busybox/networking/udhcp/dhcprelay.c
Denys Vlasenko 10ad622dc2 Spelling fixes in comments, documentation, tests and examples
By klemens <ka7@github.com>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-04-17 16:13:32 +02:00

380 lines
10 KiB
C

/* vi: set sw=4 ts=4: */
/* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
*
* 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 <mast@gmx.net>,
* 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"
#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;
int client;
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, int client)
{
struct xid_item *item;
/* create new xid entry */
item = xmalloc(sizeof(struct xid_item));
/* add xid entry */
item->ip = *ip;
item->xid = xid;
item->client = client;
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, int *client_number)
{
char *s, **iface_list;
int 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 int init_sockets(char **iface_list, int num_clients, int *fds)
{
int 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_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, int client, int *fds,
struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
{
int type;
/* check packet_type */
type = get_dhcp_packet_type(p);
if (type != DHCPDISCOVER && type != DHCPREQUEST
&& type != DHCPDECLINE && type != DHCPRELEASE
&& type != DHCPINFORM
) {
return;
}
/* create new xid entry */
xid_add(p->xid, client_addr, client);
/* 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 xid */
item = xid_find(p->xid);
if (!item) {
return;
}
/* check packet type */
type = get_dhcp_packet_type(p);
if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
return;
}
//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);
if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
return; /* send error occurred */
}
/* remove xid entry */
xid_del(p->xid);
}
int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dhcprelay_main(int argc, char **argv)
{
struct sockaddr_in server_addr;
char **iface_list;
int *fds;
int 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 (argc == 4) {
if (!inet_aton(argv[3], &server_addr.sin_addr))
bb_perror_msg_and_die("bad server IP");
} else if (argc != 3) {
bb_show_usage();
}
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;
int 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;
/* server */
if (FD_ISSET(fds[0], &rfds)) {
packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
if (packlen > 0) {
pass_to_client(&dhcp_msg, packlen, fds);
}
}
/* 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;
/* 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 */
}