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