linux/net/netfilter/xt_time.c
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   1/*
   2 *      xt_time
   3 *      Copyright © CC Computer Consultants GmbH, 2007
   4 *
   5 *      based on ipt_time by Fabrice MARIE <fabrice@netfilter.org>
   6 *      This is a module which is used for time matching
   7 *      It is using some modified code from dietlibc (localtime() function)
   8 *      that you can find at http://www.fefe.de/dietlibc/
   9 *      This file is distributed under the terms of the GNU General Public
  10 *      License (GPL). Copies of the GPL can be obtained from gnu.org/gpl.
  11 */
  12#include <linux/ktime.h>
  13#include <linux/module.h>
  14#include <linux/skbuff.h>
  15#include <linux/types.h>
  16#include <linux/netfilter/x_tables.h>
  17#include <linux/netfilter/xt_time.h>
  18
  19struct xtm {
  20        u_int8_t month;    /* (1-12) */
  21        u_int8_t monthday; /* (1-31) */
  22        u_int8_t weekday;  /* (1-7) */
  23        u_int8_t hour;     /* (0-23) */
  24        u_int8_t minute;   /* (0-59) */
  25        u_int8_t second;   /* (0-59) */
  26        unsigned int dse;
  27};
  28
  29extern struct timezone sys_tz; /* ouch */
  30
  31static const u_int16_t days_since_year[] = {
  32        0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
  33};
  34
  35static const u_int16_t days_since_leapyear[] = {
  36        0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335,
  37};
  38
  39/*
  40 * Since time progresses forward, it is best to organize this array in reverse,
  41 * to minimize lookup time.
  42 */
  43enum {
  44        DSE_FIRST = 2039,
  45};
  46static const u_int16_t days_since_epoch[] = {
  47        /* 2039 - 2030 */
  48        25202, 24837, 24472, 24106, 23741, 23376, 23011, 22645, 22280, 21915,
  49        /* 2029 - 2020 */
  50        21550, 21184, 20819, 20454, 20089, 19723, 19358, 18993, 18628, 18262,
  51        /* 2019 - 2010 */
  52        17897, 17532, 17167, 16801, 16436, 16071, 15706, 15340, 14975, 14610,
  53        /* 2009 - 2000 */
  54        14245, 13879, 13514, 13149, 12784, 12418, 12053, 11688, 11323, 10957,
  55        /* 1999 - 1990 */
  56        10592, 10227, 9862, 9496, 9131, 8766, 8401, 8035, 7670, 7305,
  57        /* 1989 - 1980 */
  58        6940, 6574, 6209, 5844, 5479, 5113, 4748, 4383, 4018, 3652,
  59        /* 1979 - 1970 */
  60        3287, 2922, 2557, 2191, 1826, 1461, 1096, 730, 365, 0,
  61};
  62
  63static inline bool is_leap(unsigned int y)
  64{
  65        return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
  66}
  67
  68/*
  69 * Each network packet has a (nano)seconds-since-the-epoch (SSTE) timestamp.
  70 * Since we match against days and daytime, the SSTE value needs to be
  71 * computed back into human-readable dates.
  72 *
  73 * This is done in three separate functions so that the most expensive
  74 * calculations are done last, in case a "simple match" can be found earlier.
  75 */
  76static inline unsigned int localtime_1(struct xtm *r, time_t time)
  77{
  78        unsigned int v, w;
  79
  80        /* Each day has 86400s, so finding the hour/minute is actually easy. */
  81        v         = time % 86400;
  82        r->second = v % 60;
  83        w         = v / 60;
  84        r->minute = w % 60;
  85        r->hour   = w / 60;
  86        return v;
  87}
  88
  89static inline void localtime_2(struct xtm *r, time_t time)
  90{
  91        /*
  92         * Here comes the rest (weekday, monthday). First, divide the SSTE
  93         * by seconds-per-day to get the number of _days_ since the epoch.
  94         */
  95        r->dse = time / 86400;
  96
  97        /*
  98         * 1970-01-01 (w=0) was a Thursday (4).
  99         * -1 and +1 map Sunday properly onto 7.
 100         */
 101        r->weekday = (4 + r->dse - 1) % 7 + 1;
 102}
 103
 104static void localtime_3(struct xtm *r, time_t time)
 105{
 106        unsigned int year, i, w = r->dse;
 107
 108        /*
 109         * In each year, a certain number of days-since-the-epoch have passed.
 110         * Find the year that is closest to said days.
 111         *
 112         * Consider, for example, w=21612 (2029-03-04). Loop will abort on
 113         * dse[i] <= w, which happens when dse[i] == 21550. This implies
 114         * year == 2009. w will then be 62.
 115         */
 116        for (i = 0, year = DSE_FIRST; days_since_epoch[i] > w;
 117            ++i, --year)
 118                /* just loop */;
 119
 120        w -= days_since_epoch[i];
 121
 122        /*
 123         * By now we have the current year, and the day of the year.
 124         * r->yearday = w;
 125         *
 126         * On to finding the month (like above). In each month, a certain
 127         * number of days-since-New Year have passed, and find the closest
 128         * one.
 129         *
 130         * Consider w=62 (in a non-leap year). Loop will abort on
 131         * dsy[i] < w, which happens when dsy[i] == 31+28 (i == 2).
 132         * Concludes i == 2, i.e. 3rd month => March.
 133         *
 134         * (A different approach to use would be to subtract a monthlength
 135         * from w repeatedly while counting.)
 136         */
 137        if (is_leap(year)) {
 138                /* use days_since_leapyear[] in a leap year */
 139                for (i = ARRAY_SIZE(days_since_leapyear) - 1;
 140                    i > 0 && days_since_leapyear[i] > w; --i)
 141                        /* just loop */;
 142                r->monthday = w - days_since_leapyear[i] + 1;
 143        } else {
 144                for (i = ARRAY_SIZE(days_since_year) - 1;
 145                    i > 0 && days_since_year[i] > w; --i)
 146                        /* just loop */;
 147                r->monthday = w - days_since_year[i] + 1;
 148        }
 149
 150        r->month    = i + 1;
 151}
 152
 153static bool
 154time_mt(const struct sk_buff *skb, struct xt_action_param *par)
 155{
 156        const struct xt_time_info *info = par->matchinfo;
 157        unsigned int packet_time;
 158        struct xtm current_time;
 159        s64 stamp;
 160
 161        /*
 162         * We cannot use get_seconds() instead of __net_timestamp() here.
 163         * Suppose you have two rules:
 164         *      1. match before 13:00
 165         *      2. match after 13:00
 166         * If you match against processing time (get_seconds) it
 167         * may happen that the same packet matches both rules if
 168         * it arrived at the right moment before 13:00.
 169         */
 170        if (skb->tstamp.tv64 == 0)
 171                __net_timestamp((struct sk_buff *)skb);
 172
 173        stamp = ktime_to_ns(skb->tstamp);
 174        stamp = div_s64(stamp, NSEC_PER_SEC);
 175
 176        if (info->flags & XT_TIME_LOCAL_TZ)
 177                /* Adjust for local timezone */
 178                stamp -= 60 * sys_tz.tz_minuteswest;
 179
 180        /*
 181         * xt_time will match when _all_ of the following hold:
 182         *   - 'now' is in the global time range date_start..date_end
 183         *   - 'now' is in the monthday mask
 184         *   - 'now' is in the weekday mask
 185         *   - 'now' is in the daytime range time_start..time_end
 186         * (and by default, libxt_time will set these so as to match)
 187         */
 188
 189        if (stamp < info->date_start || stamp > info->date_stop)
 190                return false;
 191
 192        packet_time = localtime_1(&current_time, stamp);
 193
 194        if (info->daytime_start < info->daytime_stop) {
 195                if (packet_time < info->daytime_start ||
 196                    packet_time > info->daytime_stop)
 197                        return false;
 198        } else {
 199                if (packet_time < info->daytime_start &&
 200                    packet_time > info->daytime_stop)
 201                        return false;
 202        }
 203
 204        localtime_2(&current_time, stamp);
 205
 206        if (!(info->weekdays_match & (1 << current_time.weekday)))
 207                return false;
 208
 209        /* Do not spend time computing monthday if all days match anyway */
 210        if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
 211                localtime_3(&current_time, stamp);
 212                if (!(info->monthdays_match & (1 << current_time.monthday)))
 213                        return false;
 214        }
 215
 216        return true;
 217}
 218
 219static int time_mt_check(const struct xt_mtchk_param *par)
 220{
 221        const struct xt_time_info *info = par->matchinfo;
 222
 223        if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
 224            info->daytime_stop > XT_TIME_MAX_DAYTIME) {
 225                pr_info("invalid argument - start or "
 226                        "stop time greater than 23:59:59\n");
 227                return -EDOM;
 228        }
 229
 230        return 0;
 231}
 232
 233static struct xt_match xt_time_mt_reg __read_mostly = {
 234        .name       = "time",
 235        .family     = NFPROTO_UNSPEC,
 236        .match      = time_mt,
 237        .checkentry = time_mt_check,
 238        .matchsize  = sizeof(struct xt_time_info),
 239        .me         = THIS_MODULE,
 240};
 241
 242static int __init time_mt_init(void)
 243{
 244        int minutes = sys_tz.tz_minuteswest;
 245
 246        if (minutes < 0) /* east of Greenwich */
 247                printk(KERN_INFO KBUILD_MODNAME
 248                       ": kernel timezone is +%02d%02d\n",
 249                       -minutes / 60, -minutes % 60);
 250        else /* west of Greenwich */
 251                printk(KERN_INFO KBUILD_MODNAME
 252                       ": kernel timezone is -%02d%02d\n",
 253                       minutes / 60, minutes % 60);
 254
 255        return xt_register_match(&xt_time_mt_reg);
 256}
 257
 258static void __exit time_mt_exit(void)
 259{
 260        xt_unregister_match(&xt_time_mt_reg);
 261}
 262
 263module_init(time_mt_init);
 264module_exit(time_mt_exit);
 265MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 266MODULE_DESCRIPTION("Xtables: time-based matching");
 267MODULE_LICENSE("GPL");
 268MODULE_ALIAS("ipt_time");
 269MODULE_ALIAS("ip6t_time");
 270
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