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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 };
 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");
270 

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