net/netfilter/xt_time.c

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