/*
 *      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 https://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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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,
        SECONDS_PER_DAY = 86400,
};
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, time64_t time)
{
        unsigned int v, w;

        /* Each day has 86400s, so finding the hour/minute is actually easy. */
        div_u64_rem(time, SECONDS_PER_DAY, &v);
        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, time64_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 = div_u64(time, SECONDS_PER_DAY);

        /*
         * 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, time64_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;
        time64_t stamp;

        /*
         * We need real time here, but we can neither use skb->tstamp
         * nor __net_timestamp().
         *
         * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
         * use different clock types (real vs monotonic).
         *
         * Suppose you have two rules:
         *      1. match before 13:00
         *      2. match after 13:00
         *
         * If you match against processing time (ktime_get_real_seconds) it
         * may happen that the same packet matches both rules if
         * it arrived at the right moment before 13:00, so it would be
         * better to check skb->tstamp and set it via __net_timestamp()
         * if needed.  This however breaks outgoing packets tx timestamp,
         * and causes them to get delayed forever by fq packet scheduler.
         */
        stamp = ktime_get_real_seconds();

        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)
         *
         * note: info->date_start/stop are unsigned 32-bit values that
         *       can hold values beyond y2038, but not after y2106.
         */

        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;

                /** if user asked to ignore 'next day', then e.g.
                 *  '1 PM Wed, August 1st' should be treated
                 *  like 'Tue 1 PM July 31st'.
                 *
                 * This also causes
                 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
                 * Monday 23:00 to Tuesday 01:00.
                 */
                if ((info->flags & XT_TIME_CONTIGUOUS) &&
                     packet_time <= info->daytime_stop)
                        stamp -= SECONDS_PER_DAY;
        }

        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_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
                return -EDOM;
        }

        if (info->flags & ~XT_TIME_ALL_FLAGS) {
                pr_info_ratelimited("unknown flags 0x%x\n",
                                    info->flags & ~XT_TIME_ALL_FLAGS);
                return -EINVAL;
        }

        if ((info->flags & XT_TIME_CONTIGUOUS) &&
             info->daytime_start < info->daytime_stop)
                return -EINVAL;

        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 */
                pr_info("kernel timezone is +%02d%02d\n",
                        -minutes / 60, -minutes % 60);
        else /* west of Greenwich */
                pr_info("kernel timezone is -%02d%02d\n",
                        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");