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 #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
  19 struct 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
  29 extern struct timezone sys_tz; /* ouch */
  30
  31 static const u_int16_t days_since_year[] = {
  32         0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
  33 };
  34
  35 static 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  */
  43 enum {
  44         DSE_FIRST = 2039,
  45 };
  46 static 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
  63 static 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  */
  76 static 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
  89 static 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
 104 static 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
 153 static bool
 154 time_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
 219 static 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
 233 static 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
 242 static 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
 258 static void __exit time_mt_exit(void)
 259 {
 260         xt_unregister_match(&xt_time_mt_reg);
 261 }
 262
 263 module_init(time_mt_init);
 264 module_exit(time_mt_exit);
 265 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 266 MODULE_DESCRIPTION("Xtables: time-based matching");
 267 MODULE_LICENSE("GPL");
 268 MODULE_ALIAS("ipt_time");
 269 MODULE_ALIAS("ip6t_time");