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 */
unsigned long random_xid(void)
{
	static int initialized;
	if (!initialized) {
		unsigned long seed;

		if (open_read_close("/dev/urandom", &seed, sizeof(seed)) < 0) {
			bb_info_msg("Cannot load seed "
				"from /dev/urandom: %s", strerror(errno));
			seed = time(0);
		}
		srand(seed);
		initialized++;
	}
	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(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);
	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(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;
	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(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);
	bb_info_msg("Sending renew...");
	if (server)
		ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
	else ret = udhcp_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);

	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));

}