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 static const char *excluded_class = "HOMENET";
  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                 if (sock < 0) {
  63                         syslog(LOG_ERR, "Failed to create DHCPv4 server socket: %s",
  64                                         strerror(errno));
  65                         return -1;
  66                 }
  67
  68                 // Basic IPv6 configuration
  69                 int val = 1;
  70                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  71                 setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &val, sizeof(val));
  72                 setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &val, sizeof(val));
  73
  74                 val = IPTOS_PREC_INTERNETCONTROL;
  75                 setsockopt(sock, IPPROTO_IP, IP_TOS, &val, sizeof(val));
  76
  77                 val = IP_PMTUDISC_DONT;
  78                 setsockopt(sock, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
  79
  80                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
  81                                 iface->ifname, strlen(iface->ifname));
  82
  83                 struct sockaddr_in bind_addr = {AF_INET, htons(DHCPV4_SERVER_PORT),
  84                                         {INADDR_ANY}, {0}};
  85
  86                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  87                         syslog(LOG_ERR, "Failed to open DHCPv4 server socket: %s",
  88                                         strerror(errno));
  89                         return -1;
  90                 }
  91
  92
  93                 if (ntohl(iface->dhcpv4_start.s_addr) > ntohl(iface->dhcpv4_end.s_addr)) {
  94                         syslog(LOG_ERR, "Invalid DHCP range");
  95                         return -1;
  96                 }
  97
  98                 // Create a range if not specified
  99                 struct ifreq ifreq;
 100                 strncpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 101
 102                 struct sockaddr_in *saddr = (struct sockaddr_in*)&ifreq.ifr_addr;
 103                 struct sockaddr_in *smask = (struct sockaddr_in*)&ifreq.ifr_netmask;
 104                 if (!(iface->dhcpv4_start.s_addr & htonl(0xffff0000)) &&
 105                                 !(iface->dhcpv4_end.s_addr & htonl(0xffff0000)) &&
 106                                 !ioctl(sock, SIOCGIFADDR, &ifreq)) {
 107                         struct in_addr addr = saddr->sin_addr;
 108
 109                         ioctl(sock, SIOCGIFNETMASK, &ifreq);
 110                         struct in_addr mask = smask->sin_addr;
 111
 112                         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 113                         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 114
 115                         if (start && end && start < end &&
 116                                         start > ntohl(addr.s_addr & ~mask.s_addr) &&
 117                                         (start & ntohl(mask.s_addr)) == start &&
 118                                         (end & ntohl(mask.s_addr)) == end) {
 119                                 iface->dhcpv4_start.s_addr = htonl(start) |
 120                                                 (addr.s_addr & mask.s_addr);
 121                                 iface->dhcpv4_end.s_addr = htonl(end) |
 122                                                 (addr.s_addr & mask.s_addr);
 123                         } else if (ntohl(mask.s_addr) <= 0xffffffc0) {
 124                                 start = addr.s_addr & mask.s_addr;
 125                                 end = addr.s_addr & mask.s_addr;
 126
 127                                 if (ntohl(mask.s_addr) <= 0xffffff00) {
 128                                         iface->dhcpv4_start.s_addr = start | htonl(100);
 129                                         iface->dhcpv4_end.s_addr = end | htonl(250);
 130                                 } else {
 131                                         iface->dhcpv4_start.s_addr = start | htonl(10);
 132                                         iface->dhcpv4_end.s_addr = end | htonl(59);
 133                                 }
 134                         }
 135
 136
 137                 }
 138
 139                 // Parse static entries
 140                 struct lease *lease;
 141                 list_for_each_entry(lease, &leases, head) {
 142                         // Construct entry
 143                         size_t hostlen = strlen(lease->hostname) + 1;
 144                         struct dhcpv4_assignment *a = calloc(1, sizeof(*a) + hostlen);
 145                         if (!a) {
 146                                 syslog(LOG_ERR, "Calloc failed for static lease on interface %s",
 147                                         iface->ifname);
 148                                 return -1;
 149                         }
 150                         a->addr = ntohl(lease->ipaddr.s_addr);
 151                         memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
 152                         memcpy(a->hostname, lease->hostname, hostlen);
 153
 154                         // Assign to all interfaces
 155                         struct dhcpv4_assignment *c;
 156                         list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 157                                 if (c->addr > a->addr) {
 158                                         list_add_tail(&a->head, &c->head);
 159                                 } else if (c->addr == a->addr) {
 160                                         // Already an assignment with that number
 161                                         break;
 162                                 }
 163                         }
 164
 165                         if (!a->head.next)
 166                                 free(a);
 167                 }
 168
 169                 // Clean invalid assignments
 170                 struct dhcpv4_assignment *a, *n;
 171                 list_for_each_entry_safe(a, n, &iface->dhcpv4_assignments, head) {
 172                         if ((htonl(a->addr) & smask->sin_addr.s_addr) !=
 173                                         (saddr->sin_addr.s_addr & smask->sin_addr.s_addr)) {
 174                                 list_del(&a->head);
 175                                 free(a);
 176                         }
 177                 }
 178
 179
 180                 if (iface->dhcpv4_leasetime < 60)
 181                         iface->dhcpv4_leasetime = 43200;
 182
 183                 iface->dhcpv4_event.uloop.fd = sock;
 184                 iface->dhcpv4_event.handle_dgram = handle_dhcpv4;
 185                 odhcpd_register(&iface->dhcpv4_event);
 186         } else if (iface->dhcpv4_assignments.next) {
 187                 while (!list_empty(&iface->dhcpv4_assignments)) {
 188                         struct dhcpv4_assignment *a = list_first_entry(&iface->dhcpv4_assignments,
 189                                         struct dhcpv4_assignment, head);
 190                         list_del(&a->head);
 191                         free(a->hostname);
 192                         free(a);
 193                 }
 194
 195         }
 196         return 0;
 197 }
 198
 199
 200 static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 201                 uint8_t type, uint8_t len, const void *data)
 202 {
 203         uint8_t *c = *cookie;
 204         if (*cookie + 2 + len > (uint8_t*)&msg[1])
 205                 return;
 206
 207         *c++ = type;
 208         *c++ = len;
 209         memcpy(c, data, len);
 210
 211         *cookie = c + len;
 212 }
 213
 214
 215 // Simple DHCPv6-server for information requests
 216 static void handle_dhcpv4(void *addr, void *data, size_t len,
 217                 struct interface *iface)
 218 {
 219         if (!iface->dhcpv4)
 220                 return;
 221
 222         struct dhcpv4_message *req = data;
 223         if (len < offsetof(struct dhcpv4_message, options) + 4 ||
 224                         req->op != DHCPV4_BOOTREQUEST || req->hlen != 6)
 225                 return;
 226
 227         int sock = iface->dhcpv4_event.uloop.fd;
 228         struct sockaddr_in ifaddr;
 229         struct sockaddr_in ifnetmask;
 230
 231         syslog(LOG_NOTICE, "Got DHCPv4 request");
 232
 233         struct ifreq ifreq;
 234         memcpy(ifreq.ifr_name, iface->ifname, sizeof(ifreq.ifr_name));
 235         if (ioctl(sock, SIOCGIFADDR, &ifreq)) {
 236                 syslog(LOG_WARNING, "DHCPv4 failed to detect address: %s", strerror(errno));
 237                 return;
 238         }
 239
 240         memcpy(&ifaddr, &ifreq.ifr_addr, sizeof(ifaddr));
 241         if (ioctl(sock, SIOCGIFNETMASK, &ifreq))
 242                 return;
 243
 244         memcpy(&ifnetmask, &ifreq.ifr_netmask, sizeof(ifnetmask));
 245         uint32_t network = ifaddr.sin_addr.s_addr & ifnetmask.sin_addr.s_addr;
 246
 247         if ((iface->dhcpv4_start.s_addr & ifnetmask.sin_addr.s_addr) != network ||
 248                         (iface->dhcpv4_end.s_addr & ifnetmask.sin_addr.s_addr) != network) {
 249                 syslog(LOG_WARNING, "DHCPv4 range out of assigned network");
 250                 return;
 251         }
 252
 253         struct ifreq ifr = {.ifr_name = ""};
 254         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 255
 256         struct dhcpv4_message reply = {
 257                 .op = DHCPV4_BOOTREPLY,
 258                 .htype = 1,
 259                 .hlen = 6,
 260                 .hops = 0,
 261                 .xid = req->xid,
 262                 .secs = 0,
 263                 .flags = req->flags,
 264                 .ciaddr = {INADDR_ANY},
 265                 .giaddr = req->giaddr,
 266                 .siaddr = ifaddr.sin_addr,
 267         };
 268         memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
 269
 270         reply.options[0] = 0x63;
 271         reply.options[1] = 0x82;
 272         reply.options[2] = 0x53;
 273         reply.options[3] = 0x63;
 274
 275         uint8_t *cookie = &reply.options[4];
 276         uint8_t reqmsg = DHCPV4_MSG_REQUEST;
 277         uint8_t msg = DHCPV4_MSG_ACK;
 278
 279         struct in_addr reqaddr = {INADDR_ANY};
 280         char hostname[256];
 281         hostname[0] = 0;
 282
 283         uint8_t *start = &req->options[4];
 284         uint8_t *end = ((uint8_t*)data) + len;
 285         struct dhcpv4_option *opt;
 286         dhcpv4_for_each_option(start, end, opt) {
 287                 if (opt->type == DHCPV4_OPT_MESSAGE && opt->len == 1) {
 288                         reqmsg = opt->data[0];
 289                 } else if (opt->type == DHCPV4_OPT_HOSTNAME && opt->len > 0) {
 290                         memcpy(hostname, opt->data, opt->len);
 291                         hostname[opt->len] = 0;
 292                 } else if (opt->type == DHCPV4_OPT_IPADDRESS && opt->len == 4) {
 293                         memcpy(&reqaddr, opt->data, 4);
 294                 } else if (opt->type == DHCPV4_OPT_SERVERID && opt->len == 4) {
 295                         if (memcmp(opt->data, &ifaddr.sin_addr, 4))
 296                                 return;
 297                 } else if (opt->type == DHCPV4_OPT_USER_CLASS) {
 298                         uint8_t *c = opt->data, *cend = &opt->data[opt->len];
 299                         for (; c < cend && &c[*c] < cend; c = &c[1 + *c]) {
 300                                 size_t elen = strlen(excluded_class);
 301                                 if (*c == elen && !memcmp(&c[1], excluded_class, elen))
 302                                         return; // Ignore from homenet
 303                         }
 304                 }
 305         }
 306
 307         if (reqmsg != DHCPV4_MSG_DISCOVER && reqmsg != DHCPV4_MSG_REQUEST &&
 308                         reqmsg != DHCPV4_MSG_INFORM && reqmsg != DHCPV4_MSG_DECLINE &&
 309                         reqmsg != DHCPV4_MSG_RELEASE)
 310                 return;
 311
 312         struct dhcpv4_assignment *lease = NULL;
 313         if (reqmsg != DHCPV4_MSG_INFORM)
 314                 lease = dhcpv4_lease(iface, reqmsg, req->chaddr, reqaddr, hostname);
 315
 316         if (!lease) {
 317                 if (reqmsg == DHCPV4_MSG_REQUEST)
 318                         msg = DHCPV4_MSG_NAK;
 319                 else if (reqmsg == DHCPV4_MSG_DISCOVER)
 320                         return;
 321         } else if (reqmsg == DHCPV4_MSG_DISCOVER) {
 322                 msg = DHCPV4_MSG_OFFER;
 323         }
 324
 325         if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
 326                 return;
 327
 328         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MESSAGE, 1, &msg);
 329         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_SERVERID, 4, &ifaddr.sin_addr);
 330
 331         if (lease) {
 332                 reply.yiaddr.s_addr = htonl(lease->addr);
 333
 334                 uint32_t val = htonl(iface->dhcpv4_leasetime);
 335                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_LEASETIME, 4, &val);
 336
 337                 val = htonl(500 * iface->dhcpv4_leasetime / 1000);
 338                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_RENEW, 4, &val);
 339
 340                 val = htonl(875 * iface->dhcpv4_leasetime / 1000);
 341                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_REBIND, 4, &val);
 342
 343                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_NETMASK, 4, &ifnetmask.sin_addr);
 344
 345                 if (lease->hostname[0])
 346                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_HOSTNAME,
 347                                         strlen(lease->hostname), lease->hostname);
 348
 349                 if (!ioctl(sock, SIOCGIFBRDADDR, &ifr)) {
 350                         struct sockaddr_in *ina = (struct sockaddr_in*)&ifr.ifr_broadaddr;
 351                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_BROADCAST, 4, &ina->sin_addr);
 352                 }
 353         }
 354
 355         if (!ioctl(sock, SIOCGIFMTU, &ifr)) {
 356                 uint16_t mtu = htons(ifr.ifr_mtu);
 357                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_MTU, 2, &mtu);
 358         }
 359
 360         if (iface->search) {
 361                 char b[256];
 362                 if (dn_expand(iface->search, iface->search + iface->search_len,
 363                                 iface->search, b, sizeof(b)) > 0)
 364                         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN, strlen(b), b);
 365         } else if (!res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 366                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DOMAIN,
 367                                 strlen(_res.dnsrch[0]), _res.dnsrch[0]);
 368         }
 369
 370         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
 371
 372
 373
 374         if (iface->dhcpv4_dns_cnt == 0)
 375                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER, 4, &ifaddr.sin_addr);
 376         else
 377                 dhcpv4_put(&reply, &cookie, DHCPV4_OPT_DNSSERVER,
 378                                 4 * iface->dhcpv4_dns_cnt, iface->dhcpv4_dns);
 379
 380
 381         dhcpv4_put(&reply, &cookie, DHCPV4_OPT_END, 0, NULL);
 382
 383         struct sockaddr_in dest = *((struct sockaddr_in*)addr);
 384         if (req->giaddr.s_addr) {
 385                 dest.sin_addr = req->giaddr;
 386                 dest.sin_port = htons(DHCPV4_SERVER_PORT);
 387         } else if (req->ciaddr.s_addr && req->ciaddr.s_addr != dest.sin_addr.s_addr) {
 388                 dest.sin_addr = req->ciaddr;
 389                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 390         } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
 391                         req->hlen != reply.hlen) {
 392                 dest.sin_addr.s_addr = INADDR_BROADCAST;
 393                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 394         } else {
 395                 dest.sin_addr = reply.yiaddr;
 396                 dest.sin_port = htons(DHCPV4_CLIENT_PORT);
 397
 398                 struct arpreq arp = {.arp_flags = ATF_COM};
 399                 memcpy(arp.arp_ha.sa_data, req->chaddr, 6);
 400                 memcpy(&arp.arp_pa, &dest, sizeof(arp.arp_pa));
 401                 memcpy(arp.arp_dev, iface->ifname, sizeof(arp.arp_dev));
 402                 ioctl(sock, SIOCSARP, &arp);
 403         }
 404
 405         sendto(sock, &reply, sizeof(reply), MSG_DONTWAIT,
 406                         (struct sockaddr*)&dest, sizeof(dest));
 407 }
 408
 409
 410 static bool dhcpv4_assign(struct interface *iface,
 411                 struct dhcpv4_assignment *assign, uint32_t raddr)
 412 {
 413         const unsigned tries = 10;
 414         uint32_t start = ntohl(iface->dhcpv4_start.s_addr);
 415         uint32_t end = ntohl(iface->dhcpv4_end.s_addr);
 416         uint32_t count = end - start + 1;
 417
 418         // Seed RNG with checksum of DUID
 419         uint32_t seed = 0;
 420         for (size_t i = 0; i < sizeof(assign->hwaddr); ++i)
 421                 seed += assign->hwaddr[i];
 422         srand(seed);
 423
 424         // Try to assign up to 100x
 425         for (unsigned i = 0; i < tries; ++i) {
 426                 uint32_t try = (((uint32_t)rand()) % count) + start;
 427                 if (i == 0 && raddr >= start && raddr <= end)
 428                         try = raddr;
 429                 else if (i == tries - 1)
 430                         try = start;
 431
 432                 if (list_empty(&iface->dhcpv4_assignments)) {
 433                         assign->addr = try;
 434                         list_add(&assign->head, &iface->dhcpv4_assignments);
 435                         return true;
 436                 }
 437
 438                 struct dhcpv4_assignment *c;
 439                 list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
 440                         if (c->addr > try) {
 441                                 assign->addr = try;
 442                                 list_add_tail(&assign->head, &c->head);
 443                                 return true;
 444                         } else if (c->addr == try) {
 445                                 if (i < tries - 1)
 446                                         break;
 447                                 else
 448                                         ++try;
 449                         }
 450                 }
 451         }
 452
 453         return false;
 454 }
 455
 456
 457 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 458                 enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
 459                 const char *hostname)
 460 {
 461         struct dhcpv4_assignment *lease = NULL;
 462         uint32_t raddr = ntohl(reqaddr.s_addr);
 463         time_t now = odhcpd_time();
 464
 465         struct dhcpv4_assignment *c, *n, *a = NULL;
 466         list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
 467                 if (c->addr == raddr && !memcmp(c->hwaddr, mac, 6)) {
 468                         a = c;
 469                         break;
 470                 } else if (c->valid_until < now) {
 471                         list_del(&c->head);
 472                         free(c);
 473                 }
 474         }
 475
 476         bool update_state = false;
 477         if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
 478                 bool assigned = !!a;
 479                 size_t hostlen = strlen(hostname) + 1;
 480
 481                 if (!a && !iface->no_dynamic_dhcp) { // Create new binding
 482                         a = calloc(1, sizeof(*a) + hostlen);
 483                         if (!a) {
 484                                 syslog(LOG_ERR, "Failed to calloc binding on interface %s", iface->ifname);
 485                                 return NULL;
 486                         }
 487                         memcpy(a->hwaddr, mac, sizeof(a->hwaddr));
 488                         memcpy(a->hostname, hostname, hostlen);
 489
 490                         assigned = dhcpv4_assign(iface, a, raddr);
 491                 }
 492
 493                 if (assigned && !a->hostname[0] && hostname) {
 494                         a = realloc(a, sizeof(*a) + hostlen);
 495                         if (!a) {
 496                                 syslog(LOG_ERR, "Failed to realloc binding on interface %s", iface->ifname);
 497                                 return NULL;
 498                         }
 499                         memcpy(a->hostname, hostname, hostlen);
 500
 501                         // Fixup list
 502                         a->head.next->prev = &a->head;
 503                         a->head.prev->next = &a->head;
 504                 }
 505
 506                 // Was only a solicitation: mark binding for removal
 507                 if (assigned && a->valid_until < now) {
 508                         a->valid_until = (msg == DHCPV4_MSG_DISCOVER) ? 0 :
 509                                         (now + iface->dhcpv4_leasetime);
 510                 } else if (!assigned && a) { // Cleanup failed assignment
 511                         free(a);
 512                         a = NULL;
 513                 }
 514
 515                 if (assigned && a)
 516                         lease = a;
 517         } else if (msg == DHCPV4_MSG_RELEASE) {
 518                 if (a) {
 519                         a->valid_until = 0;
 520                         update_state = true;
 521                 }
 522         } else if (msg == DHCPV4_MSG_DECLINE) {
 523                 memset(a->hwaddr, 0, sizeof(a->hwaddr));
 524                 a->valid_until = now + 3600; // Block address for 1h
 525                 update_state = true;
 526         }
 527
 528         if (update_state)
 529                 dhcpv6_write_statefile();
 530
 531         return lease;
 532 }
 533