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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 <fcntl.h>
#include "dhcpd.h"
#include "clientpacket.h"
#include "options.h"
#include "dhcpc.h"
#include "common.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: %m");
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, (uint8_t *) &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; 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(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;
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(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) != (uint16_t) (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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