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 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
  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, time_t time)
  81 {
  82         unsigned int v, w;
  83
  84         /* Each day has 86400s, so finding the hour/minute is actually easy. */
  85         v         = time % SECONDS_PER_DAY;
  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, time_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 = time / 86400;
 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, time_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         s64 stamp;
 164
 165         /*
 166          * We cannot use get_seconds() instead of __net_timestamp() here.
 167          * Suppose you have two rules:
 168          *      1. match before 13:00
 169          *      2. match after 13:00
 170          * If you match against processing time (get_seconds) it
 171          * may happen that the same packet matches both rules if
 172          * it arrived at the right moment before 13:00.
 173          */
 174         if (skb->tstamp == 0)
 175                 __net_timestamp((struct sk_buff *)skb);
 176
 177         stamp = ktime_to_ns(skb->tstamp);
 178         stamp = div_s64(stamp, NSEC_PER_SEC);
 179
 180         if (info->flags & XT_TIME_LOCAL_TZ)
 181                 /* Adjust for local timezone */
 182                 stamp -= 60 * sys_tz.tz_minuteswest;
 183
 184         /*
 185          * xt_time will match when _all_ of the following hold:
 186          *   - 'now' is in the global time range date_start..date_end
 187          *   - 'now' is in the monthday mask
 188          *   - 'now' is in the weekday mask
 189          *   - 'now' is in the daytime range time_start..time_end
 190          * (and by default, libxt_time will set these so as to match)
 191          */
 192
 193         if (stamp < info->date_start || stamp > info->date_stop)
 194                 return false;
 195
 196         packet_time = localtime_1(&current_time, stamp);
 197
 198         if (info->daytime_start < info->daytime_stop) {
 199                 if (packet_time < info->daytime_start ||
 200                     packet_time > info->daytime_stop)
 201                         return false;
 202         } else {
 203                 if (packet_time < info->daytime_start &&
 204                     packet_time > info->daytime_stop)
 205                         return false;
 206
 207                 /** if user asked to ignore 'next day', then e.g.
 208                  *  '1 PM Wed, August 1st' should be treated
 209                  *  like 'Tue 1 PM July 31st'.
 210                  *
 211                  * This also causes
 212                  * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
 213                  * Monday 23:00 to Tuesday 01:00.
 214                  */
 215                 if ((info->flags & XT_TIME_CONTIGUOUS) &&
 216                      packet_time <= info->daytime_stop)
 217                         stamp -= SECONDS_PER_DAY;
 218         }
 219
 220         localtime_2(&current_time, stamp);
 221
 222         if (!(info->weekdays_match & (1 << current_time.weekday)))
 223                 return false;
 224
 225         /* Do not spend time computing monthday if all days match anyway */
 226         if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
 227                 localtime_3(&current_time, stamp);
 228                 if (!(info->monthdays_match & (1 << current_time.monthday)))
 229                         return false;
 230         }
 231
 232         return true;
 233 }
 234
 235 static int time_mt_check(const struct xt_mtchk_param *par)
 236 {
 237         const struct xt_time_info *info = par->matchinfo;
 238
 239         if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
 240             info->daytime_stop > XT_TIME_MAX_DAYTIME) {
 241                 pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
 242                 return -EDOM;
 243         }
 244
 245         if (info->flags & ~XT_TIME_ALL_FLAGS) {
 246                 pr_info_ratelimited("unknown flags 0x%x\n",
 247                                     info->flags & ~XT_TIME_ALL_FLAGS);
 248                 return -EINVAL;
 249         }
 250
 251         if ((info->flags & XT_TIME_CONTIGUOUS) &&
 252              info->daytime_start < info->daytime_stop)
 253                 return -EINVAL;
 254
 255         return 0;
 256 }
 257
 258 static struct xt_match xt_time_mt_reg __read_mostly = {
 259         .name       = "time",
 260         .family     = NFPROTO_UNSPEC,
 261         .match      = time_mt,
 262         .checkentry = time_mt_check,
 263         .matchsize  = sizeof(struct xt_time_info),
 264         .me         = THIS_MODULE,
 265 };
 266
 267 static int __init time_mt_init(void)
 268 {
 269         int minutes = sys_tz.tz_minuteswest;
 270
 271         if (minutes < 0) /* east of Greenwich */
 272                 pr_info("kernel timezone is +%02d%02d\n",
 273                         -minutes / 60, -minutes % 60);
 274         else /* west of Greenwich */
 275                 pr_info("kernel timezone is -%02d%02d\n",
 276                         minutes / 60, minutes % 60);
 277
 278         return xt_register_match(&xt_time_mt_reg);
 279 }
 280
 281 static void __exit time_mt_exit(void)
 282 {
 283         xt_unregister_match(&xt_time_mt_reg);
 284 }
 285
 286 module_init(time_mt_init);
 287 module_exit(time_mt_exit);
 288 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 289 MODULE_DESCRIPTION("Xtables: time-based matching");
 290 MODULE_LICENSE("GPL");
 291 MODULE_ALIAS("ipt_time");
 292 MODULE_ALIAS("ip6t_time");