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 https://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
  13#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14
  15#include <linux/ktime.h>
  16#include <linux/module.h>
  17#include <linux/skbuff.h>
  18#include <linux/types.h>
  19#include <linux/netfilter/x_tables.h>
  20#include <linux/netfilter/xt_time.h>
  21
  22struct xtm {
  23        u_int8_t month;    /* (1-12) */
  24        u_int8_t monthday; /* (1-31) */
  25        u_int8_t weekday;  /* (1-7) */
  26        u_int8_t hour;     /* (0-23) */
  27        u_int8_t minute;   /* (0-59) */
  28        u_int8_t second;   /* (0-59) */
  29        unsigned int dse;
  30};
  31
  32extern struct timezone sys_tz; /* ouch */
  33
  34static const u_int16_t days_since_year[] = {
  35        0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
  36};
  37
  38static const u_int16_t days_since_leapyear[] = {
  39        0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335,
  40};
  41
  42/*
  43 * Since time progresses forward, it is best to organize this array in reverse,
  44 * to minimize lookup time.
  45 */
  46enum {
  47        DSE_FIRST = 2039,
  48        SECONDS_PER_DAY = 86400,
  49};
  50static const u_int16_t days_since_epoch[] = {
  51        /* 2039 - 2030 */
  52        25202, 24837, 24472, 24106, 23741, 23376, 23011, 22645, 22280, 21915,
  53        /* 2029 - 2020 */
  54        21550, 21184, 20819, 20454, 20089, 19723, 19358, 18993, 18628, 18262,
  55        /* 2019 - 2010 */
  56        17897, 17532, 17167, 16801, 16436, 16071, 15706, 15340, 14975, 14610,
  57        /* 2009 - 2000 */
  58        14245, 13879, 13514, 13149, 12784, 12418, 12053, 11688, 11323, 10957,
  59        /* 1999 - 1990 */
  60        10592, 10227, 9862, 9496, 9131, 8766, 8401, 8035, 7670, 7305,
  61        /* 1989 - 1980 */
  62        6940, 6574, 6209, 5844, 5479, 5113, 4748, 4383, 4018, 3652,
  63        /* 1979 - 1970 */
  64        3287, 2922, 2557, 2191, 1826, 1461, 1096, 730, 365, 0,
  65};
  66
  67static inline bool is_leap(unsigned int y)
  68{
  69        return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
  70}
  71
  72/*
  73 * Each network packet has a (nano)seconds-since-the-epoch (SSTE) timestamp.
  74 * Since we match against days and daytime, the SSTE value needs to be
  75 * computed back into human-readable dates.
  76 *
  77 * This is done in three separate functions so that the most expensive
  78 * calculations are done last, in case a "simple match" can be found earlier.
  79 */
  80static inline unsigned int localtime_1(struct xtm *r, time64_t time)
  81{
  82        unsigned int v, w;
  83
  84        /* Each day has 86400s, so finding the hour/minute is actually easy. */
  85        div_u64_rem(time, SECONDS_PER_DAY, &v);
  86        r->second = v % 60;
  87        w         = v / 60;
  88        r->minute = w % 60;
  89        r->hour   = w / 60;
  90        return v;
  91}
  92
  93static inline void localtime_2(struct xtm *r, time64_t time)
  94{
  95        /*
  96         * Here comes the rest (weekday, monthday). First, divide the SSTE
  97         * by seconds-per-day to get the number of _days_ since the epoch.
  98         */
  99        r->dse = div_u64(time, SECONDS_PER_DAY);
 100
 101        /*
 102         * 1970-01-01 (w=0) was a Thursday (4).
 103         * -1 and +1 map Sunday properly onto 7.
 104         */
 105        r->weekday = (4 + r->dse - 1) % 7 + 1;
 106}
 107
 108static void localtime_3(struct xtm *r, time64_t time)
 109{
 110        unsigned int year, i, w = r->dse;
 111
 112        /*
 113         * In each year, a certain number of days-since-the-epoch have passed.
 114         * Find the year that is closest to said days.
 115         *
 116         * Consider, for example, w=21612 (2029-03-04). Loop will abort on
 117         * dse[i] <= w, which happens when dse[i] == 21550. This implies
 118         * year == 2009. w will then be 62.
 119         */
 120        for (i = 0, year = DSE_FIRST; days_since_epoch[i] > w;
 121            ++i, --year)
 122                /* just loop */;
 123
 124        w -= days_since_epoch[i];
 125
 126        /*
 127         * By now we have the current year, and the day of the year.
 128         * r->yearday = w;
 129         *
 130         * On to finding the month (like above). In each month, a certain
 131         * number of days-since-New Year have passed, and find the closest
 132         * one.
 133         *
 134         * Consider w=62 (in a non-leap year). Loop will abort on
 135         * dsy[i] < w, which happens when dsy[i] == 31+28 (i == 2).
 136         * Concludes i == 2, i.e. 3rd month => March.
 137         *
 138         * (A different approach to use would be to subtract a monthlength
 139         * from w repeatedly while counting.)
 140         */
 141        if (is_leap(year)) {
 142                /* use days_since_leapyear[] in a leap year */
 143                for (i = ARRAY_SIZE(days_since_leapyear) - 1;
 144                    i > 0 && days_since_leapyear[i] > w; --i)
 145                        /* just loop */;
 146                r->monthday = w - days_since_leapyear[i] + 1;
 147        } else {
 148                for (i = ARRAY_SIZE(days_since_year) - 1;
 149                    i > 0 && days_since_year[i] > w; --i)
 150                        /* just loop */;
 151                r->monthday = w - days_since_year[i] + 1;
 152        }
 153
 154        r->month    = i + 1;
 155}
 156
 157static bool
 158time_mt(const struct sk_buff *skb, struct xt_action_param *par)
 159{
 160        const struct xt_time_info *info = par->matchinfo;
 161        unsigned int packet_time;
 162        struct xtm current_time;
 163        time64_t stamp;
 164
 165        /*
 166         * We need real time here, but we can neither use skb->tstamp
 167         * nor __net_timestamp().
 168         *
 169         * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
 170         * use different clock types (real vs monotonic).
 171         *
 172         * Suppose you have two rules:
 173         *      1. match before 13:00
 174         *      2. match after 13:00
 175         *
 176         * If you match against processing time (ktime_get_real_seconds) it
 177         * may happen that the same packet matches both rules if
 178         * it arrived at the right moment before 13:00, so it would be
 179         * better to check skb->tstamp and set it via __net_timestamp()
 180         * if needed.  This however breaks outgoing packets tx timestamp,
 181         * and causes them to get delayed forever by fq packet scheduler.
 182         */
 183        stamp = ktime_get_real_seconds();
 184
 185        if (info->flags & XT_TIME_LOCAL_TZ)
 186                /* Adjust for local timezone */
 187                stamp -= 60 * sys_tz.tz_minuteswest;
 188
 189        /*
 190         * xt_time will match when _all_ of the following hold:
 191         *   - 'now' is in the global time range date_start..date_end
 192         *   - 'now' is in the monthday mask
 193         *   - 'now' is in the weekday mask
 194         *   - 'now' is in the daytime range time_start..time_end
 195         * (and by default, libxt_time will set these so as to match)
 196         *
 197         * note: info->date_start/stop are unsigned 32-bit values that
 198         *       can hold values beyond y2038, but not after y2106.
 199         */
 200
 201        if (stamp < info->date_start || stamp > info->date_stop)
 202                return false;
 203
 204        packet_time = localtime_1(&current_time, stamp);
 205
 206        if (info->daytime_start < info->daytime_stop) {
 207                if (packet_time < info->daytime_start ||
 208                    packet_time > info->daytime_stop)
 209                        return false;
 210        } else {
 211                if (packet_time < info->daytime_start &&
 212                    packet_time > info->daytime_stop)
 213                        return false;
 214
 215                /** if user asked to ignore 'next day', then e.g.
 216                 *  '1 PM Wed, August 1st' should be treated
 217                 *  like 'Tue 1 PM July 31st'.
 218                 *
 219                 * This also causes
 220                 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
 221                 * Monday 23:00 to Tuesday 01:00.
 222                 */
 223                if ((info->flags & XT_TIME_CONTIGUOUS) &&
 224                     packet_time <= info->daytime_stop)
 225                        stamp -= SECONDS_PER_DAY;
 226        }
 227
 228        localtime_2(&current_time, stamp);
 229
 230        if (!(info->weekdays_match & (1 << current_time.weekday)))
 231                return false;
 232
 233        /* Do not spend time computing monthday if all days match anyway */
 234        if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
 235                localtime_3(&current_time, stamp);
 236                if (!(info->monthdays_match & (1 << current_time.monthday)))
 237                        return false;
 238        }
 239
 240        return true;
 241}
 242
 243static int time_mt_check(const struct xt_mtchk_param *par)
 244{
 245        const struct xt_time_info *info = par->matchinfo;
 246
 247        if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
 248            info->daytime_stop > XT_TIME_MAX_DAYTIME) {
 249                pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
 250                return -EDOM;
 251        }
 252
 253        if (info->flags & ~XT_TIME_ALL_FLAGS) {
 254                pr_info_ratelimited("unknown flags 0x%x\n",
 255                                    info->flags & ~XT_TIME_ALL_FLAGS);
 256                return -EINVAL;
 257        }
 258
 259        if ((info->flags & XT_TIME_CONTIGUOUS) &&
 260             info->daytime_start < info->daytime_stop)
 261                return -EINVAL;
 262
 263        return 0;
 264}
 265
 266static struct xt_match xt_time_mt_reg __read_mostly = {
 267        .name       = "time",
 268        .family     = NFPROTO_UNSPEC,
 269        .match      = time_mt,
 270        .checkentry = time_mt_check,
 271        .matchsize  = sizeof(struct xt_time_info),
 272        .me         = THIS_MODULE,
 273};
 274
 275static int __init time_mt_init(void)
 276{
 277        int minutes = sys_tz.tz_minuteswest;
 278
 279        if (minutes < 0) /* east of Greenwich */
 280                pr_info("kernel timezone is +%02d%02d\n",
 281                        -minutes / 60, -minutes % 60);
 282        else /* west of Greenwich */
 283                pr_info("kernel timezone is -%02d%02d\n",
 284                        minutes / 60, minutes % 60);
 285
 286        return xt_register_match(&xt_time_mt_reg);
 287}
 288
 289static void __exit time_mt_exit(void)
 290{
 291        xt_unregister_match(&xt_time_mt_reg);
 292}
 293
 294module_init(time_mt_init);
 295module_exit(time_mt_exit);
 296MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 297MODULE_DESCRIPTION("Xtables: time-based matching");
 298MODULE_LICENSE("GPL");
 299MODULE_ALIAS("ipt_time");
 300MODULE_ALIAS("ip6t_time");
 301