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

/* vi: set sw=4 ts=4: */
/* clientpacket.c
 *
 * Packet generation and dispatching functions for the DHCP client.
 *
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include <features.h>
#if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
#include <netpacket/packet.h>
#include <net/ethernet.h>
#else
#include <asm/types.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>
#endif

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


/* Create a random xid */
uint32_t random_xid(void)
{
    static smallint initialized;

    if (!initialized) {
        srand(monotonic_us());
        initialized = 1;
    }
    return rand();
}


/* initialize a packet with the proper defaults */
static void init_packet(struct dhcpMessage *packet, char type)
{
    udhcp_init_header(packet, type);
    memcpy(packet->chaddr, client_config.arp, 6);
    if (client_config.clientid)
        add_option_string(packet->options, client_config.clientid);
    if (client_config.hostname)
        add_option_string(packet->options, client_config.hostname);
    if (client_config.fqdn)
        add_option_string(packet->options, client_config.fqdn);
    add_option_string(packet->options, client_config.vendorclass);
}


/* Add a parameter request list for stubborn DHCP servers. Pull the data
 * from the struct in options.c. Don't do bounds checking here because it
 * goes towards the head of the packet. */
static void add_requests(struct dhcpMessage *packet)
{
    int end = end_option(packet->options);
    int i, len = 0;

    packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
    for (i = 0; dhcp_options[i].code; i++)
        if (dhcp_options[i].flags & OPTION_REQ)
            packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
    packet->options[end + OPT_LEN] = len;
    packet->options[end + OPT_DATA + len] = DHCP_END;

}


/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
int send_discover(uint32_t xid, uint32_t requested)
{
    struct dhcpMessage packet;

    init_packet(&packet, DHCPDISCOVER);
    packet.xid = xid;
    if (requested)
        add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);

    add_requests(&packet);
    bb_info_msg("Sending discover...");
    return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
            SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}


/* Broadcasts a DHCP request message */
int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
{
    struct dhcpMessage packet;
    struct in_addr addr;

    init_packet(&packet, DHCPREQUEST);
    packet.xid = xid;

    add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
    add_simple_option(packet.options, DHCP_SERVER_ID, server);

    add_requests(&packet);
    addr.s_addr = requested;
    bb_info_msg("Sending select for %s...", inet_ntoa(addr));
    return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
                SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}


/* Unicasts or broadcasts a DHCP renew message */
int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
{
    struct dhcpMessage packet;

    init_packet(&packet, DHCPREQUEST);
    packet.xid = xid;
    packet.ciaddr = ciaddr;

    add_requests(&packet);
    bb_info_msg("Sending renew...");
    if (server)
        return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);

    return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
                SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}


/* Unicasts a DHCP release message */
int send_release(uint32_t server, uint32_t ciaddr)
{
    struct dhcpMessage packet;

    init_packet(&packet, DHCPRELEASE);
    packet.xid = random_xid();
    packet.ciaddr = ciaddr;

    add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
    add_simple_option(packet.options, DHCP_SERVER_ID, server);

    bb_info_msg("Sending release...");
    return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
}


/* return -1 on errors that are fatal for the socket, -2 for those that aren't */
int get_raw_packet(struct dhcpMessage *payload, int fd)
{
    int bytes;
    struct udp_dhcp_packet packet;
    uint32_t source, dest;
    uint16_t check;

    memset(&packet, 0, sizeof(struct udp_dhcp_packet));
    bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
    if (bytes < 0) {
        DEBUG("Cannot read on raw listening socket - ignoring");
        usleep(500000); /* possible down interface, looping condition */
        return -1;
    }

    if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
        DEBUG("Message too short, ignoring");
        return -2;
    }

    if (bytes < ntohs(packet.ip.tot_len)) {
        DEBUG("Truncated packet");
        return -2;
    }

    /* ignore any extra garbage bytes */
    bytes = ntohs(packet.ip.tot_len);

    /* Make sure its the right packet for us, and that it passes sanity checks */
    if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
     || packet.ip.ihl != sizeof(packet.ip) >> 2
     || packet.udp.dest != htons(CLIENT_PORT)
     || bytes > (int) sizeof(struct udp_dhcp_packet)
     || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
    ) {
        DEBUG("Unrelated/bogus packet");
        return -2;
    }

    /* check IP checksum */
    check = packet.ip.check;
    packet.ip.check = 0;
    if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
        DEBUG("bad IP header checksum, ignoring");
        return -1;
    }

    /* verify the UDP checksum by replacing the header with a psuedo header */
    source = packet.ip.saddr;
    dest = packet.ip.daddr;
    check = packet.udp.check;
    packet.udp.check = 0;
    memset(&packet.ip, 0, sizeof(packet.ip));

    packet.ip.protocol = IPPROTO_UDP;
    packet.ip.saddr = source;
    packet.ip.daddr = dest;
    packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
    if (check && check != udhcp_checksum(&packet, bytes)) {
        bb_error_msg("packet with bad UDP checksum received, ignoring");
        return -2;
    }

    memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));

    if (ntohl(payload->cookie) != DHCP_MAGIC) {
        bb_error_msg("received bogus message (bad magic) - ignoring");
        return -2;
    }
    DEBUG("oooooh!!! got some!");
    return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
}