networking/udhcp/dhcpc.c

/* vi: set sw=4 ts=4: */
/*
 * udhcp 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 <syslog.h>
/* Override ENABLE_FEATURE_PIDFILE - ifupdown needs our pidfile to always exist */
#define WANT_PIDFILE 1
#include "common.h"
#include "dhcpd.h"
#include "dhcpc.h"
#include "options.h"

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


static int sockfd = -1;

#define LISTEN_NONE   0
#define LISTEN_KERNEL 1
#define LISTEN_RAW    2
static smallint listen_mode;

/* initial state: (re)start DHCP negotiation */
#define INIT_SELECTING  0
/* discover was sent, DHCPOFFER reply received */
#define REQUESTING      1
/* select/renew was sent, DHCPACK reply received */
#define BOUND           2
/* half of lease passed, want to renew it by sending unicast renew requests */
#define RENEWING        3
/* renew requests were not answered, lease is almost over, send broadcast renew */
#define REBINDING       4
/* manually requested renew (SIGUSR1) */
#define RENEW_REQUESTED 5
/* release, possibly manually requested (SIGUSR2) */
#define RELEASED        6
static smallint state;

/* struct client_config_t client_config is in bb_common_bufsiz1 */


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

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

/* Initialize the packet with the proper defaults */
static void init_packet(struct dhcp_packet *packet, char type)
{
	udhcp_init_header(packet, type);
	memcpy(packet->chaddr, client_config.client_mac, 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);
	if (type != DHCPDECLINE
	 && type != DHCPRELEASE
	 && client_config.vendorclass
	) {
		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_param_req_option(struct dhcp_packet *packet)
{
	uint8_t c;
	int end = end_option(packet->options);
	int i, len = 0;

	for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
		if ((   (dhcp_options[i].flags & OPTION_REQ)
		     && !client_config.no_default_options
		    )
		 || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
		) {
			packet->options[end + OPT_DATA + len] = c;
			len++;
		}
	}
	if (len) {
		packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
		packet->options[end + OPT_LEN] = len;
		packet->options[end + OPT_DATA + len] = DHCP_END;
	}
}

/* RFC 2131
 * 4.4.4 Use of broadcast and unicast
 *
 * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
 * messages, unless the client knows the address of a DHCP server.
 * The client unicasts DHCPRELEASE messages to the server. Because
 * the client is declining the use of the IP address supplied by the server,
 * the client broadcasts DHCPDECLINE messages.
 *
 * When the DHCP client knows the address of a DHCP server, in either
 * INIT or REBOOTING state, the client may use that address
 * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
 * The client may also use unicast to send DHCPINFORM messages
 * to a known DHCP server. If the client receives no response to DHCP
 * messages sent to the IP address of a known DHCP server, the DHCP
 * client reverts to using the IP broadcast address.
 */

static int raw_bcast_from_client_config_ifindex(struct dhcp_packet *packet)
{
	return udhcp_send_raw_packet(packet,
		/*src*/ INADDR_ANY, CLIENT_PORT,
		/*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
		client_config.ifindex);
}

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

	init_packet(&packet, DHCPDISCOVER);
	packet.xid = xid;
	if (requested)
		add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
	/* Explicitly saying that we want RFC-compliant packets helps
	 * some buggy DHCP servers to NOT send bigger packets */
	add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
	add_param_req_option(&packet);

	bb_info_msg("Sending discover...");
	return raw_bcast_from_client_config_ifindex(&packet);
}

/* Broadcast a DHCP request message */
/* RFC 2131 3.1 paragraph 3:
 * "The client _broadcasts_ a DHCPREQUEST message..."
 */
static int send_select(uint32_t xid, uint32_t server, uint32_t requested)
{
	struct dhcp_packet 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_param_req_option(&packet);

	addr.s_addr = requested;
	bb_info_msg("Sending select for %s...", inet_ntoa(addr));
	return raw_bcast_from_client_config_ifindex(&packet);
}

/* Unicast or broadcast a DHCP renew message */
static int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
{
	struct dhcp_packet packet;

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

	bb_info_msg("Sending renew...");
	if (server)
		return udhcp_send_kernel_packet(&packet,
			ciaddr, CLIENT_PORT,
			server, SERVER_PORT);
	return raw_bcast_from_client_config_ifindex(&packet);
}

#if ENABLE_FEATURE_UDHCPC_ARPING
/* Broadcast a DHCP decline message */
static int send_decline(uint32_t xid, uint32_t server, uint32_t requested)
{
	struct dhcp_packet packet;

	init_packet(&packet, DHCPDECLINE);
	packet.xid = xid;
	add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
	add_simple_option(packet.options, DHCP_SERVER_ID, server);

	bb_info_msg("Sending decline...");
	return raw_bcast_from_client_config_ifindex(&packet);
}
#endif

/* Unicast a DHCP release message */
static int send_release(uint32_t server, uint32_t ciaddr)
{
	struct dhcp_packet packet;

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

	add_simple_option(packet.options, DHCP_SERVER_ID, server);

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

/* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
static NOINLINE int udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
{
	int bytes;
	struct ip_udp_dhcp_packet packet;
	uint16_t check;

	memset(&packet, 0, sizeof(packet));
	bytes = safe_read(fd, &packet, sizeof(packet));
	if (bytes < 0) {
		log1("Packet read error, ignoring");
		/* NB: possible down interface, etc. Caller should pause. */
		return bytes; /* returns -1 */
	}

	if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
		log1("Packet is too short, ignoring");
		return -2;
	}

	if (bytes < ntohs(packet.ip.tot_len)) {
		/* packet is bigger than sizeof(packet), we did partial read */
		log1("Oversized packet, ignoring");
		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(packet) - can't happen */
	 || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
	) {
		log1("Unrelated/bogus packet, ignoring");
		return -2;
	}

	/* verify IP checksum */
	check = packet.ip.check;
	packet.ip.check = 0;
	if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
		log1("Bad IP header checksum, ignoring");
		return -2;
	}

	/* verify UDP checksum. IP header has to be modified for this */
	memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
	/* ip.xx fields which are not memset: protocol, check, saddr, daddr */
	packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
	check = packet.udp.check;
	packet.udp.check = 0;
	if (check && check != udhcp_checksum(&packet, bytes)) {
		log1("Packet with bad UDP checksum received, ignoring");
		return -2;
	}

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

	if (dhcp_pkt->cookie != htonl(DHCP_MAGIC)) {
		bb_info_msg("Packet with bad magic, ignoring");
		return -2;
	}
	log1("Got valid DHCP packet");
	udhcp_dump_packet(dhcp_pkt);
	return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
}

static int udhcp_raw_socket(int ifindex)
{
	int fd;
	struct sockaddr_ll sock;

	/*
	 * Comment:
	 *
	 *	I've selected not to see LL header, so BPF doesn't see it, too.
	 *	The filter may also pass non-IP and non-ARP packets, but we do
	 *	a more complete check when receiving the message in userspace.
	 *
	 * and filter shamelessly stolen from:
	 *
	 *	http://www.flamewarmaster.de/software/dhcpclient/
	 *
	 * There are a few other interesting ideas on that page (look under
	 * "Motivation").  Use of netlink events is most interesting.  Think
	 * of various network servers listening for events and reconfiguring.
	 * That would obsolete sending HUP signals and/or make use of restarts.
	 *
	 * Copyright: 2006, 2007 Stefan Rompf <sux@loplof.de>.
	 * License: GPL v2.
	 *
	 * TODO: make conditional?
	 */
#define SERVER_AND_CLIENT_PORTS  ((67 << 16) + 68)
	static const struct sock_filter filter_instr[] = {
		/* check for udp */
		BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9),
		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 2, 0),     /* L5, L1, is UDP? */
		/* ugly check for arp on ethernet-like and IPv4 */
		BPF_STMT(BPF_LD|BPF_W|BPF_ABS, 2),                      /* L1: */
		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 0x08000604, 3, 4),      /* L3, L4 */
		/* skip IP header */
		BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0),                     /* L5: */
		/* check udp source and destination ports */
		BPF_STMT(BPF_LD|BPF_W|BPF_IND, 0),
		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, SERVER_AND_CLIENT_PORTS, 0, 1),	/* L3, L4 */
		/* returns */
		BPF_STMT(BPF_RET|BPF_K, 0x0fffffff ),                   /* L3: pass */
		BPF_STMT(BPF_RET|BPF_K, 0),                             /* L4: reject */
	};
	static const struct sock_fprog filter_prog = {
		.len = sizeof(filter_instr) / sizeof(filter_instr[0]),
		/* casting const away: */
		.filter = (struct sock_filter *) filter_instr,
	};

	log1("Opening raw socket on ifindex %d", ifindex); //log2?

	fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
	log1("Got raw socket fd %d", fd); //log2?

	if (SERVER_PORT == 67 && CLIENT_PORT == 68) {
		/* Use only if standard ports are in use */
		/* Ignoring error (kernel may lack support for this) */
		if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog,
				sizeof(filter_prog)) >= 0)
			log1("Attached filter to raw socket fd %d", fd); // log?
	}

	sock.sll_family = AF_PACKET;
	sock.sll_protocol = htons(ETH_P_IP);
	sock.sll_ifindex = ifindex;
	xbind(fd, (struct sockaddr *) &sock, sizeof(sock));
	log1("Created raw socket");

	return fd;
}

/* just a little helper */
static void change_listen_mode(int new_mode)
{
	log1("Entering listen mode: %s",
		new_mode != LISTEN_NONE
			? (new_mode == LISTEN_KERNEL ? "kernel" : "raw")
			: "none"
	);

	listen_mode = new_mode;
	if (sockfd >= 0) {
		close(sockfd);
		sockfd = -1;
	}
	if (new_mode == LISTEN_KERNEL)
		sockfd = udhcp_listen_socket(/*INADDR_ANY,*/ CLIENT_PORT, client_config.interface);
	else if (new_mode != LISTEN_NONE)
		sockfd = udhcp_raw_socket(client_config.ifindex);
	/* else LISTEN_NONE: sockfd stays closed */
}

/* perform a renew */
static void perform_renew(void)
{
	bb_info_msg("Performing a DHCP renew");
	switch (state) {
	case BOUND:
		change_listen_mode(LISTEN_KERNEL);
	case RENEWING:
	case REBINDING:
		state = RENEW_REQUESTED;
		break;
	case RENEW_REQUESTED: /* impatient are we? fine, square 1 */
		udhcp_run_script(NULL, "deconfig");
	case REQUESTING:
	case RELEASED:
		change_listen_mode(LISTEN_RAW);
		state = INIT_SELECTING;
		break;
	case INIT_SELECTING:
		break;
	}
}

/* perform a release */
static void perform_release(uint32_t requested_ip, uint32_t server_addr)
{
	char buffer[sizeof("255.255.255.255")];
	struct in_addr temp_addr;

	/* send release packet */
	if (state == BOUND || state == RENEWING || state == REBINDING) {
		temp_addr.s_addr = server_addr;
		strcpy(buffer, inet_ntoa(temp_addr));
		temp_addr.s_addr = requested_ip;
		bb_info_msg("Unicasting a release of %s to %s",
				inet_ntoa(temp_addr), buffer);
		send_release(server_addr, requested_ip); /* unicast */
		udhcp_run_script(NULL, "deconfig");
	}
	bb_info_msg("Entering released state");

	change_listen_mode(LISTEN_NONE);
	state = RELEASED;
}

#if BB_MMU
static void client_background(void)
{
	bb_daemonize(0);
	logmode &= ~LOGMODE_STDIO;
	/* rewrite pidfile, as our pid is different now */
	write_pidfile(client_config.pidfile);
}
#endif

static uint8_t* alloc_dhcp_option(int code, const char *str, int extra)
{
	uint8_t *storage;
	int len = strnlen(str, 255);
	storage = xzalloc(len + extra + OPT_DATA);
	storage[OPT_CODE] = code;
	storage[OPT_LEN] = len + extra;
	memcpy(storage + extra + OPT_DATA, str, len);
	return storage;
}

int udhcpc_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int udhcpc_main(int argc UNUSED_PARAM, char **argv)
{
	uint8_t *temp, *message;
	const char *str_c, *str_V, *str_h, *str_F, *str_r;
	IF_FEATURE_UDHCP_PORT(char *str_P;)
	llist_t *list_O = NULL;
	int tryagain_timeout = 20;
	int discover_timeout = 3;
	int discover_retries = 3;
	uint32_t server_addr = server_addr; /* for compiler */
	uint32_t requested_ip = 0;
	uint32_t xid = 0;
	uint32_t lease_seconds = 0; /* can be given as 32-bit quantity */
	int packet_num;
	int timeout; /* must be signed */
	unsigned already_waited_sec;
	unsigned opt;
	int max_fd;
	int retval;
	struct timeval tv;
	struct dhcp_packet packet;
	fd_set rfds;

#if ENABLE_LONG_OPTS
	static const char udhcpc_longopts[] ALIGN1 =
		"clientid\0"       Required_argument "c"
		"clientid-none\0"  No_argument       "C"
		"vendorclass\0"    Required_argument "V"
		"hostname\0"       Required_argument "H"
		"fqdn\0"           Required_argument "F"
		"interface\0"      Required_argument "i"
		"now\0"            No_argument       "n"
		"pidfile\0"        Required_argument "p"
		"quit\0"           No_argument       "q"
		"release\0"        No_argument       "R"
		"request\0"        Required_argument "r"
		"script\0"         Required_argument "s"
		"timeout\0"        Required_argument "T"
		"version\0"        No_argument       "v"
		"retries\0"        Required_argument "t"
		"tryagain\0"       Required_argument "A"
		"syslog\0"         No_argument       "S"
		"request-option\0" Required_argument "O"
		"no-default-options\0" No_argument   "o"
		"foreground\0"     No_argument       "f"
		"background\0"     No_argument       "b"
		IF_FEATURE_UDHCPC_ARPING("arping\0"	No_argument       "a")
		IF_FEATURE_UDHCP_PORT("client-port\0"	Required_argument "P")
		;
#endif
	enum {
		OPT_c = 1 << 0,
		OPT_C = 1 << 1,
		OPT_V = 1 << 2,
		OPT_H = 1 << 3,
		OPT_h = 1 << 4,
		OPT_F = 1 << 5,
		OPT_i = 1 << 6,
		OPT_n = 1 << 7,
		OPT_p = 1 << 8,
		OPT_q = 1 << 9,
		OPT_R = 1 << 10,
		OPT_r = 1 << 11,
		OPT_s = 1 << 12,
		OPT_T = 1 << 13,
		OPT_t = 1 << 14,
		OPT_S = 1 << 15,
		OPT_A = 1 << 16,
		OPT_O = 1 << 17,
		OPT_o = 1 << 18,
		OPT_f = 1 << 19,
/* The rest has variable bit positions, need to be clever */
		OPTBIT_f = 19,
		USE_FOR_MMU(             OPTBIT_b,)
		IF_FEATURE_UDHCPC_ARPING(OPTBIT_a,)
		IF_FEATURE_UDHCP_PORT(   OPTBIT_P,)
		USE_FOR_MMU(             OPT_b = 1 << OPTBIT_b,)
		IF_FEATURE_UDHCPC_ARPING(OPT_a = 1 << OPTBIT_a,)
		IF_FEATURE_UDHCP_PORT(   OPT_P = 1 << OPTBIT_P,)
	};

	/* Default options. */
	IF_FEATURE_UDHCP_PORT(SERVER_PORT = 67;)
	IF_FEATURE_UDHCP_PORT(CLIENT_PORT = 68;)
	client_config.interface = "eth0";
	client_config.script = DEFAULT_SCRIPT;
	str_V = "udhcp "BB_VER;

	/* Parse command line */
	/* Cc: mutually exclusive; O: list; -T,-t,-A take numeric param */
	opt_complementary = "c--C:C--c:O::T+:t+:A+"
#if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
		":vv"
#endif
		;
	IF_LONG_OPTS(applet_long_options = udhcpc_longopts;)
	opt = getopt32(argv, "c:CV:H:h:F:i:np:qRr:s:T:t:SA:O:of"
		USE_FOR_MMU("b")
		IF_FEATURE_UDHCPC_ARPING("a")
		IF_FEATURE_UDHCP_PORT("P:")
		"v"
		, &str_c, &str_V, &str_h, &str_h, &str_F
		, &client_config.interface, &client_config.pidfile, &str_r /* i,p */
		, &client_config.script /* s */
		, &discover_timeout, &discover_retries, &tryagain_timeout /* T,t,A */
		, &list_O
		IF_FEATURE_UDHCP_PORT(, &str_P)
#if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
		, &dhcp_verbose
#endif
		);
	if (opt & (OPT_h|OPT_H))
		client_config.hostname = alloc_dhcp_option(DHCP_HOST_NAME, str_h, 0);
	if (opt & OPT_F) {
		/* FQDN option format: [0x51][len][flags][0][0]<fqdn> */
		client_config.fqdn = alloc_dhcp_option(DHCP_FQDN, str_F, 3);
		/* Flag bits: 0000NEOS
		 * S: 1 = Client requests server to update A RR in DNS as well as PTR
		 * O: 1 = Server indicates to client that DNS has been updated regardless
		 * E: 1 = Name is in DNS format, i.e. <4>host<6>domain<3>com<0>,
		 *    not "host.domain.com". Format 0 is obsolete.
		 * N: 1 = Client requests server to not update DNS (S must be 0 then)
		 * Two [0] bytes which follow are deprecated and must be 0.
		 */
		client_config.fqdn[OPT_DATA + 0] = 0x1;
		/*client_config.fqdn[OPT_DATA + 1] = 0; - xzalloc did it */
		/*client_config.fqdn[OPT_DATA + 2] = 0; */
	}
	if (opt & OPT_r)
		requested_ip = inet_addr(str_r);
#if ENABLE_FEATURE_UDHCP_PORT
	if (opt & OPT_P) {
		CLIENT_PORT = xatou16(str_P);
		SERVER_PORT = CLIENT_PORT - 1;
	}
#endif
	if (opt & OPT_o)
		client_config.no_default_options = 1;
	while (list_O) {
		char *optstr = llist_pop(&list_O);
		int n = index_in_strings(dhcp_option_strings, optstr);
		if (n < 0)
			bb_error_msg_and_die("unknown option '%s'", optstr);
		n = dhcp_options[n].code;
		client_config.opt_mask[n >> 3] |= 1 << (n & 7);
	}

	if (udhcp_read_interface(client_config.interface,
			&client_config.ifindex,
			NULL,
			client_config.client_mac)
	) {
		return 1;
	}

	if (opt & OPT_c) {
		client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, str_c, 0);
	} else if (!(opt & OPT_C)) {
		/* not set and not suppressed, set the default client ID */
		client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, "", 7);
		client_config.clientid[OPT_DATA] = 1; /* type: ethernet */
		memcpy(client_config.clientid + OPT_DATA+1, client_config.client_mac, 6);
	}
	if (str_V[0] != '\0')
		client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, str_V, 0);
#if !BB_MMU
	/* on NOMMU reexec (i.e., background) early */
	if (!(opt & OPT_f)) {
		bb_daemonize_or_rexec(0 /* flags */, argv);
		logmode = LOGMODE_NONE;
	}
#endif
	if (opt & OPT_S) {
		openlog(applet_name, LOG_PID, LOG_DAEMON);
		logmode |= LOGMODE_SYSLOG;
	}

	/* Make sure fd 0,1,2 are open */
	bb_sanitize_stdio();
	/* Equivalent of doing a fflush after every \n */
	setlinebuf(stdout);

	/* Create pidfile */
	write_pidfile(client_config.pidfile);

	/* Goes to stdout (unless NOMMU) and possibly syslog */
	bb_info_msg("%s (v"BB_VER") started", applet_name);

	/* Set up the signal pipe */
	udhcp_sp_setup();

	state = INIT_SELECTING;
	udhcp_run_script(NULL, "deconfig");
	change_listen_mode(LISTEN_RAW);
	packet_num = 0;
	timeout = 0;
	already_waited_sec = 0;

	/* Main event loop. select() waits on signal pipe and possibly
	 * on sockfd.
	 * "continue" statements in code below jump to the top of the loop.
	 */
	for (;;) {
		/* silence "uninitialized!" warning */
		unsigned timestamp_before_wait = timestamp_before_wait;

		//bb_error_msg("sockfd:%d, listen_mode:%d", sockfd, listen_mode);

		/* Was opening raw or udp socket here
		 * if (listen_mode != LISTEN_NONE && sockfd < 0),
		 * but on fast network renew responses return faster
		 * than we open sockets. Thus this code is moved
		 * to change_listen_mode(). Thus we open listen socket
		 * BEFORE we send renew request (see "case BOUND:"). */

		max_fd = udhcp_sp_fd_set(&rfds, sockfd);

		tv.tv_sec = timeout - already_waited_sec;
		tv.tv_usec = 0;
		retval = 0; /* If we already timed out, fall through, else... */
		if ((int)tv.tv_sec > 0) {
			timestamp_before_wait = (unsigned)monotonic_sec();
			log1("Waiting on select...");
			retval = select(max_fd + 1, &rfds, NULL, NULL, &tv);
			if (retval < 0) {
				/* EINTR? A signal was caught, don't panic */
				if (errno == EINTR) {
					already_waited_sec += (unsigned)monotonic_sec() - timestamp_before_wait;
					continue;
				}
				/* Else: an error occured, panic! */
				bb_perror_msg_and_die("select");
			}
		}

		/* If timeout dropped to zero, time to become active:
		 * resend discover/renew/whatever
		 */
		if (retval == 0) {
			/* We will restart the wait in any case */
			already_waited_sec = 0;

			switch (state) {
			case INIT_SELECTING:
				if (packet_num < discover_retries) {
					if (packet_num == 0)
						xid = random_xid();
					/* broadcast */
					send_discover(xid, requested_ip);
					timeout = discover_timeout;
					packet_num++;
					continue;
				}
 leasefail:
				udhcp_run_script(NULL, "leasefail");
#if BB_MMU /* -b is not supported on NOMMU */
				if (opt & OPT_b) { /* background if no lease */
					bb_info_msg("No lease, forking to background");
					client_background();
					/* do not background again! */
					opt = ((opt & ~OPT_b) | OPT_f);
				} else
#endif
				if (opt & OPT_n) { /* abort if no lease */
					bb_info_msg("No lease, failing");
					retval = 1;
					goto ret;
				}
				/* wait before trying again */
				timeout = tryagain_timeout;
				packet_num = 0;
				continue;
			case REQUESTING:
				if (packet_num < discover_retries) {
					/* send broadcast select packet */
					send_select(xid, server_addr, requested_ip);
					timeout = discover_timeout;
					packet_num++;
					continue;
				}
				/* Timed out, go back to init state.
				 * "discover...select...discover..." loops
				 * were seen in the wild. Treat them similarly
				 * to "no response to discover" case */
				change_listen_mode(LISTEN_RAW);
				state = INIT_SELECTING;
				goto leasefail;
			case BOUND:
				/* 1/2 lease passed, enter renewing state */
				state = RENEWING;
				change_listen_mode(LISTEN_KERNEL);
				log1("Entering renew state");
				/* fall right through */
			case RENEW_REQUESTED: /* manual (SIGUSR1) renew */
			case_RENEW_REQUESTED:
			case RENEWING:
				if (timeout > 60) {
					/* send an unicast renew request */
			/* Sometimes observed to fail (EADDRNOTAVAIL) to bind
			 * a new UDP socket for sending inside send_renew.
			 * I hazard to guess existing listening socket
			 * is somehow conflicting with it, but why is it
			 * not deterministic then?! Strange.
			 * Anyway, it does recover by eventually failing through
			 * into INIT_SELECTING state.
			 */
					send_renew(xid, server_addr, requested_ip);
					timeout >>= 1;
					continue;
				}
				/* Timed out, enter rebinding state */
				log1("Entering rebinding state");
				state = REBINDING;
				/* fall right through */
			case REBINDING:
				/* Switch to bcast receive */
				change_listen_mode(LISTEN_RAW);
				/* Lease is *really* about to run out,
				 * try to find DHCP server using broadcast */
				if (timeout > 0) {
					/* send a broadcast renew request */
					send_renew(xid, 0 /*INADDR_ANY*/, requested_ip);
					timeout >>= 1;
					continue;
				}
				/* Timed out, enter init state */
				bb_info_msg("Lease lost, entering init state");
				udhcp_run_script(NULL, "deconfig");
				state = INIT_SELECTING;
				/*timeout = 0; - already is */
				packet_num = 0;
				continue;
			/* case RELEASED: */
			}
			/* yah, I know, *you* say it would never happen */
			timeout = INT_MAX;
			continue; /* back to main loop */
		} /* if select timed out */

		/* select() didn't timeout, something happened */

		/* Is it a signal? */
		/* note: udhcp_sp_read checks FD_ISSET before reading */
		switch (udhcp_sp_read(&rfds)) {
		case SIGUSR1:
			perform_renew();
			if (state == RENEW_REQUESTED)
				goto case_RENEW_REQUESTED;
			/* Start things over */
			packet_num = 0;
			/* Kill any timeouts, user wants this to hurry along */
			timeout = 0;
			continue;
		case SIGUSR2:
			perform_release(requested_ip, server_addr);
			timeout = INT_MAX;
			continue;
		case SIGTERM:
			bb_info_msg("Received SIGTERM");
			if (opt & OPT_R) /* release on quit */
				perform_release(requested_ip, server_addr);
			goto ret0;
		}

		/* Is it a packet? */
		if (listen_mode == LISTEN_NONE || !FD_ISSET(sockfd, &rfds))
			continue; /* no */

		{
			int len;

			/* A packet is ready, read it */
			if (listen_mode == LISTEN_KERNEL)
				len = udhcp_recv_kernel_packet(&packet, sockfd);
			else
				len = udhcp_recv_raw_packet(&packet, sockfd);
			if (len == -1) {
				/* Error is severe, reopen socket */
				bb_info_msg("Read error: %s, reopening socket", strerror(errno));
				sleep(discover_timeout); /* 3 seconds by default */
				change_listen_mode(listen_mode); /* just close and reopen */
			}
			/* If this packet will turn out to be unrelated/bogus,
			 * we will go back and wait for next one.
			 * Be sure timeout is properly decreased. */
			already_waited_sec += (unsigned)monotonic_sec() - timestamp_before_wait;
			if (len < 0)
				continue;
		}

		if (packet.xid != xid) {
			log1("xid %x (our is %x), ignoring packet",
				(unsigned)packet.xid, (unsigned)xid);
			continue;
		}

		/* Ignore packets that aren't for us */
		if (packet.hlen != 6
		 || memcmp(packet.chaddr, client_config.client_mac, 6)
		) {
//FIXME: need to also check that last 10 bytes are zero
			log1("chaddr does not match, ignoring packet"); // log2?
			continue;
		}

		message = get_option(&packet, DHCP_MESSAGE_TYPE);
		if (message == NULL) {
			bb_error_msg("no message type option, ignoring packet");
			continue;
		}

		switch (state) {
		case INIT_SELECTING:
			/* Must be a DHCPOFFER to one of our xid's */
			if (*message == DHCPOFFER) {
		/* TODO: why we don't just fetch server's IP from IP header? */
				temp = get_option(&packet, DHCP_SERVER_ID);
				if (!temp) {
					bb_error_msg("no server ID in message");
					continue;
					/* still selecting - this server looks bad */
				}
				/* it IS unaligned sometimes, don't "optimize" */
				move_from_unaligned32(server_addr, temp);
				xid = packet.xid;
				requested_ip = packet.yiaddr;

				/* enter requesting state */
				state = REQUESTING;
				timeout = 0;
				packet_num = 0;
				already_waited_sec = 0;
			}
			continue;
		case REQUESTING:
		case RENEWING:
		case RENEW_REQUESTED:
		case REBINDING:
			if (*message == DHCPACK) {
				temp = get_option(&packet, DHCP_LEASE_TIME);
				if (!temp) {
					bb_error_msg("no lease time with ACK, using 1 hour lease");
					lease_seconds = 60 * 60;
				} else {
					/* it IS unaligned sometimes, don't "optimize" */
					move_from_unaligned32(lease_seconds, temp);
					lease_seconds = ntohl(lease_seconds);
					lease_seconds &= 0x0fffffff; /* paranoia: must not be prone to overflows */
					if (lease_seconds < 10) /* and not too small */
						lease_seconds = 10;
				}
#if ENABLE_FEATURE_UDHCPC_ARPING
				if (opt & OPT_a) {
/* RFC 2131 3.1 paragraph 5:
 * "The client receives the DHCPACK message with configuration
 * parameters. The client SHOULD perform a final check on the
 * parameters (e.g., ARP for allocated network address), and notes
 * the duration of the lease specified in the DHCPACK message. At this
 * point, the client is configured. If the client detects that the
 * address is already in use (e.g., through the use of ARP),
 * the client MUST send a DHCPDECLINE message to the server and restarts
 * the configuration process..." */
					if (!arpping(packet.yiaddr,
							NULL,
							(uint32_t) 0,
							client_config.client_mac,
							client_config.interface)
					) {
						bb_info_msg("Offered address is in use "
							"(got ARP reply), declining");
						send_decline(xid, server_addr, packet.yiaddr);

						if (state != REQUESTING)
							udhcp_run_script(NULL, "deconfig");
						change_listen_mode(LISTEN_RAW);
						state = INIT_SELECTING;
						requested_ip = 0;
						timeout = tryagain_timeout;
						packet_num = 0;
						already_waited_sec = 0;
						continue; /* back to main loop */
					}
				}
#endif
				/* enter bound state */
				timeout = lease_seconds / 2;
				{
					struct in_addr temp_addr;
					temp_addr.s_addr = packet.yiaddr;
					bb_info_msg("Lease of %s obtained, lease time %u",
						inet_ntoa(temp_addr), (unsigned)lease_seconds);
				}
				requested_ip = packet.yiaddr;
				udhcp_run_script(&packet, state == REQUESTING ? "bound" : "renew");

				state = BOUND;
				change_listen_mode(LISTEN_NONE);
				if (opt & OPT_q) { /* quit after lease */
					if (opt & OPT_R) /* release on quit */
						perform_release(requested_ip, server_addr);
					goto ret0;
				}
				/* future renew failures should not exit (JM) */
				opt &= ~OPT_n;
#if BB_MMU /* NOMMU case backgrounded earlier */
				if (!(opt & OPT_f)) {
					client_background();
					/* do not background again! */
					opt = ((opt & ~OPT_b) | OPT_f);
				}
#endif
				already_waited_sec = 0;
				continue; /* back to main loop */
			}
			if (*message == DHCPNAK) {
				/* return to init state */
				bb_info_msg("Received DHCP NAK");
				udhcp_run_script(&packet, "nak");
				if (state != REQUESTING)
					udhcp_run_script(NULL, "deconfig");
				change_listen_mode(LISTEN_RAW);
				sleep(3); /* avoid excessive network traffic */
				state = INIT_SELECTING;
				requested_ip = 0;
				timeout = 0;
				packet_num = 0;
				already_waited_sec = 0;
			}
			continue;
		/* case BOUND: - ignore all packets */
		/* case RELEASED: - ignore all packets */
		}
		/* back to main loop */
	} /* for (;;) - main loop ends */

 ret0:
	retval = 0;
 ret:
	/*if (client_config.pidfile) - remove_pidfile has its own check */
		remove_pidfile(client_config.pidfile);
	return retval;
}