src/dhcpv4.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  * Copyright (C) 2016 Hans Dedecker <dedeckeh@gmail.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License v2 as published by
   7  * the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  *
  15  */
  16
  17 #include <time.h>
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <unistd.h>
  21 #include <stddef.h>
  22 #include <stdlib.h>
  23 #include <resolv.h>
  24 #include <limits.h>
  25 #include <net/if.h>
  26 #include <net/if_arp.h>
  27 #include <netinet/ip.h>
  28 #include <sys/ioctl.h>
  29 #include <sys/timerfd.h>
  30 #include <arpa/inet.h>
  31
  32 #include <libubox/md5.h>
  33
  34 #include "odhcpd.h"
  35 #include "dhcpv4.h"
  36 #include "dhcpv6.h"
  37
  38 static int setup_dhcpv4_addresses(struct interface *iface);
  39 static void update_static_assignments(struct interface *iface);
  40 static void free_dhcpv4_assignment(struct dhcpv4_assignment *a);
  41 static void dhcpv4_fr_start(struct dhcpv4_assignment *a);
  42 static void dhcpv4_fr_stop(struct dhcpv4_assignment *a);
  43 static void handle_dhcpv4(void *addr, void *data, size_t len,
  44                 struct interface *iface, void *dest_addr);
  45 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
  46                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
  47                 uint32_t *leasetime, const char *hostname, const size_t hostname_len,
  48                 const bool accept_fr_nonce, bool *incl_fr_opt, uint32_t *fr_serverid);
  49 static uint32_t serial = 0;
  50
  51 struct odhcpd_ref_ip {
  52         struct list_head head;
  53         int ref_cnt;
  54         struct odhcpd_ipaddr addr;
  55 };
  56
  57 /* Create socket and register events */
  58 int init_dhcpv4(void)
  59 {
  60         return 0;
  61 }
  62
  63 int setup_dhcpv4_interface(struct interface *iface, bool enable)
  64 {
  65         if (iface->dhcpv4_event.uloop.fd > 0) {
  66                 uloop_fd_delete(&iface->dhcpv4_event.uloop);
  67                 close(iface->dhcpv4_event.uloop.fd);
  68                 iface->dhcpv4_event.uloop.fd = -1;
  69         }
  70
  71         if (iface->dhcpv4 && enable) {
  72                 if (!iface->dhcpv4_assignments.next)
  73                         INIT_LIST_HEAD(&iface->dhcpv4_assignments);
  74
  75                 if (!iface->dhcpv4_fr_ips.next)
  76                         INIT_LIST_HEAD(&iface->dhcpv4_fr_ips);
  77
  78                 int sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  79                 if (sock < 0) {
  80                         syslog(LOG_ERR, "Failed to create DHCPv4 server socket: %s",
  81                                         strerror(errno));
  82                         return -1;
  83                 }
  84
  85                 /* Basic IPv4 configuration */
  86                 int val = 1;
  87                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  88                 setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &val, sizeof(val));
  89                 setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &val, sizeof(val));
  90
  91                 val = IPTOS_PREC_INTERNETCONTROL;
  92                 setsockopt(sock, IPPROTO_IP, IP_TOS, &val, sizeof(val));
  93
  94                 val = IP_PMTUDISC_DONT;
  95                 setsockopt(sock, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
  96
  97                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
  98                                 iface->ifname, strlen(iface->ifname));
  99
 100                 struct sockaddr_in bind_addr = {AF_INET, htons(DHCPV4_SERVER_PORT),
 101                                         {INADDR_ANY}, {0}};
 102
 103                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
 104                         syslog(LOG_ERR, "Failed to open DHCPv4 server socket: %s",
 105                                         strerror(errno));
 106                         return -1;
 107                 }
 108
 109                 iface->dhcpv4_event.uloop.fd = sock;
 110                 iface->dhcpv4_event.handle_dgram = handle_dhcpv4;
 111                 odhcpd_register(&iface->dhcpv4_event);
 112
 113                 if (setup_dhcpv4_addresses(iface) < 0)
 114                         return -1;
 115
 116                 update_static_assignments(iface);
 117         } else if (iface->dhcpv4_assignments.next) {
 118                 while (!list_empty(&iface->dhcpv4_assignments))
 119                         free_dhcpv4_assignment(list_first_entry(&iface->dhcpv4_assignments,
 120                                                         struct dhcpv4_assignment, head));
 121         }
 122         return 0;
 123 }
 124
 125 static struct dhcpv4_assignment *find_assignment_by_hwaddr(struct interface *iface, const uint8_t *hwaddr)
 126 {
 127         struct dhcpv4_assignment *a;
 128
 129         list_for_each_entry(a, &iface->dhcpv4_assignments, head)
 130                 if (!memcmp(a->hwaddr, hwaddr, 6))
 131                         return a;
 132
 133         return NULL;
 134 }
 135
 136 static struct dhcpv4_assignment *find_assignment_by_addr(struct interface *iface, const uint32_t addr)
 137 {
 138         struct dhcpv4_assignment *a;
 139
 140         list_for_each_entry(a, &iface->dhcpv4_assignments, head)
 141                 if (a->addr == addr)
 142                         return a;
 143
 144         return NULL;
 145 }
 146
 147 static int setup_dhcpv4_addresses(struct interface *iface)
 148 {
 149         iface->dhcpv4_start_ip.s_addr = INADDR_ANY;
 150         iface->dhcpv4_end_ip.s_addr = INADDR_ANY;
 151         iface->dhcpv4_local.s_addr = INADDR_ANY;
 152         iface->dhcpv4_bcast.s_addr = INADDR_ANY;
 153         iface->dhcpv4_mask.s_addr = INADDR_ANY;
 154
 155         /* Sanity checks */
 156         if (iface->dhcpv4_start.s_addr & htonl(0xffff0000) ||
 157             iface->dhcpv4_end.s_addr & htonl(0xffff0000) ||
 158             ntohl(iface->dhcpv4_start.s_addr) > ntohl(iface->dhcpv4_end.s_addr)) {
 159                 syslog(LOG_ERR, "invalid DHCP range for %s", iface->name);
 160                 return -1;
 161         }
 162
 163         if (!iface->addr4_len) {
 164                 syslog(LOG_WARNING, "no network(s) available on %s", iface->name);
 165                 return -1;
 166         }
 167
 168         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 169         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 170
 171         for (size_t i = 0; i < iface->addr4_len && start && end; i++) {
 172                 struct in_addr *addr = &iface->addr4[i].addr.in;
 173                 struct in_addr mask;
 174
 175                 odhcpd_bitlen2netmask(false, iface->addr4[i].prefix, &mask);
 176                 if ((start & ntohl(~mask.s_addr)) == start &&
 177                             (end & ntohl(~mask.s_addr)) == end) {
 178                         iface->dhcpv4_start_ip.s_addr = htonl(start) |
 179                                                         (addr->s_addr & mask.s_addr);
 180                         iface->dhcpv4_end_ip.s_addr = htonl(end) |
 181                                                         (addr->s_addr & mask.s_addr);
 182                         iface->dhcpv4_local = *addr;
 183                         iface->dhcpv4_bcast = iface->addr4[i].broadcast;
 184                         iface->dhcpv4_mask = mask;
 185                         return 0;
 186                 }
 187         }
 188
 189         /* Don't allocate IP range for subnets bigger than 28 */
 190         if (iface->addr4[0].prefix > 28) {
 191                 syslog(LOG_WARNING, "auto allocation of DHCP range fails on %s", iface->name);
 192                 return -1;
 193         }
 194
 195         iface->dhcpv4_local = iface->addr4[0].addr.in;
 196         iface->dhcpv4_bcast = iface->addr4[0].broadcast;
 197         odhcpd_bitlen2netmask(false, iface->addr4[0].prefix, &iface->dhcpv4_mask);
 198         end = start = iface->dhcpv4_local.s_addr & iface->dhcpv4_mask.s_addr;
 199
 200         /* Auto allocate ranges */
 201         if (ntohl(iface->dhcpv4_mask.s_addr) <= 0xffffff00) {
 202                 iface->dhcpv4_start_ip.s_addr = start | htonl(100);
 203                 iface->dhcpv4_end_ip.s_addr = end | htonl(250);
 204         } else if (ntohl(iface->dhcpv4_mask.s_addr) <= 0xffffffc0) {
 205                 iface->dhcpv4_start_ip.s_addr = start | htonl(10);
 206                 iface->dhcpv4_end_ip.s_addr = end | htonl(60);
 207         } else if (ntohl(iface->dhcpv4_mask.s_addr) <= 0xffffffe0) {
 208                 iface->dhcpv4_start_ip.s_addr = start | htonl(10);
 209                 iface->dhcpv4_end_ip.s_addr = end | htonl(30);
 210         } else {
 211                 iface->dhcpv4_start_ip.s_addr = start | htonl(3);
 212                 iface->dhcpv4_end_ip.s_addr = end | htonl(12);
 213         }
 214
 215         return 0;
 216 }
 217
 218 static void update_static_assignments(struct interface *iface)
 219 {
 220         struct dhcpv4_assignment *a, *c;
 221
 222         /* Cleanup static entries not belonging to the network */
 223         list_for_each_entry_safe(a, c, &iface->dhcpv4_assignments, head) {
 224                 if ((a->flags & OAF_STATIC) &&
 225                                 ((a->addr & iface->dhcpv4_mask.s_addr) !=
 226                                  (iface->dhcpv4_start.s_addr & iface->dhcpv4_mask.s_addr)))
 227                         free_dhcpv4_assignment(a);
 228         }
 229
 230         /* Parse static entries */
 231         struct lease *lease;
 232         list_for_each_entry(lease, &leases, head) {
 233                 if ((iface->dhcpv4_start_ip.s_addr & iface->dhcpv4_mask.s_addr) !=
 234                                 (lease->ipaddr.s_addr & iface->dhcpv4_mask.s_addr)) {
 235                         continue;
 236                 }
 237
 238                 a = find_assignment_by_hwaddr(iface, lease->mac.ether_addr_octet);
 239
 240                 if (!a) {
 241                         /* Check if there's an assignment with the specified IP address */
 242                         if (find_assignment_by_addr(iface, lease->ipaddr.s_addr))
 243                                 continue;
 244
 245                         /* Construct entry */
 246                         a = calloc(1, sizeof(*a));
 247                         if (!a) {
 248                                 syslog(LOG_ERR, "Calloc failed for static lease on interface %s",
 249                                         iface->ifname);
 250                                 continue;
 251                         }
 252                         memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
 253                 }
 254
 255                 a->leasetime = lease->dhcpv4_leasetime;
 256
 257                 a->addr = lease->ipaddr.s_addr;
 258                 /* Static assignment */
 259                 a->flags |= OAF_STATIC;
 260                 /* Infinite valid */
 261                 a->valid_until = 0;
 262                 a->iface = iface;
 263                 if (lease->hostname[0]) {
 264                         free(a->hostname);
 265                         a->hostname = strdup(lease->hostname);
 266                 }
 267
 268                 /* Assign to all interfaces */
 269                 list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 270                         if (ntohl(c->addr) > ntohl(a->addr)) {
 271                                 list_add_tail(&a->head, &c->head);
 272                                 break;
 273                         }
 274                 }
 275
 276                 if (&c->head == &iface->dhcpv4_assignments)
 277                         list_add(&a->head, &iface->dhcpv4_assignments);
 278         }
 279 }
 280
 281 static void inc_ref_cnt_ip(struct odhcpd_ref_ip **ptr, struct odhcpd_ref_ip *ip)
 282 {
 283         *ptr = ip;
 284         ip->ref_cnt++;
 285 }
 286
 287 static void decr_ref_cnt_ip(struct odhcpd_ref_ip **ptr, struct interface *iface)
 288 {
 289         struct odhcpd_ref_ip *ip = *ptr;
 290
 291         if (--ip->ref_cnt == 0) {
 292                 odhcpd_setup_addr(&ip->addr, iface, false, false);
 293
 294                 list_del(&ip->head);
 295                 free(ip);
 296         }
 297
 298         *ptr = NULL;
 299 }
 300
 301 static bool leases_require_fr(struct interface *iface, struct odhcpd_ipaddr *addr,
 302                                 uint32_t mask)
 303 {
 304         struct dhcpv4_assignment *a = NULL;
 305         struct odhcpd_ref_ip *fr_ip = NULL;
 306
 307         list_for_each_entry(a, &iface->dhcpv4_assignments, head) {
 308                 if ((a->accept_fr_nonce || iface->dhcpv4_forcereconf) &&
 309                     !a->fr_ip &&
 310                     ((a->addr & mask) == (addr->addr.in.s_addr & mask))) {
 311                         if (!fr_ip) {
 312                                 fr_ip = calloc(1, sizeof(*fr_ip));
 313                                 if (!fr_ip)
 314                                         break;
 315
 316                                 list_add(&fr_ip->head, &iface->dhcpv4_fr_ips);
 317                                 fr_ip->addr = *addr;
 318                         }
 319                         inc_ref_cnt_ip(&a->fr_ip, fr_ip);
 320                 }
 321         }
 322
 323         return fr_ip ? true : false;
 324 }
 325
 326 void dhcpv4_addr_update(struct interface *iface)
 327 {
 328         if (iface->dhcpv4 == MODE_DISABLED)
 329                 return;
 330
 331         struct odhcpd_ipaddr ip;
 332         struct odhcpd_ref_ip *a;
 333         struct dhcpv4_assignment *c;
 334         uint32_t mask = iface->dhcpv4_mask.s_addr;
 335
 336         memset(&ip, sizeof(ip), 0);
 337         ip.addr.in = iface->dhcpv4_local;
 338         ip.prefix = odhcpd_netmask2bitlen(false, &iface->dhcpv4_mask);
 339         ip.broadcast = iface->dhcpv4_bcast;
 340
 341         setup_dhcpv4_addresses(iface);
 342
 343         if ((ip.addr.in.s_addr & mask) ==
 344             (iface->dhcpv4_local.s_addr & iface->dhcpv4_mask.s_addr))
 345                 return;
 346
 347         if (ip.addr.in.s_addr && !leases_require_fr(iface, &ip, mask))
 348                 return;
 349
 350         if (iface->dhcpv4_local.s_addr == INADDR_ANY || list_empty(&iface->dhcpv4_fr_ips))
 351                 return;
 352
 353         a = list_first_entry(&iface->dhcpv4_fr_ips, struct odhcpd_ref_ip, head);
 354
 355         if (odhcpd_setup_addr(&a->addr, iface, false, true)) {
 356                 syslog(LOG_ERR, "Failed to add ip address");
 357                 return;
 358         }
 359
 360         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 361                 if ((c->flags & OAF_BOUND) && c->fr_ip && !c->fr_cnt) {
 362                         if (c->accept_fr_nonce || iface->dhcpv4_forcereconf)
 363                                 dhcpv4_fr_start(c);
 364                         else
 365                                 dhcpv4_fr_stop(c);
 366                 }
 367         }
 368 }
 369
 370 static char *dhcpv4_msg_to_string(uint8_t reqmsg)
 371 {
 372         switch (reqmsg) {
 373         case (DHCPV4_MSG_DISCOVER):
 374                 return "DHCPV4_MSG_DISCOVER";
 375         case (DHCPV4_MSG_OFFER):
 376                 return "DHCPV4_MSG_OFFER";
 377         case (DHCPV4_MSG_REQUEST):
 378                 return "DHCPV4_MSG_REQUEST";
 379         case (DHCPV4_MSG_DECLINE):
 380                 return "DHCPV4_MSG_DECLINE";
 381         case (DHCPV4_MSG_ACK):
 382                 return "DHCPV4_MSG_ACK";
 383         case (DHCPV4_MSG_NAK):
 384                 return "DHCPV4_MSG_NAK";
 385         case (DHCPV4_MSG_RELEASE):
 386                 return "DHCPV4_MSG_RELEASE";
 387         case (DHCPV4_MSG_INFORM):
 388                 return "DHCPV4_MSG_INFORM";
 389         case (DHCPV4_MSG_FORCERENEW):
 390                 return "DHCPV4_MSG_FORCERENEW";
 391         default:
 392                 return "UNKNOWN";
 393         }
 394 }
 395
 396 static void free_dhcpv4_assignment(struct dhcpv4_assignment *a)
 397 {
 398         if (a->head.next)
 399                 list_del(&a->head);
 400
 401         if (a->fr_ip)
 402                 dhcpv4_fr_stop(a);
 403
 404         free(a->hostname);
 405         free(a);
 406 }
 407
 408 static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 409                 uint8_t type, uint8_t len, const void *data)
 410 {
 411         uint8_t *c = *cookie;
 412         if (*cookie + 2 + len > (uint8_t*)&msg[1])
 413                 return;
 414
 415         *c++ = type;
 416         *c++ = len;
 417         memcpy(c, data, len);
 418
 419         *cookie = c + len;
 420 }
 421
 422 static void dhcpv4_fr_send(struct dhcpv4_assignment *a)
 423 {
 424         struct dhcpv4_message fr_msg = {
 425                 .op = DHCPV4_BOOTREPLY,
 426                 .htype = 1,
 427                 .hlen = 6,
 428                 .hops = 0,
 429                 .secs = 0,
 430                 .flags = 0,
 431                 .ciaddr = {INADDR_ANY},
 432                 .yiaddr = {INADDR_ANY},
 433                 .siaddr = {INADDR_ANY},
 434                 .giaddr = {INADDR_ANY},
 435                 .chaddr = {0},
 436                 .sname = {0},
 437                 .file = {0},
 438         };
 439         struct dhcpv4_auth_forcerenew *auth_o, auth = {
 440                 .protocol = 3,
 441                 .algorithm = 1,
 442                 .rdm = 0,
 443                 .replay = {htonl(time(NULL)), htonl(++serial)},
 444                 .type = 2,
 445                 .key = {0},
 446         };
 447         struct interface *iface = a->iface;
 448
 449         odhcpd_urandom(&fr_msg.xid, sizeof(fr_msg.xid));
 450         memcpy(fr_msg.chaddr, a->hwaddr, fr_msg.hlen);
 451
 452         fr_msg.options[0] = 0x63;
 453         fr_msg.options[1] = 0x82;
 454         fr_msg.options[2] = 0x53;
 455         fr_msg.options[3] = 0x63;
 456
 457         uint8_t *cookie = &fr_msg.options[4];
 458         uint8_t msg = DHCPV4_MSG_FORCERENEW;
 459
 460         dhcpv4_put(&fr_msg, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 461         if (a->accept_fr_nonce) {
 462                 dhcpv4_put(&fr_msg, &cookie, DHCPV4_OPT_AUTHENTICATION, sizeof(auth), &auth);
 463                 auth_o = (struct dhcpv4_auth_forcerenew *)(cookie - sizeof(auth));
 464                 dhcpv4_put(&fr_msg, &cookie, DHCPV4_OPT_END, 0, NULL);
 465
 466                 md5_ctx_t md5;
 467                 uint8_t secretbytes[64];
 468                 memset(secretbytes, 0, sizeof(secretbytes));
 469                 memcpy(secretbytes, a->key, sizeof(a->key));
 470
 471                 for (size_t i = 0; i < sizeof(secretbytes); ++i)
 472                         secretbytes[i] ^= 0x36;
 473
 474                 md5_begin(&md5);
 475                 md5_hash(secretbytes, sizeof(secretbytes), &md5);
 476                 md5_hash(&fr_msg, sizeof(fr_msg), &md5);
 477                 md5_end(auth_o->key, &md5);
 478
 479                 for (size_t i = 0; i < sizeof(secretbytes); ++i) {
 480                         secretbytes[i] ^= 0x36;
 481                         secretbytes[i] ^= 0x5c;
 482                 }
 483
 484                 md5_begin(&md5);
 485                 md5_hash(secretbytes, sizeof(secretbytes), &md5);
 486                 md5_hash(auth_o->key, sizeof(auth_o->key), &md5);
 487                 md5_end(auth_o->key, &md5);
 488         } else {
 489                 dhcpv4_put(&fr_msg, &cookie, DHCPV4_OPT_SERVERID, 4,
 490                                 &a->fr_ip->addr.addr.in.s_addr);
 491                 dhcpv4_put(&fr_msg, &cookie, DHCPV4_OPT_END, 0, NULL);
 492         }
 493
 494         struct sockaddr_in dest;
 495         memset(&dest, 0, sizeof(dest));
 496         dest.sin_family = AF_INET;
 497         dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 498         dest.sin_addr.s_addr = a->addr;
 499
 500         syslog(LOG_WARNING, "sending %s to %02x:%02x:%02x:%02x:%02x:%02x - %s",
 501                         dhcpv4_msg_to_string(msg),
 502                         a->hwaddr[0], a->hwaddr[1], a->hwaddr[2],
 503                         a->hwaddr[3], a->hwaddr[4], a->hwaddr[5],
 504                         inet_ntoa(dest.sin_addr));
 505
 506         sendto(iface->dhcpv4_event.uloop.fd, &fr_msg, sizeof(fr_msg),
 507                         MSG_DONTWAIT, (struct sockaddr*)&dest, sizeof(dest));
 508 }
 509
 510 static void dhcpv4_fr_timer(struct uloop_timeout *event)
 511 {
 512         struct dhcpv4_assignment *a = container_of(event, struct dhcpv4_assignment, fr_timer);
 513
 514         if (a->fr_cnt > 0 && a->fr_cnt < 8) {
 515                 dhcpv4_fr_send(a);
 516                 uloop_timeout_set(&a->fr_timer, 1000 << a->fr_cnt);
 517                 a->fr_cnt++;
 518         } else
 519                 dhcpv4_fr_stop(a);
 520 }
 521
 522 static void dhcpv4_fr_start(struct dhcpv4_assignment *a)
 523 {
 524         uloop_timeout_set(&a->fr_timer, 1000 << a->fr_cnt);
 525         a->fr_timer.cb = dhcpv4_fr_timer;
 526         a->fr_cnt++;
 527
 528         dhcpv4_fr_send(a);
 529 }
 530
 531 static void dhcpv4_fr_stop(struct dhcpv4_assignment *a)
 532 {
 533         uloop_timeout_cancel(&a->fr_timer);
 534         decr_ref_cnt_ip(&a->fr_ip, a->iface);
 535         a->fr_cnt = 0;
 536         a->fr_timer.cb = NULL;
 537 }
 538
 539 // Handler for DHCPv4 messages
 540 static void handle_dhcpv4(void *addr, void *data, size_t len,
 541                 struct interface *iface, _unused void *dest_addr)
 542 {
 543         if (!iface->dhcpv4)
 544                 return;
 545
 546         struct dhcpv4_message *req = data;
 547         if (len < offsetof(struct dhcpv4_message, options) + 4 ||
 548                         req->op != DHCPV4_BOOTREQUEST || req->hlen != 6)
 549                 return;
 550
 551
 552         syslog(LOG_NOTICE, "Got DHCPv4 request");
 553
 554         if (!iface->dhcpv4_start_ip.s_addr && !iface->dhcpv4_end_ip.s_addr) {
 555                 syslog(LOG_WARNING, "No DHCP range available on %s", iface->name);
 556                 return;
 557         }
 558
 559         int sock = iface->dhcpv4_event.uloop.fd;
 560
 561         struct dhcpv4_message reply = {
 562                 .op = DHCPV4_BOOTREPLY,
 563                 .htype = req->htype,
 564                 .hlen = req->hlen,
 565                 .hops = 0,
 566                 .xid = req->xid,
 567                 .secs = 0,
 568                 .flags = req->flags,
 569                 .ciaddr = {INADDR_ANY},
 570                 .giaddr = req->giaddr,
 571                 .siaddr = iface->dhcpv4_local,
 572         };
 573         memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
 574
 575         reply.options[0] = 0x63;
 576         reply.options[1] = 0x82;
 577         reply.options[2] = 0x53;
 578         reply.options[3] = 0x63;
 579
 580         uint8_t *cookie = &reply.options[4];
 581         uint8_t reqmsg = DHCPV4_MSG_REQUEST;
 582         uint8_t msg = DHCPV4_MSG_ACK;
 583
 584         struct in_addr reqaddr = {INADDR_ANY};
 585         uint32_t leasetime = 0;
 586         size_t hostname_len = 0;
 587         char hostname[256];
 588         bool accept_fr_nonce = false;
 589         bool incl_fr_opt = false;
 590
 591         uint8_t *start = &req->options[4];
 592         uint8_t *end = ((uint8_t*)data) + len;
 593         struct dhcpv4_option *opt;
 594         dhcpv4_for_each_option(start, end, opt) {
 595                 if (opt->type == DHCPV4_OPT_MESSAGE && opt->len == 1)
 596                         reqmsg = opt->data[0];
 597                 else if (opt->type == DHCPV4_OPT_HOSTNAME && opt->len > 0) {
 598                         hostname_len = opt->len;
 599                         memcpy(hostname, opt->data, hostname_len);
 600                         hostname[hostname_len] = 0;
 601                 } else if (opt->type == DHCPV4_OPT_IPADDRESS && opt->len == 4)
 602                         memcpy(&reqaddr, opt->data, 4);
 603                 else if (opt->type == DHCPV4_OPT_SERVERID && opt->len == 4) {
 604                         if (memcmp(opt->data, &iface->dhcpv4_local, 4))
 605                                 return;
 606                 } else if (iface->filter_class && opt->type == DHCPV4_OPT_USER_CLASS) {
 607                         uint8_t *c = opt->data, *cend = &opt->data[opt->len];
 608                         for (; c < cend && &c[*c] < cend; c = &c[1 + *c]) {
 609                                 size_t elen = strlen(iface->filter_class);
 610                                 if (*c == elen && !memcmp(&c[1], iface->filter_class, elen))
 611                                         return; // Ignore from homenet
 612                         }
 613                 } else if (opt->type == DHCPV4_OPT_LEASETIME && opt->len == 4)
 614                         memcpy(&leasetime, opt->data, 4);
 615                 else if (opt->type == DHCPV4_OPT_FORCERENEW_NONCE_CAPABLE && opt->len > 0) {
 616                         for (uint8_t i = 0; i < opt->len; i++) {
 617                                 if (opt->data[i] == 1) {
 618                                         accept_fr_nonce = true;
 619                                         break;
 620                                 }
 621                         }
 622
 623                 }
 624         }
 625
 626         if (reqmsg != DHCPV4_MSG_DISCOVER && reqmsg != DHCPV4_MSG_REQUEST &&
 627                         reqmsg != DHCPV4_MSG_INFORM && reqmsg != DHCPV4_MSG_DECLINE &&
 628                         reqmsg != DHCPV4_MSG_RELEASE)
 629                 return;
 630
 631         struct dhcpv4_assignment *lease = NULL;
 632         uint32_t serverid = iface->dhcpv4_local.s_addr;
 633         uint32_t fr_serverid = INADDR_ANY;
 634
 635         if (reqmsg != DHCPV4_MSG_INFORM)
 636                 lease = dhcpv4_lease(iface, reqmsg, req->chaddr, reqaddr,
 637                                         &leasetime, hostname, hostname_len,
 638                                         accept_fr_nonce, &incl_fr_opt, &fr_serverid);
 639
 640         if (!lease) {
 641                 if (reqmsg == DHCPV4_MSG_REQUEST)
 642                         msg = DHCPV4_MSG_NAK;
 643                 else if (reqmsg == DHCPV4_MSG_DISCOVER)
 644                         return;
 645         } else if (reqmsg == DHCPV4_MSG_DISCOVER)
 646                 msg = DHCPV4_MSG_OFFER;
 647         else if (reqmsg == DHCPV4_MSG_REQUEST &&
 648                         ((reqaddr.s_addr && reqaddr.s_addr != lease->addr) ||
 649                          (req->ciaddr.s_addr && req->ciaddr.s_addr != lease->addr))) {
 650                 msg = DHCPV4_MSG_NAK;
 651                 /*
 652                  * DHCP client requested an IP which we can't offer to him. Probably the
 653                  * client changed the network or the network has been changed. The reply
 654                  * type is set to DHCPV4_MSG_NAK, because the client should not use that IP.
 655                  *
 656                  * For modern devices we build an answer that includes a valid IP, like
 657                  * a DHCPV4_MSG_ACK. The client will use that IP and doesn't need to
 658                  * perform additional DHCP round trips.
 659                  *
 660                  */
 661
 662                 /*
 663                  *
 664                  * Buggy clients do serverid checking in nack messages; therefore set the
 665                  * serverid in nack messages triggered by a previous force renew equal to
 666                  * the server id in use at that time by the server
 667                  *
 668                  */
 669                 if (fr_serverid)
 670                         serverid = fr_serverid;
 671
 672                 if (req->ciaddr.s_addr &&
 673                                 ((iface->dhcpv4_start_ip.s_addr & iface->dhcpv4_mask.s_addr) !=
 674                                  (req->ciaddr.s_addr & iface->dhcpv4_mask.s_addr)))
 675                         req->ciaddr.s_addr = INADDR_ANY;
 676         }
 677
 678         syslog(LOG_WARNING, "received %s from %02x:%02x:%02x:%02x:%02x:%02x",
 679                         dhcpv4_msg_to_string(reqmsg),
 680                         req->chaddr[0],req->chaddr[1],req->chaddr[2],
 681                         req->chaddr[3],req->chaddr[4],req->chaddr[5]);
 682
 683         if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
 684                 return;
 685
 686         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 687         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SERVERID, 4, &serverid);
 688
 689         if (lease) {
 690                 uint32_t val;
 691
 692                 reply.yiaddr.s_addr = lease->addr;
 693
 694                 val = htonl(leasetime);
 695                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_LEASETIME, 4, &val);
 696
 697                 if (leasetime != UINT32_MAX) {
 698                         val = htonl(500 * leasetime / 1000);
 699                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_RENEW, 4, &val);
 700
 701                         val = htonl(875 * leasetime / 1000);
 702                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_REBIND, 4, &val);
 703                 }
 704
 705                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_NETMASK, 4,
 706                                 &iface->dhcpv4_mask.s_addr);
 707
 708                 if (lease->hostname)
 709                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_HOSTNAME,
 710                                         strlen(lease->hostname), lease->hostname);
 711
 712                 if (iface->dhcpv4_bcast.s_addr != INADDR_ANY)
 713                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_BROADCAST, 4, &iface->dhcpv4_bcast);
 714
 715                 if (incl_fr_opt) {
 716                         if (reqmsg == DHCPV4_MSG_REQUEST) {
 717                                 struct dhcpv4_auth_forcerenew auth = {
 718                                         .protocol = 3,
 719                                         .algorithm = 1,
 720                                         .rdm = 0,
 721                                         .replay = {htonl(time(NULL)), htonl(++serial)},
 722                                         .type = 1,
 723                                         .key = {0},
 724                                 };
 725
 726                                 memcpy(auth.key, lease->key, sizeof(auth.key));
 727                                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_AUTHENTICATION, sizeof(auth), &auth);
 728                         } else {
 729                                 uint8_t one = 1;
 730                                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_FORCERENEW_NONCE_CAPABLE,
 731                                         sizeof(one), &one);
 732                         }
 733                 }
 734         }
 735
 736         struct ifreq ifr = {.ifr_name = ""};
 737         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 738
 739         if (!ioctl(sock, SIOCGIFMTU, &ifr)) {
 740                 uint16_t mtu = htons(ifr.ifr_mtu);
 741                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MTU, 2, &mtu);
 742         }
 743
 744         if (iface->search && iface->search_len <= 255)
 745                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SEARCH_DOMAIN,
 746                                 iface->search_len, iface->search);
 747         else if (!res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 748                 uint8_t search_buf[256];
 749                 int len = dn_comp(_res.dnsrch[0], search_buf,
 750                                                 sizeof(search_buf), NULL, NULL);
 751                 if (len > 0)
 752                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SEARCH_DOMAIN,
 753                                         len, search_buf);
 754         }
 755
 756         if (iface->dhcpv4_router_cnt == 0)
 757                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &iface->dhcpv4_local);
 758         else
 759                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER,
 760                                 4 * iface->dhcpv4_router_cnt, iface->dhcpv4_router);
 761
 762
 763         if (iface->dhcpv4_dns_cnt == 0)
 764                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER, 4, &iface->dhcpv4_local);
 765         else
 766                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER,
 767                                 4 * iface->dhcpv4_dns_cnt, iface->dhcpv4_dns);
 768
 769
 770         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_END, 0, NULL);
 771
 772         struct sockaddr_in dest = *((struct sockaddr_in*)addr);
 773         if (req->giaddr.s_addr) {
 774                 /*
 775                  * relay agent is configured, send reply to the agent
 776                  */
 777                 dest.sin_addr = req->giaddr;
 778                 dest.sin_port = htons(DHCPV4_SERVER_PORT);
 779         } else if (req->ciaddr.s_addr && req->ciaddr.s_addr != dest.sin_addr.s_addr) {
 780                 /*
 781                  * client has existing configuration (ciaddr is set) AND this address is
 782                  * not the address it used for the dhcp message
 783                  */
 784                 dest.sin_addr = req->ciaddr;
 785                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 786         } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
 787                         req->hlen != reply.hlen || !reply.yiaddr.s_addr) {
 788                 /*
 789                  * client requests a broadcast reply OR we can't offer an IP
 790                  */
 791                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 792                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 793         } else if (!req->ciaddr.s_addr && msg == DHCPV4_MSG_NAK) {
 794                 /*
 795                  * client has no previous configuration -> no IP, so we need to reply
 796                  * with a broadcast packet
 797                  */
 798                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 799                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 800         } else {
 801                 /*
 802                  * send reply to the newly (in this proccess) allocated IP
 803                  */
 804                 dest.sin_addr = reply.yiaddr;
 805                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 806
 807                 struct arpreq arp = {.arp_flags = ATF_COM};
 808                 memcpy(arp.arp_ha.sa_data, req->chaddr, 6);
 809                 memcpy(&arp.arp_pa, &dest, sizeof(arp.arp_pa));
 810                 memcpy(arp.arp_dev, iface->ifname, sizeof(arp.arp_dev));
 811                 ioctl(sock, SIOCSARP, &arp);
 812         }
 813
 814         if (dest.sin_addr.s_addr == INADDR_BROADCAST)
 815                 /* reply goes to IP broadcast -> MAC broadcast */
 816                 syslog(LOG_WARNING, "sending %s to ff:ff:ff:ff:ff:ff - %s",
 817                                 dhcpv4_msg_to_string(msg),
 818                                 inet_ntoa(dest.sin_addr));
 819         else
 820                 /*
 821                  * reply is send directly to IP,
 822                  * MAC is assumed to be the same as the request
 823                  */
 824                 syslog(LOG_WARNING, "sending %s to %02x:%02x:%02x:%02x:%02x:%02x - %s",
 825                                 dhcpv4_msg_to_string(msg),
 826                                 req->chaddr[0],req->chaddr[1],req->chaddr[2],
 827                                 req->chaddr[3],req->chaddr[4],req->chaddr[5],
 828                                 inet_ntoa(dest.sin_addr));
 829
 830         sendto(sock, &reply, sizeof(reply), MSG_DONTWAIT,
 831                         (struct sockaddr*)&dest, sizeof(dest));
 832 }
 833
 834 static bool dhcpv4_test(struct interface *iface, uint32_t try)
 835 {
 836         struct dhcpv4_assignment *c;
 837         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 838                 if (c->addr == try)
 839                         return false;
 840         }
 841
 842         return true;
 843 }
 844
 845 static bool dhcpv4_assign(struct interface *iface,
 846                 struct dhcpv4_assignment *assign, uint32_t raddr)
 847 {
 848         uint32_t start = ntohl(iface->dhcpv4_start_ip.s_addr);
 849         uint32_t end = ntohl(iface->dhcpv4_end_ip.s_addr);
 850         uint32_t count = end - start + 1;
 851
 852         // try to assign the IP the client asked for
 853         if (start <= ntohl(raddr) && ntohl(raddr) <= end && dhcpv4_test(iface, raddr)) {
 854                 assign->addr = raddr;
 855                 syslog(LOG_INFO, "assigning the IP the client asked for: %u.%u.%u.%u",
 856                                 ((uint8_t *)&assign->addr)[0],
 857                                 ((uint8_t *)&assign->addr)[1],
 858                                 ((uint8_t *)&assign->addr)[2],
 859                                 ((uint8_t *)&assign->addr)[3]);
 860                 return true;
 861         }
 862
 863         // Seed RNG with checksum of hwaddress
 864         uint32_t seed = 0;
 865         for (size_t i = 0; i < sizeof(assign->hwaddr); ++i) {
 866                 // Knuth's multiplicative method
 867                 uint8_t o = assign->hwaddr[i];
 868                 seed += (o*2654435761) % UINT32_MAX;
 869         }
 870
 871         srand(seed);
 872
 873         uint32_t try = (((uint32_t)rand()) % count) + start;
 874
 875         if (list_empty(&iface->dhcpv4_assignments)) {
 876                 assign->addr = htonl(try);
 877                 syslog(LOG_INFO, "assigning mapped IP (empty list): %u.%u.%u.%u",
 878                                 ((uint8_t *)&assign->addr)[0],
 879                                 ((uint8_t *)&assign->addr)[1],
 880                                 ((uint8_t *)&assign->addr)[2],
 881                                 ((uint8_t *)&assign->addr)[3]);
 882                 return true;
 883         }
 884
 885         for (uint32_t i = 0; i < count; ++i) {
 886                 if (dhcpv4_test(iface, htonl(try))) {
 887                         /* test was successful: IP address is not assigned, assign it */
 888                         assign->addr = htonl(try);
 889                         syslog(LOG_DEBUG, "assigning mapped IP: %u.%u.%u.%u (try %u of %u)",
 890                                         ((uint8_t *)&assign->addr)[0],
 891                                         ((uint8_t *)&assign->addr)[1],
 892                                         ((uint8_t *)&assign->addr)[2],
 893                                         ((uint8_t *)&assign->addr)[3],
 894                                         i, count);
 895                         return true;
 896                 }
 897                 try = (((try - start) + 1) % count) + start;
 898         }
 899
 900         syslog(LOG_WARNING, "can't assign any IP address -> address space is full");
 901         return false;
 902 }
 903
 904
 905 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 906                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
 907                 uint32_t *leasetime, const char *hostname, const size_t hostname_len,
 908                 const bool accept_fr_nonce, bool *incl_fr_opt, uint32_t *fr_serverid)
 909 {
 910         struct dhcpv4_assignment *lease = NULL;
 911         time_t now = odhcpd_time();
 912
 913         struct dhcpv4_assignment *c, *n, *a = NULL;
 914         list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
 915                 if (!memcmp(c->hwaddr, mac, 6)) {
 916                         a = c;
 917                         if (c->addr == reqaddr.s_addr)
 918                                 break;
 919                 } else if (!INFINITE_VALID(c->valid_until) && c->valid_until < now)
 920                         free_dhcpv4_assignment(c);
 921         }
 922
 923         if (a && (a->flags & OAF_BOUND) && a->fr_ip) {
 924                 *fr_serverid = a->fr_ip->addr.addr.in.s_addr;
 925                 dhcpv4_fr_stop(a);
 926         }
 927
 928         if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
 929                 bool assigned = !!a;
 930
 931                 if (!a) {
 932                         if (!iface->no_dynamic_dhcp) {
 933                                 /* Create new binding */
 934                                 a = calloc(1, sizeof(*a));
 935                                 if (!a) {
 936                                         syslog(LOG_ERR, "Failed to calloc binding on interface %s",
 937                                                         iface->ifname);
 938                                         return NULL;
 939                                 }
 940                                 memcpy(a->hwaddr, mac, sizeof(a->hwaddr));
 941                                 /* Don't consider new assignment as infinite */
 942                                 a->valid_until = now;
 943
 944                                 assigned = dhcpv4_assign(iface, a, reqaddr.s_addr);
 945                                 if (assigned) {
 946                                         a->iface = iface;
 947                                         list_add(&a->head, &iface->dhcpv4_assignments);
 948                                 }
 949                         }
 950                 } else if ((a->addr & iface->dhcpv4_mask.s_addr) !=
 951                                 (iface->dhcpv4_start_ip.s_addr & iface->dhcpv4_mask.s_addr)) {
 952                         list_del(&a->head);
 953
 954                         assigned = dhcpv4_assign(iface, a, reqaddr.s_addr);
 955                         if (assigned)
 956                                 list_add(&a->head, &iface->dhcpv4_assignments);
 957                 }
 958
 959                 if (assigned) {
 960                         uint32_t my_leasetime;
 961
 962                         if (a->leasetime)
 963                                 my_leasetime = a->leasetime;
 964                         else
 965                                 my_leasetime = iface->dhcpv4_leasetime;
 966
 967                         if ((*leasetime == 0) || (my_leasetime < *leasetime))
 968                                 *leasetime = my_leasetime;
 969
 970                         if (msg == DHCPV4_MSG_DISCOVER) {
 971                                 a->flags &= ~OAF_BOUND;
 972
 973                                 *incl_fr_opt = accept_fr_nonce;
 974                                 if (!(a->flags & OAF_STATIC))
 975                                         a->valid_until = now;
 976                         } else {
 977                                 if (hostname_len > 0) {
 978                                         a->hostname = realloc(a->hostname, hostname_len + 1);
 979                                         if (a->hostname) {
 980                                                 memcpy(a->hostname, hostname, hostname_len);
 981                                                 a->hostname[hostname_len] = 0;
 982                                         }
 983                                 }
 984
 985                                 if (!(a->flags & OAF_BOUND)) {
 986                                         a->accept_fr_nonce = accept_fr_nonce;
 987                                         *incl_fr_opt = accept_fr_nonce;
 988                                         odhcpd_urandom(a->key, sizeof(a->key));
 989                                         a->flags |= OAF_BOUND;
 990                                 } else
 991                                         *incl_fr_opt = false;
 992
 993                                 if (!(a->flags & OAF_STATIC))
 994                                         a->valid_until = ((*leasetime == UINT32_MAX) ? 0 : (time_t)(now + *leasetime));
 995                         }
 996                 } else if (!assigned && a) {
 997                         /* Cleanup failed assignment */
 998                         free_dhcpv4_assignment(a);
 999                         a = NULL;
1000                 }
1001
1002                 if (assigned && a)
1003                         lease = a;
1004         } else if (msg == DHCPV4_MSG_RELEASE && a) {
1005                 a->flags &= ~OAF_BOUND;
1006
1007                 if (!(a->flags & OAF_STATIC))
1008                         a->valid_until = now - 1;
1009
1010         } else if (msg == DHCPV4_MSG_DECLINE && a) {
1011                 a->flags &= ~OAF_BOUND;
1012
1013                 if (!(a->flags & OAF_STATIC)) {
1014                         memset(a->hwaddr, 0, sizeof(a->hwaddr));
1015                         a->valid_until = now + 3600; /* Block address for 1h */
1016                 }
1017         }
1018
1019         dhcpv6_write_statefile();
1020
1021         return lease;
1022 }