source: MondoRescue/branches/stable/mindi-busybox/networking/udhcp/dhcprelay.c

/* vi: set sw=4 ts=4: */
/* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
 *
 * Licensed under GPL v2, see file LICENSE in this tarball for details.
 *
 * 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
 */

#include "common.h"
#include "dhcpd.h"
#include "options.h"

/* constants */
#define SELECT_TIMEOUT 5 /* select timeout in sec. */
#define MAX_LIFETIME 2*60 /* lifetime of an xid entry in sec. */
#define MAX_INTERFACES 9


/* This list holds information about clients. The xid_* functions manipulate this list. */
static struct xid_item {
    uint32_t xid;
    struct sockaddr_in ip;
    int client;
    time_t timestamp;
    struct xid_item *next;
} dhcprelay_xid_list = {0, {0}, 0, 0, NULL};


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 = time(NULL);
    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;
    time_t current_time = time(NULL);

    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) {
            return item;
        }
        item = item->next;
    }
    return NULL;
}

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 dhcpMessage *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 = get_option(p, DHCP_MESSAGE_TYPE);
    if (op != NULL)
        return op[0];
    return -1;
}

/**
 * signal_handler - handles signals ;-)
 * sig - sent signal
 */
static smallint dhcprelay_stopflag;

static void dhcprelay_signal_handler(int sig)
{
    dhcprelay_stopflag = 1;
}

/**
 * get_client_devices - parses the devices list
 * dev_list - comma separated list of devices
 * returns array
 */
static char **get_client_devices(char *dev_list, int *client_number)
{
    char *s, *list, **client_dev;
    int i, cn;

    /* copy list */
    list = xstrdup(dev_list);
    if (list == NULL) return NULL;

    /* get number of items */
    for (s = dev_list, cn = 1; *s; s++)
        if (*s == ',')
            cn++;

    client_dev = xzalloc(cn * sizeof(*client_dev));

    /* parse list */
    s = strtok(list, ",");
    i = 0;
    while (s != NULL) {
        client_dev[i++] = xstrdup(s);
        s = strtok(NULL, ",");
    }

    /* free copy and exit */
    free(list);
    *client_number = cn;
    return client_dev;
}


/* Creates listen sockets (in fds) and returns the number allocated. */
static int init_sockets(char **client, int num_clients,
            char *server, int *fds, int *max_socket)
{
    int i;

    /* talk to real server on bootps */
    fds[0] = listen_socket(/*INADDR_ANY,*/ 67, server);
    *max_socket = fds[0];

    /* array starts at 1 since server is 0 */
    num_clients++;

    for (i = 1; i < num_clients; i++) {
        /* listen for clients on bootps */
        fds[i] = listen_socket(/*NADDR_ANY,*/ 67, client[i-1]);
        if (fds[i] > *max_socket)
            *max_socket = fds[i];
    }

    return i;
}


/**
 * pass_on() - forwards dhcp packets from client to server
 * p - packet to send
 * client - number of the client
 */
static void pass_on(struct dhcpMessage *p, int packet_len, int client, int *fds,
            struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
{
    int res, type;
    struct xid_item *item;

    /* 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 */
    item = xid_add(p->xid, client_addr, client);

    /* forward request to LAN (server) */
    res = sendto(fds[0], p, packet_len, 0, (struct sockaddr*)server_addr,
            sizeof(struct sockaddr_in));
    if (res != packet_len) {
        bb_perror_msg("pass_on");
        return;
    }
}

/**
 * pass_back() - forwards dhcp packets from server to client
 * p - packet to send
 */
static void pass_back(struct dhcpMessage *p, int packet_len, int *fds)
{
    int res, 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;
    }

    if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
        item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
    if (item->client > MAX_INTERFACES)
        return;
    res = sendto(fds[item->client], p, packet_len, 0, (struct sockaddr*)(&item->ip),
                sizeof(item->ip));
    if (res != packet_len) {
        bb_perror_msg("pass_back");
        return;
    }

    /* remove xid entry */
    xid_del(p->xid);
}

static void dhcprelay_loop(int *fds, int num_sockets, int max_socket, char **clients,
        struct sockaddr_in *server_addr, uint32_t gw_ip)
{
    struct dhcpMessage dhcp_msg;
    fd_set rfds;
    size_t packlen;
    socklen_t addr_size;
    struct sockaddr_in client_addr;
    struct timeval tv;
    int i;

    while (!dhcprelay_stopflag) {
        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) {
            /* server */
            if (FD_ISSET(fds[0], &rfds)) {
                packlen = udhcp_get_packet(&dhcp_msg, fds[0]);
                if (packlen > 0) {
                    pass_back(&dhcp_msg, packlen, fds);
                }
            }
            for (i = 1; i < num_sockets; i++) {
                /* clients */
                if (!FD_ISSET(fds[i], &rfds))
                    continue;
                addr_size = sizeof(struct sockaddr_in);
                packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
                            (struct sockaddr *)(&client_addr), &addr_size);
                if (packlen <= 0)
                    continue;
                if (read_interface(clients[i-1], NULL, &dhcp_msg.giaddr, NULL))
                    dhcp_msg.giaddr = gw_ip;
                pass_on(&dhcp_msg, packlen, i, fds, &client_addr, server_addr);
            }
        }
        xid_expire();
    }
}

int dhcprelay_main(int argc, char **argv);
int dhcprelay_main(int argc, char **argv)
{
    int i, num_sockets, max_socket, fds[MAX_INTERFACES];
    uint32_t gw_ip;
    char **clients;
    struct sockaddr_in server_addr;

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(67);
    if (argc == 4) {
        if (!inet_aton(argv[3], &server_addr.sin_addr))
            bb_perror_msg_and_die("didn't grok server");
    } else if (argc == 3) {
        server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
    } else {
        bb_show_usage();
    }
    clients = get_client_devices(argv[1], &num_sockets);
    if (!clients) return 0;

    signal(SIGTERM, dhcprelay_signal_handler);
    signal(SIGQUIT, dhcprelay_signal_handler);
    signal(SIGINT, dhcprelay_signal_handler);

    num_sockets = init_sockets(clients, num_sockets, argv[2], fds, &max_socket);

    if (read_interface(argv[2], NULL, &gw_ip, NULL))
        return 1;

    dhcprelay_loop(fds, num_sockets, max_socket, clients, &server_addr, gw_ip);

    if (ENABLE_FEATURE_CLEAN_UP) {
        for (i = 0; i < num_sockets; i++) {
            close(fds[i]);
            free(clients[i]);
        }
    }

    return 0;
}