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