/*
   *	xt_time

   *	Copyright © CC Computer Consultants GmbH, 2007

   *
   *	based on ipt_time by Fabrice MARIE <fabrice@netfilter.org>
   *	This is a module which is used for time matching
   *	It is using some modified code from dietlibc (localtime() function)
   *	that you can find at http://www.fefe.de/dietlibc/
   *	This file is distributed under the terms of the GNU General Public
   *	License (GPL). Copies of the GPL can be obtained from gnu.org/gpl.
   */
  #include <linux/ktime.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/types.h>
  #include <linux/netfilter/x_tables.h>
  #include <linux/netfilter/xt_time.h>
  
  struct xtm {
  	u_int8_t month;    /* (1-12) */
  	u_int8_t monthday; /* (1-31) */
  	u_int8_t weekday;  /* (1-7) */
  	u_int8_t hour;     /* (0-23) */
  	u_int8_t minute;   /* (0-59) */
  	u_int8_t second;   /* (0-59) */
  	unsigned int dse;
  };
  
  extern struct timezone sys_tz; /* ouch */
  
  static const u_int16_t days_since_year[] = {
  	0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
  };
  
  static const u_int16_t days_since_leapyear[] = {
  	0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335,
  };
  
  /*
   * Since time progresses forward, it is best to organize this array in reverse,
   * to minimize lookup time.
   */
  enum {
  	DSE_FIRST = 2039,
  };
  static const u_int16_t days_since_epoch[] = {
  	/* 2039 - 2030 */
  	25202, 24837, 24472, 24106, 23741, 23376, 23011, 22645, 22280, 21915,
  	/* 2029 - 2020 */
  	21550, 21184, 20819, 20454, 20089, 19723, 19358, 18993, 18628, 18262,
  	/* 2019 - 2010 */
  	17897, 17532, 17167, 16801, 16436, 16071, 15706, 15340, 14975, 14610,
  	/* 2009 - 2000 */
  	14245, 13879, 13514, 13149, 12784, 12418, 12053, 11688, 11323, 10957,
  	/* 1999 - 1990 */
  	10592, 10227, 9862, 9496, 9131, 8766, 8401, 8035, 7670, 7305,
  	/* 1989 - 1980 */
  	6940, 6574, 6209, 5844, 5479, 5113, 4748, 4383, 4018, 3652,
  	/* 1979 - 1970 */
  	3287, 2922, 2557, 2191, 1826, 1461, 1096, 730, 365, 0,
  };
  
  static inline bool is_leap(unsigned int y)
  {
  	return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
  }
  
  /*
   * Each network packet has a (nano)seconds-since-the-epoch (SSTE) timestamp.
   * Since we match against days and daytime, the SSTE value needs to be
   * computed back into human-readable dates.
   *
   * This is done in three separate functions so that the most expensive
   * calculations are done last, in case a "simple match" can be found earlier.
   */
  static inline unsigned int localtime_1(struct xtm *r, time_t time)
  {
  	unsigned int v, w;
  
  	/* Each day has 86400s, so finding the hour/minute is actually easy. */
  	v         = time % 86400;
  	r->second = v % 60;
  	w         = v / 60;
  	r->minute = w % 60;
  	r->hour   = w / 60;
  	return v;
  }
  
  static inline void localtime_2(struct xtm *r, time_t time)
  {
  	/*
  	 * Here comes the rest (weekday, monthday). First, divide the SSTE
  	 * by seconds-per-day to get the number of _days_ since the epoch.
  	 */
  	r->dse = time / 86400;

  	/*
  	 * 1970-01-01 (w=0) was a Thursday (4).
  	 * -1 and +1 map Sunday properly onto 7.
  	 */
  	r->weekday = (4 + r->dse - 1) % 7 + 1;

  }
  
  static void localtime_3(struct xtm *r, time_t time)
  {
  	unsigned int year, i, w = r->dse;
  
  	/*
  	 * In each year, a certain number of days-since-the-epoch have passed.
  	 * Find the year that is closest to said days.
  	 *
  	 * Consider, for example, w=21612 (2029-03-04). Loop will abort on
  	 * dse[i] <= w, which happens when dse[i] == 21550. This implies
  	 * year == 2009. w will then be 62.
  	 */
  	for (i = 0, year = DSE_FIRST; days_since_epoch[i] > w;
  	    ++i, --year)
  		/* just loop */;
  
  	w -= days_since_epoch[i];
  
  	/*
  	 * By now we have the current year, and the day of the year.
  	 * r->yearday = w;
  	 *
  	 * On to finding the month (like above). In each month, a certain
  	 * number of days-since-New Year have passed, and find the closest
  	 * one.
  	 *
  	 * Consider w=62 (in a non-leap year). Loop will abort on
  	 * dsy[i] < w, which happens when dsy[i] == 31+28 (i == 2).
  	 * Concludes i == 2, i.e. 3rd month => March.
  	 *
  	 * (A different approach to use would be to subtract a monthlength
  	 * from w repeatedly while counting.)
  	 */
  	if (is_leap(year)) {

  		/* use days_since_leapyear[] in a leap year */

  		for (i = ARRAY_SIZE(days_since_leapyear) - 1;

  		    i > 0 && days_since_leapyear[i] > w; --i)

  			/* just loop */;

  		r->monthday = w - days_since_leapyear[i] + 1;

  	} else {
  		for (i = ARRAY_SIZE(days_since_year) - 1;
  		    i > 0 && days_since_year[i] > w; --i)
  			/* just loop */;

  		r->monthday = w - days_since_year[i] + 1;

  	}
  
  	r->month    = i + 1;

  }

  static bool

  time_mt(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_time_info *info = par->matchinfo;

  	unsigned int packet_time;
  	struct xtm current_time;
  	s64 stamp;
  
  	/*
  	 * We cannot use get_seconds() instead of __net_timestamp() here.
  	 * Suppose you have two rules:
  	 * 	1. match before 13:00
  	 * 	2. match after 13:00
  	 * If you match against processing time (get_seconds) it
  	 * may happen that the same packet matches both rules if
  	 * it arrived at the right moment before 13:00.
  	 */
  	if (skb->tstamp.tv64 == 0)
  		__net_timestamp((struct sk_buff *)skb);

  	stamp = ktime_to_ns(skb->tstamp);

  	stamp = div_s64(stamp, NSEC_PER_SEC);

  
  	if (info->flags & XT_TIME_LOCAL_TZ)
  		/* Adjust for local timezone */
  		stamp -= 60 * sys_tz.tz_minuteswest;
  
  	/*
  	 * xt_time will match when _all_ of the following hold:
  	 *   - 'now' is in the global time range date_start..date_end
  	 *   - 'now' is in the monthday mask
  	 *   - 'now' is in the weekday mask
  	 *   - 'now' is in the daytime range time_start..time_end
  	 * (and by default, libxt_time will set these so as to match)
  	 */
  
  	if (stamp < info->date_start || stamp > info->date_stop)
  		return false;
  
  	packet_time = localtime_1(&current_time, stamp);
  
  	if (info->daytime_start < info->daytime_stop) {
  		if (packet_time < info->daytime_start ||
  		    packet_time > info->daytime_stop)
  			return false;
  	} else {
  		if (packet_time < info->daytime_start &&
  		    packet_time > info->daytime_stop)
  			return false;
  	}
  
  	localtime_2(&current_time, stamp);
  
  	if (!(info->weekdays_match & (1 << current_time.weekday)))
  		return false;
  
  	/* Do not spend time computing monthday if all days match anyway */
  	if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
  		localtime_3(&current_time, stamp);
  		if (!(info->monthdays_match & (1 << current_time.monthday)))
  			return false;
  	}
  
  	return true;
  }

  static int time_mt_check(const struct xt_mtchk_param *par)

  {

  	const struct xt_time_info *info = par->matchinfo;

  
  	if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
  	    info->daytime_stop > XT_TIME_MAX_DAYTIME) {

  		pr_info("invalid argument - start or "
  			"stop time greater than 23:59:59
  ");

  		return -EDOM;

  	}

  	return 0;

  }

  static struct xt_match xt_time_mt_reg __read_mostly = {
  	.name       = "time",
  	.family     = NFPROTO_UNSPEC,
  	.match      = time_mt,
  	.checkentry = time_mt_check,
  	.matchsize  = sizeof(struct xt_time_info),
  	.me         = THIS_MODULE,

  };

  static int __init time_mt_init(void)

  {

  	int minutes = sys_tz.tz_minuteswest;
  
  	if (minutes < 0) /* east of Greenwich */
  		printk(KERN_INFO KBUILD_MODNAME
  		       ": kernel timezone is +%02d%02d
  ",
  		       -minutes / 60, -minutes % 60);
  	else /* west of Greenwich */
  		printk(KERN_INFO KBUILD_MODNAME
  		       ": kernel timezone is -%02d%02d
  ",
  		       minutes / 60, minutes % 60);

  	return xt_register_match(&xt_time_mt_reg);

  }

  static void __exit time_mt_exit(void)

  {

  	xt_unregister_match(&xt_time_mt_reg);

  }

  module_init(time_mt_init);
  module_exit(time_mt_exit);

  MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");

  MODULE_DESCRIPTION("Xtables: time-based matching");

  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ipt_time");
  MODULE_ALIAS("ip6t_time");