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 // Magic option for hnet internal (4B enterprise ID, 1B data-len, 1B subopt-code, 1B subopt-len)
  42 static uint8_t hnet_internal_data[7] = {0x00, 0x00, 0x76, 0xfe, 2, 1, 0};
  43
  44 // Create socket and register events
  45 int init_dhcpv4(void)
  46 {
  47         return 0;
  48 }
  49
  50
  51 int setup_dhcpv4_interface(struct interface *iface, bool enable)
  52 {
  53         if (iface->dhcpv4_event.uloop.fd > 0) {
  54                 uloop_fd_delete(&iface->dhcpv4_event.uloop);
  55                 close(iface->dhcpv4_event.uloop.fd);
  56                 iface->dhcpv4_event.uloop.fd = -1;
  57         }
  58
  59         if (iface->dhcpv4 && enable) {
  60                 if (!iface->dhcpv4_assignments.next)
  61                         INIT_LIST_HEAD(&iface->dhcpv4_assignments);
  62
  63                 int sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  64                 if (sock < 0) {
  65                         syslog(LOG_ERR, "Failed to create DHCPv4 server socket: %s",
  66                                         strerror(errno));
  67                         return -1;
  68                 }
  69
  70                 // Basic IPv6 configuration
  71                 int val = 1;
  72                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  73                 setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &val, sizeof(val));
  74                 setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &val, sizeof(val));
  75
  76                 val = IPTOS_PREC_INTERNETCONTROL;
  77                 setsockopt(sock, IPPROTO_IP, IP_TOS, &val, sizeof(val));
  78
  79                 val = IP_PMTUDISC_DONT;
  80                 setsockopt(sock, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
  81
  82                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
  83                                 iface->ifname, strlen(iface->ifname));
  84
  85                 struct sockaddr_in bind_addr = {AF_INET, htons(DHCPV4_SERVER_PORT),
  86                                         {INADDR_ANY}, {0}};
  87
  88                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  89                         syslog(LOG_ERR, "Failed to open DHCPv4 server socket: %s",
  90                                         strerror(errno));
  91                         return -1;
  92                 }
  93
  94
  95                 if (ntohl(iface->dhcpv4_start.s_addr) > ntohl(iface->dhcpv4_end.s_addr)) {
  96                         syslog(LOG_ERR, "Invalid DHCP range");
  97                         return -1;
  98                 }
  99
 100                 // Create a range if not specified
 101                 struct ifreq ifreq;
 102                 strncpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 103
 104                 struct sockaddr_in *saddr = (struct sockaddr_in*)&ifreq.ifr_addr;
 105                 struct sockaddr_in *smask = (struct sockaddr_in*)&ifreq.ifr_netmask;
 106                 if (!(iface->dhcpv4_start.s_addr & htonl(0xffff0000)) &&
 107                                 !(iface->dhcpv4_end.s_addr & htonl(0xffff0000)) &&
 108                                 !ioctl(sock, SIOCGIFADDR, &ifreq)) {
 109                         struct in_addr addr = saddr->sin_addr;
 110
 111                         ioctl(sock, SIOCGIFNETMASK, &ifreq);
 112                         struct in_addr mask = smask->sin_addr;
 113
 114                         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 115                         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 116
 117                         if (start && end && start < end &&
 118                                         start > ntohl(addr.s_addr & ~mask.s_addr) &&
 119                                         (start & ntohl(mask.s_addr)) == start &&
 120                                         (end & ntohl(mask.s_addr)) == end) {
 121                                 iface->dhcpv4_start.s_addr = htonl(start) |
 122                                                 (addr.s_addr & mask.s_addr);
 123                                 iface->dhcpv4_end.s_addr = htonl(end) |
 124                                                 (addr.s_addr & mask.s_addr);
 125                         } else if (ntohl(mask.s_addr) <= 0xffffffc0) {
 126                                 start = addr.s_addr & mask.s_addr;
 127                                 end = addr.s_addr & mask.s_addr;
 128
 129                                 if (ntohl(mask.s_addr) <= 0xffffff00) {
 130                                         iface->dhcpv4_start.s_addr = start | htonl(100);
 131                                         iface->dhcpv4_end.s_addr = end | htonl(250);
 132                                 } else {
 133                                         iface->dhcpv4_start.s_addr = start | htonl(10);
 134                                         iface->dhcpv4_end.s_addr = end | htonl(59);
 135                                 }
 136                         }
 137
 138
 139                 }
 140
 141                 // Parse static entries
 142                 struct lease *lease;
 143                 list_for_each_entry(lease, &leases, head) {
 144                         // Construct entry
 145                         size_t hostlen = strlen(lease->hostname) + 1;
 146                         struct dhcpv4_assignment *a = calloc(1, sizeof(*a) + hostlen);
 147                         if (!a) {
 148                                 syslog(LOG_ERR, "Calloc failed for static lease on interface %s",
 149                                         iface->ifname);
 150                                 return -1;
 151                         }
 152                         a->addr = ntohl(lease->ipaddr.s_addr);
 153                         memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
 154                         memcpy(a->hostname, lease->hostname, hostlen);
 155
 156                         // Assign to all interfaces
 157                         struct dhcpv4_assignment *c;
 158                         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 159                                 if (c->addr > a->addr) {
 160                                         list_add_tail(&a->head, &c->head);
 161                                 } else if (c->addr == a->addr) {
 162                                         // Already an assignment with that number
 163                                         break;
 164                                 }
 165                         }
 166
 167                         if (!a->head.next)
 168                                 free(a);
 169                 }
 170
 171                 // Clean invalid assignments
 172                 struct dhcpv4_assignment *a, *n;
 173                 list_for_each_entry_safe(a, n, &iface->dhcpv4_assignments, head) {
 174                         if ((htonl(a->addr) & smask->sin_addr.s_addr) !=
 175                                         (saddr->sin_addr.s_addr & smask->sin_addr.s_addr)) {
 176                                 list_del(&a->head);
 177                                 free(a);
 178                         }
 179                 }
 180
 181
 182                 if (iface->dhcpv4_leasetime < 60)
 183                         iface->dhcpv4_leasetime = 43200;
 184
 185                 iface->dhcpv4_event.uloop.fd = sock;
 186                 iface->dhcpv4_event.handle_dgram = handle_dhcpv4;
 187                 odhcpd_register(&iface->dhcpv4_event);
 188         } else if (iface->dhcpv4_assignments.next) {
 189                 while (!list_empty(&iface->dhcpv4_assignments)) {
 190                         struct dhcpv4_assignment *a = list_first_entry(&iface->dhcpv4_assignments,
 191                                         struct dhcpv4_assignment, head);
 192                         list_del(&a->head);
 193                         free(a->hostname);
 194                         free(a);
 195                 }
 196
 197         }
 198         return 0;
 199 }
 200
 201
 202 static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 203                 uint8_t type, uint8_t len, const void *data)
 204 {
 205         uint8_t *c = *cookie;
 206         if (*cookie + 2 + len > (uint8_t*)&msg[1])
 207                 return;
 208
 209         *c++ = type;
 210         *c++ = len;
 211         memcpy(c, data, len);
 212
 213         *cookie = c + len;
 214 }
 215
 216
 217 // Simple DHCPv6-server for information requests
 218 static void handle_dhcpv4(void *addr, void *data, size_t len,
 219                 struct interface *iface)
 220 {
 221         if (!iface->dhcpv4)
 222                 return;
 223
 224         struct dhcpv4_message *req = data;
 225         if (len < offsetof(struct dhcpv4_message, options) + 4 ||
 226                         req->op != DHCPV4_BOOTREQUEST || req->hlen != 6)
 227                 return;
 228
 229         int sock = iface->dhcpv4_event.uloop.fd;
 230         struct sockaddr_in ifaddr;
 231         struct sockaddr_in ifnetmask;
 232
 233         syslog(LOG_NOTICE, "Got DHCPv4 request");
 234
 235         struct ifreq ifreq;
 236         memcpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 237         if (ioctl(sock, SIOCGIFADDR, &ifreq)) {
 238                 syslog(LOG_WARNING, "DHCPv4 failed to detect address: %s", strerror(errno));
 239                 return;
 240         }
 241
 242         memcpy(&ifaddr, &ifreq.ifr_addr, sizeof(ifaddr));
 243         if (ioctl(sock, SIOCGIFNETMASK, &ifreq))
 244                 return;
 245
 246         memcpy(&ifnetmask, &ifreq.ifr_netmask, sizeof(ifnetmask));
 247         uint32_t network = ifaddr.sin_addr.s_addr & ifnetmask.sin_addr.s_addr;
 248
 249         if ((iface->dhcpv4_start.s_addr & ifnetmask.sin_addr.s_addr) != network ||
 250                         (iface->dhcpv4_end.s_addr & ifnetmask.sin_addr.s_addr) != network) {
 251                 syslog(LOG_WARNING, "DHCPv4 range out of assigned network");
 252                 return;
 253         }
 254
 255         struct ifreq ifr = {.ifr_name = ""};
 256         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 257
 258         struct dhcpv4_message reply = {
 259                 .op = DHCPV4_BOOTREPLY,
 260                 .htype = 1,
 261                 .hlen = 6,
 262                 .hops = 0,
 263                 .xid = req->xid,
 264                 .secs = 0,
 265                 .flags = req->flags,
 266                 .ciaddr = {INADDR_ANY},
 267                 .giaddr = req->giaddr,
 268                 .siaddr = ifaddr.sin_addr,
 269         };
 270         memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
 271
 272         reply.options[0] = 0x63;
 273         reply.options[1] = 0x82;
 274         reply.options[2] = 0x53;
 275         reply.options[3] = 0x63;
 276
 277         uint8_t *cookie = &reply.options[4];
 278         uint8_t reqmsg = DHCPV4_MSG_REQUEST;
 279         uint8_t msg = DHCPV4_MSG_ACK;
 280
 281         struct in_addr reqaddr = {INADDR_ANY};
 282         char hostname[256];
 283         hostname[0] = 0;
 284
 285         uint8_t *start = &req->options[4];
 286         uint8_t *end = ((uint8_t*)data) + len;
 287         struct dhcpv4_option *opt;
 288         dhcpv4_for_each_option(start, end, opt) {
 289                 if (opt->type == DHCPV4_OPT_MESSAGE && opt->len == 1) {
 290                         reqmsg = opt->data[0];
 291                 } else if (opt->type == DHCPV4_OPT_HOSTNAME && opt->len > 0) {
 292                         memcpy(hostname, opt->data, opt->len);
 293                         hostname[opt->len] = 0;
 294                 } else if (opt->type == DHCPV4_OPT_IPADDRESS && opt->len == 4) {
 295                         memcpy(&reqaddr, opt->data, 4);
 296                 } else if (opt->type == DHCPV4_OPT_SERVERID && opt->len == 4) {
 297                         if (memcmp(opt->data, &ifaddr.sin_addr, 4))
 298                                 return;
 299                 } else if (opt->type == DHCPV4_OPT_VENDOR_SPECIFIC_INFORMATION &&
 300                                 opt->len == sizeof(hnet_internal_data)) {
 301                         if (!memcmp(opt->data, hnet_internal_data, sizeof(hnet_internal_data)))
 302                                 return; // Ignoring hnet internal routers
 303                 }
 304         }
 305
 306         if (reqmsg != DHCPV4_MSG_DISCOVER && reqmsg != DHCPV4_MSG_REQUEST &&
 307                         reqmsg != DHCPV4_MSG_INFORM && reqmsg != DHCPV4_MSG_DECLINE &&
 308                         reqmsg != DHCPV4_MSG_RELEASE)
 309                 return;
 310
 311         struct dhcpv4_assignment *lease = NULL;
 312         if (reqmsg != DHCPV4_MSG_INFORM)
 313                 lease = dhcpv4_lease(iface, reqmsg, req->chaddr, reqaddr, hostname);
 314
 315         if (!lease) {
 316                 if (reqmsg == DHCPV4_MSG_REQUEST)
 317                         msg = DHCPV4_MSG_NAK;
 318                 else if (reqmsg == DHCPV4_MSG_DISCOVER)
 319                         return;
 320         } else if (reqmsg == DHCPV4_MSG_DISCOVER) {
 321                 msg = DHCPV4_MSG_OFFER;
 322         }
 323
 324         if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
 325                 return;
 326
 327         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 328         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SERVERID, 4, &ifaddr.sin_addr);
 329
 330         if (lease) {
 331                 reply.yiaddr.s_addr = htonl(lease->addr);
 332
 333                 uint32_t val = htonl(iface->dhcpv4_leasetime);
 334                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_LEASETIME, 4, &val);
 335
 336                 val = htonl(500 * iface->dhcpv4_leasetime / 1000);
 337                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_RENEW, 4, &val);
 338
 339                 val = htonl(875 * iface->dhcpv4_leasetime / 1000);
 340                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_REBIND, 4, &val);
 341
 342                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_NETMASK, 4, &ifnetmask.sin_addr);
 343
 344                 if (lease->hostname[0])
 345                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_HOSTNAME,
 346                                         strlen(lease->hostname), lease->hostname);
 347
 348                 if (!ioctl(sock, SIOCGIFBRDADDR, &ifr)) {
 349                         struct sockaddr_in *ina = (struct sockaddr_in*)&ifr.ifr_broadaddr;
 350                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_BROADCAST, 4, &ina->sin_addr);
 351                 }
 352         }
 353
 354         if (!ioctl(sock, SIOCGIFMTU, &ifr)) {
 355                 uint16_t mtu = htons(ifr.ifr_mtu);
 356                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MTU, 2, &mtu);
 357         }
 358
 359         if (iface->search) {
 360                 char b[256];
 361                 if (dn_expand(iface->search, iface->search + iface->search_len,
 362                                 iface->search, b, sizeof(b)) > 0)
 363                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN, strlen(b), b);
 364         } else if (!res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 365                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN,
 366                                 strlen(_res.dnsrch[0]), _res.dnsrch[0]);
 367         }
 368
 369         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
 370
 371
 372
 373         if (iface->dhcpv4_dns_cnt == 0)
 374                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER, 4, &ifaddr.sin_addr);
 375         else
 376                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER,
 377                                 4 * iface->dhcpv4_dns_cnt, iface->dhcpv4_dns);
 378
 379
 380         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_END, 0, NULL);
 381
 382         struct sockaddr_in dest = *((struct sockaddr_in*)addr);
 383         if (req->giaddr.s_addr) {
 384                 dest.sin_addr = req->giaddr;
 385                 dest.sin_port = htons(DHCPV4_SERVER_PORT);
 386         } else if (req->ciaddr.s_addr && req->ciaddr.s_addr != dest.sin_addr.s_addr) {
 387                 dest.sin_addr = req->ciaddr;
 388                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 389         } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
 390                         req->hlen != reply.hlen) {
 391                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 392                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 393         } else {
 394                 dest.sin_addr = reply.yiaddr;
 395                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 396
 397                 struct arpreq arp = {.arp_flags = ATF_COM};
 398                 memcpy(arp.arp_ha.sa_data, req->chaddr, 6);
 399                 memcpy(&arp.arp_pa, &dest, sizeof(arp.arp_pa));
 400                 memcpy(arp.arp_dev, iface->ifname, sizeof(arp.arp_dev));
 401                 ioctl(sock, SIOCSARP, &arp);
 402         }
 403
 404         sendto(sock, &reply, sizeof(reply), MSG_DONTWAIT,
 405                         (struct sockaddr*)&dest, sizeof(dest));
 406 }
 407
 408
 409 static bool dhcpv4_assign(struct interface *iface,
 410                 struct dhcpv4_assignment *assign, uint32_t raddr)
 411 {
 412         const unsigned tries = 10;
 413         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 414         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 415         uint32_t count = end - start + 1;
 416
 417         // Seed RNG with checksum of DUID
 418         uint32_t seed = 0;
 419         for (size_t i = 0; i < sizeof(assign->hwaddr); ++i)
 420                 seed += assign->hwaddr[i];
 421         srand(seed);
 422
 423         // Try to assign up to 100x
 424         for (unsigned i = 0; i < tries; ++i) {
 425                 uint32_t try = (((uint32_t)rand()) % count) + start;
 426                 if (i == 0 && raddr >= start && raddr <= end)
 427                         try = raddr;
 428                 else if (i == tries - 1)
 429                         try = start;
 430
 431                 if (list_empty(&iface->dhcpv4_assignments)) {
 432                         assign->addr = try;
 433                         list_add(&assign->head, &iface->dhcpv4_assignments);
 434                         return true;
 435                 }
 436
 437                 struct dhcpv4_assignment *c;
 438                 list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 439                         if (c->addr > try) {
 440                                 assign->addr = try;
 441                                 list_add_tail(&assign->head, &c->head);
 442                                 return true;
 443                         } else if (c->addr == try) {
 444                                 if (i < tries - 1)
 445                                         break;
 446                                 else
 447                                         ++try;
 448                         }
 449                 }
 450         }
 451
 452         return false;
 453 }
 454
 455
 456 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 457                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
 458                 const char *hostname)
 459 {
 460         struct dhcpv4_assignment *lease = NULL;
 461         uint32_t raddr = ntohl(reqaddr.s_addr);
 462         time_t now = odhcpd_time();
 463
 464         struct dhcpv4_assignment *c, *n, *a = NULL;
 465         list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
 466                 if (c->addr == raddr && !memcmp(c->hwaddr, mac, 6)) {
 467                         a = c;
 468                         break;
 469                 } else if (c->valid_until < now) {
 470                         list_del(&c->head);
 471                         free(c);
 472                 }
 473         }
 474
 475         bool update_state = false;
 476         if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
 477                 bool assigned = !!a;
 478                 size_t hostlen = strlen(hostname) + 1;
 479
 480                 if (!a && !iface->no_dynamic_dhcp) { // Create new binding
 481                         a = calloc(1, sizeof(*a) + hostlen);
 482                         if (!a) {
 483                                 syslog(LOG_ERR, "Failed to calloc binding on interface %s", iface->ifname);
 484                                 return NULL;
 485                         }
 486                         memcpy(a->hwaddr, mac, sizeof(a->hwaddr));
 487                         memcpy(a->hostname, hostname, hostlen);
 488
 489                         assigned = dhcpv4_assign(iface, a, raddr);
 490                 }
 491
 492                 if (assigned && !a->hostname[0] && hostname) {
 493                         a = realloc(a, sizeof(*a) + hostlen);
 494                         if (!a) {
 495                                 syslog(LOG_ERR, "Failed to realloc binding on interface %s", iface->ifname);
 496                                 return NULL;
 497                         }
 498                         memcpy(a->hostname, hostname, hostlen);
 499
 500                         // Fixup list
 501                         a->head.next->prev = &a->head;
 502                         a->head.prev->next = &a->head;
 503                 }
 504
 505                 // Was only a solicitation: mark binding for removal
 506                 if (assigned && a->valid_until < now) {
 507                         a->valid_until = (msg == DHCPV4_MSG_DISCOVER) ? 0 :
 508                                         (now + iface->dhcpv4_leasetime);
 509                 } else if (!assigned && a) { // Cleanup failed assignment
 510                         free(a);
 511                         a = NULL;
 512                 }
 513
 514                 if (assigned && a)
 515                         lease = a;
 516         } else if (msg == DHCPV4_MSG_RELEASE) {
 517                 if (a) {
 518                         a->valid_until = 0;
 519                         update_state = true;
 520                 }
 521         } else if (msg == DHCPV4_MSG_DECLINE) {
 522                 memset(a->hwaddr, 0, sizeof(a->hwaddr));
 523                 a->valid_until = now + 3600; // Block address for 1h
 524                 update_state = true;
 525         }
 526
 527         if (update_state)
 528                 dhcpv6_write_statefile();
 529
 530         return lease;
 531 }
 532