/* vi: set sw=4 ts=4: */ /* * Port to Busybox Copyright (C) 2006 Jesse Dutton * * Licensed under GPLv2, see file LICENSE in this source tree. * * DHCP Relay for 'DHCPv4 Configuration of IPSec Tunnel Mode' support * Copyright (C) 2002 Mario Strasser , * Zuercher Hochschule Winterthur, * Netbeat AG * Upstream has GPL v2 or later */ //applet:IF_DHCPRELAY(APPLET(dhcprelay, BB_DIR_USR_SBIN, BB_SUID_DROP)) //kbuild:lib-$(CONFIG_DHCPRELAY) += dhcprelay.o //usage:#define dhcprelay_trivial_usage //usage: "CLIENT_IFACE[,CLIENT_IFACE2]... SERVER_IFACE [SERVER_IP]" //usage:#define dhcprelay_full_usage "\n\n" //usage: "Relay DHCP requests between clients and server.\n" //usage: "Without SERVER_IP, requests are broadcast on SERVER_IFACE." #include "common.h" #define SERVER_PORT 67 /* lifetime of an xid entry in sec. */ #define MAX_LIFETIME 2*60 /* select timeout in sec. */ #define SELECT_TIMEOUT (MAX_LIFETIME / 8) /* This list holds information about clients. The xid_* functions manipulate this list. */ struct xid_item { unsigned timestamp; unsigned iface_no; uint32_t xid; struct sockaddr_in ip; struct xid_item *next; } FIX_ALIASING; #define dhcprelay_xid_list (*(struct xid_item*)bb_common_bufsiz1) #define INIT_G() do { setup_common_bufsiz(); } while (0) static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, unsigned iface_no) { struct xid_item *item; /* create new xid entry */ item = xmalloc(sizeof(struct xid_item)); /* add xid entry */ item->ip = *ip; item->xid = xid; item->iface_no = iface_no; item->timestamp = monotonic_sec(); item->next = dhcprelay_xid_list.next; dhcprelay_xid_list.next = item; return item; } static void xid_expire(void) { struct xid_item *item = dhcprelay_xid_list.next; struct xid_item *last = &dhcprelay_xid_list; unsigned current_time = monotonic_sec(); while (item != NULL) { if ((current_time - item->timestamp) > MAX_LIFETIME) { last->next = item->next; free(item); item = last->next; } else { last = item; item = item->next; } } } static struct xid_item *xid_find(uint32_t xid) { struct xid_item *item = dhcprelay_xid_list.next; while (item != NULL) { if (item->xid == xid) { break; } item = item->next; } return item; } static void xid_del(uint32_t xid) { struct xid_item *item = dhcprelay_xid_list.next; struct xid_item *last = &dhcprelay_xid_list; while (item != NULL) { if (item->xid == xid) { last->next = item->next; free(item); item = last->next; } else { last = item; item = item->next; } } } /** * get_dhcp_packet_type - gets the message type of a dhcp packet * p - pointer to the dhcp packet * returns the message type on success, -1 otherwise */ static int get_dhcp_packet_type(struct dhcp_packet *p) { uint8_t *op; /* it must be either a BOOTREQUEST or a BOOTREPLY */ if (p->op != BOOTREQUEST && p->op != BOOTREPLY) return -1; /* get message type option */ op = udhcp_get_option(p, DHCP_MESSAGE_TYPE); if (op != NULL) return op[0]; return -1; } /** * make_iface_list - parses client/server interface names * returns array */ static char **make_iface_list(char **client_and_server_ifaces, unsigned *client_number) { char *s, **iface_list; unsigned i, cn; /* get number of items */ cn = 2; /* 1 server iface + at least 1 client one */ s = client_and_server_ifaces[0]; /* list of client ifaces */ while (*s) { if (*s == ',') cn++; s++; } *client_number = cn; /* create vector of pointers */ iface_list = xzalloc(cn * sizeof(iface_list[0])); iface_list[0] = client_and_server_ifaces[1]; /* server iface */ i = 1; s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */ goto store_client_iface_name; while (i < cn) { if (*s++ == ',') { s[-1] = '\0'; store_client_iface_name: iface_list[i++] = s; } } return iface_list; } /* Creates listen sockets (in fds) bound to client and server ifaces, * and returns numerically max fd. */ static unsigned init_sockets(char **iface_list, unsigned num_clients, int *fds) { unsigned i, n; n = 0; for (i = 0; i < num_clients; i++) { fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]); if (n < fds[i]) n = fds[i]; } return n; } static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to) { int err; errno = 0; err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to)); err -= msg_len; if (err) bb_simple_perror_msg("sendto"); return err; } /** * pass_to_server() - forwards dhcp packets from client to server * p - packet to send * client - number of the client */ static void pass_to_server(struct dhcp_packet *p, int packet_len, unsigned from_iface_no, int *fds, struct sockaddr_in *client_addr, struct sockaddr_in *server_addr) { int type; /* check packet_type */ type = get_dhcp_packet_type(p); //FIXME: the above does not consider packet_len! if (type != DHCPDISCOVER && type != DHCPREQUEST && type != DHCPDECLINE && type != DHCPRELEASE && type != DHCPINFORM ) { return; } /* create new xid entry */ xid_add(p->xid, client_addr, from_iface_no); //TODO: since we key request/reply pairs on xid values, shouldn't we drop new requests //with xid accidentally matching a xid of one of requests we currently hold //waiting for their replies? /* forward request to server */ /* note that we send from fds[0] which is bound to SERVER_PORT (67). * IOW: we send _from_ SERVER_PORT! Although this may look strange, * RFC 1542 not only allows, but prescribes this for BOOTP relays. */ sendto_ip4(fds[0], p, packet_len, server_addr); } /** * pass_to_client() - forwards dhcp packets from server to client * p - packet to send */ static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds) { int type; struct xid_item *item; /* check packet type */ type = get_dhcp_packet_type(p); //FIXME: the above does not consider packet_len! if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) { return; } /* check xid */ item = xid_find(p->xid); if (!item) { return; } //NB: RFC 1542 section 4.1 seems to envision the logic that //relay agents use giaddr (dhcp_msg.gateway_nip in our code) //to find out on which interface to reply. //(server is meant to copy giaddr from our request packet to its reply). //Above, we don't use that logic, instead we use xid as a key. //TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set! if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY)) item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST); sendto_ip4(fds[item->iface_no], p, packet_len, &item->ip); /* ^^^ if send error occurred, we can't do much, hence no check */ /* remove xid entry */ xid_del(p->xid); } int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int dhcprelay_main(int argc UNUSED_PARAM, char **argv) { struct sockaddr_in server_addr; char **iface_list; int *fds; unsigned num_sockets, max_socket; uint32_t our_nip; INIT_G(); server_addr.sin_family = AF_INET; server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST); server_addr.sin_port = htons(SERVER_PORT); /* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */ if (!argv[1] || !argv[2]) bb_show_usage(); if (argv[3]) { if (!inet_aton(argv[3], &server_addr.sin_addr)) bb_simple_perror_msg_and_die("bad server IP"); } iface_list = make_iface_list(argv + 1, &num_sockets); fds = xmalloc(num_sockets * sizeof(fds[0])); /* Create sockets and bind one to every iface */ max_socket = init_sockets(iface_list, num_sockets, fds); /* Get our IP on server_iface */ if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL)) return 1; /* Main loop */ while (1) { // reinit stuff from time to time? go back to make_iface_list // every N minutes? fd_set rfds; struct timeval tv; unsigned i; FD_ZERO(&rfds); for (i = 0; i < num_sockets; i++) FD_SET(fds[i], &rfds); tv.tv_sec = SELECT_TIMEOUT; tv.tv_usec = 0; if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) { int packlen; struct dhcp_packet dhcp_msg; /* from server */ if (FD_ISSET(fds[0], &rfds)) { packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]); //NB: we do not check source port here. Should we? //It should be SERVER_PORT. if (packlen > 0) { pass_to_client(&dhcp_msg, packlen, fds); } } /* from clients */ for (i = 1; i < num_sockets; i++) { struct sockaddr_in client_addr; socklen_t addr_size; if (!FD_ISSET(fds[i], &rfds)) continue; addr_size = sizeof(client_addr); packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0, (struct sockaddr *)(&client_addr), &addr_size); if (packlen <= 0) continue; //NB: we do not check source port here. Should we? //It should be CLIENT_PORT for clients. //It can be SERVER_PORT for relay agents (in which case giaddr must be != 0.0.0.0), //but is it even supported to chain relay agents like this? //(we still copy client_addr.port and use it to reply to the port we got request from) /* Get our IP on corresponding client_iface */ // RFC 1542 // 4.1 General BOOTP Processing for Relay Agents // 4.1.1 BOOTREQUEST Messages // If the relay agent does decide to relay the request, it MUST examine // the 'giaddr' ("gateway" IP address) field. If this field is zero, // the relay agent MUST fill this field with the IP address of the // interface on which the request was received. If the interface has // more than one IP address logically associated with it, the relay // agent SHOULD choose one IP address associated with that interface and // use it consistently for all BOOTP messages it relays. If the // 'giaddr' field contains some non-zero value, the 'giaddr' field MUST // NOT be modified. The relay agent MUST NOT, under any circumstances, // fill the 'giaddr' field with a broadcast address as is suggested in // [1] (Section 8, sixth paragraph). // but why? what if server can't route such IP? Client ifaces may be, say, NATed! // 4.1.2 BOOTREPLY Messages // BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients. // It is the responsibility of BOOTP servers to send BOOTREPLY messages // directly to the relay agent identified in the 'giaddr' field. // (yeah right, unless it is impossible... see comment above) // Therefore, a relay agent may assume that all BOOTREPLY messages it // receives are intended for BOOTP clients on its directly-connected // networks. // // When a relay agent receives a BOOTREPLY message, it should examine // the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields. // These fields should provide adequate information for the relay agent // to deliver the BOOTREPLY message to the client. // // The 'giaddr' field can be used to identify the logical interface from // which the reply must be sent (i.e., the host or router interface // connected to the same network as the BOOTP client). If the content // of the 'giaddr' field does not match one of the relay agent's // directly-connected logical interfaces, the BOOTREPLY message MUST be // silently discarded. if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) { /* Fall back to our IP on server iface */ // this makes more sense! dhcp_msg.gateway_nip = our_nip; } // maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)? pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr); } } xid_expire(); } /* while (1) */ /* return 0; - not reached */ }