb_info_msg("Received a SIGTERM");
 390                         goto ret0;
 391                 case 0: /* no signal: read a packet */
 392                         break;
 393                 default: /* signal or error (probably EINTR): back to select */
 394                         continue;
 395                 }
 396
 397                 bytes = udhcp_recv_kernel_packet(&packet, server_socket);
 398                 if (bytes < 0) {
 399                         /* bytes can also be -2 ("bad packet data") */
 400                         if (bytes == -1 && errno != EINTR) {
 401                                 log1("Read error: %s, reopening socket", strerror(errno));
 402                                 close(server_socket);
 403                                 server_socket = -1;
 404                         }
 405                         continue;
 406                 }
 407
 408                 if (packet.hlen != 6) {
 409                         bb_error_msg("MAC length != 6, ignoring packet");
 410                         continue;
 411                 }
 412
 413                 state = get_option(&packet, DHCP_MESSAGE_TYPE);
 414                 if (state == NULL) {
 415                         bb_error_msg("no message type option, ignoring packet");
 416                         continue;
 417                 }
 418
 419                 /* Look for a static lease */
 420                 static_lease_nip = get_static_nip_by_mac(server_config.static_leases, &packet.chaddr);
 421                 if (static_lease_nip) {
 422                         bb_info_msg("Found static lease: %x", static_lease_nip);
 423
 424                         memcpy(&fake_lease.lease_mac, &packet.chaddr, 6);
 425                         fake_lease.lease_nip = static_lease_nip;
 426                         fake_lease.expires = 0;
 427
 428                         lease = &fake_lease;
 429                 } else {
 430                         lease = find_lease_by_mac(packet.chaddr);
 431                 }
 432
 433                 switch (state[0]) {
 434                 case DHCPDISCOVER:
 435                         log1("Received DISCOVER");
 436
 437                         if (send_offer(&packet, static_lease_nip, lease) < 0) {
 438                                 bb_error_msg("send OFFER failed");
 439                         }
 440                         break;
 441                 case DHCPREQUEST: {
 442                         uint8_t *server_id_opt, *requested_opt;
 443                         uint32_t server_id_net = server_id_net; /* for compiler */
 444                         uint32_t requested_nip = requested_nip; /* for compiler */
 445
 446                         log1("Received REQUEST");
 447
 448                         requested_opt = get_option(&packet, DHCP_REQUESTED_IP);
 449                         server_id_opt = get_option(&packet, DHCP_SERVER_ID);
 450                         if (requested_opt)
 451                                 move_from_unaligned32(requested_nip, requested_opt);
 452                         if (server_id_opt)
 453                                 move_from_unaligned32(server_id_net, server_id_opt);
 454
 455                         if (lease) {
 456                                 if (server_id_opt) {
 457                                         /* SELECTING State */
 458                                         if (server_id_net == server_config.server_nip
 459                                          && requested_opt
 460                                          && requested_nip == lease->lease_nip
 461                                         ) {
 462                                                 send_ACK(&packet, lease->lease_nip);
 463                                         }
 464                                 } else if (requested_opt) {
 465                                         /* INIT-REBOOT State */
 466                                         if (lease->lease_nip == requested_nip)
 467                                                 send_ACK(&packet, lease->lease_nip);
 468                                         else
 469                                                 send_NAK(&packet);
 470                                 } else if (lease->lease_nip == packet.ciaddr) {
 471                                         /* RENEWING or REBINDING State */
 472                                         send_ACK(&packet, lease->lease_nip);
 473                                 } else { /* don't know what to do!!!! */
 474                                         send_NAK(&packet);
 475                                 }
 476
 477                         /* what to do if we have no record of the client */
 478                         } else if (server_id_opt) {
 479                                 /* SELECTING State */
 480
 481                         } else if (requested_opt) {
 482                                 /* INIT-REBOOT State */
 483                                 lease = find_lease_by_nip(requested_nip);
 484                                 if (lease) {
 485                                         if (is_expired_lease(lease)) {
 486                                                 /* probably best if we drop this lease */
 487                                                 memset(lease->lease_mac, 0, sizeof(lease->lease_mac));
 488                                         } else {
 489                                                 /* make some contention for this address */
 490                                                 send_NAK(&packet);
 491                                         }
 492                                 } else {
 493                                         uint32_t r = ntohl(requested_nip);
 494                                         if (r < server_config.start_ip
 495                                          || r > server_config.end_ip
 496                                         ) {
 497                                                 send_NAK(&packet);
 498                                         }
 499                                         /* else remain silent */
 500                                 }
 501
 502                         } else {
 503                                 /* RENEWING or REBINDING State */
 504                         }
 505                         break;
 506                 }
 507                 case DHCPDECLINE:
 508                         log1("Received DECLINE");
 509                         if (lease) {
 510                                 memset(lease->lease_mac, 0, sizeof(lease->lease_mac));
 511                                 lease->expires = time(NULL) + server_config.decline_time;
 512                         }
 513                         break;
 514                 case DHCPRELEASE:
 515                         log1("Received RELEASE");
 516                         if (lease)
 517                                 lease->expires = time(NULL);
 518                         break;
 519                 case DHCPINFORM:
 520                         log1("Received INFORM");
 521                         send_inform(&packet);
 522                         break;
 523                 default:
 524                         bb_info_msg("Unsupported DHCP message (%02x) - ignoring", state[0]);
 525                 }
 526         }
 527  ret0:
 528         retval = 0;
 529  ret:
 530         /*if (server_config.pidfile) - server_config.pidfile is never NULL */
 531                 remove_pidfile(server_config.pidfile);
 532         return retval;
 533 }