/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 1999, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2016-2017, Chris Fraire <cfraire@me.com>.
 */

#include <sys/types.h>
#include <time.h>
#include <netinet/in.h>
#include <netinet/dhcp.h>
#include <netinet/udp.h>
#include <netinet/ip_var.h>
#include <netinet/udp_var.h>
#include <libinetutil.h>
#include <dhcpmsg.h>
#include <dhcp_hostconf.h>
#include <string.h>

#include "packet.h"
#include "agent.h"
#include "script_handler.h"
#include "interface.h"
#include "states.h"
#include "util.h"

/*
 * Number of seconds to wait for a retry if the user is interacting with the
 * daemon.
 */
#define RETRY_DELAY     10

/*
 * If the renew timer fires within this number of seconds of the rebind timer,
 * then skip renew.  This prevents us from sending back-to-back renew and
 * rebind messages -- a pointless activity.
 */
#define TOO_CLOSE       2

static boolean_t stop_extending(dhcp_smach_t *, unsigned int);

/*
 * dhcp_renew(): attempts to renew a DHCP lease on expiration of the T1 timer.
 *
 *   input: iu_tq_t *: unused
 *          void *: the lease to renew (dhcp_lease_t)
 *  output: void
 *
 *   notes: The primary expense involved with DHCP (like most UDP protocols) is
 *          with the generation and handling of packets, not the contents of
 *          those packets.  Thus, we try to reduce the number of packets that
 *          are sent.  It would be nice to just renew all leases here (each one
 *          added has trivial added overhead), but the DHCPv6 RFC doesn't
 *          explicitly allow that behavior.  Rather than having that argument,
 *          we settle for ones that are close in expiry to the one that fired.
 *          For v4, we repeatedly reschedule the T1 timer to do the
 *          retransmissions.  For v6, we rely on the common timer computation
 *          in packet.c.
 */

/* ARGSUSED */
void
dhcp_renew(iu_tq_t *tqp, void *arg)
{
        dhcp_lease_t *dlp = arg;
        dhcp_smach_t *dsmp = dlp->dl_smach;
        uint32_t        t2;

        dhcpmsg(MSG_VERBOSE, "dhcp_renew: T1 timer expired on %s",
            dsmp->dsm_name);

        dlp->dl_t1.dt_id = -1;

        if (dsmp->dsm_state == RENEWING || dsmp->dsm_state == REBINDING) {
                dhcpmsg(MSG_DEBUG, "dhcp_renew: already renewing");
                release_lease(dlp);
                return;
        }

        /*
         * Sanity check: don't send packets if we're past T2, or if we're
         * extremely close.
         */

        t2 = dsmp->dsm_curstart_monosec + dlp->dl_t2.dt_start;
        if (monosec() + TOO_CLOSE >= t2) {
                dhcpmsg(MSG_DEBUG, "dhcp_renew: %spast T2 on %s",
                    monosec() > t2 ? "" : "almost ", dsmp->dsm_name);
                release_lease(dlp);
                return;
        }

        /*
         * If there isn't an async event pending, or if we can cancel the one
         * that's there, then try to renew by sending an extension request.  If
         * that fails, we'll try again when the next timer fires.
         */
        if (!async_cancel(dsmp) || !async_start(dsmp, DHCP_EXTEND, B_FALSE) ||
            !dhcp_extending(dsmp)) {
                if (monosec() + RETRY_DELAY < t2) {
                        /*
                         * Try again in RETRY_DELAY seconds; user command
                         * should be gone.
                         */
                        init_timer(&dlp->dl_t1, RETRY_DELAY);
                        (void) set_smach_state(dsmp, BOUND);
                        if (!schedule_lease_timer(dlp, &dlp->dl_t1,
                            dhcp_renew)) {
                                dhcpmsg(MSG_INFO, "dhcp_renew: unable to "
                                    "reschedule renewal around user command "
                                    "on %s; will wait for rebind",
                                    dsmp->dsm_name);
                        }
                } else {
                        dhcpmsg(MSG_DEBUG, "dhcp_renew: user busy on %s; will "
                            "wait for rebind", dsmp->dsm_name);
                }
        }
        release_lease(dlp);
}

/*
 * dhcp_rebind(): attempts to renew a DHCP lease from the REBINDING state (T2
 *                timer expiry).
 *
 *   input: iu_tq_t *: unused
 *          void *: the lease to renew
 *  output: void
 *   notes: For v4, we repeatedly reschedule the T2 timer to do the
 *          retransmissions.  For v6, we rely on the common timer computation
 *          in packet.c.
 */

/* ARGSUSED */
void
dhcp_rebind(iu_tq_t *tqp, void *arg)
{
        dhcp_lease_t    *dlp = arg;
        dhcp_smach_t    *dsmp = dlp->dl_smach;
        int             nlifs;
        dhcp_lif_t      *lif;
        boolean_t       some_valid;
        uint32_t        expiremax;
        DHCPSTATE       oldstate;

        dhcpmsg(MSG_VERBOSE, "dhcp_rebind: T2 timer expired on %s",
            dsmp->dsm_name);

        dlp->dl_t2.dt_id = -1;

        if ((oldstate = dsmp->dsm_state) == REBINDING) {
                dhcpmsg(MSG_DEBUG, "dhcp_renew: already rebinding");
                release_lease(dlp);
                return;
        }

        /*
         * Sanity check: don't send packets if we've already expired on all of
         * the addresses.  We compute the maximum expiration time here, because
         * it won't matter for v4 (there's only one lease) and for v6 we need
         * to know when the last lease ages away.
         */

        some_valid = B_FALSE;
        expiremax = monosec();
        lif = dlp->dl_lifs;
        for (nlifs = dlp->dl_nlifs; nlifs > 0; nlifs--, lif = lif->lif_next) {
                uint32_t expire;

                expire = dsmp->dsm_curstart_monosec + lif->lif_expire.dt_start;
                if (expire > expiremax) {
                        expiremax = expire;
                        some_valid = B_TRUE;
                }
        }
        if (!some_valid) {
                dhcpmsg(MSG_DEBUG, "dhcp_rebind: all leases expired on %s",
                    dsmp->dsm_name);
                release_lease(dlp);
                return;
        }

        /*
         * This is our first venture into the REBINDING state, so reset the
         * server address.  We know the renew timer has already been cancelled
         * (or we wouldn't be here).
         */
        if (dsmp->dsm_isv6) {
                dsmp->dsm_server = ipv6_all_dhcp_relay_and_servers;
        } else {
                IN6_IPADDR_TO_V4MAPPED(htonl(INADDR_BROADCAST),
                    &dsmp->dsm_server);
        }

        /* {Bound,Renew}->rebind transitions cannot fail */
        (void) set_smach_state(dsmp, REBINDING);

        /*
         * If there isn't an async event pending, or if we can cancel the one
         * that's there, then try to rebind by sending an extension request.
         * If that fails, we'll clean up when the lease expires.
         */
        if (!async_cancel(dsmp) || !async_start(dsmp, DHCP_EXTEND, B_FALSE) ||
            !dhcp_extending(dsmp)) {
                if (monosec() + RETRY_DELAY < expiremax) {
                        /*
                         * Try again in RETRY_DELAY seconds; user command
                         * should be gone.
                         */
                        init_timer(&dlp->dl_t2, RETRY_DELAY);
                        (void) set_smach_state(dsmp, oldstate);
                        if (!schedule_lease_timer(dlp, &dlp->dl_t2,
                            dhcp_rebind)) {
                                dhcpmsg(MSG_INFO, "dhcp_rebind: unable to "
                                    "reschedule rebind around user command on "
                                    "%s; lease may expire", dsmp->dsm_name);
                        }
                } else {
                        dhcpmsg(MSG_WARNING, "dhcp_rebind: user busy on %s; "
                            "will expire", dsmp->dsm_name);
                }
        }
        release_lease(dlp);
}

/*
 * dhcp_finish_expire(): finish expiration of a lease after the user script
 *                       runs.  If this is the last lease, then restart DHCP.
 *                       The caller has a reference to the LIF, which will be
 *                       dropped.
 *
 *   input: dhcp_smach_t *: the state machine to be restarted
 *          void *: logical interface that has expired
 *  output: int: always 1
 */

static int
dhcp_finish_expire(dhcp_smach_t *dsmp, void *arg)
{
        dhcp_lif_t *lif = arg;
        dhcp_lease_t *dlp;

        dhcpmsg(MSG_DEBUG, "lease expired on %s; removing", lif->lif_name);

        dlp = lif->lif_lease;
        unplumb_lif(lif);
        if (dlp->dl_nlifs == 0)
                remove_lease(dlp);
        release_lif(lif);

        /* If some valid leases remain, then drive on */
        if (dsmp->dsm_leases != NULL) {
                dhcpmsg(MSG_DEBUG,
                    "dhcp_finish_expire: some leases remain on %s",
                    dsmp->dsm_name);
                return (1);
        }

        (void) remove_hostconf(dsmp->dsm_name, dsmp->dsm_isv6);

        dhcpmsg(MSG_INFO, "last lease expired on %s -- restarting DHCP",
            dsmp->dsm_name);

        /*
         * in the case where the lease is less than DHCP_REBIND_MIN
         * seconds, we will never enter dhcp_renew() and thus the packet
         * counters will not be reset.  in that case, reset them here.
         */

        if (dsmp->dsm_state == BOUND) {
                dsmp->dsm_bad_offers    = 0;
                dsmp->dsm_sent          = 0;
                dsmp->dsm_received      = 0;
        }

        deprecate_leases(dsmp);

        /* reset_smach() in dhcp_selecting() will clean up any leftover state */
        dhcp_selecting(dsmp);

        return (1);
}

/*
 * dhcp_deprecate(): deprecates an address on a given logical interface when
 *                   the preferred lifetime expires.
 *
 *   input: iu_tq_t *: unused
 *          void *: the logical interface whose lease is expiring
 *  output: void
 */

/* ARGSUSED */
void
dhcp_deprecate(iu_tq_t *tqp, void *arg)
{
        dhcp_lif_t *lif = arg;

        set_lif_deprecated(lif);
        release_lif(lif);
}

/*
 * dhcp_expire(): expires a lease on a given logical interface and, if there
 *                are no more leases, restarts DHCP.
 *
 *   input: iu_tq_t *: unused
 *          void *: the logical interface whose lease has expired
 *  output: void
 */

/* ARGSUSED */
void
dhcp_expire(iu_tq_t *tqp, void *arg)
{
        dhcp_lif_t      *lif = arg;
        dhcp_smach_t    *dsmp;
        const char      *event;

        dhcpmsg(MSG_VERBOSE, "dhcp_expire: lease timer expired on %s",
            lif->lif_name);

        lif->lif_expire.dt_id = -1;
        if (lif->lif_lease == NULL) {
                release_lif(lif);
                return;
        }

        set_lif_deprecated(lif);

        dsmp = lif->lif_lease->dl_smach;

        if (!async_cancel(dsmp)) {

                dhcpmsg(MSG_WARNING,
                    "dhcp_expire: cannot cancel current asynchronous command "
                    "on %s", dsmp->dsm_name);

                /*
                 * Try to schedule ourselves for callback.  We're really
                 * situation-critical here; there's not much hope for us if
                 * this fails.
                 */
                init_timer(&lif->lif_expire, DHCP_EXPIRE_WAIT);
                if (schedule_lif_timer(lif, &lif->lif_expire, dhcp_expire))
                        return;

                dhcpmsg(MSG_CRIT, "dhcp_expire: cannot reschedule dhcp_expire "
                    "to get called back, proceeding...");
        }

        if (!async_start(dsmp, DHCP_START, B_FALSE))
                dhcpmsg(MSG_WARNING, "dhcp_expire: cannot start asynchronous "
                    "transaction on %s, continuing...", dsmp->dsm_name);

        /*
         * Determine if this state machine has any non-expired LIFs left in it.
         * If it doesn't, then this is an "expire" event.  Otherwise, if some
         * valid leases remain, it's a "loss" event.  The SOMEEXP case can
         * occur only with DHCPv6.
         */
        if (expired_lif_state(dsmp) == DHCP_EXP_SOMEEXP)
                event = EVENT_LOSS6;
        else if (dsmp->dsm_isv6)
                event = EVENT_EXPIRE6;
        else
                event = EVENT_EXPIRE;

        /*
         * just march on if this fails; at worst someone will be able
         * to async_start() while we're actually busy with our own
         * asynchronous transaction.  better than not having a lease.
         */

        (void) script_start(dsmp, event, dhcp_finish_expire, lif, NULL);
}

/*
 * dhcp_extending(): sends a REQUEST (IPv4 DHCP) or Rebind/Renew (DHCPv6) to
 *                   extend a lease on a given state machine
 *
 *   input: dhcp_smach_t *: the state machine to send the message from
 *  output: boolean_t: B_TRUE if the extension request was sent
 */

boolean_t
dhcp_extending(dhcp_smach_t *dsmp)
{
        dhcp_pkt_t              *dpkt;

        stop_pkt_retransmission(dsmp);

        /*
         * We change state here because this function is also called when
         * adopting a lease and on demand by the user.
         */
        if (dsmp->dsm_state == BOUND) {
                dsmp->dsm_neg_hrtime    = gethrtime();
                dsmp->dsm_bad_offers    = 0;
                dsmp->dsm_sent          = 0;
                dsmp->dsm_received      = 0;
                /* Bound->renew can't fail */
                (void) set_smach_state(dsmp, RENEWING);
        }

        dhcpmsg(MSG_DEBUG, "dhcp_extending: sending request on %s",
            dsmp->dsm_name);

        if (dsmp->dsm_isv6) {
                dhcp_lease_t *dlp;
                dhcp_lif_t *lif;
                uint_t nlifs;
                uint_t irt, mrt;

                /*
                 * Start constructing the Renew/Rebind message.  Only Renew has
                 * a server ID, as we still think our server might be
                 * reachable.
                 */
                if (dsmp->dsm_state == RENEWING) {
                        dpkt = init_pkt(dsmp, DHCPV6_MSG_RENEW);
                        (void) add_pkt_opt(dpkt, DHCPV6_OPT_SERVERID,
                            dsmp->dsm_serverid, dsmp->dsm_serveridlen);
                        irt = DHCPV6_REN_TIMEOUT;
                        mrt = DHCPV6_REN_MAX_RT;
                } else {
                        dpkt = init_pkt(dsmp, DHCPV6_MSG_REBIND);
                        irt = DHCPV6_REB_TIMEOUT;
                        mrt = DHCPV6_REB_MAX_RT;
                }

                /*
                 * Loop over the leases, and add an IA_NA for each and an
                 * IAADDR for each address.
                 */
                for (dlp = dsmp->dsm_leases; dlp != NULL; dlp = dlp->dl_next) {
                        lif = dlp->dl_lifs;
                        for (nlifs = dlp->dl_nlifs; nlifs > 0;
                            nlifs--, lif = lif->lif_next) {
                                (void) add_pkt_lif(dpkt, lif,
                                    DHCPV6_STAT_SUCCESS, NULL);
                        }
                }

                /* Add required Option Request option */
                (void) add_pkt_prl(dpkt, dsmp);

                return (send_pkt_v6(dsmp, dpkt, dsmp->dsm_server,
                    stop_extending, irt, mrt));
        } else {
                dhcp_lif_t *lif = dsmp->dsm_lif;
                ipaddr_t server;

                /* assemble the DHCPREQUEST message. */
                dpkt = init_pkt(dsmp, REQUEST);
                dpkt->pkt->ciaddr.s_addr = lif->lif_addr;

                /*
                 * The max dhcp message size option is set to the interface
                 * max, minus the size of the udp and ip headers.
                 */
                (void) add_pkt_opt16(dpkt, CD_MAX_DHCP_SIZE,
                    htons(lif->lif_pif->pif_mtu - sizeof (struct udpiphdr)));
                (void) add_pkt_opt32(dpkt, CD_LEASE_TIME, htonl(DHCP_PERM));

                if (class_id_len != 0) {
                        (void) add_pkt_opt(dpkt, CD_CLASS_ID, class_id,
                            class_id_len);
                }
                (void) add_pkt_prl(dpkt, dsmp);
                /*
                 * dsm_reqhost was set for this state machine in
                 * dhcp_selecting() if the REQUEST_HOSTNAME option was set and
                 * a host name was found.
                 */
                if (!dhcp_add_fqdn_opt(dpkt, dsmp) &&
                    dsmp->dsm_reqhost != NULL) {
                        (void) add_pkt_opt(dpkt, CD_HOSTNAME, dsmp->dsm_reqhost,
                            strlen(dsmp->dsm_reqhost));
                }
                (void) add_pkt_opt(dpkt, CD_END, NULL, 0);

                IN6_V4MAPPED_TO_IPADDR(&dsmp->dsm_server, server);
                return (send_pkt(dsmp, dpkt, server, stop_extending));
        }
}

/*
 * stop_extending(): decides when to stop retransmitting v4 REQUEST or v6
 *                   Renew/Rebind messages.  If we're renewing, then stop if
 *                   T2 is soon approaching.
 *
 *   input: dhcp_smach_t *: the state machine REQUESTs are being sent from
 *          unsigned int: the number of REQUESTs sent so far
 *  output: boolean_t: B_TRUE if retransmissions should stop
 */

/* ARGSUSED */
static boolean_t
stop_extending(dhcp_smach_t *dsmp, unsigned int n_requests)
{
        dhcp_lease_t *dlp;

        /*
         * If we're renewing and rebind time is soon approaching, then don't
         * schedule
         */
        if (dsmp->dsm_state == RENEWING) {
                monosec_t t2;

                t2 = 0;
                for (dlp = dsmp->dsm_leases; dlp != NULL; dlp = dlp->dl_next) {
                        if (dlp->dl_t2.dt_start > t2)
                                t2 = dlp->dl_t2.dt_start;
                }
                t2 += dsmp->dsm_curstart_monosec;
                if (monosec() + TOO_CLOSE >= t2) {
                        dhcpmsg(MSG_DEBUG, "stop_extending: %spast T2 on %s",
                            monosec() > t2 ? "" : "almost ", dsmp->dsm_name);
                        return (B_TRUE);
                }
        }

        /*
         * Note that returning B_TRUE cancels both this transmission and the
         * one that would occur at dsm_send_timeout, and that for v4 we cut the
         * time in half for each retransmission.  Thus we check here against
         * half of the minimum.
         */
        if (!dsmp->dsm_isv6 &&
            dsmp->dsm_send_timeout < DHCP_REBIND_MIN * MILLISEC / 2) {
                dhcpmsg(MSG_DEBUG, "stop_extending: next retry would be in "
                    "%d.%03d; stopping", dsmp->dsm_send_timeout / MILLISEC,
                    dsmp->dsm_send_timeout % MILLISEC);
                return (B_TRUE);
        }

        /* Otherwise, w stop only when the next timer (rebind, expire) fires */
        return (B_FALSE);
}