release/src/router/busybox/networking/udhcp/dhcprelay.c

   1 /* vi: set sw=4 ts=4: */
   2 /* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
   3  *
   4  * Licensed under GPLv2, see file LICENSE in this source tree.
   5  *
   6  * DHCP Relay for 'DHCPv4 Configuration of IPSec Tunnel Mode' support
   7  * Copyright (C) 2002 Mario Strasser <mast@gmx.net>,
   8  *                   Zuercher Hochschule Winterthur,
   9  *                   Netbeat AG
  10  * Upstream has GPL v2 or later
  11  */
  12
  13 //usage:#define dhcprelay_trivial_usage
  14 //usage:       "CLIENT_IFACE[,CLIENT_IFACE2]... SERVER_IFACE [SERVER_IP]"
  15 //usage:#define dhcprelay_full_usage "\n\n"
  16 //usage:       "Relay DHCP requests between clients and server"
  17
  18 #include "common.h"
  19
  20 #define SERVER_PORT    67
  21
  22 /* lifetime of an xid entry in sec. */
  23 #define MAX_LIFETIME   2*60
  24 /* select timeout in sec. */
  25 #define SELECT_TIMEOUT (MAX_LIFETIME / 8)
  26
  27 /* This list holds information about clients. The xid_* functions manipulate this list. */
  28 struct xid_item {
  29         unsigned timestamp;
  30         int client;
  31         uint32_t xid;
  32         struct sockaddr_in ip;
  33         struct xid_item *next;
  34 } FIX_ALIASING;
  35
  36 #define dhcprelay_xid_list (*(struct xid_item*)&bb_common_bufsiz1)
  37
  38 static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client)
  39 {
  40         struct xid_item *item;
  41
  42         /* create new xid entry */
  43         item = xmalloc(sizeof(struct xid_item));
  44
  45         /* add xid entry */
  46         item->ip = *ip;
  47         item->xid = xid;
  48         item->client = client;
  49         item->timestamp = monotonic_sec();
  50         item->next = dhcprelay_xid_list.next;
  51         dhcprelay_xid_list.next = item;
  52
  53         return item;
  54 }
  55
  56 static void xid_expire(void)
  57 {
  58         struct xid_item *item = dhcprelay_xid_list.next;
  59         struct xid_item *last = &dhcprelay_xid_list;
  60         unsigned current_time = monotonic_sec();
  61
  62         while (item != NULL) {
  63                 if ((current_time - item->timestamp) > MAX_LIFETIME) {
  64                         last->next = item->next;
  65                         free(item);
  66                         item = last->next;
  67                 } else {
  68                         last = item;
  69                         item = item->next;
  70                 }
  71         }
  72 }
  73
  74 static struct xid_item *xid_find(uint32_t xid)
  75 {
  76         struct xid_item *item = dhcprelay_xid_list.next;
  77         while (item != NULL) {
  78                 if (item->xid == xid) {
  79                         break;
  80                 }
  81                 item = item->next;
  82         }
  83         return item;
  84 }
  85
  86 static void xid_del(uint32_t xid)
  87 {
  88         struct xid_item *item = dhcprelay_xid_list.next;
  89         struct xid_item *last = &dhcprelay_xid_list;
  90         while (item != NULL) {
  91                 if (item->xid == xid) {
  92                         last->next = item->next;
  93                         free(item);
  94                         item = last->next;
  95                 } else {
  96                         last = item;
  97                         item = item->next;
  98                 }
  99         }
 100 }
 101
 102 /**
 103  * get_dhcp_packet_type - gets the message type of a dhcp packet
 104  * p - pointer to the dhcp packet
 105  * returns the message type on success, -1 otherwise
 106  */
 107 static int get_dhcp_packet_type(struct dhcp_packet *p)
 108 {
 109         uint8_t *op;
 110
 111         /* it must be either a BOOTREQUEST or a BOOTREPLY */
 112         if (p->op != BOOTREQUEST && p->op != BOOTREPLY)
 113                 return -1;
 114         /* get message type option */
 115         op = udhcp_get_option(p, DHCP_MESSAGE_TYPE);
 116         if (op != NULL)
 117                 return op[0];
 118         return -1;
 119 }
 120
 121 /**
 122  * make_iface_list - parses client/server interface names
 123  * returns array
 124  */
 125 static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
 126 {
 127         char *s, **iface_list;
 128         int i, cn;
 129
 130         /* get number of items */
 131         cn = 2; /* 1 server iface + at least 1 client one */
 132         s = client_and_server_ifaces[0]; /* list of client ifaces */
 133         while (*s) {
 134                 if (*s == ',')
 135                         cn++;
 136                 s++;
 137         }
 138         *client_number = cn;
 139
 140         /* create vector of pointers */
 141         iface_list = xzalloc(cn * sizeof(iface_list[0]));
 142
 143         iface_list[0] = client_and_server_ifaces[1]; /* server iface */
 144
 145         i = 1;
 146         s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */
 147         goto store_client_iface_name;
 148
 149         while (i < cn) {
 150                 if (*s++ == ',') {
 151                         s[-1] = '\0';
 152  store_client_iface_name:
 153                         iface_list[i++] = s;
 154                 }
 155         }
 156
 157         return iface_list;
 158 }
 159
 160 /* Creates listen sockets (in fds) bound to client and server ifaces,
 161  * and returns numerically max fd.
 162  */
 163 static int init_sockets(char **iface_list, int num_clients, int *fds)
 164 {
 165         int i, n;
 166
 167         n = 0;
 168         for (i = 0; i < num_clients; i++) {
 169                 fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]);
 170                 if (n < fds[i])
 171                         n = fds[i];
 172         }
 173         return n;
 174 }
 175
 176 static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to)
 177 {
 178         int err;
 179
 180         errno = 0;
 181         err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to));
 182         err -= msg_len;
 183         if (err)
 184                 bb_perror_msg("sendto");
 185         return err;
 186 }
 187
 188 /**
 189  * pass_to_server() - forwards dhcp packets from client to server
 190  * p - packet to send
 191  * client - number of the client
 192  */
 193 static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
 194                         struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
 195 {
 196         int type;
 197
 198         /* check packet_type */
 199         type = get_dhcp_packet_type(p);
 200         if (type != DHCPDISCOVER && type != DHCPREQUEST
 201          && type != DHCPDECLINE && type != DHCPRELEASE
 202          && type != DHCPINFORM
 203         ) {
 204                 return;
 205         }
 206
 207         /* create new xid entry */
 208         xid_add(p->xid, client_addr, client);
 209
 210         /* forward request to server */
 211         /* note that we send from fds[0] which is bound to SERVER_PORT (67).
 212          * IOW: we send _from_ SERVER_PORT! Although this may look strange,
 213          * RFC 1542 not only allows, but prescribes this for BOOTP relays.
 214          */
 215         sendto_ip4(fds[0], p, packet_len, server_addr);
 216 }
 217
 218 /**
 219  * pass_to_client() - forwards dhcp packets from server to client
 220  * p - packet to send
 221  */
 222 static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
 223 {
 224         int type;
 225         struct xid_item *item;
 226
 227         /* check xid */
 228         item = xid_find(p->xid);
 229         if (!item) {
 230                 return;
 231         }
 232
 233         /* check packet type */
 234         type = get_dhcp_packet_type(p);
 235         if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
 236                 return;
 237         }
 238
 239 //TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set!
 240         if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
 241                 item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
 242
 243         if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
 244                 return; /* send error occurred */
 245         }
 246
 247         /* remove xid entry */
 248         xid_del(p->xid);
 249 }
 250
 251 int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 252 int dhcprelay_main(int argc, char **argv)
 253 {
 254         struct sockaddr_in server_addr;
 255         char **iface_list;
 256         int *fds;
 257         int num_sockets, max_socket;
 258         uint32_t our_nip;
 259
 260         server_addr.sin_family = AF_INET;
 261         server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
 262         server_addr.sin_port = htons(SERVER_PORT);
 263
 264         /* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
 265         if (argc == 4) {
 266                 if (!inet_aton(argv[3], &server_addr.sin_addr))
 267                         bb_perror_msg_and_die("bad server IP");
 268         } else if (argc != 3) {
 269                 bb_show_usage();
 270         }
 271
 272         iface_list = make_iface_list(argv + 1, &num_sockets);
 273
 274         fds = xmalloc(num_sockets * sizeof(fds[0]));
 275
 276         /* Create sockets and bind one to every iface */
 277         max_socket = init_sockets(iface_list, num_sockets, fds);
 278
 279         /* Get our IP on server_iface */
 280         if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL, NULL))
 281                 return 1;
 282
 283         /* Main loop */
 284         while (1) {
 285 // reinit stuff from time to time? go back to make_iface_list
 286 // every N minutes?
 287                 fd_set rfds;
 288                 struct timeval tv;
 289                 int i;
 290
 291                 FD_ZERO(&rfds);
 292                 for (i = 0; i < num_sockets; i++)
 293                         FD_SET(fds[i], &rfds);
 294                 tv.tv_sec = SELECT_TIMEOUT;
 295                 tv.tv_usec = 0;
 296                 if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
 297                         int packlen;
 298                         struct dhcp_packet dhcp_msg;
 299
 300                         /* server */
 301                         if (FD_ISSET(fds[0], &rfds)) {
 302                                 packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
 303                                 if (packlen > 0) {
 304                                         pass_to_client(&dhcp_msg, packlen, fds);
 305                                 }
 306                         }
 307
 308                         /* clients */
 309                         for (i = 1; i < num_sockets; i++) {
 310                                 struct sockaddr_in client_addr;
 311                                 socklen_t addr_size;
 312
 313                                 if (!FD_ISSET(fds[i], &rfds))
 314                                         continue;
 315
 316                                 addr_size = sizeof(client_addr);
 317                                 packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
 318                                                 (struct sockaddr *)(&client_addr), &addr_size);
 319                                 if (packlen <= 0)
 320                                         continue;
 321
 322                                 /* Get our IP on corresponding client_iface */
 323 // RFC 1542
 324 // 4.1 General BOOTP Processing for Relay Agents
 325 // 4.1.1 BOOTREQUEST Messages
 326 //   If the relay agent does decide to relay the request, it MUST examine
 327 //   the 'giaddr' ("gateway" IP address) field.  If this field is zero,
 328 //   the relay agent MUST fill this field with the IP address of the
 329 //   interface on which the request was received.  If the interface has
 330 //   more than one IP address logically associated with it, the relay
 331 //   agent SHOULD choose one IP address associated with that interface and
 332 //   use it consistently for all BOOTP messages it relays.  If the
 333 //   'giaddr' field contains some non-zero value, the 'giaddr' field MUST
 334 //   NOT be modified.  The relay agent MUST NOT, under any circumstances,
 335 //   fill the 'giaddr' field with a broadcast address as is suggested in
 336 //   [1] (Section 8, sixth paragraph).
 337
 338 // but why? what if server can't route such IP? Client ifaces may be, say, NATed!
 339
 340 // 4.1.2 BOOTREPLY Messages
 341 //   BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
 342 //   It is the responsibility of BOOTP servers to send BOOTREPLY messages
 343 //   directly to the relay agent identified in the 'giaddr' field.
 344 // (yeah right, unless it is impossible... see comment above)
 345 //   Therefore, a relay agent may assume that all BOOTREPLY messages it
 346 //   receives are intended for BOOTP clients on its directly-connected
 347 //   networks.
 348 //
 349 //   When a relay agent receives a BOOTREPLY message, it should examine
 350 //   the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
 351 //   These fields should provide adequate information for the relay agent
 352 //   to deliver the BOOTREPLY message to the client.
 353 //
 354 //   The 'giaddr' field can be used to identify the logical interface from
 355 //   which the reply must be sent (i.e., the host or router interface
 356 //   connected to the same network as the BOOTP client).  If the content
 357 //   of the 'giaddr' field does not match one of the relay agent's
 358 //   directly-connected logical interfaces, the BOOTREPLY messsage MUST be
 359 //   silently discarded.
 360                                 if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL, NULL)) {
 361                                         /* Fall back to our IP on server iface */
 362 // this makes more sense!
 363                                         dhcp_msg.gateway_nip = our_nip;
 364                                 }
 365 // maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
 366                                 pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
 367                         }
 368                 }
 369                 xid_expire();
 370         } /* while (1) */
 371
 372         /* return 0; - not reached */
 373 }