src/dhcpv4.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License v2 as published by
   6  * the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  *
  14  */
  15
  16 #include <time.h>
  17 #include <errno.h>
  18 #include <fcntl.h>
  19 #include <unistd.h>
  20 #include <stddef.h>
  21 #include <stdlib.h>
  22 #include <resolv.h>
  23 #include <limits.h>
  24 #include <net/if.h>
  25 #include <net/if_arp.h>
  26 #include <netinet/ip.h>
  27 #include <sys/ioctl.h>
  28 #include <sys/timerfd.h>
  29 #include <arpa/inet.h>
  30
  31 #include "odhcpd.h"
  32 #include "dhcpv4.h"
  33 #include "dhcpv6.h"
  34
  35
  36 static void handle_dhcpv4(void *addr, void *data, size_t len,
  37                 struct interface *iface, void *dest_addr);
  38 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
  39                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
  40                 const char *hostname);
  41
  42 // Create socket and register events
  43 int init_dhcpv4(void)
  44 {
  45         return 0;
  46 }
  47
  48 char *dhcpv4_msg_to_string(uint8_t reqmsg)
  49 {
  50         switch (reqmsg) {
  51         case (DHCPV4_MSG_DISCOVER):
  52                 return "DHCPV4_MSG_DISCOVER";
  53         case (DHCPV4_MSG_OFFER):
  54                 return "DHCPV4_MSG_OFFER";
  55         case (DHCPV4_MSG_REQUEST):
  56                 return "DHCPV4_MSG_REQUEST";
  57         case (DHCPV4_MSG_DECLINE):
  58                 return "DHCPV4_MSG_DECLINE";
  59         case (DHCPV4_MSG_ACK):
  60                 return "DHCPV4_MSG_ACK";
  61         case (DHCPV4_MSG_NAK):
  62                 return "DHCPV4_MSG_NAK";
  63         case (DHCPV4_MSG_RELEASE):
  64                 return "DHCPV4_MSG_RELEASE";
  65         case (DHCPV4_MSG_INFORM):
  66                 return "DHCPV4_MSG_INFORM";
  67         default:
  68                 return "UNKNOWN";
  69         }
  70 }
  71
  72 int setup_dhcpv4_interface(struct interface *iface, bool enable)
  73 {
  74         if (iface->dhcpv4_event.uloop.fd > 0) {
  75                 uloop_fd_delete(&iface->dhcpv4_event.uloop);
  76                 close(iface->dhcpv4_event.uloop.fd);
  77                 iface->dhcpv4_event.uloop.fd = -1;
  78         }
  79
  80         if (iface->dhcpv4 && enable) {
  81                 if (!iface->dhcpv4_assignments.next)
  82                         INIT_LIST_HEAD(&iface->dhcpv4_assignments);
  83
  84                 int sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  85                 if (sock < 0) {
  86                         syslog(LOG_ERR, "Failed to create DHCPv4 server socket: %s",
  87                                         strerror(errno));
  88                         return -1;
  89                 }
  90
  91                 // Basic IPv6 configuration
  92                 int val = 1;
  93                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  94                 setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &val, sizeof(val));
  95                 setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &val, sizeof(val));
  96
  97                 val = IPTOS_PREC_INTERNETCONTROL;
  98                 setsockopt(sock, IPPROTO_IP, IP_TOS, &val, sizeof(val));
  99
 100                 val = IP_PMTUDISC_DONT;
 101                 setsockopt(sock, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
 102
 103                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
 104                                 iface->ifname, strlen(iface->ifname));
 105
 106                 struct sockaddr_in bind_addr = {AF_INET, htons(DHCPV4_SERVER_PORT),
 107                                         {INADDR_ANY}, {0}};
 108
 109                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
 110                         syslog(LOG_ERR, "Failed to open DHCPv4 server socket: %s",
 111                                         strerror(errno));
 112                         return -1;
 113                 }
 114
 115
 116                 if (ntohl(iface->dhcpv4_start.s_addr) > ntohl(iface->dhcpv4_end.s_addr)) {
 117                         syslog(LOG_ERR, "Invalid DHCP range");
 118                         return -1;
 119                 }
 120
 121                 // Create a range if not specified
 122                 struct ifreq ifreq;
 123                 strncpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 124
 125                 struct sockaddr_in *saddr = (struct sockaddr_in*)&ifreq.ifr_addr;
 126                 struct sockaddr_in *smask = (struct sockaddr_in*)&ifreq.ifr_netmask;
 127                 if (!(iface->dhcpv4_start.s_addr & htonl(0xffff0000)) &&
 128                                 !(iface->dhcpv4_end.s_addr & htonl(0xffff0000)) &&
 129                                 !ioctl(sock, SIOCGIFADDR, &ifreq)) {
 130                         struct in_addr addr = saddr->sin_addr;
 131
 132                         ioctl(sock, SIOCGIFNETMASK, &ifreq);
 133                         struct in_addr mask = smask->sin_addr;
 134
 135                         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 136                         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 137
 138                         if (start && end && start < end &&
 139                                         start > ntohl(addr.s_addr & ~mask.s_addr) &&
 140                                         (start & ntohl(~mask.s_addr)) == start &&
 141                                         (end & ntohl(~mask.s_addr)) == end) {
 142                                 iface->dhcpv4_start.s_addr = htonl(start) |
 143                                                 (addr.s_addr & mask.s_addr);
 144                                 iface->dhcpv4_end.s_addr = htonl(end) |
 145                                                 (addr.s_addr & mask.s_addr);
 146                         } else if (ntohl(mask.s_addr) <= 0xfffffff0) {
 147                                 start = addr.s_addr & mask.s_addr;
 148                                 end = addr.s_addr & mask.s_addr;
 149
 150                                 if (ntohl(mask.s_addr) <= 0xffffff00) {
 151                                         iface->dhcpv4_start.s_addr = start | htonl(100);
 152                                         iface->dhcpv4_end.s_addr = end | htonl(250);
 153                                 } else if (ntohl(mask.s_addr) <= 0xffffffc0) {
 154                                         iface->dhcpv4_start.s_addr = start | htonl(10);
 155                                         iface->dhcpv4_end.s_addr = end | htonl(60);
 156                                 } else if (ntohl(mask.s_addr) <= 0xffffffe0) {
 157                                         iface->dhcpv4_start.s_addr = start | htonl(10);
 158                                         iface->dhcpv4_end.s_addr = end | htonl(30);
 159                                 } else {
 160                                         iface->dhcpv4_start.s_addr = start | htonl(3);
 161                                         iface->dhcpv4_end.s_addr = end | htonl(12);
 162                                 }
 163                         }
 164
 165
 166                 }
 167
 168                 // Parse static entries
 169                 struct lease *lease;
 170                 list_for_each_entry(lease, &leases, head) {
 171                         // Construct entry
 172                         size_t hostlen = strlen(lease->hostname) + 1;
 173                         struct dhcpv4_assignment *a = calloc(1, sizeof(*a) + hostlen);
 174                         if (!a) {
 175                                 syslog(LOG_ERR, "Calloc failed for static lease on interface %s",
 176                                         iface->ifname);
 177                                 return -1;
 178                         }
 179                         a->addr = ntohl(lease->ipaddr.s_addr);
 180                         memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
 181                         memcpy(a->hostname, lease->hostname, hostlen);
 182                         a->valid_until = LONG_MAX;
 183
 184                         // Assign to all interfaces
 185                         struct dhcpv4_assignment *c;
 186                         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 187                                 if (c->addr > a->addr) {
 188                                         list_add_tail(&a->head, &c->head);
 189                                         break;
 190                                 } else if (c->addr == a->addr) {
 191                                         // Already an assignment with that number
 192                                         break;
 193                                 }
 194                         }
 195                         if (&c->head == &iface->dhcpv4_assignments) {
 196                                 list_add(&a->head, &iface->dhcpv4_assignments);
 197                         }
 198
 199                         if (!a->head.next)
 200                                 free(a);
 201                 }
 202
 203                 // Clean invalid assignments
 204                 struct dhcpv4_assignment *a, *n;
 205                 list_for_each_entry_safe(a, n, &iface->dhcpv4_assignments, head) {
 206                         if ((htonl(a->addr) & smask->sin_addr.s_addr) !=
 207                                         (iface->dhcpv4_start.s_addr & smask->sin_addr.s_addr)) {
 208                                 list_del(&a->head);
 209                                 free(a);
 210                         }
 211                 }
 212
 213
 214                 if (iface->dhcpv4_leasetime < 60)
 215                         iface->dhcpv4_leasetime = 43200;
 216
 217                 iface->dhcpv4_event.uloop.fd = sock;
 218                 iface->dhcpv4_event.handle_dgram = handle_dhcpv4;
 219                 odhcpd_register(&iface->dhcpv4_event);
 220         } else if (iface->dhcpv4_assignments.next) {
 221                 while (!list_empty(&iface->dhcpv4_assignments)) {
 222                         struct dhcpv4_assignment *a = list_first_entry(&iface->dhcpv4_assignments,
 223                                         struct dhcpv4_assignment, head);
 224                         list_del(&a->head);
 225                         free(a);
 226                 }
 227
 228         }
 229         return 0;
 230 }
 231
 232
 233 static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 234                 uint8_t type, uint8_t len, const void *data)
 235 {
 236         uint8_t *c = *cookie;
 237         if (*cookie + 2 + len > (uint8_t*)&msg[1])
 238                 return;
 239
 240         *c++ = type;
 241         *c++ = len;
 242         memcpy(c, data, len);
 243
 244         *cookie = c + len;
 245 }
 246
 247
 248 // Simple DHCPv6-server for information requests
 249 static void handle_dhcpv4(void *addr, void *data, size_t len,
 250                 struct interface *iface, _unused void *dest_addr)
 251 {
 252         if (!iface->dhcpv4)
 253                 return;
 254
 255         struct dhcpv4_message *req = data;
 256         if (len < offsetof(struct dhcpv4_message, options) + 4 ||
 257                         req->op != DHCPV4_BOOTREQUEST || req->hlen != 6)
 258                 return;
 259
 260         int sock = iface->dhcpv4_event.uloop.fd;
 261         struct sockaddr_in ifaddr;
 262         struct sockaddr_in ifnetmask;
 263
 264         syslog(LOG_NOTICE, "Got DHCPv4 request");
 265
 266         struct ifreq ifreq;
 267         memcpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 268         if (ioctl(sock, SIOCGIFADDR, &ifreq)) {
 269                 syslog(LOG_WARNING, "DHCPv4 failed to detect address: %s", strerror(errno));
 270                 return;
 271         }
 272
 273         memcpy(&ifaddr, &ifreq.ifr_addr, sizeof(ifaddr));
 274         if (ioctl(sock, SIOCGIFNETMASK, &ifreq))
 275                 return;
 276
 277         memcpy(&ifnetmask, &ifreq.ifr_netmask, sizeof(ifnetmask));
 278         uint32_t network = ifaddr.sin_addr.s_addr & ifnetmask.sin_addr.s_addr;
 279
 280         if ((iface->dhcpv4_start.s_addr & ifnetmask.sin_addr.s_addr) != network ||
 281                         (iface->dhcpv4_end.s_addr & ifnetmask.sin_addr.s_addr) != network) {
 282                 syslog(LOG_WARNING, "DHCPv4 range out of assigned network");
 283                 return;
 284         }
 285
 286         struct ifreq ifr = {.ifr_name = ""};
 287         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 288
 289         struct dhcpv4_message reply = {
 290                 .op = DHCPV4_BOOTREPLY,
 291                 .htype = 1,
 292                 .hlen = 6,
 293                 .hops = 0,
 294                 .xid = req->xid,
 295                 .secs = 0,
 296                 .flags = req->flags,
 297                 .ciaddr = {INADDR_ANY},
 298                 .giaddr = req->giaddr,
 299                 .siaddr = ifaddr.sin_addr,
 300         };
 301         memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
 302
 303         reply.options[0] = 0x63;
 304         reply.options[1] = 0x82;
 305         reply.options[2] = 0x53;
 306         reply.options[3] = 0x63;
 307
 308         uint8_t *cookie = &reply.options[4];
 309         uint8_t reqmsg = DHCPV4_MSG_REQUEST;
 310         uint8_t msg = DHCPV4_MSG_ACK;
 311
 312         struct in_addr reqaddr = {INADDR_ANY};
 313         char hostname[256];
 314         hostname[0] = 0;
 315
 316         uint8_t *start = &req->options[4];
 317         uint8_t *end = ((uint8_t*)data) + len;
 318         struct dhcpv4_option *opt;
 319         dhcpv4_for_each_option(start, end, opt) {
 320                 if (opt->type == DHCPV4_OPT_MESSAGE && opt->len == 1) {
 321                         reqmsg = opt->data[0];
 322                 } else if (opt->type == DHCPV4_OPT_HOSTNAME && opt->len > 0) {
 323                         memcpy(hostname, opt->data, opt->len);
 324                         hostname[opt->len] = 0;
 325                 } else if (opt->type == DHCPV4_OPT_IPADDRESS && opt->len == 4) {
 326                         memcpy(&reqaddr, opt->data, 4);
 327                 } else if (opt->type == DHCPV4_OPT_SERVERID && opt->len == 4) {
 328                         if (memcmp(opt->data, &ifaddr.sin_addr, 4))
 329                                 return;
 330                 } else if (iface->filter_class && opt->type == DHCPV4_OPT_USER_CLASS) {
 331                         uint8_t *c = opt->data, *cend = &opt->data[opt->len];
 332                         for (; c < cend && &c[*c] < cend; c = &c[1 + *c]) {
 333                                 size_t elen = strlen(iface->filter_class);
 334                                 if (*c == elen && !memcmp(&c[1], iface->filter_class, elen))
 335                                         return; // Ignore from homenet
 336                         }
 337                 }
 338         }
 339
 340         if (reqmsg != DHCPV4_MSG_DISCOVER && reqmsg != DHCPV4_MSG_REQUEST &&
 341                         reqmsg != DHCPV4_MSG_INFORM && reqmsg != DHCPV4_MSG_DECLINE &&
 342                         reqmsg != DHCPV4_MSG_RELEASE)
 343                 return;
 344
 345         struct dhcpv4_assignment *lease = NULL;
 346         if (reqmsg != DHCPV4_MSG_INFORM)
 347                 lease = dhcpv4_lease(iface, reqmsg, req->chaddr, reqaddr, hostname);
 348
 349         if (!lease) {
 350                 if (reqmsg == DHCPV4_MSG_REQUEST)
 351                         msg = DHCPV4_MSG_NAK;
 352                 else if (reqmsg == DHCPV4_MSG_DISCOVER)
 353                         return;
 354         } else if (reqmsg == DHCPV4_MSG_DISCOVER) {
 355                 msg = DHCPV4_MSG_OFFER;
 356         } else if (reqmsg == DHCPV4_MSG_REQUEST && reqaddr.s_addr &&
 357                         reqaddr.s_addr != htonl(lease->addr)) {
 358                 msg = DHCPV4_MSG_NAK;
 359                 /*
 360                  * DHCP client requested an IP which we can't offer to him. Probably the
 361                  * client changed the network. The reply type is set to DHCPV4_MSG_NAK,
 362                  * because the client should not use that IP.
 363                  *
 364                  * For modern devices we build an answer that includes a valid IP, like
 365                  * a DHCPV4_MSG_ACK. The client will use that IP and doesn't need to
 366                  * perform additional DHCP round trips.
 367                  *
 368                  */
 369         }
 370
 371         syslog(LOG_WARNING, "received %s from %x:%x:%x:%x:%x:%x",
 372                         dhcpv4_msg_to_string(reqmsg),
 373                         req->chaddr[0],req->chaddr[1],req->chaddr[2],
 374                         req->chaddr[3],req->chaddr[4],req->chaddr[5]);
 375
 376         if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
 377                 return;
 378
 379         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 380         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SERVERID, 4, &ifaddr.sin_addr);
 381
 382         if (lease) {
 383                 reply.yiaddr.s_addr = htonl(lease->addr);
 384
 385                 uint32_t val = htonl(iface->dhcpv4_leasetime);
 386                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_LEASETIME, 4, &val);
 387
 388                 val = htonl(500 * iface->dhcpv4_leasetime / 1000);
 389                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_RENEW, 4, &val);
 390
 391                 val = htonl(875 * iface->dhcpv4_leasetime / 1000);
 392                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_REBIND, 4, &val);
 393
 394                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_NETMASK, 4, &ifnetmask.sin_addr);
 395
 396                 if (lease->hostname[0])
 397                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_HOSTNAME,
 398                                         strlen(lease->hostname), lease->hostname);
 399
 400                 if (!ioctl(sock, SIOCGIFBRDADDR, &ifr)) {
 401                         struct sockaddr_in *ina = (struct sockaddr_in*)&ifr.ifr_broadaddr;
 402                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_BROADCAST, 4, &ina->sin_addr);
 403                 }
 404         }
 405
 406         if (!ioctl(sock, SIOCGIFMTU, &ifr)) {
 407                 uint16_t mtu = htons(ifr.ifr_mtu);
 408                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MTU, 2, &mtu);
 409         }
 410
 411         if (iface->search && iface->search_len <= 255) {
 412                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SEARCH_DOMAIN,
 413                                 iface->search_len, iface->search);
 414         } else if (!res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 415                 uint8_t search_buf[256];
 416                 int len = dn_comp(_res.dnsrch[0], search_buf,
 417                                                 sizeof(search_buf), NULL, NULL);
 418                 if (len > 0)
 419                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SEARCH_DOMAIN,
 420                                         len, search_buf);
 421         }
 422
 423         if (iface->dhcpv4_router_cnt == 0)
 424                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
 425         else
 426                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER,
 427                                 4 * iface->dhcpv4_router_cnt, iface->dhcpv4_router);
 428
 429
 430         if (iface->dhcpv4_dns_cnt == 0)
 431                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER, 4, &ifaddr.sin_addr);
 432         else
 433                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER,
 434                                 4 * iface->dhcpv4_dns_cnt, iface->dhcpv4_dns);
 435
 436
 437         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_END, 0, NULL);
 438
 439         struct sockaddr_in dest = *((struct sockaddr_in*)addr);
 440         if (req->giaddr.s_addr) {
 441                 /*
 442                  * relay agent is configured, send reply to the agent
 443                  */
 444                 dest.sin_addr = req->giaddr;
 445                 dest.sin_port = htons(DHCPV4_SERVER_PORT);
 446         } else if (req->ciaddr.s_addr && req->ciaddr.s_addr != dest.sin_addr.s_addr) {
 447                 /*
 448                  * client has existing configuration (ciaddr is set) AND this address is
 449                  * not the address it used for the dhcp message
 450                  */
 451                 dest.sin_addr = req->ciaddr;
 452                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 453         } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
 454                         req->hlen != reply.hlen || !reply.yiaddr.s_addr) {
 455                 /*
 456                  * client requests a broadcast reply OR we can't offer an IP
 457                  */
 458                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 459                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 460         } else if (!req->ciaddr.s_addr && msg == DHCPV4_MSG_NAK) {
 461                 /*
 462                  * client has no previous configuration -> no IP, so we need to reply
 463                  * with a broadcast packet
 464                  */
 465                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 466                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 467         } else {
 468                 /*
 469                  * send reply to the newly (in this proccess) allocated IP
 470                  */
 471                 dest.sin_addr = reply.yiaddr;
 472                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 473
 474                 struct arpreq arp = {.arp_flags = ATF_COM};
 475                 memcpy(arp.arp_ha.sa_data, req->chaddr, 6);
 476                 memcpy(&arp.arp_pa, &dest, sizeof(arp.arp_pa));
 477                 memcpy(arp.arp_dev, iface->ifname, sizeof(arp.arp_dev));
 478                 ioctl(sock, SIOCSARP, &arp);
 479         }
 480
 481         if (dest.sin_addr.s_addr == INADDR_BROADCAST) {
 482                 /*
 483                  * reply goes to IP broadcast -> MAC broadcast
 484                  */
 485                 syslog(LOG_WARNING, "sending %s to ff:ff:ff:ff:ff:ff - %s",
 486                                 dhcpv4_msg_to_string(msg),
 487                                 inet_ntoa(dest.sin_addr));
 488         } else {
 489                 /*
 490                  * reply is send directly to IP,
 491                  * MAC is assumed to be the same as the request
 492                  */
 493                 syslog(LOG_WARNING, "sending %s to %x:%x:%x:%x:%x:%x - %s",
 494                                 dhcpv4_msg_to_string(msg),
 495                                 req->chaddr[0],req->chaddr[1],req->chaddr[2],
 496                                 req->chaddr[3],req->chaddr[4],req->chaddr[5],
 497                                 inet_ntoa(dest.sin_addr));
 498         }
 499
 500         sendto(sock, &reply, sizeof(reply), MSG_DONTWAIT,
 501                         (struct sockaddr*)&dest, sizeof(dest));
 502 }
 503
 504 static bool dhcpv4_test(struct interface *iface, uint32_t try)
 505 {
 506         struct dhcpv4_assignment *c;
 507         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 508                 if (c->addr == try) {
 509                         return false;
 510                 }
 511         }
 512         return true;
 513 }
 514
 515 static bool dhcpv4_assign(struct interface *iface,
 516                 struct dhcpv4_assignment *assign, uint32_t raddr)
 517 {
 518         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 519         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 520         uint32_t count = end - start + 1;
 521
 522         // try to assign the IP the client asked for
 523         if (start <= raddr && raddr <= end && dhcpv4_test(iface, raddr)) {
 524                 assign->addr = raddr;
 525                 list_add(&assign->head, &iface->dhcpv4_assignments);
 526                 syslog(LOG_DEBUG, "assigning the IP the client asked for: %u.%u.%u.%u",
 527                                 (assign->addr & 0xff000000) >> 24,
 528                                 (assign->addr & 0x00ff0000) >> 16,
 529                                 (assign->addr & 0x0000ff00) >> 8,
 530                                 (assign->addr & 0x000000ff));
 531                 return true;
 532         }
 533
 534         // Seed RNG with checksum of hwaddress
 535         uint32_t seed = 0;
 536         for (size_t i = 0; i < sizeof(assign->hwaddr); ++i) {
 537                 // Knuth's multiplicative method
 538                 uint8_t o = assign->hwaddr[i];
 539                 seed += (o*2654435761) % UINT32_MAX;
 540         }
 541         srand(seed);
 542
 543         uint32_t try = (((uint32_t)rand()) % count) + start;
 544
 545         if (list_empty(&iface->dhcpv4_assignments)) {
 546                 assign->addr = try;
 547                 list_add(&assign->head, &iface->dhcpv4_assignments);
 548                 syslog(LOG_DEBUG, "assigning mapped IP (empty list): %u.%u.%u.%u",
 549                                 (assign->addr & 0xff000000) >> 24,
 550                                 (assign->addr & 0x00ff0000) >> 16,
 551                                 (assign->addr & 0x0000ff00) >> 8,
 552                                 (assign->addr & 0x000000ff));
 553                 return true;
 554         }
 555
 556         for (uint32_t i = 0; i < count; ++i) {
 557                 if (dhcpv4_test(iface, try)) {
 558                         /* test was successful: IP address is not assigned, assign it */
 559                         assign->addr = try;
 560                         list_add(&assign->head, &iface->dhcpv4_assignments);
 561                         syslog(LOG_DEBUG, "assigning mapped IP: %u.%u.%u.%u (try %u of %u)",
 562                                         (assign->addr & 0xff000000) >> 24,
 563                                         (assign->addr & 0x00ff0000) >> 16,
 564                                         (assign->addr & 0x0000ff00) >> 8,
 565                                         (assign->addr & 0x000000ff), i, count);
 566                         return true;
 567                 }
 568                 try = (((try - start) + 1) % count) + start;
 569         }
 570
 571         syslog(LOG_DEBUG, "can't assign any IP address -> address space is full");
 572         return false;
 573 }
 574
 575
 576 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 577                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
 578                 const char *hostname)
 579 {
 580         struct dhcpv4_assignment *lease = NULL;
 581         uint32_t raddr = ntohl(reqaddr.s_addr);
 582         time_t now = odhcpd_time();
 583
 584         struct dhcpv4_assignment *c, *n, *a = NULL;
 585         list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
 586                 if (!memcmp(c->hwaddr, mac, 6)) {
 587                         a = c;
 588                         if (c->addr == raddr)
 589                                 break;
 590                 } else if (c->valid_until < now) {
 591                         list_del(&c->head);
 592                         free(c);
 593                 }
 594         }
 595
 596         if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
 597                 bool assigned = !!a;
 598                 size_t hostlen = strlen(hostname) + 1;
 599
 600                 if (!a && !iface->no_dynamic_dhcp) { // Create new binding
 601                         a = calloc(1, sizeof(*a) + hostlen);
 602                         if (!a) {
 603                                 syslog(LOG_ERR, "Failed to calloc binding on interface %s", iface->ifname);
 604                                 return NULL;
 605                         }
 606                         memcpy(a->hwaddr, mac, sizeof(a->hwaddr));
 607                         memcpy(a->hostname, hostname, hostlen);
 608
 609                         assigned = dhcpv4_assign(iface, a, raddr);
 610                 }
 611
 612                 if (assigned && !a->hostname[0] && hostname) {
 613                         a = realloc(a, sizeof(*a) + hostlen);
 614                         if (!a) {
 615                                 syslog(LOG_ERR, "Failed to realloc binding on interface %s", iface->ifname);
 616                                 return NULL;
 617                         }
 618                         memcpy(a->hostname, hostname, hostlen);
 619
 620                         // Fixup list
 621                         a->head.next->prev = &a->head;
 622                         a->head.prev->next = &a->head;
 623                 }
 624
 625                 // Was only a solicitation: mark binding for removal
 626                 if (assigned && a->valid_until < now) {
 627                         a->valid_until = (msg == DHCPV4_MSG_DISCOVER) ? 0 :
 628                                         (now + iface->dhcpv4_leasetime);
 629                 } else if (!assigned && a) { // Cleanup failed assignment
 630                         free(a);
 631                         a = NULL;
 632                 }
 633
 634                 if (assigned && a)
 635                         lease = a;
 636         } else if (msg == DHCPV4_MSG_RELEASE) {
 637                 if (a && a->valid_until != LONG_MAX)
 638                         a->valid_until = 0;
 639         } else if (msg == DHCPV4_MSG_DECLINE && a && a->valid_until != LONG_MAX) {
 640                 memset(a->hwaddr, 0, sizeof(a->hwaddr));
 641                 a->valid_until = now + 3600; // Block address for 1h
 642         }
 643
 644         dhcpv6_write_statefile();
 645
 646         return lease;
 647 }
 648