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 <net/if.h>
  24 #include <net/if_arp.h>
  25 #include <netinet/ip.h>
  26 #include <sys/ioctl.h>
  27 #include <sys/timerfd.h>
  28 #include <arpa/inet.h>
  29
  30 #include "odhcpd.h"
  31 #include "dhcpv4.h"
  32 #include "dhcpv6.h"
  33
  34
  35 static void handle_dhcpv4(void *addr, void *data, size_t len,
  36                 struct interface *iface);
  37 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
  38                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
  39                 const char *hostname);
  40
  41
  42 // Create socket and register events
  43 int init_dhcpv4(void)
  44 {
  45         return 0;
  46 }
  47
  48
  49 int setup_dhcpv4_interface(struct interface *iface, bool enable)
  50 {
  51         if (iface->dhcpv4_event.uloop.fd > 0) {
  52                 close(iface->dhcpv4_event.uloop.fd);
  53                 iface->dhcpv4_event.uloop.fd = -1;
  54         }
  55
  56         if (iface->dhcpv4 && enable) {
  57                 if (!iface->dhcpv4_assignments.next)
  58                         INIT_LIST_HEAD(&iface->dhcpv4_assignments);
  59
  60                 int sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  61
  62                 // Basic IPv6 configuration
  63                 int val = 1;
  64                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  65                 setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &val, sizeof(val));
  66                 setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &val, sizeof(val));
  67
  68                 val = IPTOS_PREC_INTERNETCONTROL;
  69                 setsockopt(sock, IPPROTO_IP, IP_TOS, &val, sizeof(val));
  70
  71                 val = IP_PMTUDISC_DONT;
  72                 setsockopt(sock, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
  73
  74                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
  75                                 iface->ifname, strlen(iface->ifname));
  76
  77                 struct sockaddr_in bind_addr = {AF_INET, htons(DHCPV4_SERVER_PORT),
  78                                         {INADDR_ANY}, {0}};
  79
  80                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  81                         syslog(LOG_ERR, "Failed to open DHCPv4 server socket: %s",
  82                                         strerror(errno));
  83                         return -1;
  84                 }
  85
  86
  87                 if (ntohl(iface->dhcpv4_start.s_addr) > ntohl(iface->dhcpv4_end.s_addr)) {
  88                         syslog(LOG_ERR, "Invalid DHCP range");
  89                         return -1;
  90                 }
  91
  92                 // Create a range if not specified
  93                 struct ifreq ifreq;
  94                 strncpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
  95
  96                 struct sockaddr_in *saddr = (struct sockaddr_in*)&ifreq.ifr_addr;
  97                 struct sockaddr_in *smask = (struct sockaddr_in*)&ifreq.ifr_netmask;
  98                 if (!(iface->dhcpv4_start.s_addr & htonl(0xffff0000)) &&
  99                                 !(iface->dhcpv4_end.s_addr & htonl(0xffff0000)) &&
 100                                 !ioctl(sock, SIOCGIFADDR, &ifreq)) {
 101                         struct in_addr addr = saddr->sin_addr;
 102
 103                         ioctl(sock, SIOCGIFNETMASK, &ifreq);
 104                         struct in_addr mask = smask->sin_addr;
 105
 106                         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 107                         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 108
 109                         if (start && end && start < end &&
 110                                         start > ntohl(addr.s_addr & ~mask.s_addr) &&
 111                                         (start & ntohl(mask.s_addr)) == start &&
 112                                         (end & ntohl(mask.s_addr)) == end) {
 113                                 iface->dhcpv4_start.s_addr = htonl(start) |
 114                                                 (addr.s_addr & mask.s_addr);
 115                                 iface->dhcpv4_end.s_addr = htonl(end) |
 116                                                 (addr.s_addr & mask.s_addr);
 117                         } else if (ntohl(mask.s_addr) <= 0xffffffc0) {
 118                                 start = addr.s_addr & mask.s_addr;
 119                                 end = addr.s_addr & mask.s_addr;
 120
 121                                 if (ntohl(mask.s_addr) <= 0xffffff00) {
 122                                         iface->dhcpv4_start.s_addr = start | htonl(100);
 123                                         iface->dhcpv4_end.s_addr = end | htonl(250);
 124                                 } else {
 125                                         iface->dhcpv4_start.s_addr = start | htonl(10);
 126                                         iface->dhcpv4_end.s_addr = end | htonl(59);
 127                                 }
 128                         }
 129
 130
 131                 }
 132
 133                 // Parse static entries
 134                 struct lease *lease;
 135                 list_for_each_entry(lease, &leases, head) {
 136                         // Construct entry
 137                         size_t hostlen = strlen(lease->hostname) + 1;
 138                         struct dhcpv4_assignment *a = calloc(1, sizeof(*a) + hostlen);
 139
 140                         a->addr = ntohl(lease->ipaddr.s_addr);
 141                         memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
 142                         memcpy(a->hostname, lease->hostname, hostlen);
 143
 144                         // Assign to all interfaces
 145                         struct dhcpv4_assignment *c;
 146                         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 147                                 if (c->addr > a->addr) {
 148                                         list_add_tail(&a->head, &c->head);
 149                                 } else if (c->addr == a->addr) {
 150                                         // Already an assignment with that number
 151                                         break;
 152                                 }
 153                         }
 154
 155                         if (!a->head.next)
 156                                 free(a);
 157                 }
 158
 159                 // Clean invalid assignments
 160                 struct dhcpv4_assignment *a, *n;
 161                 list_for_each_entry_safe(a, n, &iface->dhcpv4_assignments, head) {
 162                         if ((htonl(a->addr) & smask->sin_addr.s_addr) !=
 163                                         (saddr->sin_addr.s_addr & smask->sin_addr.s_addr)) {
 164                                 list_del(&a->head);
 165                                 free(a);
 166                         }
 167                 }
 168
 169
 170                 if (iface->dhcpv4_leasetime < 60)
 171                         iface->dhcpv4_leasetime = 43200;
 172
 173                 iface->dhcpv4_event.uloop.fd = sock;
 174                 iface->dhcpv4_event.handle_dgram = handle_dhcpv4;
 175                 odhcpd_register(&iface->dhcpv4_event);
 176         } else if (iface->dhcpv4_assignments.next) {
 177                 while (!list_empty(&iface->dhcpv4_assignments)) {
 178                         struct dhcpv4_assignment *a = list_first_entry(&iface->dhcpv4_assignments,
 179                                         struct dhcpv4_assignment, head);
 180                         list_del(&a->head);
 181                         free(a->hostname);
 182                         free(a);
 183                 }
 184
 185         }
 186         return 0;
 187 }
 188
 189
 190 static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 191                 uint8_t type, uint8_t len, const void *data)
 192 {
 193         uint8_t *c = *cookie;
 194         if (*cookie + 2 + len > (uint8_t*)&msg[1])
 195                 return;
 196
 197         *c++ = type;
 198         *c++ = len;
 199         memcpy(c, data, len);
 200
 201         *cookie = c + len;
 202 }
 203
 204
 205 // Simple DHCPv6-server for information requests
 206 static void handle_dhcpv4(void *addr, void *data, size_t len,
 207                 struct interface *iface)
 208 {
 209         if (!iface->dhcpv4)
 210                 return;
 211
 212         struct dhcpv4_message *req = data;
 213         if (len < offsetof(struct dhcpv4_message, options) + 4 ||
 214                         req->op != DHCPV4_BOOTREQUEST || req->hlen != 6)
 215                 return;
 216
 217         int sock = iface->dhcpv4_event.uloop.fd;
 218         struct sockaddr_in ifaddr;
 219         struct sockaddr_in ifnetmask;
 220
 221         syslog(LOG_NOTICE, "Got DHCPv4 request");
 222
 223         struct ifreq ifreq;
 224         memcpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 225         if (ioctl(sock, SIOCGIFADDR, &ifreq)) {
 226                 syslog(LOG_WARNING, "DHCPv4 failed to detect address: %s", strerror(errno));
 227                 return;
 228         }
 229
 230         memcpy(&ifaddr, &ifreq.ifr_addr, sizeof(ifaddr));
 231         if (ioctl(sock, SIOCGIFNETMASK, &ifreq))
 232                 return;
 233
 234         memcpy(&ifnetmask, &ifreq.ifr_netmask, sizeof(ifnetmask));
 235         uint32_t network = ifaddr.sin_addr.s_addr & ifnetmask.sin_addr.s_addr;
 236
 237         if ((iface->dhcpv4_start.s_addr & ifnetmask.sin_addr.s_addr) != network ||
 238                         (iface->dhcpv4_end.s_addr & ifnetmask.sin_addr.s_addr) != network) {
 239                 syslog(LOG_WARNING, "DHCPv4 range out of assigned network");
 240                 return;
 241         }
 242
 243         struct ifreq ifr = {.ifr_name = ""};
 244         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 245
 246         struct dhcpv4_message reply = {
 247                 .op = DHCPV4_BOOTREPLY,
 248                 .htype = 1,
 249                 .hlen = 6,
 250                 .hops = 0,
 251                 .xid = req->xid,
 252                 .secs = 0,
 253                 .flags = req->flags,
 254                 .ciaddr = {INADDR_ANY},
 255                 .giaddr = req->giaddr,
 256                 .siaddr = ifaddr.sin_addr,
 257         };
 258         memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
 259
 260         reply.options[0] = 0x63;
 261         reply.options[1] = 0x82;
 262         reply.options[2] = 0x53;
 263         reply.options[3] = 0x63;
 264
 265         uint8_t *cookie = &reply.options[4];
 266         uint8_t reqmsg = DHCPV4_MSG_REQUEST;
 267         uint8_t msg = DHCPV4_MSG_ACK;
 268
 269         struct in_addr reqaddr = {INADDR_ANY};
 270         char hostname[256];
 271         hostname[0] = 0;
 272
 273         uint8_t *start = &req->options[4];
 274         uint8_t *end = ((uint8_t*)data) + len;
 275         struct dhcpv4_option *opt;
 276         dhcpv4_for_each_option(start, end, opt) {
 277                 if (opt->type == DHCPV4_OPT_MESSAGE && opt->len == 1) {
 278                         reqmsg = opt->data[0];
 279                 } else if (opt->type == DHCPV4_OPT_HOSTNAME && opt->len > 0) {
 280                         memcpy(hostname, opt->data, opt->len);
 281                         hostname[opt->len] = 0;
 282                 } else if (opt->type == DHCPV4_OPT_IPADDRESS && opt->len == 4) {
 283                         memcpy(&reqaddr, opt->data, 4);
 284                 } else if (opt->type == DHCPV4_OPT_SERVERID && opt->len == 4) {
 285                         if (memcmp(opt->data, &ifaddr.sin_addr, 4))
 286                                 return;
 287                 }
 288         }
 289
 290         if (reqmsg != DHCPV4_MSG_DISCOVER && reqmsg != DHCPV4_MSG_REQUEST &&
 291                         reqmsg != DHCPV4_MSG_INFORM && reqmsg != DHCPV4_MSG_DECLINE &&
 292                         reqmsg != DHCPV4_MSG_RELEASE)
 293                 return;
 294
 295         struct dhcpv4_assignment *lease = NULL;
 296         if (reqmsg != DHCPV4_MSG_INFORM)
 297                 lease = dhcpv4_lease(iface, reqmsg, req->chaddr, reqaddr, hostname);
 298
 299         if (!lease) {
 300                 if (reqmsg == DHCPV4_MSG_REQUEST)
 301                         msg = DHCPV4_MSG_NAK;
 302                 else if (reqmsg == DHCPV4_MSG_DISCOVER)
 303                         return;
 304         } else if (reqmsg == DHCPV4_MSG_DISCOVER) {
 305                 msg = DHCPV4_MSG_OFFER;
 306         }
 307
 308         if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
 309                 return;
 310
 311         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 312         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SERVERID, 4, &ifaddr.sin_addr);
 313
 314         if (lease) {
 315                 reply.yiaddr.s_addr = htonl(lease->addr);
 316
 317                 uint32_t val = htonl(iface->dhcpv4_leasetime);
 318                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_LEASETIME, 4, &val);
 319
 320                 val = htonl(500 * iface->dhcpv4_leasetime / 1000);
 321                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_RENEW, 4, &val);
 322
 323                 val = htonl(875 * iface->dhcpv4_leasetime / 1000);
 324                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_REBIND, 4, &val);
 325
 326                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_NETMASK, 4, &ifnetmask.sin_addr);
 327
 328                 if (lease->hostname[0])
 329                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_HOSTNAME,
 330                                         strlen(lease->hostname), lease->hostname);
 331
 332                 if (!ioctl(sock, SIOCGIFBRDADDR, &ifr)) {
 333                         struct sockaddr_in *ina = (struct sockaddr_in*)&ifr.ifr_broadaddr;
 334                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_BROADCAST, 4, &ina->sin_addr);
 335                 }
 336         }
 337
 338         if (!ioctl(sock, SIOCGIFMTU, &ifr)) {
 339                 uint16_t mtu = htons(ifr.ifr_mtu);
 340                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MTU, 2, &mtu);
 341         }
 342
 343         if (iface->search) {
 344                 char b[256];
 345                 if (dn_expand(iface->search, iface->search + iface->search_len,
 346                                 iface->search, b, sizeof(b)) > 0)
 347                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN, strlen(b), b);
 348         } else if (!res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 349                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN,
 350                                 strlen(_res.dnsrch[0]), _res.dnsrch[0]);
 351         }
 352
 353         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
 354
 355
 356
 357         if (iface->dhcpv4_dns_cnt == 0)
 358                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER, 4, &ifaddr.sin_addr);
 359         else
 360                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER,
 361                                 4 * iface->dhcpv4_dns_cnt, iface->dhcpv4_dns);
 362
 363
 364         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_END, 0, NULL);
 365
 366         struct sockaddr_in dest = *((struct sockaddr_in*)addr);
 367         if (req->giaddr.s_addr) {
 368                 dest.sin_addr = req->giaddr;
 369                 dest.sin_port = htons(DHCPV4_SERVER_PORT);
 370         } else if (req->ciaddr.s_addr && req->ciaddr.s_addr != dest.sin_addr.s_addr) {
 371                 dest.sin_addr = req->ciaddr;
 372                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 373         } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
 374                         req->hlen != reply.hlen) {
 375                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 376                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 377         } else {
 378                 dest.sin_addr = reply.yiaddr;
 379                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 380
 381                 struct arpreq arp = {.arp_flags = ATF_COM};
 382                 memcpy(arp.arp_ha.sa_data, req->chaddr, 6);
 383                 memcpy(&arp.arp_pa, &dest, sizeof(arp.arp_pa));
 384                 memcpy(arp.arp_dev, iface->ifname, sizeof(arp.arp_dev));
 385                 ioctl(sock, SIOCSARP, &arp);
 386         }
 387
 388         sendto(sock, &reply, sizeof(reply), MSG_DONTWAIT,
 389                         (struct sockaddr*)&dest, sizeof(dest));
 390 }
 391
 392
 393 static bool dhcpv4_assign(struct interface *iface,
 394                 struct dhcpv4_assignment *assign, uint32_t raddr)
 395 {
 396         const unsigned tries = 10;
 397         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 398         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 399         uint32_t count = end - start + 1;
 400
 401         // Seed RNG with checksum of DUID
 402         uint32_t seed = 0;
 403         for (size_t i = 0; i < sizeof(assign->hwaddr); ++i)
 404                 seed += assign->hwaddr[i];
 405         srand(seed);
 406
 407         // Try to assign up to 100x
 408         for (unsigned i = 0; i < tries; ++i) {
 409                 uint32_t try = (((uint32_t)rand()) % count) + start;
 410                 if (i == 0 && raddr >= start && raddr <= end)
 411                         try = raddr;
 412                 else if (i == tries - 1)
 413                         try = start;
 414
 415                 if (list_empty(&iface->dhcpv4_assignments)) {
 416                         assign->addr = try;
 417                         list_add(&assign->head, &iface->dhcpv4_assignments);
 418                         return true;
 419                 }
 420
 421                 struct dhcpv4_assignment *c;
 422                 list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 423                         if (c->addr > try) {
 424                                 assign->addr = try;
 425                                 list_add_tail(&assign->head, &c->head);
 426                                 return true;
 427                         } else if (c->addr == try) {
 428                                 if (i < tries - 1)
 429                                         break;
 430                                 else
 431                                         ++try;
 432                         }
 433                 }
 434         }
 435
 436         return false;
 437 }
 438
 439
 440 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 441                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
 442                 const char *hostname)
 443 {
 444         struct dhcpv4_assignment *lease = NULL;
 445         uint32_t raddr = ntohl(reqaddr.s_addr);
 446         time_t now = odhcpd_time();
 447
 448         struct dhcpv4_assignment *c, *n, *a = NULL;
 449         list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
 450                 if (c->addr == raddr && !memcmp(c->hwaddr, mac, 6)) {
 451                         a = c;
 452                         break;
 453                 } else if (c->valid_until < now) {
 454                         list_del(&c->head);
 455                         free(c);
 456                 }
 457         }
 458
 459         bool update_state = false;
 460         if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
 461                 bool assigned = !!a;
 462                 size_t hostlen = strlen(hostname) + 1;
 463
 464                 if (!a && !iface->no_dynamic_dhcp) { // Create new binding
 465                         a = calloc(1, sizeof(*a) + hostlen);
 466                         memcpy(a->hwaddr, mac, sizeof(a->hwaddr));
 467                         memcpy(a->hostname, hostname, hostlen);
 468
 469                         assigned = dhcpv4_assign(iface, a, raddr);
 470                 }
 471
 472                 if (assigned && !a->hostname[0] && hostname) {
 473                         a = realloc(a, sizeof(*a) + hostlen);
 474                         memcpy(a->hostname, hostname, hostlen);
 475
 476                         // Fixup list
 477                         a->head.next->prev = &a->head;
 478                         a->head.prev->next = &a->head;
 479                 }
 480
 481                 // Was only a solicitation: mark binding for removal
 482                 if (assigned && a->valid_until < now) {
 483                         a->valid_until = (msg == DHCPV4_MSG_DISCOVER) ? 0 :
 484                                         (now + iface->dhcpv4_leasetime);
 485                 } else if (!assigned && a) { // Cleanup failed assignment
 486                         free(a);
 487                         a = NULL;
 488                 }
 489
 490                 if (assigned && a)
 491                         lease = a;
 492         } else if (msg == DHCPV4_MSG_RELEASE) {
 493                 if (a) {
 494                         a->valid_until = 0;
 495                         update_state = true;
 496                 }
 497         } else if (msg == DHCPV4_MSG_DECLINE) {
 498                 memset(a->hwaddr, 0, sizeof(a->hwaddr));
 499                 a->valid_until = now + 3600; // Block address for 1h
 500                 update_state = true;
 501         }
 502
 503         if (update_state)
 504                 dhcpv6_write_statefile();
 505
 506         return lease;
 507 }
 508