/* timer event handling
 * Copyright (C) 1997 Angelos D. Keromytis.
 * Copyright (C) 1998-2001  D. Hugh Redelmeier.
 * Copyright (C) 2009 Andreas Steffen - Hochschule fuer Technik Rapperswil
 *
 * 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.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * 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.
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/queue.h>

#include <freeswan.h>

#include <library.h>
#include <crypto/rngs/rng.h>

#include "constants.h"
#include "defs.h"
#include "connections.h"
#include "state.h"
#include "demux.h"
#include "ipsec_doi.h"  /* needs demux.h and state.h */
#include "kernel.h"
#include "server.h"
#include "log.h"
#include "timer.h"
#include "whack.h"
#include "nat_traversal.h"

/**
 * monotonic version of time(3)
 */
time_t now(void)
{
	static time_t delta = 0
		, last_time = 0;
	time_t n = time(NULL);

	passert(n != (time_t)-1);
	if (last_time > n)
	{
		plog("time moved backwards %ld seconds", (long)(last_time - n));
		delta += last_time - n;
	}
	last_time = n;
	return n + delta;
}

/* This file has the event handling routines. Events are
 * kept as a linked list of event structures. These structures
 * have information like event type, expiration time and a pointer
 * to event specific data (for example, to a state structure).
 */

static struct event *evlist = (struct event *) NULL;

/**
 * This routine places an event in the event list.
 */
void event_schedule(enum event_type type, time_t tm, struct state *st)
{
	struct event *ev = malloc_thing(struct event);

	ev->ev_type = type;
	ev->ev_time = tm + now();
	ev->ev_state = st;

	/* If the event is associated with a state, put a backpointer to the
	 * event in the state object, so we can find and delete the event
	 * if we need to (for example, if we receive a reply).
	 */
	if (st != NULL)
	{
		if (type == EVENT_DPD || type == EVENT_DPD_TIMEOUT)
		{
			passert(st->st_dpd_event == NULL);
			st->st_dpd_event = ev;
		}
		else
		{
			passert(st->st_event == NULL);
			st->st_event = ev;
		}
	}

	DBG(DBG_CONTROL,
		if (st == NULL)
			DBG_log("inserting event %N, timeout in %lu seconds"
				, timer_event_names, type, (unsigned long)tm);
		else
			DBG_log("inserting event %N, timeout in %lu seconds for #%lu"
				, timer_event_names, type, (unsigned long)tm
				, ev->ev_state->st_serialno));

	if (evlist == (struct event *) NULL
	|| evlist->ev_time >= ev->ev_time)
	{
		ev->ev_next = evlist;
		evlist = ev;
	}
	else
	{
		struct event *evt;

		for (evt = evlist; evt->ev_next != NULL; evt = evt->ev_next)
			if (evt->ev_next->ev_time >= ev->ev_time)
				break;

#ifdef NEVER    /* this seems to be overkill */
		DBG(DBG_CONTROL,
			if (evt->ev_state == NULL)
				DBG_log("event added after event %N"
					, timer_event_names, evt->ev_type);
			else
				DBG_log("event added after event %N for #%lu"
					, timer_event_names, evt->ev_type,
					, evt->ev_state->st_serialno));
#endif /* NEVER */

		ev->ev_next = evt->ev_next;
		evt->ev_next = ev;
	}
}

/**
 * Generate the secret value for responder cookies, and
 * schedule an event for refresh.
 */
bool init_secret(void)
{
	rng_t *rng;

	rng = lib->crypto->create_rng(lib->crypto, RNG_STRONG);

	if (rng == NULL)
	{
		plog("secret initialization failed, no RNG supported");
		return FALSE;
	}
	rng->get_bytes(rng, sizeof(secret_of_the_day), secret_of_the_day);
	rng->destroy(rng);
    event_schedule(EVENT_REINIT_SECRET, EVENT_REINIT_SECRET_DELAY, NULL);
	return true;
}

/**
 * Handle the first event on the list.
 */
void handle_timer_event(void)
{
	time_t tm;
	struct event *ev = evlist;
	int type;
	struct state *st;
	connection_t *c = NULL;
	ip_address peer;

	if (ev == (struct event *) NULL)    /* Just paranoid */
	{
		DBG(DBG_CONTROL, DBG_log("empty event list, yet we're called"));
		return;
	}

	type = ev->ev_type;
	st = ev->ev_state;

	tm = now();

	if (tm < ev->ev_time)
	{
		DBG(DBG_CONTROL, DBG_log("called while no event expired (%lu/%lu, %N)"
			, (unsigned long)tm, (unsigned long)ev->ev_time
			, timer_event_names, type));

		/* This will happen if the most close-to-expire event was
		 * a retransmission or cleanup, and we received a packet
		 * at the same time as the event expired. Due to the processing
		 * order in call_server(), the packet processing will happen first,
		 * and the event will be removed.
		 */
		return;
	}

	evlist = evlist->ev_next;           /* Ok, we'll handle this event */

	DBG(DBG_CONTROL,
		if (evlist != (struct event *) NULL)
			DBG_log("event after this is %N in %ld seconds"
				, timer_event_names, evlist->ev_type
				, (long) (evlist->ev_time - tm)));

	/* for state-associated events, pick up the state pointer
	 * and remove the backpointer from the state object.
	 * We'll eventually either schedule a new event, or delete the state.
	 */
	passert(GLOBALS_ARE_RESET());
	if (st != NULL)
	{
		c = st->st_connection;
		if (type  == EVENT_DPD || type == EVENT_DPD_TIMEOUT)
		{
			passert(st->st_dpd_event == ev);
			st->st_dpd_event = NULL;
		}
		else
		{
			passert(st->st_event == ev);
			st->st_event = NULL;
		}
		peer = c->spd.that.host_addr;
		set_cur_state(st);
	}

	switch (type)
	{
		case EVENT_REINIT_SECRET:
			passert(st == NULL);
			DBG(DBG_CONTROL, DBG_log("event EVENT_REINIT_SECRET handled"));
			init_secret();
			break;

		case EVENT_LOG_DAILY:
			daily_log_event();
			break;

		case EVENT_RETRANSMIT:
			/* Time to retransmit, or give up.
			 *
			 * Generally, we'll only try to send the message
			 * MAXIMUM_RETRANSMISSIONS times.  Each time we double
			 * our patience.
			 *
			 * As a special case, if this is the first initiating message
			 * of a Main Mode exchange, and we have been directed to try
			 * forever, we'll extend the number of retransmissions to
			 * MAXIMUM_RETRANSMISSIONS_INITIAL times, with all these
			 * extended attempts having the same patience.  The intention
			 * is to reduce the bother when nobody is home.
			 */
			{
				time_t delay = 0;

				DBG(DBG_CONTROL, DBG_log(
					"handling event EVENT_RETRANSMIT for %s \"%s\" #%lu"
					, ip_str(&peer), c->name, st->st_serialno));

				if (st->st_retransmit < MAXIMUM_RETRANSMISSIONS)
					delay = EVENT_RETRANSMIT_DELAY_0 << (st->st_retransmit + 1);
				else if (st->st_state == STATE_MAIN_I1
				&& c->sa_keying_tries == 0
				&& st->st_retransmit < MAXIMUM_RETRANSMISSIONS_INITIAL)
					delay = EVENT_RETRANSMIT_DELAY_0 << MAXIMUM_RETRANSMISSIONS;

				if (delay != 0)
				{
					st->st_retransmit++;
					whack_log(RC_RETRANSMISSION
						, "%s: retransmission; will wait %lus for response"
						, enum_name(&state_names, st->st_state)
						, (unsigned long)delay);
					send_packet(st, "EVENT_RETRANSMIT");
					event_schedule(EVENT_RETRANSMIT, delay, st);
				}
				else
				{
					/* check if we've tried rekeying enough times.
					 * st->st_try == 0 means that this should be the only try.
					 * c->sa_keying_tries == 0 means that there is no limit.
					 */
					unsigned long try = st->st_try;
					unsigned long try_limit = c->sa_keying_tries;
					const char *details = "";

					switch (st->st_state)
					{
					case STATE_MAIN_I3:
						details = ".  Possible authentication failure:"
							" no acceptable response to our"
							" first encrypted message";
						break;
					case STATE_MAIN_I1:
						details = ".  No response (or no acceptable response) to our"
							" first IKE message";
						break;
					case STATE_QUICK_I1:
						if (c->newest_ipsec_sa == SOS_NOBODY)
							details = ".  No acceptable response to our"
								" first Quick Mode message:"
								" perhaps peer likes no proposal";
						break;
					default:
						break;
					}
					loglog(RC_NORETRANSMISSION
						, "max number of retransmissions (%d) reached %s%s"
						, st->st_retransmit
						, enum_show(&state_names, st->st_state), details);
					if (try != 0 && try != try_limit)
					{
						/* A lot like EVENT_SA_REPLACE, but over again.
						 * Since we know that st cannot be in use,
						 * we can delete it right away.
						 */
						char story[80]; /* arbitrary limit */

						try++;
						snprintf(story, sizeof(story), try_limit == 0
							? "starting keying attempt %ld of an unlimited number"
							: "starting keying attempt %ld of at most %ld"
							, try, try_limit);

						if (st->st_whack_sock != NULL_FD)
						{
							/* Release whack because the observer will get bored. */
							loglog(RC_COMMENT, "%s, but releasing whack"
								, story);
							release_pending_whacks(st, story);
						}
						else
						{
							/* no whack: just log to syslog */
							plog("%s", story);
						}
						ipsecdoi_replace(st, try);
					}
					delete_state(st);
				}
			}
			break;

		case EVENT_SA_REPLACE:
		case EVENT_SA_REPLACE_IF_USED:
			{
				so_serial_t newest = IS_PHASE1(st->st_state)
					? c->newest_isakmp_sa : c->newest_ipsec_sa;

				if (newest != st->st_serialno
				&& newest != SOS_NOBODY)
				{
					/* not very interesting: no need to replace */
					DBG(DBG_LIFECYCLE
						, plog("not replacing stale %s SA: #%lu will do"
							, IS_PHASE1(st->st_state)? "ISAKMP" : "IPsec"
							, newest));
				}
				else if (type == EVENT_SA_REPLACE_IF_USED
				&& st->st_outbound_time <= tm - c->sa_rekey_margin)
				{
					/* we observed no recent use: no need to replace
					 *
					 * The sampling effects mean that st_outbound_time
					 * could be up to SHUNT_SCAN_INTERVAL more recent
					 * than actual traffic because the sampler looks at change
					 * over that interval.
					 * st_outbound_time could also not yet reflect traffic
					 * in the last SHUNT_SCAN_INTERVAL.
					 * We expect that SHUNT_SCAN_INTERVAL is smaller than
					 * c->sa_rekey_margin so that the effects of this will
					 * be unimportant.
					 * This is just an optimization: correctness is not
					 * at stake.
					 *
					 * Note: we are abusing the DBG mechanism to control
					 * normal log output.
					 */
					DBG(DBG_LIFECYCLE
						, plog("not replacing stale %s SA: inactive for %lus"
							, IS_PHASE1(st->st_state)? "ISAKMP" : "IPsec"
							, (unsigned long)(tm - st->st_outbound_time)));
				}
				else
				{
					DBG(DBG_LIFECYCLE
						, plog("replacing stale %s SA"
							, IS_PHASE1(st->st_state)? "ISAKMP" : "IPsec"));
					ipsecdoi_replace(st, 1);
				}
				delete_dpd_event(st);
				event_schedule(EVENT_SA_EXPIRE, st->st_margin, st);
			}
			break;

		case EVENT_SA_EXPIRE:
			{
				const char *satype;
				so_serial_t latest;

				if (IS_PHASE1(st->st_state))
				{
					satype = "ISAKMP";
					latest = c->newest_isakmp_sa;
				}
				else
				{
					satype = "IPsec";
					latest = c->newest_ipsec_sa;
				}

				if (st->st_serialno != latest)
				{
					/* not very interesting: already superseded */
					DBG(DBG_LIFECYCLE
						, plog("%s SA expired (superseded by #%lu)"
							, satype, latest));
				}
				else
				{
					plog("%s SA expired (%s)", satype
						, (c->policy & POLICY_DONT_REKEY)
							? "--dontrekey"
							: "LATEST!"
						);
				}
			}
			/* FALLTHROUGH */
		case EVENT_SO_DISCARD:
			/* Delete this state object.  It must be in the hash table. */
			delete_state(st);
			break;

		case EVENT_DPD:
			dpd_outI(st);
			break;
		case EVENT_DPD_TIMEOUT:
			dpd_timeout(st);
			break;
		case EVENT_NAT_T_KEEPALIVE:
			nat_traversal_ka_event();
			break;
		default:
			loglog(RC_LOG_SERIOUS, "INTERNAL ERROR: ignoring unknown expiring event %N"
				, timer_event_names, type);
	}

	free(ev);
	reset_cur_state();
}

/**
 * Return the time until the next event in the queue
 * expires (never negative), or -1 if no jobs in queue.
 */
long next_event(void)
{
	time_t tm;

	if (evlist == (struct event *) NULL)
		return -1;

	tm = now();

	DBG(DBG_CONTROL,
		if (evlist->ev_state == NULL)
			DBG_log("next event %N in %ld seconds"
				, timer_event_names, evlist->ev_type
				, (long)evlist->ev_time - (long)tm);
		else
			DBG_log("next event %N in %ld seconds for #%lu"
				, timer_event_names, evlist->ev_type
				, (long)evlist->ev_time - (long)tm
				, evlist->ev_state->st_serialno));

	if (evlist->ev_time - tm <= 0)
		return 0;
	else
		return evlist->ev_time - tm;
}

/**
 * Delete an event.
 */
void delete_event(struct state *st)
{
	if (st->st_event != (struct event *) NULL)
	{
		struct event **ev;

		for (ev = &evlist; ; ev = &(*ev)->ev_next)
		{
			if (*ev == NULL)
			{
				DBG(DBG_CONTROL, DBG_log("event %N to be deleted not found",
					timer_event_names, st->st_event->ev_type));
				break;
			}
			if ((*ev) == st->st_event)
			{
				*ev = (*ev)->ev_next;

				if (st->st_event->ev_type == EVENT_RETRANSMIT)
				{
					st->st_retransmit = 0;
				}
				free(st->st_event);
				st->st_event = (struct event *) NULL;

				break;
			}
		}
	}
}

/**
 * Delete a DPD event.
 */
void delete_dpd_event(struct state *st)
{
	if (st->st_dpd_event != (struct event *) NULL)
	{
		struct event **ev;

		for (ev = &evlist; ; ev = &(*ev)->ev_next)
		{
			if (*ev == NULL)
			{
				DBG(DBG_CONTROL, DBG_log("event %N to be deleted not found",
					timer_event_names, st->st_dpd_event->ev_type));
				break;
			}
			if ((*ev) == st->st_dpd_event)
			{
				*ev = (*ev)->ev_next;
				free(st->st_dpd_event);
				st->st_dpd_event = (struct event *) NULL;
				break;
			}
		}
	}
}

/**
 * Free remaining events
 */
void free_events(void)
{
	struct event *ev_tmp, *ev;

	ev = evlist;
	evlist = NULL;

	while (ev)
	{
		ev_tmp = ev;
		ev = ev->ev_next;
		free(ev_tmp);
	}
}