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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 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         SECONDS_PER_DAY = 86400,
 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 % SECONDS_PER_DAY;
 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 }
153 
154 static bool
155 time_mt(const struct sk_buff *skb, struct xt_action_param *par)
156 {
157         const struct xt_time_info *info = par->matchinfo;
158         unsigned int packet_time;
159         struct xtm current_time;
160         s64 stamp;
161 
162         /*
163          * We cannot use get_seconds() instead of __net_timestamp() here.
164          * Suppose you have two rules:
165          *      1. match before 13:00
166          *      2. match after 13:00
167          * If you match against processing time (get_seconds) it
168          * may happen that the same packet matches both rules if
169          * it arrived at the right moment before 13:00.
170          */
171         if (skb->tstamp.tv64 == 0)
172                 __net_timestamp((struct sk_buff *)skb);
173 
174         stamp = ktime_to_ns(skb->tstamp);
175         stamp = div_s64(stamp, NSEC_PER_SEC);
176 
177         if (info->flags & XT_TIME_LOCAL_TZ)
178                 /* Adjust for local timezone */
179                 stamp -= 60 * sys_tz.tz_minuteswest;
180 
181         /*
182          * xt_time will match when _all_ of the following hold:
183          *   - 'now' is in the global time range date_start..date_end
184          *   - 'now' is in the monthday mask
185          *   - 'now' is in the weekday mask
186          *   - 'now' is in the daytime range time_start..time_end
187          * (and by default, libxt_time will set these so as to match)
188          */
189 
190         if (stamp < info->date_start || stamp > info->date_stop)
191                 return false;
192 
193         packet_time = localtime_1(&current_time, stamp);
194 
195         if (info->daytime_start < info->daytime_stop) {
196                 if (packet_time < info->daytime_start ||
197                     packet_time > info->daytime_stop)
198                         return false;
199         } else {
200                 if (packet_time < info->daytime_start &&
201                     packet_time > info->daytime_stop)
202                         return false;
203 
204                 /** if user asked to ignore 'next day', then e.g.
205                  *  '1 PM Wed, August 1st' should be treated
206                  *  like 'Tue 1 PM July 31st'.
207                  *
208                  * This also causes
209                  * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
210                  * Monday 23:00 to Tuesday 01:00.
211                  */
212                 if ((info->flags & XT_TIME_CONTIGUOUS) &&
213                      packet_time <= info->daytime_stop)
214                         stamp -= SECONDS_PER_DAY;
215         }
216 
217         localtime_2(&current_time, stamp);
218 
219         if (!(info->weekdays_match & (1 << current_time.weekday)))
220                 return false;
221 
222         /* Do not spend time computing monthday if all days match anyway */
223         if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
224                 localtime_3(&current_time, stamp);
225                 if (!(info->monthdays_match & (1 << current_time.monthday)))
226                         return false;
227         }
228 
229         return true;
230 }
231 
232 static int time_mt_check(const struct xt_mtchk_param *par)
233 {
234         const struct xt_time_info *info = par->matchinfo;
235 
236         if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
237             info->daytime_stop > XT_TIME_MAX_DAYTIME) {
238                 pr_info("invalid argument - start or "
239                         "stop time greater than 23:59:59\n");
240                 return -EDOM;
241         }
242 
243         if (info->flags & ~XT_TIME_ALL_FLAGS) {
244                 pr_info("unknown flags 0x%x\n", info->flags & ~XT_TIME_ALL_FLAGS);
245                 return -EINVAL;
246         }
247 
248         if ((info->flags & XT_TIME_CONTIGUOUS) &&
249              info->daytime_start < info->daytime_stop)
250                 return -EINVAL;
251 
252         return 0;
253 }
254 
255 static struct xt_match xt_time_mt_reg __read_mostly = {
256         .name       = "time",
257         .family     = NFPROTO_UNSPEC,
258         .match      = time_mt,
259         .checkentry = time_mt_check,
260         .matchsize  = sizeof(struct xt_time_info),
261         .me         = THIS_MODULE,
262 };
263 
264 static int __init time_mt_init(void)
265 {
266         int minutes = sys_tz.tz_minuteswest;
267 
268         if (minutes < 0) /* east of Greenwich */
269                 printk(KERN_INFO KBUILD_MODNAME
270                        ": kernel timezone is +%02d%02d\n",
271                        -minutes / 60, -minutes % 60);
272         else /* west of Greenwich */
273                 printk(KERN_INFO KBUILD_MODNAME
274                        ": kernel timezone is -%02d%02d\n",
275                        minutes / 60, minutes % 60);
276 
277         return xt_register_match(&xt_time_mt_reg);
278 }
279 
280 static void __exit time_mt_exit(void)
281 {
282         xt_unregister_match(&xt_time_mt_reg);
283 }
284 
285 module_init(time_mt_init);
286 module_exit(time_mt_exit);
287 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
288 MODULE_DESCRIPTION("Xtables: time-based matching");
289 MODULE_LICENSE("GPL");
290 MODULE_ALIAS("ipt_time");
291 MODULE_ALIAS("ip6t_time");
292 

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