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 a specific mac address and ip address by creating our own ip packet */
  32 static void send_packet_to_client(struct dhcp_packet *dhcp_pkt, int force_broadcast)
  33 {
  34         const uint8_t *chaddr;
  35         uint32_t ciaddr;
  36
  37         // Was:
  38         //if (force_broadcast) { /* broadcast */ }
  39         //else if (dhcp_pkt->ciaddr) { /* unicast to dhcp_pkt->ciaddr */ }
  40         //else if (dhcp_pkt->flags & htons(BROADCAST_FLAG)) { /* broadcast */ }
  41         //else { /* unicast to dhcp_pkt->yiaddr */ }
  42         // But this is wrong: yiaddr is _our_ idea what client's IP is
  43         // (for example, from lease file). Client may not know that,
  44         // and may not have UDP socket listening on that IP!
  45         // We should never unicast to dhcp_pkt->yiaddr!
  46         // dhcp_pkt->ciaddr, OTOH, comes from client's request packet,
  47         // and can be used.
  48
  49         if (force_broadcast
  50          || (dhcp_pkt->flags & htons(BROADCAST_FLAG))
  51          || !dhcp_pkt->ciaddr
  52         ) {
  53                 log1("Broadcasting packet to client");
  54                 ciaddr = INADDR_BROADCAST;
  55                 chaddr = MAC_BCAST_ADDR;
  56         } else {
  57                 log1("Unicasting packet to client ciaddr");
  58                 ciaddr = dhcp_pkt->ciaddr;
  59                 chaddr = dhcp_pkt->chaddr;
  60         }
  61
  62         udhcp_send_raw_packet(dhcp_pkt,
  63                 /*src*/ server_config.server_nip, SERVER_PORT,
  64                 /*dst*/ ciaddr, CLIENT_PORT, chaddr,
  65                 server_config.ifindex);
  66 }
  67
  68 /* Send a packet to gateway_nip using the kernel ip stack */
  69 static void send_packet_to_relay(struct dhcp_packet *dhcp_pkt)
  70 {
  71         log1("Forwarding packet to relay");
  72
  73         udhcp_send_kernel_packet(dhcp_pkt,
  74                         server_config.server_nip, SERVER_PORT,
  75                         dhcp_pkt->gateway_nip, SERVER_PORT);
  76 }
  77
  78 static void send_packet(struct dhcp_packet *dhcp_pkt, int force_broadcast)
  79 {
  80         if (dhcp_pkt->gateway_nip)
  81                 send_packet_to_relay(dhcp_pkt);
  82         else
  83                 send_packet_to_client(dhcp_pkt, force_broadcast);
  84 }
  85
  86 static void init_packet(struct dhcp_packet *packet, struct dhcp_packet *oldpacket, char type)
  87 {
  88         /* Sets op, htype, hlen, cookie fields
  89          * and adds DHCP_MESSAGE_TYPE option */
  90         udhcp_init_header(packet, type);
  91
  92         packet->xid = oldpacket->xid;
  93         memcpy(packet->chaddr, oldpacket->chaddr, sizeof(oldpacket->chaddr));
  94         packet->flags = oldpacket->flags;
  95         packet->gateway_nip = oldpacket->gateway_nip;
  96         packet->ciaddr = oldpacket->ciaddr;
  97         add_simple_option(packet->options, DHCP_SERVER_ID, server_config.server_nip);
  98 }
  99
 100 /* Fill options field, siaddr_nip, and sname and boot_file fields.
 101  * TODO: teach this code to use overload option.
 102  */
 103 static void add_server_options(struct dhcp_packet *packet)
 104 {
 105         struct option_set *curr = server_config.options;
 106
 107         while (curr) {
 108                 if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
 109                         add_option_string(packet->options, curr->data);
 110                 curr = curr->next;
 111         }
 112
 113         packet->siaddr_nip = server_config.siaddr_nip;
 114
 115         if (server_config.sname)
 116                 strncpy((char*)packet->sname, server_config.sname, sizeof(packet->sname) - 1);
 117         if (server_config.boot_file)
 118                 strncpy((char*)packet->file, server_config.boot_file, sizeof(packet->file) - 1);
 119 }
 120
 121 static uint32_t select_lease_time(struct dhcp_packet *packet)
 122 {
 123         uint32_t lease_time_sec = server_config.max_lease_sec;
 124         uint8_t *lease_time_opt = get_option(packet, DHCP_LEASE_TIME);
 125         if (lease_time_opt) {
 126                 move_from_unaligned32(lease_time_sec, lease_time_opt);
 127                 lease_time_sec = ntohl(lease_time_sec);
 128                 if (lease_time_sec > server_config.max_lease_sec)
 129                         lease_time_sec = server_config.max_lease_sec;
 130                 if (lease_time_sec < server_config.min_lease_sec)
 131                         lease_time_sec = server_config.min_lease_sec;
 132         }
 133         return lease_time_sec;
 134 }
 135
 136 /* We got a DHCP DISCOVER. Send an OFFER. */
 137 static void send_offer(struct dhcp_packet *oldpacket, uint32_t static_lease_nip, struct dyn_lease *lease)
 138 {
 139         struct dhcp_packet packet;
 140         uint32_t lease_time_sec;
 141         struct in_addr addr;
 142
 143         init_packet(&packet, oldpacket, DHCPOFFER);
 144
 145         /* If it is a static lease, use its IP */
 146         packet.yiaddr = static_lease_nip;
 147         /* Else: */
 148         if (!static_lease_nip) {
 149                 /* We have no static lease for client's chaddr */
 150                 uint32_t req_nip;
 151                 uint8_t *req_ip_opt;
 152                 const char *p_host_name;
 153
 154                 if (lease) {
 155                         /* We have a dynamic lease for client's chaddr.
 156                          * Reuse its IP (even if lease is expired).
 157                          * Note that we ignore requested IP in this case.
 158                          */
 159                         packet.yiaddr = lease->lease_nip;
 160                 }
 161                 /* Or: if client has requested an IP */
 162                 else if ((req_ip_opt = get_option(oldpacket, DHCP_REQUESTED_IP)) != NULL
 163                  /* (read IP) */
 164                  && (move_from_unaligned32(req_nip, req_ip_opt), 1)
 165                  /* and the IP is in the lease range */
 166                  && ntohl(req_nip) >= server_config.start_ip
 167                  && ntohl(req_nip) <= server_config.end_ip
 168                  /* and */
 169                  && (  !(lease = find_lease_by_nip(req_nip)) /* is not already taken */
 170                     || is_expired_lease(lease) /* or is taken, but expired */
 171                     )
 172                 ) {
 173                         packet.yiaddr = req_nip;
 174                 }
 175                 else {
 176                         /* Otherwise, find a free IP */
 177                         packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr);
 178                 }
 179
 180                 if (!packet.yiaddr) {
 181                         bb_error_msg("no free IP addresses. OFFER abandoned");
 182                         return;
 183                 }
 184                 /* Reserve the IP for a short time hoping to get DHCPREQUEST soon */
 185                 p_host_name = (const char*) get_option(oldpacket, DHCP_HOST_NAME);
 186                 lease = add_lease(packet.chaddr, packet.yiaddr,
 187                                 server_config.offer_time,
 188                                 p_host_name,
 189                                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 190                 );
 191                 if (!lease) {
 192                         bb_error_msg("no free IP addresses. OFFER abandoned");
 193                         return;
 194                 }
 195         }
 196
 197         lease_time_sec = select_lease_time(oldpacket);
 198         add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
 199         add_server_options(&packet);
 200
 201         addr.s_addr = packet.yiaddr;
 202         bb_info_msg("Sending OFFER of %s", inet_ntoa(addr));
 203         /* send_packet emits error message itself if it detects failure */
 204         send_packet(&packet, /*force_bcast:*/ 0);
 205 }
 206
 207 static void send_NAK(struct dhcp_packet *oldpacket)
 208 {
 209         struct dhcp_packet packet;
 210
 211         init_packet(&packet, oldpacket, DHCPNAK);
 212
 213         log1("Sending NAK");
 214         send_packet(&packet, /*force_bcast:*/ 1);
 215 }
 216
 217 static void send_ACK(struct dhcp_packet *oldpacket, uint32_t yiaddr)
 218 {
 219         struct dhcp_packet packet;
 220         uint32_t lease_time_sec;
 221         struct in_addr addr;
 222         const char *p_host_name;
 223
 224         init_packet(&packet, oldpacket, DHCPACK);
 225         packet.yiaddr = yiaddr;
 226
 227         lease_time_sec = select_lease_time(oldpacket);
 228         add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
 229
 230         add_server_options(&packet);
 231
 232         addr.s_addr = yiaddr;
 233         bb_info_msg("Sending ACK to %s", inet_ntoa(addr));
 234         send_packet(&packet, /*force_bcast:*/ 0);
 235
 236         p_host_name = (const char*) get_option(oldpacket, DHCP_HOST_NAME);
 237         add_lease(packet.chaddr, packet.yiaddr,
 238                 lease_time_sec,
 239                 p_host_name,
 240                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 241         );
 242         if (ENABLE_FEATURE_UDHCPD_WRITE_LEASES_EARLY) {
 243                 /* rewrite the file with leases at every new acceptance */
 244                 write_leases();
 245         }
 246 }
 247
 248 static void send_inform(struct dhcp_packet *oldpacket)
 249 {
 250         struct dhcp_packet packet;
 251
 252         /* "The server responds to a DHCPINFORM message by sending a DHCPACK
 253          * message directly to the address given in the 'ciaddr' field
 254          * of the DHCPINFORM message.  The server MUST NOT send a lease
 255          * expiration time to the client and SHOULD NOT fill in 'yiaddr'."
 256          */
 257         init_packet(&packet, oldpacket, DHCPACK);
 258         add_server_options(&packet);
 259
 260         send_packet(&packet, /*force_bcast:*/ 0);
 261 }
 262
 263
 264 /* globals */
 265 struct dyn_lease *g_leases;
 266 /* struct server_config_t server_config is in bb_common_bufsiz1 */
 267
 268
 269 int udhcpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 270 int udhcpd_main(int argc UNUSED_PARAM, char **argv)
 271 {
 272         fd_set rfds;
 273         int server_socket = -1, retval, max_sock;
 274         struct dhcp_packet packet;
 275         uint8_t *state;
 276         uint32_t static_lease_nip;
 277         unsigned timeout_end;
 278         unsigned num_ips;
 279         unsigned opt;
 280         struct option_set *option;
 281         struct dyn_lease *lease, fake_lease;
 282         IF_FEATURE_UDHCP_PORT(char *str_P;)
 283
 284 #if ENABLE_FEATURE_UDHCP_PORT
 285         SERVER_PORT = 67;
 286         CLIENT_PORT = 68;
 287 #endif
 288
 289 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 290         opt_complementary = "vv";
 291 #endif
 292         opt = getopt32(argv, "fSv"
 293                 IF_FEATURE_UDHCP_PORT("P:", &str_P)
 294 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 295                 , &dhcp_verbose
 296 #endif
 297                 );
 298         argv += optind;
 299         if (!(opt & 1)) { /* no -f */
 300                 bb_daemonize_or_rexec(0, argv);
 301                 logmode = LOGMODE_NONE;
 302         }
 303         if (opt & 2) { /* -S */
 304                 openlog(applet_name, LOG_PID, LOG_DAEMON);
 305                 logmode |= LOGMODE_SYSLOG;
 306         }
 307 #if ENABLE_FEATURE_UDHCP_PORT
 308         if (opt & 4) { /* -P */
 309                 SERVER_PORT = xatou16(str_P);
 310                 CLIENT_PORT = SERVER_PORT + 1;
 311         }
 312 #endif
 313         /* Would rather not do read_config before daemonization -
 314          * otherwise NOMMU machines will parse config twice */
 315         read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE);
 316
 317         /* Make sure fd 0,1,2 are open */
 318         bb_sanitize_stdio();
 319         /* Equivalent of doing a fflush after every \n */
 320         setlinebuf(stdout);
 321
 322         /* Create pidfile */
 323         write_pidfile(server_config.pidfile);
 324         /* if (!..) bb_perror_msg("can't create pidfile %s", pidfile); */
 325
 326         bb_info_msg("%s (v"BB_VER") started", applet_name);
 327
 328         option = find_option(server_config.options, DHCP_LEASE_TIME);
 329         server_config.max_lease_sec = DEFAULT_LEASE_TIME;
 330         if (option) {
 331                 move_from_unaligned32(server_config.max_lease_sec, option->data + OPT_DATA);
 332                 server_config.max_lease_sec = ntohl(server_config.max_lease_sec);
 333         }
 334
 335         /* Sanity check */
 336         num_ips = server_config.end_ip - server_config.start_ip + 1;
 337         if (server_config.max_leases > num_ips) {
 338                 bb_error_msg("max_leases=%u is too big, setting to %u",
 339                         (unsigned)server_config.max_leases, num_ips);
 340                 server_config.max_leases = num_ips;
 341         }
 342
 343         g_leases = xzalloc(server_config.max_leases * sizeof(g_leases[0]));
 344         read_leases(server_config.lease_file);
 345
 346         if (udhcp_read_interface(server_config.interface,
 347                         &server_config.ifindex,
 348                         &server_config.server_nip,
 349                         server_config.server_mac)
 350         ) {
 351                 retval = 1;
 352                 goto ret;
 353         }
 354
 355         /* Setup the signal pipe */
 356         udhcp_sp_setup();
 357
 358         timeout_end = monotonic_sec() + server_config.auto_time;
 359         while (1) { /* loop until universe collapses */
 360                 int bytes;
 361                 struct timeval tv;
 362                 uint8_t *server_id_opt;
 363                 uint8_t *requested_opt;
 364                 uint32_t requested_nip = requested_nip; /* for compiler */
 365
 366                 if (server_socket < 0) {
 367                         server_socket = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT,
 368                                         server_config.interface);
 369                 }
 370
 371                 max_sock = udhcp_sp_fd_set(&rfds, server_socket);
 372                 if (server_config.auto_time) {
 373                         tv.tv_sec = timeout_end - monotonic_sec();
 374                         tv.tv_usec = 0;
 375                 }
 376                 retval = 0;
 377                 if (!server_config.auto_time || tv.tv_sec > 0) {
 378                         retval = select(max_sock + 1, &rfds, NULL, NULL,
 379                                         server_config.auto_time ? &tv : NULL);
 380                 }
 381                 if (retval == 0) {
 382                         write_leases();
 383                         timeout_end = monotonic_sec() + server_config.auto_time;
 384                         continue;
 385                 }
 386                 if (retval < 0 && errno != EINTR) {
 387                         log1("Error on select");
 388                         continue;
 389                 }
 390
 391                 switch (udhcp_sp_read(&rfds)) {
 392                 case SIGUSR1:
 393                         bb_info_msg("Received a SIGUSR1");
 394                         write_leases();
 395                         /* why not just reset the timeout, eh */
 396                         timeout_end = monotonic_sec() + server_config.auto_time;
 397                         continue;
 398                 case SIGTERM:
 399                         bb_info_msg("Received a SIGTERM");
 400                         goto ret0;
 401                 case 0: /* no signal: read a packet */
 402                         break;
 403                 default: /* signal or error (probably EINTR): back to select */
 404                         continue;
 405                 }
 406
 407                 bytes = udhcp_recv_kernel_packet(&packet, server_socket);
 408                 if (bytes < 0) {
 409                         /* bytes can also be -2 ("bad packet data") */
 410                         if (bytes == -1 && errno != EINTR) {
 411                                 log1("Read error: %s, reopening socket", strerror(errno));
 412                                 close(server_socket);
 413                                 server_socket = -1;
 414                         }
 415                         continue;
 416                 }
 417                 if (packet.hlen != 6) {
 418                         bb_error_msg("MAC length != 6, ignoring packet");
 419                         continue;
 420                 }
 421                 if (packet.op != BOOTREQUEST) {
 422                         bb_error_msg("not a REQUEST, ignoring packet");
 423                         continue;
 424                 }
 425                 state = get_option(&packet, DHCP_MESSAGE_TYPE);
 426                 if (state == NULL || state[0] < DHCP_MINTYPE || state[0] > DHCP_MAXTYPE) {
 427                         bb_error_msg("no or bad message type option, ignoring packet");
 428                         continue;
 429                 }
 430
 431                 /* Look for a static/dynamic lease */
 432                 static_lease_nip = get_static_nip_by_mac(server_config.static_leases, &packet.chaddr);
 433                 if (static_lease_nip) {
 434                         bb_info_msg("Found static lease: %x", static_lease_nip);
 435                         memcpy(&fake_lease.lease_mac, &packet.chaddr, 6);
 436                         fake_lease.lease_nip = static_lease_nip;
 437                         fake_lease.expires = 0;
 438                         lease = &fake_lease;
 439                 } else {
 440                         lease = find_lease_by_mac(packet.chaddr);
 441                 }
 442
 443                 /* Get REQUESTED_IP and SERVER_ID if present */
 444                 server_id_opt = get_option(&packet, DHCP_SERVER_ID);
 445                 if (server_id_opt) {
 446                         uint32_t server_id_net;
 447                         move_from_unaligned32(server_id_net, server_id_opt);
 448                         if (server_id_net != server_config.server_nip) {
 449                                 /* client talks to somebody else */
 450                                 log1("server ID doesn't match, ignoring");
 451                                 continue;
 452                         }
 453                 }
 454                 requested_opt = get_option(&packet, DHCP_REQUESTED_IP);
 455                 if (requested_opt) {
 456                         move_from_unaligned32(requested_nip, requested_opt);
 457                 }
 458
 459                 switch (state[0]) {
 460
 461                 case DHCPDISCOVER:
 462                         log1("Received DISCOVER");
 463
 464                         send_offer(&packet, static_lease_nip, lease);
 465                         break;
 466
 467                 case DHCPREQUEST:
 468                         log1("Received REQUEST");
 469
 470                         /* RFC 2131: "The REQUESTED_IP option MUST be set
 471                          * to the value of 'yiaddr' in the DHCPOFFER message
 472                          * from the server." */
 473                         if (!requested_opt) {
 474                                 log1("no requested IP, ignoring");
 475                                 break;
 476                         }
 477                         if (lease && requested_nip == lease->lease_nip) {
 478                                 /* client requests IP which matches the lease.
 479                                  * ACK it, and bump lease expiration time. */
 480                                 send_ACK(&packet, lease->lease_nip);
 481                                 break;
 482                         }
 483                         if (server_id_opt) {
 484                                 /* client was talking specifically to us.
 485                                  * "No, we don't have this IP for you". */
 486                                 send_NAK(&packet);
 487                         }
 488                         break;
 489
 490                 case DHCPDECLINE:
 491                         /* RFC 2131:
 492                          * "If the server receives a DHCPDECLINE message,
 493                          * the client has discovered through some other means
 494                          * that the suggested network address is already
 495                          * in use. The server MUST mark the network address
 496                          * as not available and SHOULD notify the local
 497                          * sysadmin of a possible configuration problem."
 498                          *
 499                          * SERVER_ID must be present,
 500                          * REQUESTED_IP must be present,
 501                          * chaddr must be filled in,
 502                          * ciaddr must be 0 (we do not check this)
 503                          */
 504                         log1("Received DECLINE");
 505                         if (server_id_opt
 506                          && requested_opt
 507                          && lease  /* chaddr matches this lease */
 508                          && requested_nip == lease->lease_nip
 509                         ) {
 510                                 memset(lease->lease_mac, 0, sizeof(lease->lease_mac));
 511                                 lease->expires = time(NULL) + server_config.decline_time;
 512                         }
 513                         break;
 514
 515                 case DHCPRELEASE:
 516                         /* "Upon receipt of a DHCPRELEASE message, the server
 517                          * marks the network address as not allocated."
 518                          *
 519                          * SERVER_ID must be present,
 520                          * REQUESTED_IP must not be present (we do not check this),
 521                          * chaddr must be filled in,
 522                          * ciaddr must be filled in
 523                          */
 524                         log1("Received RELEASE");
 525                         if (server_id_opt
 526                          && lease  /* chaddr matches this lease */
 527                          && packet.ciaddr == lease->lease_nip
 528                         ) {
 529                                 lease->expires = time(NULL);
 530                         }
 531                         break;
 532
 533                 case DHCPINFORM:
 534                         log1("Received INFORM");
 535                         send_inform(&packet);
 536                         break;
 537                 }
 538         }
 539  ret0:
 540         retval = 0;
 541  ret:
 542         /*if (server_config.pidfile) - server_config.pidfile is never NULL */
 543                 remove_pidfile(server_config.pidfile);
 544         return retval;
 545 }