xt_time.c

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/*
 *  xt_time
 *  Copyright © CC Computer Consultants GmbH, 2007
 *
 *  based on ipt_time by Fabrice MARIE <[email protected]>
 *  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,
    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, time_t time)
{
    unsigned int v, w;

    /* Each day has 86400s, so finding the hour/minute is actually easy. */
    v         = time % SECONDS_PER_DAY;
    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;

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

    if (info->flags & ~XT_TIME_ALL_FLAGS) {
        pr_info("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 */
        printk(KERN_INFO KBUILD_MODNAME
               ": kernel timezone is +%02d%02d\n",
               -minutes / 60, -minutes % 60);
    else /* west of Greenwich */
        printk(KERN_INFO KBUILD_MODNAME
               ": 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 <[email protected]>");
MODULE_DESCRIPTION("Xtables: time-based matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_time");
MODULE_ALIAS("ip6t_time");