/* vi: set sw=4 ts=4: */
/*
 * udhcp 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 <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>

/* struct client_config_t client_config is in bb_common_bufsiz1 */


/*** Script execution code ***/

/* get a rough idea of how long an option will be (rounding up...) */
static const uint8_t len_of_option_as_string[] = {
        [OPTION_IP              ] = sizeof("255.255.255.255 "),
        [OPTION_IP_PAIR         ] = sizeof("255.255.255.255 ") * 2,
        [OPTION_STATIC_ROUTES   ] = sizeof("255.255.255.255/32 255.255.255.255 "),
        [OPTION_STRING          ] = 1,
#if ENABLE_FEATURE_UDHCP_RFC3397
        [OPTION_DNS_STRING      ] = 1, /* unused */
        /* Hmmm, this severely overestimates size if SIP_SERVERS option
         * is in domain name form: N-byte option in binary form
         * mallocs ~16*N bytes. But it is freed almost at once.
         */
        [OPTION_SIP_SERVERS     ] = sizeof("255.255.255.255 "),
#endif
//      [OPTION_BOOLEAN         ] = sizeof("yes "),
        [OPTION_U8              ] = sizeof("255 "),
        [OPTION_U16             ] = sizeof("65535 "),
//      [OPTION_S16             ] = sizeof("-32768 "),
        [OPTION_U32             ] = sizeof("4294967295 "),
        [OPTION_S32             ] = sizeof("-2147483684 "),
};

/* note: ip is a pointer to an IP in network order, possibly misaliged */
static int sprint_nip(char *dest, const char *pre, const uint8_t *ip)
{
        return sprintf(dest, "%s%u.%u.%u.%u", pre, ip[0], ip[1], ip[2], ip[3]);
}

/* really simple implementation, just count the bits */
static int mton(uint32_t mask)
{
        int i = 0;
        mask = ntohl(mask); /* 111110000-like bit pattern */
        while (mask) {
                i++;
                mask <<= 1;
        }
        return i;
}

/* Create "opt_name=opt_value" string */
static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_optflag *optflag, const char *opt_name)
{
        unsigned upper_length;
        int len, type, optlen;
        char *dest, *ret;

        /* option points to OPT_DATA, need to go back and get OPT_LEN */
        len = option[OPT_LEN - OPT_DATA];
        type = optflag->flags & OPTION_TYPE_MASK;
        optlen = dhcp_option_lengths[type];
        upper_length = len_of_option_as_string[type] * ((unsigned)len / (unsigned)optlen);

        dest = ret = xmalloc(upper_length + strlen(opt_name) + 2);
        dest += sprintf(ret, "%s=", opt_name);

        while (len >= optlen) {
                switch (type) {
                case OPTION_IP_PAIR:
                        dest += sprint_nip(dest, "", option);
                        *dest++ = '/';
                        option += 4;
                        optlen = 4;
                case OPTION_IP:
                        dest += sprint_nip(dest, "", option);
// TODO: it can be a list only if (optflag->flags & OPTION_LIST).
// Should we bail out/warn if we see multi-ip option which is
// not allowed to be such? For example, DHCP_BROADCAST...
                        break;
//              case OPTION_BOOLEAN:
//                      dest += sprintf(dest, *option ? "yes" : "no");
//                      break;
                case OPTION_U8:
                        dest += sprintf(dest, "%u", *option);
                        break;
//              case OPTION_S16:
                case OPTION_U16: {
                        uint16_t val_u16;
                        move_from_unaligned16(val_u16, option);
                        dest += sprintf(dest, "%u", ntohs(val_u16));
                        break;
                }
                case OPTION_S32:
                case OPTION_U32: {
                        uint32_t val_u32;
                        move_from_unaligned32(val_u32, option);
                        dest += sprintf(dest, type == OPTION_U32 ? "%lu" : "%ld", (unsigned long) ntohl(val_u32));
                        break;
                }
                case OPTION_STRING:
                        memcpy(dest, option, len);
                        dest[len] = '\0';
                        return ret;      /* Short circuit this case */
                case OPTION_STATIC_ROUTES: {
                        /* Option binary format:
                         * mask [one byte, 0..32]
                         * ip [big endian, 0..4 bytes depending on mask]
                         * router [big endian, 4 bytes]
                         * may be repeated
                         *
                         * We convert it to a string "IP/MASK ROUTER IP2/MASK2 ROUTER2"
                         */
                        const char *pfx = "";

                        while (len >= 1 + 4) { /* mask + 0-byte ip + router */
                                uint32_t nip;
                                uint8_t *p;
                                unsigned mask;
                                int bytes;

                                mask = *option++;
                                if (mask > 32)
                                        break;
                                len--;

                                nip = 0;
                                p = (void*) &nip;
                                bytes = (mask + 7) / 8; /* 0 -> 0, 1..8 -> 1, 9..16 -> 2 etc */
                                while (--bytes >= 0) {
                                        *p++ = *option++;
                                        len--;
                                }
                                if (len < 4)
                                        break;

                                /* print ip/mask */
                                dest += sprint_nip(dest, pfx, (void*) &nip);
                                pfx = " ";
                                dest += sprintf(dest, "/%u ", mask);
                                /* print router */
                                dest += sprint_nip(dest, "", option);
                                option += 4;
                                len -= 4;
                        }

                        return ret;
                }
#if ENABLE_FEATURE_UDHCP_RFC3397
                case OPTION_DNS_STRING:
                        /* unpack option into dest; use ret for prefix (i.e., "optname=") */
                        dest = dname_dec(option, len, ret);
                        if (dest) {
                                free(ret);
                                return dest;
                        }
                        /* error. return "optname=" string */
                        return ret;
                case OPTION_SIP_SERVERS:
                        /* Option binary format:
                         * type: byte
                         * type=0: domain names, dns-compressed
                         * type=1: IP addrs
                         */
                        option++;
                        len--;
                        if (option[-1] == 0) {
                                dest = dname_dec(option, len, ret);
                                if (dest) {
                                        free(ret);
                                        return dest;
                                }
                        } else
                        if (option[-1] == 1) {
                                const char *pfx = "";
                                while (1) {
                                        len -= 4;
                                        if (len < 0)
                                                break;
                                        dest += sprint_nip(dest, pfx, option);
                                        pfx = " ";
                                        option += 4;
                                }
                        }
                        return ret;
#endif
                } /* switch */
                option += optlen;
                len -= optlen;
                if (len <= 0)
                        break;
                *dest++ = ' ';
                *dest = '\0';
        }
        return ret;
}

/* put all the parameters into the environment */
static char **fill_envp(struct dhcp_packet *packet)
{
        int envc;
        int i;
        char **envp, **curr;
        const char *opt_name;
        uint8_t *temp;
        uint8_t overload = 0;

        /* We need 6 elements for:
         * "interface=IFACE"
         * "ip=N.N.N.N" from packet->yiaddr
         * "siaddr=IP" from packet->siaddr_nip (unless 0)
         * "boot_file=FILE" from packet->file (unless overloaded)
         * "sname=SERVER_HOSTNAME" from packet->sname (unless overloaded)
         * terminating NULL
         */
        envc = 6;
        /* +1 element for each option, +2 for subnet option: */
        if (packet) {
                for (i = 0; dhcp_optflags[i].code; i++) {
                        if (udhcp_get_option(packet, dhcp_optflags[i].code)) {
                                if (dhcp_optflags[i].code == DHCP_SUBNET)
                                        envc++; /* for mton */
                                envc++;
                        }
                }
                temp = udhcp_get_option(packet, DHCP_OPTION_OVERLOAD);
                if (temp)
                        overload = *temp;
        }
        curr = envp = xzalloc(sizeof(char *) * envc);

        *curr = xasprintf("interface=%s", client_config.interface);
        putenv(*curr++);

        if (!packet)
                return envp;

        *curr = xmalloc(sizeof("ip=255.255.255.255"));
        sprint_nip(*curr, "ip=", (uint8_t *) &packet->yiaddr);
        putenv(*curr++);

        opt_name = dhcp_option_strings;
        i = 0;
        while (*opt_name) {
                temp = udhcp_get_option(packet, dhcp_optflags[i].code);
                if (!temp)
                        goto next;
                *curr = xmalloc_optname_optval(temp, &dhcp_optflags[i], opt_name);
                putenv(*curr++);
                if (dhcp_optflags[i].code == DHCP_SUBNET) {
                        /* Subnet option: make things like "$ip/$mask" possible */
                        uint32_t subnet;
                        move_from_unaligned32(subnet, temp);
                        *curr = xasprintf("mask=%d", mton(subnet));
                        putenv(*curr++);
                }
 next:
                opt_name += strlen(opt_name) + 1;
                i++;
        }
        if (packet->siaddr_nip) {
                *curr = xmalloc(sizeof("siaddr=255.255.255.255"));
                sprint_nip(*curr, "siaddr=", (uint8_t *) &packet->siaddr_nip);
                putenv(*curr++);
        }
        if (!(overload & FILE_FIELD) && packet->file[0]) {
                /* watch out for invalid packets */
                *curr = xasprintf("boot_file=%."DHCP_PKT_FILE_LEN_STR"s", packet->file);
                putenv(*curr++);
        }
        if (!(overload & SNAME_FIELD) && packet->sname[0]) {
                /* watch out for invalid packets */
                *curr = xasprintf("sname=%."DHCP_PKT_SNAME_LEN_STR"s", packet->sname);
                putenv(*curr++);
        }
        return envp;
}

/* Call a script with a par file and env vars */
static void udhcp_run_script(struct dhcp_packet *packet, const char *name)
{
        char **envp, **curr;
        char *argv[3];

        if (client_config.script == NULL)
                return;

        envp = fill_envp(packet);

        /* call script */
        log1("Executing %s %s", client_config.script, name);
        argv[0] = (char*) client_config.script;
        argv[1] = (char*) name;
        argv[2] = NULL;
        spawn_and_wait(argv);

        for (curr = envp; *curr; curr++) {
                log2(" %s", *curr);
                bb_unsetenv_and_free(*curr);
        }
        free(envp);
}


/*** Sending/receiving packets ***/

static ALWAYS_INLINE uint32_t random_xid(void)
{
        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)
                udhcp_add_binary_option(packet, client_config.clientid);
        if (client_config.hostname)
                udhcp_add_binary_option(packet, client_config.hostname);
        if (client_config.fqdn)
                udhcp_add_binary_option(packet, client_config.fqdn);
        if (type != DHCPDECLINE
         && type != DHCPRELEASE
         && client_config.vendorclass
        ) {
                udhcp_add_binary_option(packet, client_config.vendorclass);
        }
}

static void add_client_options(struct dhcp_packet *packet)
{
        /* Add a "param req" option with the list of options we'd like to have
         * from stubborn DHCP servers. Pull the data from the struct in common.c.
         * No bounds checking because it goes towards the head of the packet. */
        uint8_t c;
        int end = udhcp_end_option(packet->options);
        int i, len = 0;

        for (i = 0; (c = dhcp_optflags[i].code) != 0; i++) {
                if ((   (dhcp_optflags[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;
        }

        /* Add -x options if any */
        {
                struct option_set *curr = client_config.options;
                while (curr) {
                        udhcp_add_binary_option(packet, curr->data);
                        curr = curr->next;
                }
//              if (client_config.sname)
//                      strncpy((char*)packet->sname, client_config.sname, sizeof(packet->sname) - 1);
//              if (client_config.boot_file)
//                      strncpy((char*)packet->file, client_config.boot_file, sizeof(packet->file) - 1);
        }
}

/* 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)
                udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);
        /* Explicitly saying that we want RFC-compliant packets helps
         * some buggy DHCP servers to NOT send bigger packets */
        udhcp_add_simple_option(&packet, DHCP_MAX_SIZE, htons(576));
        add_client_options(&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;
        udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);
        udhcp_add_simple_option(&packet, DHCP_SERVER_ID, server);
        add_client_options(&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_client_options(&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;
        udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);
        udhcp_add_simple_option(&packet, 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;

        udhcp_add_simple_option(&packet, 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));
}


/*** Main ***/

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;

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;
}

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 */
}

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;
        }
}

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;
}

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;
}

#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

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;
        llist_t *list_x = 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_x = 1 << 19,
                OPT_f = 1 << 20,
/* The rest has variable bit positions, need to be clever */
                OPTBIT_f = 20,
                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 = CONFIG_UDHCPC_DEFAULT_SCRIPT;
        str_V = "udhcp "BB_VER;

        /* Parse command line */
        /* Cc: mutually exclusive; O,x: list; -T,-t,-A take numeric param */
        opt_complementary = "c--C:C--c:O::x::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:ox:f"
                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
                , &list_x
                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);
                unsigned n = udhcp_option_idx(optstr);
                n = dhcp_optflags[n].code;
                client_config.opt_mask[n >> 3] |= 1 << (n & 7);
        }
        while (list_x) {
                char *optstr = llist_pop(&list_x);
                char *colon = strchr(optstr, ':');
                if (colon)
                        *colon = ' ';
                /* now it looks similar to udhcpd's config file line:
                 * "optname optval", using the common routine: */
                udhcp_str2optset(optstr, &client_config.options);
        }

        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();
        /* We want random_xid to be random... */
        srand(monotonic_us());

        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 with retval = 0, 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 = udhcp_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 = udhcp_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 = udhcp_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;
}