clientpacket.c

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/* clientpacket.c
 *
 * Packet generation and dispatching functions for the DHCP client.
 *
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
#include <string.h>
#include <sys/socket.h>
#include <features.h>
#if __GLIBC__ >=2 && __GLIBC_MINOR >= 1
#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 <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


#include "dhcpd.h"
#include "packet.h"
#include "options.h"
#include "dhcpc.h"
#include "debug.h"


/* Create a random xid */
unsigned long random_xid(void)
{
        static int initialized;
        if (!initialized) {
                int fd;
                unsigned long seed;

                fd = open("/dev/urandom", 0);
                if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
                        LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %s",
                                strerror(errno));
                        seed = time(0);
                }
                if (fd >= 0) close(fd);
                srand(seed);
                initialized++;
        }
        return rand();
}


/* initialize a packet with the proper defaults */
static void init_packet(struct dhcpMessage *packet, char type)
{
        struct vendor  {
                char vendor, length;
                char str[sizeof("udhcp "VERSION)];
        } vendor_id = { DHCP_VENDOR,  sizeof("udhcp "VERSION) - 1, "udhcp "VERSION};
        
        init_header(packet, type);
        memcpy(packet->chaddr, client_config.arp, 6);
        add_option_string(packet->options, client_config.clientid);
        if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
        add_option_string(packet->options, (unsigned char *) &vendor_id);
}


/* Add a paramater 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; options[i].code; i++)
                if (options[i].flags & OPTION_REQ)
                        packet->options[end + OPT_DATA + len++] = 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(unsigned long xid, unsigned long 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);
        LOG(LOG_DEBUG, "Sending discover...");
        return 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(unsigned long xid, unsigned long server, unsigned long 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;
        LOG(LOG_DEBUG, "Sending select for %s...", inet_ntoa(addr));
        return 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(unsigned long xid, unsigned long server, unsigned long ciaddr)
{
        struct dhcpMessage packet;
        int ret = 0;

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

        add_requests(&packet);
        LOG(LOG_DEBUG, "Sending renew...");
        if (server) 
                ret = kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
        else ret = raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
                                SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
        return ret;
}       


/* Unicasts a DHCP release message */
int send_release(unsigned long server, unsigned long 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);

        LOG(LOG_DEBUG, "Sending release...");
        return 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;
        u_int32_t source, dest;
        u_int16_t check;

        memset(&packet, 0, sizeof(struct udp_dhcp_packet));
        bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
        if (bytes < 0) {
                DEBUG(LOG_INFO, "couldn't 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(LOG_INFO, "message too short, ignoring");
                return -2;
        }
        
        if (bytes < ntohs(packet.ip.tot_len)) {
                DEBUG(LOG_INFO, "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) != (short) (bytes - sizeof(packet.ip))) {
                DEBUG(LOG_INFO, "unrelated/bogus packet");
                return -2;
        }

        /* check IP checksum */
        check = packet.ip.check;
        packet.ip.check = 0;
        if (check != checksum(&(packet.ip), sizeof(packet.ip))) {
                DEBUG(LOG_INFO, "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 != checksum(&packet, bytes)) {
                DEBUG(LOG_ERR, "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) {
                LOG(LOG_ERR, "received bogus message (bad magic) -- ignoring");
                return -2;
        }
        DEBUG(LOG_INFO, "oooooh!!! got some!");
        return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
        
}

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