net/netfilter/xt_time.c

   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
  22 struct 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
  32 extern struct timezone sys_tz; /* ouch */
  33
  34 static const u_int16_t days_since_year[] = {
  35         0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
  36 };
  37
  38 static 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  */
  46 enum {
  47         DSE_FIRST = 2039,
  48         SECONDS_PER_DAY = 86400,
  49 };
  50 static 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
  67 static 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  */
  80 static 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
  93 static 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
 108 static 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
 157 static bool
 158 time_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
 243 static 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
 266 static 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
 275 static 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
 289 static void __exit time_mt_exit(void)
 290 {
 291         xt_unregister_match(&xt_time_mt_reg);
 292 }
 293
 294 module_init(time_mt_init);
 295 module_exit(time_mt_exit);
 296 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 297 MODULE_DESCRIPTION("Xtables: time-based matching");
 298 MODULE_LICENSE("GPL");
 299 MODULE_ALIAS("ipt_time");
 300 MODULE_ALIAS("ip6t_time");