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 https://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 
is_leap(unsigned int y)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  */
localtime_1(struct xtm * r,time64_t time)80 static inline unsigned int localtime_1(struct xtm *r, time64_t time)
81 {
82 	unsigned int v, w;
83 
84 	/* Each day has 86400s, so finding the hour/minute is actually easy. */
85 	div_u64_rem(time, SECONDS_PER_DAY, &v);
86 	r->second = v % 60;
87 	w         = v / 60;
88 	r->minute = w % 60;
89 	r->hour   = w / 60;
90 	return v;
91 }
92 
localtime_2(struct xtm * r,time64_t time)93 static inline void localtime_2(struct xtm *r, time64_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 = div_u64(time, SECONDS_PER_DAY);
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 
localtime_3(struct xtm * r,time64_t time)108 static void localtime_3(struct xtm *r, time64_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
time_mt(const struct sk_buff * skb,struct xt_action_param * par)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 	time64_t stamp;
164 
165 	/*
166 	 * We need real time here, but we can neither use skb->tstamp
167 	 * nor __net_timestamp().
168 	 *
169 	 * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
170 	 * use different clock types (real vs monotonic).
171 	 *
172 	 * Suppose you have two rules:
173 	 *	1. match before 13:00
174 	 *	2. match after 13:00
175 	 *
176 	 * If you match against processing time (ktime_get_real_seconds) it
177 	 * may happen that the same packet matches both rules if
178 	 * it arrived at the right moment before 13:00, so it would be
179 	 * better to check skb->tstamp and set it via __net_timestamp()
180 	 * if needed.  This however breaks outgoing packets tx timestamp,
181 	 * and causes them to get delayed forever by fq packet scheduler.
182 	 */
183 	stamp = ktime_get_real_seconds();
184 
185 	if (info->flags & XT_TIME_LOCAL_TZ)
186 		/* Adjust for local timezone */
187 		stamp -= 60 * sys_tz.tz_minuteswest;
188 
189 	/*
190 	 * xt_time will match when _all_ of the following hold:
191 	 *   - 'now' is in the global time range date_start..date_end
192 	 *   - 'now' is in the monthday mask
193 	 *   - 'now' is in the weekday mask
194 	 *   - 'now' is in the daytime range time_start..time_end
195 	 * (and by default, libxt_time will set these so as to match)
196 	 *
197 	 * note: info->date_start/stop are unsigned 32-bit values that
198 	 *	 can hold values beyond y2038, but not after y2106.
199 	 */
200 
201 	if (stamp < info->date_start || stamp > info->date_stop)
202 		return false;
203 
204 	packet_time = localtime_1(&current_time, stamp);
205 
206 	if (info->daytime_start < info->daytime_stop) {
207 		if (packet_time < info->daytime_start ||
208 		    packet_time > info->daytime_stop)
209 			return false;
210 	} else {
211 		if (packet_time < info->daytime_start &&
212 		    packet_time > info->daytime_stop)
213 			return false;
214 
215 		/** if user asked to ignore 'next day', then e.g.
216 		 *  '1 PM Wed, August 1st' should be treated
217 		 *  like 'Tue 1 PM July 31st'.
218 		 *
219 		 * This also causes
220 		 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
221 		 * Monday 23:00 to Tuesday 01:00.
222 		 */
223 		if ((info->flags & XT_TIME_CONTIGUOUS) &&
224 		     packet_time <= info->daytime_stop)
225 			stamp -= SECONDS_PER_DAY;
226 	}
227 
228 	localtime_2(&current_time, stamp);
229 
230 	if (!(info->weekdays_match & (1 << current_time.weekday)))
231 		return false;
232 
233 	/* Do not spend time computing monthday if all days match anyway */
234 	if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
235 		localtime_3(&current_time, stamp);
236 		if (!(info->monthdays_match & (1 << current_time.monthday)))
237 			return false;
238 	}
239 
240 	return true;
241 }
242 
time_mt_check(const struct xt_mtchk_param * par)243 static int time_mt_check(const struct xt_mtchk_param *par)
244 {
245 	const struct xt_time_info *info = par->matchinfo;
246 
247 	if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
248 	    info->daytime_stop > XT_TIME_MAX_DAYTIME) {
249 		pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
250 		return -EDOM;
251 	}
252 
253 	if (info->flags & ~XT_TIME_ALL_FLAGS) {
254 		pr_info_ratelimited("unknown flags 0x%x\n",
255 				    info->flags & ~XT_TIME_ALL_FLAGS);
256 		return -EINVAL;
257 	}
258 
259 	if ((info->flags & XT_TIME_CONTIGUOUS) &&
260 	     info->daytime_start < info->daytime_stop)
261 		return -EINVAL;
262 
263 	return 0;
264 }
265 
266 static struct xt_match xt_time_mt_reg __read_mostly = {
267 	.name       = "time",
268 	.family     = NFPROTO_UNSPEC,
269 	.match      = time_mt,
270 	.checkentry = time_mt_check,
271 	.matchsize  = sizeof(struct xt_time_info),
272 	.me         = THIS_MODULE,
273 };
274 
time_mt_init(void)275 static int __init time_mt_init(void)
276 {
277 	int minutes = sys_tz.tz_minuteswest;
278 
279 	if (minutes < 0) /* east of Greenwich */
280 		pr_info("kernel timezone is +%02d%02d\n",
281 			-minutes / 60, -minutes % 60);
282 	else /* west of Greenwich */
283 		pr_info("kernel timezone is -%02d%02d\n",
284 			minutes / 60, minutes % 60);
285 
286 	return xt_register_match(&xt_time_mt_reg);
287 }
288 
time_mt_exit(void)289 static void __exit time_mt_exit(void)
290 {
291 	xt_unregister_match(&xt_time_mt_reg);
292 }
293 
294 module_init(time_mt_init);
295 module_exit(time_mt_exit);
296 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
297 MODULE_DESCRIPTION("Xtables: time-based matching");
298 MODULE_LICENSE("GPL");
299 MODULE_ALIAS("ipt_time");
300 MODULE_ALIAS("ip6t_time");
301