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 //applet:IF_UDHCPD(APPLET(udhcpd, BB_DIR_USR_SBIN, BB_SUID_DROP))
  24
  25 //kbuild:lib-$(CONFIG_UDHCPD) += common.o packet.o signalpipe.o socket.o
  26 //kbuild:lib-$(CONFIG_UDHCPD) += dhcpd.o arpping.o
  27 //kbuild:lib-$(CONFIG_FEATURE_UDHCP_RFC3397) += domain_codec.o
  28
  29 //usage:#define udhcpd_trivial_usage
  30 //usage:       "[-fS] [-I ADDR]" IF_FEATURE_UDHCP_PORT(" [-P N]") " [CONFFILE]"
  31 //usage:#define udhcpd_full_usage "\n\n"
  32 //usage:       "DHCP server\n"
  33 //usage:     "\n        -f      Run in foreground"
  34 //usage:     "\n        -S      Log to syslog too"
  35 //usage:     "\n        -I ADDR Local address"
  36 //usage:     "\n        -a MSEC Timeout for ARP ping (default 2000)"
  37 //usage:        IF_FEATURE_UDHCP_PORT(
  38 //usage:     "\n        -P N    Use port N (default 67)"
  39 //usage:        )
  40
  41 #include <netinet/ether.h>
  42 #include <syslog.h>
  43 #include "common.h"
  44 #include "dhcpc.h"
  45 #include "dhcpd.h"
  46
  47 /* globals */
  48 struct dyn_lease *g_leases;
  49 /* struct server_config_t server_config is in bb_common_bufsiz1 */
  50
  51 /* Takes the address of the pointer to the static_leases linked list,
  52  * address to a 6 byte mac address,
  53  * 4 byte IP address */
  54 static void add_static_lease(struct static_lease **st_lease_pp,
  55                 uint8_t *mac,
  56                 uint32_t nip)
  57 {
  58         struct static_lease *st_lease;
  59
  60         /* Find the tail of the list */
  61         while ((st_lease = *st_lease_pp) != NULL) {
  62                 st_lease_pp = &st_lease->next;
  63         }
  64
  65         /* Add new node */
  66         *st_lease_pp = st_lease = xzalloc(sizeof(*st_lease));
  67         memcpy(st_lease->mac, mac, 6);
  68         st_lease->nip = nip;
  69         /*st_lease->next = NULL;*/
  70 }
  71
  72 /* Find static lease IP by mac */
  73 static uint32_t get_static_nip_by_mac(struct static_lease *st_lease, void *mac)
  74 {
  75         while (st_lease) {
  76                 if (memcmp(st_lease->mac, mac, 6) == 0)
  77                         return st_lease->nip;
  78                 st_lease = st_lease->next;
  79         }
  80
  81         return 0;
  82 }
  83
  84 static int is_nip_reserved(struct static_lease *st_lease, uint32_t nip)
  85 {
  86         while (st_lease) {
  87                 if (st_lease->nip == nip)
  88                         return 1;
  89                 st_lease = st_lease->next;
  90         }
  91
  92         return 0;
  93 }
  94
  95 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
  96 /* Print out static leases just to check what's going on */
  97 /* Takes the address of the pointer to the static_leases linked list */
  98 static void log_static_leases(struct static_lease **st_lease_pp)
  99 {
 100         struct static_lease *cur;
 101
 102         if (dhcp_verbose < 2)
 103                 return;
 104
 105         cur = *st_lease_pp;
 106         while (cur) {
 107                 bb_error_msg("static lease: mac:%02x:%02x:%02x:%02x:%02x:%02x nip:%x",
 108                         cur->mac[0], cur->mac[1], cur->mac[2],
 109                         cur->mac[3], cur->mac[4], cur->mac[5],
 110                         cur->nip
 111                 );
 112                 cur = cur->next;
 113         }
 114 }
 115 #else
 116 # define log_static_leases(st_lease_pp) ((void)0)
 117 #endif
 118
 119 /* Find the oldest expired lease, NULL if there are no expired leases */
 120 static struct dyn_lease *oldest_expired_lease(void)
 121 {
 122         struct dyn_lease *oldest_lease = NULL;
 123         leasetime_t oldest_time = time(NULL);
 124         unsigned i;
 125
 126         /* Unexpired leases have g_leases[i].expires >= current time
 127          * and therefore can't ever match */
 128         for (i = 0; i < server_config.max_leases; i++) {
 129                 if (g_leases[i].expires == 0 /* empty entry */
 130                  || g_leases[i].expires < oldest_time
 131                 ) {
 132                         oldest_time = g_leases[i].expires;
 133                         oldest_lease = &g_leases[i];
 134                 }
 135         }
 136         return oldest_lease;
 137 }
 138
 139 /* Clear out all leases with matching nonzero chaddr OR yiaddr.
 140  * If chaddr == NULL, this is a conflict lease.
 141  */
 142 static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
 143 {
 144         unsigned i;
 145
 146         for (i = 0; i < server_config.max_leases; i++) {
 147                 if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
 148                  || (yiaddr && g_leases[i].lease_nip == yiaddr)
 149                 ) {
 150                         memset(&g_leases[i], 0, sizeof(g_leases[i]));
 151                 }
 152         }
 153 }
 154
 155 /* Add a lease into the table, clearing out any old ones.
 156  * If chaddr == NULL, this is a conflict lease.
 157  */
 158 static struct dyn_lease *add_lease(
 159                 const uint8_t *chaddr, uint32_t yiaddr,
 160                 leasetime_t leasetime,
 161                 const char *hostname, int hostname_len)
 162 {
 163         struct dyn_lease *oldest;
 164
 165         /* clean out any old ones */
 166         clear_leases(chaddr, yiaddr);
 167
 168         oldest = oldest_expired_lease();
 169
 170         if (oldest) {
 171                 memset(oldest, 0, sizeof(*oldest));
 172                 if (hostname) {
 173                         char *p;
 174
 175                         hostname_len++; /* include NUL */
 176                         if (hostname_len > sizeof(oldest->hostname))
 177                                 hostname_len = sizeof(oldest->hostname);
 178                         p = safe_strncpy(oldest->hostname, hostname, hostname_len);
 179                         /*
 180                          * Sanitization (s/bad_char/./g).
 181                          * The intent is not to allow only "DNS-valid" hostnames,
 182                          * but merely make dumpleases output safe for shells to use.
 183                          * We accept "0-9A-Za-z._-", all other chars turn to dots.
 184                          */
 185                         while (*p) {
 186                                 if (!isalnum(*p) && *p != '-' && *p != '_')
 187                                         *p = '.';
 188                                 p++;
 189                         }
 190                 }
 191                 if (chaddr)
 192                         memcpy(oldest->lease_mac, chaddr, 6);
 193                 oldest->lease_nip = yiaddr;
 194                 oldest->expires = time(NULL) + leasetime;
 195         }
 196
 197         return oldest;
 198 }
 199
 200 /* True if a lease has expired */
 201 static int is_expired_lease(struct dyn_lease *lease)
 202 {
 203         return (lease->expires < (leasetime_t) time(NULL));
 204 }
 205
 206 /* Find the first lease that matches MAC, NULL if no match */
 207 static struct dyn_lease *find_lease_by_mac(const uint8_t *mac)
 208 {
 209         unsigned i;
 210
 211         for (i = 0; i < server_config.max_leases; i++)
 212                 if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
 213                         return &g_leases[i];
 214
 215         return NULL;
 216 }
 217
 218 /* Find the first lease that matches IP, NULL is no match */
 219 static struct dyn_lease *find_lease_by_nip(uint32_t nip)
 220 {
 221         unsigned i;
 222
 223         for (i = 0; i < server_config.max_leases; i++)
 224                 if (g_leases[i].lease_nip == nip)
 225                         return &g_leases[i];
 226
 227         return NULL;
 228 }
 229
 230 /* Check if the IP is taken; if it is, add it to the lease table */
 231 static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
 232 {
 233         struct in_addr temp;
 234         int r;
 235
 236         r = arpping(nip, safe_mac,
 237                         server_config.server_nip,
 238                         server_config.server_mac,
 239                         server_config.interface,
 240                         arpping_ms);
 241         if (r)
 242                 return r;
 243
 244         temp.s_addr = nip;
 245         bb_error_msg("%s belongs to someone, reserving it for %u seconds",
 246                 inet_ntoa(temp), (unsigned)server_config.conflict_time);
 247         add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
 248         return 0;
 249 }
 250
 251 /* Find a new usable (we think) address */
 252 static uint32_t find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
 253 {
 254         uint32_t addr;
 255         struct dyn_lease *oldest_lease = NULL;
 256
 257 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 258         uint32_t stop;
 259         unsigned i, hash;
 260
 261         /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
 262          * dispersal even with similarly-valued "strings".
 263          */
 264         hash = 0;
 265         for (i = 0; i < 6; i++)
 266                 hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
 267
 268         /* pick a seed based on hwaddr then iterate until we find a free address. */
 269         addr = server_config.start_ip
 270                 + (hash % (1 + server_config.end_ip - server_config.start_ip));
 271         stop = addr;
 272 #else
 273         addr = server_config.start_ip;
 274 #define stop (server_config.end_ip + 1)
 275 #endif
 276         do {
 277                 uint32_t nip;
 278                 struct dyn_lease *lease;
 279
 280                 /* ie, 192.168.55.0 */
 281                 if ((addr & 0xff) == 0)
 282                         goto next_addr;
 283                 /* ie, 192.168.55.255 */
 284                 if ((addr & 0xff) == 0xff)
 285                         goto next_addr;
 286                 nip = htonl(addr);
 287                 /* skip our own address */
 288                 if (nip == server_config.server_nip)
 289                         goto next_addr;
 290                 /* is this a static lease addr? */
 291                 if (is_nip_reserved(server_config.static_leases, nip))
 292                         goto next_addr;
 293
 294                 lease = find_lease_by_nip(nip);
 295                 if (!lease) {
 296 //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
 297                         if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
 298                                 return nip;
 299                 } else {
 300                         if (!oldest_lease || lease->expires < oldest_lease->expires)
 301                                 oldest_lease = lease;
 302                 }
 303
 304  next_addr:
 305                 addr++;
 306 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 307                 if (addr > server_config.end_ip)
 308                         addr = server_config.start_ip;
 309 #endif
 310         } while (addr != stop);
 311
 312         if (oldest_lease
 313          && is_expired_lease(oldest_lease)
 314          && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
 315         ) {
 316                 return oldest_lease->lease_nip;
 317         }
 318
 319         return 0;
 320 }
 321
 322 /* On these functions, make sure your datatype matches */
 323 static int FAST_FUNC read_str(const char *line, void *arg)
 324 {
 325         char **dest = arg;
 326
 327         free(*dest);
 328         *dest = xstrdup(line);
 329         return 1;
 330 }
 331
 332 static int FAST_FUNC read_u32(const char *line, void *arg)
 333 {
 334         *(uint32_t*)arg = bb_strtou32(line, NULL, 10);
 335         return errno == 0;
 336 }
 337
 338 static int FAST_FUNC read_staticlease(const char *const_line, void *arg)
 339 {
 340         char *line;
 341         char *mac_string;
 342         char *ip_string;
 343         struct ether_addr mac_bytes; /* it's "struct { uint8_t mac[6]; }" */
 344         uint32_t nip;
 345
 346         /* Read mac */
 347         line = (char *) const_line;
 348         mac_string = strtok_r(line, " \t", &line);
 349         if (!mac_string || !ether_aton_r(mac_string, &mac_bytes))
 350                 return 0;
 351
 352         /* Read ip */
 353         ip_string = strtok_r(NULL, " \t", &line);
 354         if (!ip_string || !udhcp_str2nip(ip_string, &nip))
 355                 return 0;
 356
 357         add_static_lease(arg, (uint8_t*) &mac_bytes, nip);
 358
 359         log_static_leases(arg);
 360
 361         return 1;
 362 }
 363
 364 static int FAST_FUNC read_optset(const char *line, void *arg) {
 365         return udhcp_str2optset(line, arg, dhcp_optflags, dhcp_option_strings);
 366 }
 367
 368 struct config_keyword {
 369         const char *keyword;
 370         int (*handler)(const char *line, void *var) FAST_FUNC;
 371         unsigned ofs;
 372         const char *def;
 373 };
 374
 375 #define OFS(field) offsetof(struct server_config_t, field)
 376
 377 static const struct config_keyword keywords[] = {
 378         /* keyword        handler           variable address               default */
 379         {"start"        , udhcp_str2nip   , OFS(start_ip     ), "192.168.0.20"},
 380         {"end"          , udhcp_str2nip   , OFS(end_ip       ), "192.168.0.254"},
 381         {"interface"    , read_str        , OFS(interface    ), "eth0"},
 382         /* Avoid "max_leases value not sane" warning by setting default
 383          * to default_end_ip - default_start_ip + 1: */
 384         {"max_leases"   , read_u32        , OFS(max_leases   ), "235"},
 385         {"auto_time"    , read_u32        , OFS(auto_time    ), "7200"},
 386         {"decline_time" , read_u32        , OFS(decline_time ), "3600"},
 387         {"conflict_time", read_u32        , OFS(conflict_time), "3600"},
 388         {"offer_time"   , read_u32        , OFS(offer_time   ), "60"},
 389         {"min_lease"    , read_u32        , OFS(min_lease_sec), "60"},
 390         {"lease_file"   , read_str        , OFS(lease_file   ), LEASES_FILE},
 391         {"pidfile"      , read_str        , OFS(pidfile      ), "/var/run/udhcpd.pid"},
 392         {"siaddr"       , udhcp_str2nip   , OFS(siaddr_nip   ), "0.0.0.0"},
 393         /* keywords with no defaults must be last! */
 394         {"option"       , read_optset     , OFS(options      ), ""},
 395         {"opt"          , read_optset     , OFS(options      ), ""},
 396         {"notify_file"  , read_str        , OFS(notify_file  ), NULL},
 397         {"sname"        , read_str        , OFS(sname        ), NULL},
 398         {"boot_file"    , read_str        , OFS(boot_file    ), NULL},
 399         {"static_lease" , read_staticlease, OFS(static_leases), ""},
 400 };
 401 enum { KWS_WITH_DEFAULTS = ARRAY_SIZE(keywords) - 6 };
 402
 403 static NOINLINE void read_config(const char *file)
 404 {
 405         parser_t *parser;
 406         const struct config_keyword *k;
 407         unsigned i;
 408         char *token[2];
 409
 410         for (i = 0; i < KWS_WITH_DEFAULTS; i++)
 411                 keywords[i].handler(keywords[i].def, (char*)&server_config + keywords[i].ofs);
 412
 413         parser = config_open(file);
 414         while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
 415                 for (k = keywords, i = 0; i < ARRAY_SIZE(keywords); k++, i++) {
 416                         if (strcasecmp(token[0], k->keyword) == 0) {
 417                                 if (!k->handler(token[1], (char*)&server_config + k->ofs)) {
 418                                         bb_error_msg("can't parse line %u in %s",
 419                                                         parser->lineno, file);
 420                                         /* reset back to the default value */
 421                                         k->handler(k->def, (char*)&server_config + k->ofs);
 422                                 }
 423                                 break;
 424                         }
 425                 }
 426         }
 427         config_close(parser);
 428
 429         server_config.start_ip = ntohl(server_config.start_ip);
 430         server_config.end_ip = ntohl(server_config.end_ip);
 431 }
 432
 433 static void write_leases(void)
 434 {
 435         int fd;
 436         unsigned i;
 437         leasetime_t curr;
 438         int64_t written_at;
 439
 440         fd = open_or_warn(server_config.lease_file, O_WRONLY|O_CREAT|O_TRUNC);
 441         if (fd < 0)
 442                 return;
 443
 444         curr = written_at = time(NULL);
 445
 446         written_at = SWAP_BE64(written_at);
 447         full_write(fd, &written_at, sizeof(written_at));
 448
 449         for (i = 0; i < server_config.max_leases; i++) {
 450                 leasetime_t tmp_time;
 451
 452                 if (g_leases[i].lease_nip == 0)
 453                         continue;
 454
 455                 /* Screw with the time in the struct, for easier writing */
 456                 tmp_time = g_leases[i].expires;
 457
 458                 g_leases[i].expires -= curr;
 459                 if ((signed_leasetime_t) g_leases[i].expires < 0)
 460                         g_leases[i].expires = 0;
 461                 g_leases[i].expires = htonl(g_leases[i].expires);
 462
 463                 /* No error check. If the file gets truncated,
 464                  * we lose some leases on restart. Oh well. */
 465                 full_write(fd, &g_leases[i], sizeof(g_leases[i]));
 466
 467                 /* Then restore it when done */
 468                 g_leases[i].expires = tmp_time;
 469         }
 470         close(fd);
 471
 472         if (server_config.notify_file) {
 473                 char *argv[3];
 474                 argv[0] = server_config.notify_file;
 475                 argv[1] = server_config.lease_file;
 476                 argv[2] = NULL;
 477                 spawn_and_wait(argv);
 478         }
 479 }
 480
 481 static NOINLINE void read_leases(const char *file)
 482 {
 483         struct dyn_lease lease;
 484         int64_t written_at, time_passed;
 485         int fd;
 486 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 487         unsigned i = 0;
 488 #endif
 489
 490         fd = open_or_warn(file, O_RDONLY);
 491         if (fd < 0)
 492                 return;
 493
 494         if (full_read(fd, &written_at, sizeof(written_at)) != sizeof(written_at))
 495                 goto ret;
 496         written_at = SWAP_BE64(written_at);
 497
 498         time_passed = time(NULL) - written_at;
 499         /* Strange written_at, or lease file from old version of udhcpd
 500          * which had no "written_at" field? */
 501         if ((uint64_t)time_passed > 12 * 60 * 60)
 502                 goto ret;
 503
 504         while (full_read(fd, &lease, sizeof(lease)) == sizeof(lease)) {
 505                 uint32_t y = ntohl(lease.lease_nip);
 506                 if (y >= server_config.start_ip && y <= server_config.end_ip) {
 507                         signed_leasetime_t expires = ntohl(lease.expires) - (signed_leasetime_t)time_passed;
 508                         uint32_t static_nip;
 509
 510                         if (expires <= 0)
 511                                 /* We keep expired leases: add_lease() will add
 512                                  * a lease with 0 seconds remaining.
 513                                  * Fewer IP address changes this way for mass reboot scenario.
 514                                  */
 515                                 expires = 0;
 516
 517                         /* Check if there is a different static lease for this IP or MAC */
 518                         static_nip = get_static_nip_by_mac(server_config.static_leases, lease.lease_mac);
 519                         if (static_nip) {
 520                                 /* NB: we do not add lease even if static_nip == lease.lease_nip.
 521                                  */
 522                                 continue;
 523                         }
 524                         if (is_nip_reserved(server_config.static_leases, lease.lease_nip))
 525                                 continue;
 526
 527                         /* NB: add_lease takes "relative time", IOW,
 528                          * lease duration, not lease deadline. */
 529                         if (add_lease(lease.lease_mac, lease.lease_nip,
 530                                         expires,
 531                                         lease.hostname, sizeof(lease.hostname)
 532                                 ) == 0
 533                         ) {
 534                                 bb_error_msg("too many leases while loading %s", file);
 535                                 break;
 536                         }
 537 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 538                         i++;
 539 #endif
 540                 }
 541         }
 542         log1("read %d leases", i);
 543  ret:
 544         close(fd);
 545 }
 546
 547 /* Send a packet to a specific mac address and ip address by creating our own ip packet */
 548 static void send_packet_to_client(struct dhcp_packet *dhcp_pkt, int force_broadcast)
 549 {
 550         const uint8_t *chaddr;
 551         uint32_t ciaddr;
 552
 553         // Was:
 554         //if (force_broadcast) { /* broadcast */ }
 555         //else if (dhcp_pkt->ciaddr) { /* unicast to dhcp_pkt->ciaddr */ }
 556         //else if (dhcp_pkt->flags & htons(BROADCAST_FLAG)) { /* broadcast */ }
 557         //else { /* unicast to dhcp_pkt->yiaddr */ }
 558         // But this is wrong: yiaddr is _our_ idea what client's IP is
 559         // (for example, from lease file). Client may not know that,
 560         // and may not have UDP socket listening on that IP!
 561         // We should never unicast to dhcp_pkt->yiaddr!
 562         // dhcp_pkt->ciaddr, OTOH, comes from client's request packet,
 563         // and can be used.
 564
 565         if (force_broadcast
 566          || (dhcp_pkt->flags & htons(BROADCAST_FLAG))
 567          || dhcp_pkt->ciaddr == 0
 568         ) {
 569                 log1("broadcasting packet to client");
 570                 ciaddr = INADDR_BROADCAST;
 571                 chaddr = MAC_BCAST_ADDR;
 572         } else {
 573                 log1("unicasting packet to client ciaddr");
 574                 ciaddr = dhcp_pkt->ciaddr;
 575                 chaddr = dhcp_pkt->chaddr;
 576         }
 577
 578         udhcp_send_raw_packet(dhcp_pkt,
 579                 /*src*/ server_config.server_nip, SERVER_PORT,
 580                 /*dst*/ ciaddr, CLIENT_PORT, chaddr,
 581                 server_config.ifindex);
 582 }
 583
 584 /* Send a packet to gateway_nip using the kernel ip stack */
 585 static void send_packet_to_relay(struct dhcp_packet *dhcp_pkt)
 586 {
 587         log1("forwarding packet to relay");
 588
 589         udhcp_send_kernel_packet(dhcp_pkt,
 590                         server_config.server_nip, SERVER_PORT,
 591                         dhcp_pkt->gateway_nip, SERVER_PORT);
 592 }
 593
 594 static void send_packet(struct dhcp_packet *dhcp_pkt, int force_broadcast)
 595 {
 596         if (dhcp_pkt->gateway_nip)
 597                 send_packet_to_relay(dhcp_pkt);
 598         else
 599                 send_packet_to_client(dhcp_pkt, force_broadcast);
 600 }
 601
 602 static void init_packet(struct dhcp_packet *packet, struct dhcp_packet *oldpacket, char type)
 603 {
 604         /* Sets op, htype, hlen, cookie fields
 605          * and adds DHCP_MESSAGE_TYPE option */
 606         udhcp_init_header(packet, type);
 607
 608         packet->xid = oldpacket->xid;
 609         memcpy(packet->chaddr, oldpacket->chaddr, sizeof(oldpacket->chaddr));
 610         packet->flags = oldpacket->flags;
 611         packet->gateway_nip = oldpacket->gateway_nip;
 612         packet->ciaddr = oldpacket->ciaddr;
 613         udhcp_add_simple_option(packet, DHCP_SERVER_ID, server_config.server_nip);
 614 }
 615
 616 /* Fill options field, siaddr_nip, and sname and boot_file fields.
 617  * TODO: teach this code to use overload option.
 618  */
 619 static void add_server_options(struct dhcp_packet *packet)
 620 {
 621         struct option_set *curr = server_config.options;
 622
 623         while (curr) {
 624                 if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
 625                         udhcp_add_binary_option(packet, curr->data);
 626                 curr = curr->next;
 627         }
 628
 629         packet->siaddr_nip = server_config.siaddr_nip;
 630
 631         if (server_config.sname)
 632                 strncpy((char*)packet->sname, server_config.sname, sizeof(packet->sname) - 1);
 633         if (server_config.boot_file)
 634                 strncpy((char*)packet->file, server_config.boot_file, sizeof(packet->file) - 1);
 635 }
 636
 637 static uint32_t select_lease_time(struct dhcp_packet *packet)
 638 {
 639         uint32_t lease_time_sec = server_config.max_lease_sec;
 640         uint8_t *lease_time_opt = udhcp_get_option(packet, DHCP_LEASE_TIME);
 641         if (lease_time_opt) {
 642                 move_from_unaligned32(lease_time_sec, lease_time_opt);
 643                 lease_time_sec = ntohl(lease_time_sec);
 644                 if (lease_time_sec > server_config.max_lease_sec)
 645                         lease_time_sec = server_config.max_lease_sec;
 646                 if (lease_time_sec < server_config.min_lease_sec)
 647                         lease_time_sec = server_config.min_lease_sec;
 648         }
 649         return lease_time_sec;
 650 }
 651
 652 /* We got a DHCP DISCOVER. Send an OFFER. */
 653 /* NOINLINE: limit stack usage in caller */
 654 static NOINLINE void send_offer(struct dhcp_packet *oldpacket,
 655                 uint32_t static_lease_nip,
 656                 struct dyn_lease *lease,
 657                 uint8_t *requested_ip_opt,
 658                 unsigned arpping_ms)
 659 {
 660         struct dhcp_packet packet;
 661         uint32_t lease_time_sec;
 662         struct in_addr addr;
 663
 664         init_packet(&packet, oldpacket, DHCPOFFER);
 665
 666         /* If it is a static lease, use its IP */
 667         packet.yiaddr = static_lease_nip;
 668         /* Else: */
 669         if (!static_lease_nip) {
 670                 /* We have no static lease for client's chaddr */
 671                 uint32_t req_nip;
 672                 const char *p_host_name;
 673
 674                 if (lease) {
 675                         /* We have a dynamic lease for client's chaddr.
 676                          * Reuse its IP (even if lease is expired).
 677                          * Note that we ignore requested IP in this case.
 678                          */
 679                         packet.yiaddr = lease->lease_nip;
 680                 }
 681                 /* Or: if client has requested an IP */
 682                 else if (requested_ip_opt != NULL
 683                  /* (read IP) */
 684                  && (move_from_unaligned32(req_nip, requested_ip_opt), 1)
 685                  /* and the IP is in the lease range */
 686                  && ntohl(req_nip) >= server_config.start_ip
 687                  && ntohl(req_nip) <= server_config.end_ip
 688                  /* and */
 689                  && (  !(lease = find_lease_by_nip(req_nip)) /* is not already taken */
 690                     || is_expired_lease(lease) /* or is taken, but expired */
 691                     )
 692                 ) {
 693                         packet.yiaddr = req_nip;
 694                 }
 695                 else {
 696                         /* Otherwise, find a free IP */
 697                         packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr, arpping_ms);
 698                 }
 699
 700                 if (!packet.yiaddr) {
 701                         bb_error_msg("no free IP addresses. OFFER abandoned");
 702                         return;
 703                 }
 704                 /* Reserve the IP for a short time hoping to get DHCPREQUEST soon */
 705                 p_host_name = (const char*) udhcp_get_option(oldpacket, DHCP_HOST_NAME);
 706                 lease = add_lease(packet.chaddr, packet.yiaddr,
 707                                 server_config.offer_time,
 708                                 p_host_name,
 709                                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 710                 );
 711                 if (!lease) {
 712                         bb_error_msg("no free IP addresses. OFFER abandoned");
 713                         return;
 714                 }
 715         }
 716
 717         lease_time_sec = select_lease_time(oldpacket);
 718         udhcp_add_simple_option(&packet, DHCP_LEASE_TIME, htonl(lease_time_sec));
 719         add_server_options(&packet);
 720
 721         addr.s_addr = packet.yiaddr;
 722         bb_error_msg("sending OFFER of %s", inet_ntoa(addr));
 723         /* send_packet emits error message itself if it detects failure */
 724         send_packet(&packet, /*force_bcast:*/ 0);
 725 }
 726
 727 /* NOINLINE: limit stack usage in caller */
 728 static NOINLINE void send_NAK(struct dhcp_packet *oldpacket)
 729 {
 730         struct dhcp_packet packet;
 731
 732         init_packet(&packet, oldpacket, DHCPNAK);
 733
 734         log1("sending %s", "NAK");
 735         send_packet(&packet, /*force_bcast:*/ 1);
 736 }
 737
 738 /* NOINLINE: limit stack usage in caller */
 739 static NOINLINE void send_ACK(struct dhcp_packet *oldpacket, uint32_t yiaddr)
 740 {
 741         struct dhcp_packet packet;
 742         uint32_t lease_time_sec;
 743         struct in_addr addr;
 744         const char *p_host_name;
 745
 746         init_packet(&packet, oldpacket, DHCPACK);
 747         packet.yiaddr = yiaddr;
 748
 749         lease_time_sec = select_lease_time(oldpacket);
 750         udhcp_add_simple_option(&packet, DHCP_LEASE_TIME, htonl(lease_time_sec));
 751
 752         add_server_options(&packet);
 753
 754         addr.s_addr = yiaddr;
 755         bb_error_msg("sending ACK to %s", inet_ntoa(addr));
 756         send_packet(&packet, /*force_bcast:*/ 0);
 757
 758         p_host_name = (const char*) udhcp_get_option(oldpacket, DHCP_HOST_NAME);
 759         add_lease(packet.chaddr, packet.yiaddr,
 760                 lease_time_sec,
 761                 p_host_name,
 762                 p_host_name ? (unsigned char)p_host_name[OPT_LEN - OPT_DATA] : 0
 763         );
 764         if (ENABLE_FEATURE_UDHCPD_WRITE_LEASES_EARLY) {
 765                 /* rewrite the file with leases at every new acceptance */
 766                 write_leases();
 767         }
 768 }
 769
 770 /* NOINLINE: limit stack usage in caller */
 771 static NOINLINE void send_inform(struct dhcp_packet *oldpacket)
 772 {
 773         struct dhcp_packet packet;
 774
 775         /* "If a client has obtained a network address through some other means
 776          * (e.g., manual configuration), it may use a DHCPINFORM request message
 777          * to obtain other local configuration parameters.  Servers receiving a
 778          * DHCPINFORM message construct a DHCPACK message with any local
 779          * configuration parameters appropriate for the client without:
 780          * allocating a new address, checking for an existing binding, filling
 781          * in 'yiaddr' or including lease time parameters.  The servers SHOULD
 782          * unicast the DHCPACK reply to the address given in the 'ciaddr' field
 783          * of the DHCPINFORM message.
 784          * ...
 785          * The server responds to a DHCPINFORM message by sending a DHCPACK
 786          * message directly to the address given in the 'ciaddr' field
 787          * of the DHCPINFORM message.  The server MUST NOT send a lease
 788          * expiration time to the client and SHOULD NOT fill in 'yiaddr'."
 789          */
 790 //TODO: do a few sanity checks: is ciaddr set?
 791 //Better yet: is ciaddr == IP source addr?
 792         init_packet(&packet, oldpacket, DHCPACK);
 793         add_server_options(&packet);
 794
 795         send_packet(&packet, /*force_bcast:*/ 0);
 796 }
 797
 798 int udhcpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 799 int udhcpd_main(int argc UNUSED_PARAM, char **argv)
 800 {
 801         int server_socket = -1, retval;
 802         uint8_t *state;
 803         unsigned timeout_end;
 804         unsigned num_ips;
 805         unsigned opt;
 806         struct option_set *option;
 807         char *str_I = str_I;
 808         const char *str_a = "2000";
 809         unsigned arpping_ms;
 810         IF_FEATURE_UDHCP_PORT(char *str_P;)
 811
 812         setup_common_bufsiz();
 813
 814         IF_FEATURE_UDHCP_PORT(SERVER_PORT = 67;)
 815         IF_FEATURE_UDHCP_PORT(CLIENT_PORT = 68;)
 816
 817         opt = getopt32(argv, "^"
 818                 "fSI:va:"IF_FEATURE_UDHCP_PORT("P:")
 819                 "\0"
 820 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
 821                 "vv"
 822 #endif
 823                 , &str_I
 824                 , &str_a
 825                 IF_FEATURE_UDHCP_PORT(, &str_P)
 826                 IF_UDHCP_VERBOSE(, &dhcp_verbose)
 827                 );
 828         if (!(opt & 1)) { /* no -f */
 829                 bb_daemonize_or_rexec(0, argv);
 830                 logmode = LOGMODE_NONE;
 831         }
 832         /* update argv after the possible vfork+exec in daemonize */
 833         argv += optind;
 834         if (opt & 2) { /* -S */
 835                 openlog(applet_name, LOG_PID, LOG_DAEMON);
 836                 logmode |= LOGMODE_SYSLOG;
 837         }
 838         if (opt & 4) { /* -I */
 839                 len_and_sockaddr *lsa = xhost_and_af2sockaddr(str_I, 0, AF_INET);
 840                 server_config.server_nip = lsa->u.sin.sin_addr.s_addr;
 841                 free(lsa);
 842         }
 843 #if ENABLE_FEATURE_UDHCP_PORT
 844         if (opt & 32) { /* -P */
 845                 SERVER_PORT = xatou16(str_P);
 846                 CLIENT_PORT = SERVER_PORT + 1;
 847         }
 848 #endif
 849         arpping_ms = xatou(str_a);
 850
 851         /* Would rather not do read_config before daemonization -
 852          * otherwise NOMMU machines will parse config twice */
 853         read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE);
 854
 855         /* Make sure fd 0,1,2 are open */
 856         bb_sanitize_stdio();
 857         /* Equivalent of doing a fflush after every \n */
 858         setlinebuf(stdout);
 859
 860         /* Create pidfile */
 861         write_pidfile(server_config.pidfile);
 862         /* if (!..) bb_perror_msg("can't create pidfile %s", pidfile); */
 863
 864         bb_error_msg("started, v"BB_VER);
 865
 866         option = udhcp_find_option(server_config.options, DHCP_LEASE_TIME);
 867         server_config.max_lease_sec = DEFAULT_LEASE_TIME;
 868         if (option) {
 869                 move_from_unaligned32(server_config.max_lease_sec, option->data + OPT_DATA);
 870                 server_config.max_lease_sec = ntohl(server_config.max_lease_sec);
 871         }
 872
 873         /* Sanity check */
 874         num_ips = server_config.end_ip - server_config.start_ip + 1;
 875         if (server_config.max_leases > num_ips) {
 876                 bb_error_msg("max_leases=%u is too big, setting to %u",
 877                         (unsigned)server_config.max_leases, num_ips);
 878                 server_config.max_leases = num_ips;
 879         }
 880
 881         g_leases = xzalloc(server_config.max_leases * sizeof(g_leases[0]));
 882         read_leases(server_config.lease_file);
 883
 884         if (udhcp_read_interface(server_config.interface,
 885                         &server_config.ifindex,
 886                         (server_config.server_nip == 0 ? &server_config.server_nip : NULL),
 887                         server_config.server_mac)
 888         ) {
 889                 retval = 1;
 890                 goto ret;
 891         }
 892
 893         /* Setup the signal pipe */
 894         udhcp_sp_setup();
 895
 896  continue_with_autotime:
 897         timeout_end = monotonic_sec() + server_config.auto_time;
 898         while (1) { /* loop until universe collapses */
 899                 struct pollfd pfds[2];
 900                 struct dhcp_packet packet;
 901                 int bytes;
 902                 int tv;
 903                 uint8_t *server_id_opt;
 904                 uint8_t *requested_ip_opt;
 905                 uint32_t requested_nip = requested_nip; /* for compiler */
 906                 uint32_t static_lease_nip;
 907                 struct dyn_lease *lease, fake_lease;
 908
 909                 if (server_socket < 0) {
 910                         server_socket = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT,
 911                                         server_config.interface);
 912                 }
 913
 914                 udhcp_sp_fd_set(pfds, server_socket);
 915                 tv = timeout_end - monotonic_sec();
 916                 retval = 0;
 917                 if (!server_config.auto_time || tv > 0) {
 918                         retval = poll(pfds, 2, server_config.auto_time ? tv * 1000 : -1);
 919                 }
 920                 if (retval == 0) {
 921                         write_leases();
 922                         goto continue_with_autotime;
 923                 }
 924                 if (retval < 0 && errno != EINTR) {
 925                         log1("error on select");
 926                         continue;
 927                 }
 928
 929                 switch (udhcp_sp_read(pfds)) {
 930                 case SIGUSR1:
 931                         bb_error_msg("received %s", "SIGUSR1");
 932                         write_leases();
 933                         /* why not just reset the timeout, eh */
 934                         goto continue_with_autotime;
 935                 case SIGTERM:
 936                         bb_error_msg("received %s", "SIGTERM");
 937                         write_leases();
 938                         goto ret0;
 939                 case 0: /* no signal: read a packet */
 940                         break;
 941                 default: /* signal or error (probably EINTR): back to select */
 942                         continue;
 943                 }
 944
 945                 bytes = udhcp_recv_kernel_packet(&packet, server_socket);
 946                 if (bytes < 0) {
 947                         /* bytes can also be -2 ("bad packet data") */
 948                         if (bytes == -1 && errno != EINTR) {
 949                                 log1("read error: %s, reopening socket", strerror(errno));
 950                                 close(server_socket);
 951                                 server_socket = -1;
 952                         }
 953                         continue;
 954                 }
 955                 if (packet.hlen != 6) {
 956                         bb_error_msg("MAC length != 6, ignoring packet");
 957                         continue;
 958                 }
 959                 if (packet.op != BOOTREQUEST) {
 960                         bb_error_msg("not a REQUEST, ignoring packet");
 961                         continue;
 962                 }
 963                 state = udhcp_get_option(&packet, DHCP_MESSAGE_TYPE);
 964                 if (state == NULL || state[0] < DHCP_MINTYPE || state[0] > DHCP_MAXTYPE) {
 965                         bb_error_msg("no or bad message type option, ignoring packet");
 966                         continue;
 967                 }
 968
 969                 /* Get SERVER_ID if present */
 970                 server_id_opt = udhcp_get_option(&packet, DHCP_SERVER_ID);
 971                 if (server_id_opt) {
 972                         uint32_t server_id_network_order;
 973                         move_from_unaligned32(server_id_network_order, server_id_opt);
 974                         if (server_id_network_order != server_config.server_nip) {
 975                                 /* client talks to somebody else */
 976                                 log1("server ID doesn't match, ignoring");
 977                                 continue;
 978                         }
 979                 }
 980
 981                 /* Look for a static/dynamic lease */
 982                 static_lease_nip = get_static_nip_by_mac(server_config.static_leases, &packet.chaddr);
 983                 if (static_lease_nip) {
 984                         bb_error_msg("found static lease: %x", static_lease_nip);
 985                         memcpy(&fake_lease.lease_mac, &packet.chaddr, 6);
 986                         fake_lease.lease_nip = static_lease_nip;
 987                         fake_lease.expires = 0;
 988                         lease = &fake_lease;
 989                 } else {
 990                         lease = find_lease_by_mac(packet.chaddr);
 991                 }
 992
 993                 /* Get REQUESTED_IP if present */
 994                 requested_ip_opt = udhcp_get_option(&packet, DHCP_REQUESTED_IP);
 995                 if (requested_ip_opt) {
 996                         move_from_unaligned32(requested_nip, requested_ip_opt);
 997                 }
 998
 999                 switch (state[0]) {
1000
1001                 case DHCPDISCOVER:
1002                         log1("received %s", "DISCOVER");
1003
1004                         send_offer(&packet, static_lease_nip, lease, requested_ip_opt, arpping_ms);
1005                         break;
1006
1007                 case DHCPREQUEST:
1008                         log1("received %s", "REQUEST");
1009 /* RFC 2131:
1010
1011 o DHCPREQUEST generated during SELECTING state:
1012
1013    Client inserts the address of the selected server in 'server
1014    identifier', 'ciaddr' MUST be zero, 'requested IP address' MUST be
1015    filled in with the yiaddr value from the chosen DHCPOFFER.
1016
1017    Note that the client may choose to collect several DHCPOFFER
1018    messages and select the "best" offer.  The client indicates its
1019    selection by identifying the offering server in the DHCPREQUEST
1020    message.  If the client receives no acceptable offers, the client
1021    may choose to try another DHCPDISCOVER message.  Therefore, the
1022    servers may not receive a specific DHCPREQUEST from which they can
1023    decide whether or not the client has accepted the offer.
1024
1025 o DHCPREQUEST generated during INIT-REBOOT state:
1026
1027    'server identifier' MUST NOT be filled in, 'requested IP address'
1028    option MUST be filled in with client's notion of its previously
1029    assigned address. 'ciaddr' MUST be zero. The client is seeking to
1030    verify a previously allocated, cached configuration. Server SHOULD
1031    send a DHCPNAK message to the client if the 'requested IP address'
1032    is incorrect, or is on the wrong network.
1033
1034    Determining whether a client in the INIT-REBOOT state is on the
1035    correct network is done by examining the contents of 'giaddr', the
1036    'requested IP address' option, and a database lookup. If the DHCP
1037    server detects that the client is on the wrong net (i.e., the
1038    result of applying the local subnet mask or remote subnet mask (if
1039    'giaddr' is not zero) to 'requested IP address' option value
1040    doesn't match reality), then the server SHOULD send a DHCPNAK
1041    message to the client.
1042
1043    If the network is correct, then the DHCP server should check if
1044    the client's notion of its IP address is correct. If not, then the
1045    server SHOULD send a DHCPNAK message to the client. If the DHCP
1046    server has no record of this client, then it MUST remain silent,
1047    and MAY output a warning to the network administrator. This
1048    behavior is necessary for peaceful coexistence of non-
1049    communicating DHCP servers on the same wire.
1050
1051    If 'giaddr' is 0x0 in the DHCPREQUEST message, the client is on
1052    the same subnet as the server.  The server MUST broadcast the
1053    DHCPNAK message to the 0xffffffff broadcast address because the
1054    client may not have a correct network address or subnet mask, and
1055    the client may not be answering ARP requests.
1056
1057    If 'giaddr' is set in the DHCPREQUEST message, the client is on a
1058    different subnet.  The server MUST set the broadcast bit in the
1059    DHCPNAK, so that the relay agent will broadcast the DHCPNAK to the
1060    client, because the client may not have a correct network address
1061    or subnet mask, and the client may not be answering ARP requests.
1062
1063 o DHCPREQUEST generated during RENEWING state:
1064
1065    'server identifier' MUST NOT be filled in, 'requested IP address'
1066    option MUST NOT be filled in, 'ciaddr' MUST be filled in with
1067    client's IP address. In this situation, the client is completely
1068    configured, and is trying to extend its lease. This message will
1069    be unicast, so no relay agents will be involved in its
1070    transmission.  Because 'giaddr' is therefore not filled in, the
1071    DHCP server will trust the value in 'ciaddr', and use it when
1072    replying to the client.
1073
1074    A client MAY choose to renew or extend its lease prior to T1.  The
1075    server may choose not to extend the lease (as a policy decision by
1076    the network administrator), but should return a DHCPACK message
1077    regardless.
1078
1079 o DHCPREQUEST generated during REBINDING state:
1080
1081    'server identifier' MUST NOT be filled in, 'requested IP address'
1082    option MUST NOT be filled in, 'ciaddr' MUST be filled in with
1083    client's IP address. In this situation, the client is completely
1084    configured, and is trying to extend its lease. This message MUST
1085    be broadcast to the 0xffffffff IP broadcast address.  The DHCP
1086    server SHOULD check 'ciaddr' for correctness before replying to
1087    the DHCPREQUEST.
1088
1089    The DHCPREQUEST from a REBINDING client is intended to accommodate
1090    sites that have multiple DHCP servers and a mechanism for
1091    maintaining consistency among leases managed by multiple servers.
1092    A DHCP server MAY extend a client's lease only if it has local
1093    administrative authority to do so.
1094 */
1095                         if (!requested_ip_opt) {
1096                                 requested_nip = packet.ciaddr;
1097                                 if (requested_nip == 0) {
1098                                         log1("no requested IP and no ciaddr, ignoring");
1099                                         break;
1100                                 }
1101                         }
1102                         if (lease && requested_nip == lease->lease_nip) {
1103                                 /* client requested or configured IP matches the lease.
1104                                  * ACK it, and bump lease expiration time. */
1105                                 send_ACK(&packet, lease->lease_nip);
1106                                 break;
1107                         }
1108                         /* No lease for this MAC, or lease IP != requested IP */
1109
1110                         if (server_id_opt    /* client is in SELECTING state */
1111                          || requested_ip_opt /* client is in INIT-REBOOT state */
1112                         ) {
1113                                 /* "No, we don't have this IP for you" */
1114                                 send_NAK(&packet);
1115                         } /* else: client is in RENEWING or REBINDING, do not answer */
1116
1117                         break;
1118
1119                 case DHCPDECLINE:
1120                         /* RFC 2131:
1121                          * "If the server receives a DHCPDECLINE message,
1122                          * the client has discovered through some other means
1123                          * that the suggested network address is already
1124                          * in use. The server MUST mark the network address
1125                          * as not available and SHOULD notify the local
1126                          * sysadmin of a possible configuration problem."
1127                          *
1128                          * SERVER_ID must be present,
1129                          * REQUESTED_IP must be present,
1130                          * chaddr must be filled in,
1131                          * ciaddr must be 0 (we do not check this)
1132                          */
1133                         log1("received %s", "DECLINE");
1134                         if (server_id_opt
1135                          && requested_ip_opt
1136                          && lease  /* chaddr matches this lease */
1137                          && requested_nip == lease->lease_nip
1138                         ) {
1139                                 memset(lease->lease_mac, 0, sizeof(lease->lease_mac));
1140                                 lease->expires = time(NULL) + server_config.decline_time;
1141                         }
1142                         break;
1143
1144                 case DHCPRELEASE:
1145                         /* "Upon receipt of a DHCPRELEASE message, the server
1146                          * marks the network address as not allocated."
1147                          *
1148                          * SERVER_ID must be present,
1149                          * REQUESTED_IP must not be present (we do not check this),
1150                          * chaddr must be filled in,
1151                          * ciaddr must be filled in
1152                          */
1153                         log1("received %s", "RELEASE");
1154                         if (server_id_opt
1155                          && lease  /* chaddr matches this lease */
1156                          && packet.ciaddr == lease->lease_nip
1157                         ) {
1158                                 lease->expires = time(NULL);
1159                         }
1160                         break;
1161
1162                 case DHCPINFORM:
1163                         log1("received %s", "INFORM");
1164                         send_inform(&packet);
1165                         break;
1166                 }
1167         }
1168  ret0:
1169         retval = 0;
1170  ret:
1171         /*if (server_config.pidfile) - server_config.pidfile is never NULL */
1172                 remove_pidfile(server_config.pidfile);
1173         return retval;
1174 }