1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * xt_time
4 * Copyright © CC Computer Consultants GmbH, 2007
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 https://www.fefe.de/dietlibc/
10 */
11
12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13
14 #include <linux/ktime.h>
15 #include <linux/module.h>
16 #include <linux/rtc.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
67 /*
68 * Each network packet has a (nano)seconds-since-the-epoch (SSTE) timestamp.
69 * Since we match against days and daytime, the SSTE value needs to be
70 * computed back into human-readable dates.
71 *
72 * This is done in three separate functions so that the most expensive
73 * calculations are done last, in case a "simple match" can be found earlier.
74 */
localtime_1(struct xtm * r,time64_t time)75 static inline unsigned int localtime_1(struct xtm *r, time64_t time)
76 {
77 unsigned int v, w;
78
79 /* Each day has 86400s, so finding the hour/minute is actually easy. */
80 div_u64_rem(time, SECONDS_PER_DAY, &v);
81 r->second = v % 60;
82 w = v / 60;
83 r->minute = w % 60;
84 r->hour = w / 60;
85 return v;
86 }
87
localtime_2(struct xtm * r,time64_t time)88 static inline void localtime_2(struct xtm *r, time64_t time)
89 {
90 /*
91 * Here comes the rest (weekday, monthday). First, divide the SSTE
92 * by seconds-per-day to get the number of _days_ since the epoch.
93 */
94 r->dse = div_u64(time, SECONDS_PER_DAY);
95
96 /*
97 * 1970-01-01 (w=0) was a Thursday (4).
98 * -1 and +1 map Sunday properly onto 7.
99 */
100 r->weekday = (4 + r->dse - 1) % 7 + 1;
101 }
102
localtime_3(struct xtm * r,time64_t time)103 static void localtime_3(struct xtm *r, time64_t time)
104 {
105 unsigned int year, i, w = r->dse;
106
107 /*
108 * In each year, a certain number of days-since-the-epoch have passed.
109 * Find the year that is closest to said days.
110 *
111 * Consider, for example, w=21612 (2029-03-04). Loop will abort on
112 * dse[i] <= w, which happens when dse[i] == 21550. This implies
113 * year == 2009. w will then be 62.
114 */
115 for (i = 0, year = DSE_FIRST; days_since_epoch[i] > w;
116 ++i, --year)
117 /* just loop */;
118
119 w -= days_since_epoch[i];
120
121 /*
122 * By now we have the current year, and the day of the year.
123 * r->yearday = w;
124 *
125 * On to finding the month (like above). In each month, a certain
126 * number of days-since-New Year have passed, and find the closest
127 * one.
128 *
129 * Consider w=62 (in a non-leap year). Loop will abort on
130 * dsy[i] < w, which happens when dsy[i] == 31+28 (i == 2).
131 * Concludes i == 2, i.e. 3rd month => March.
132 *
133 * (A different approach to use would be to subtract a monthlength
134 * from w repeatedly while counting.)
135 */
136 if (is_leap_year(year)) {
137 /* use days_since_leapyear[] in a leap year */
138 for (i = ARRAY_SIZE(days_since_leapyear) - 1;
139 i > 0 && days_since_leapyear[i] > w; --i)
140 /* just loop */;
141 r->monthday = w - days_since_leapyear[i] + 1;
142 } else {
143 for (i = ARRAY_SIZE(days_since_year) - 1;
144 i > 0 && days_since_year[i] > w; --i)
145 /* just loop */;
146 r->monthday = w - days_since_year[i] + 1;
147 }
148
149 r->month = i + 1;
150 }
151
152 static bool
time_mt(const struct sk_buff * skb,struct xt_action_param * par)153 time_mt(const struct sk_buff *skb, struct xt_action_param *par)
154 {
155 const struct xt_time_info *info = par->matchinfo;
156 unsigned int packet_time;
157 struct xtm current_time;
158 time64_t stamp;
159
160 /*
161 * We need real time here, but we can neither use skb->tstamp
162 * nor __net_timestamp().
163 *
164 * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
165 * use different clock types (real vs monotonic).
166 *
167 * Suppose you have two rules:
168 * 1. match before 13:00
169 * 2. match after 13:00
170 *
171 * If you match against processing time (ktime_get_real_seconds) it
172 * may happen that the same packet matches both rules if
173 * it arrived at the right moment before 13:00, so it would be
174 * better to check skb->tstamp and set it via __net_timestamp()
175 * if needed. This however breaks outgoing packets tx timestamp,
176 * and causes them to get delayed forever by fq packet scheduler.
177 */
178 stamp = ktime_get_real_seconds();
179
180 if (info->flags & XT_TIME_LOCAL_TZ)
181 /* Adjust for local timezone */
182 stamp -= 60 * sys_tz.tz_minuteswest;
183
184 /*
185 * xt_time will match when _all_ of the following hold:
186 * - 'now' is in the global time range date_start..date_end
187 * - 'now' is in the monthday mask
188 * - 'now' is in the weekday mask
189 * - 'now' is in the daytime range time_start..time_end
190 * (and by default, libxt_time will set these so as to match)
191 *
192 * note: info->date_start/stop are unsigned 32-bit values that
193 * can hold values beyond y2038, but not after y2106.
194 */
195
196 if (stamp < info->date_start || stamp > info->date_stop)
197 return false;
198
199 packet_time = localtime_1(¤t_time, stamp);
200
201 if (info->daytime_start < info->daytime_stop) {
202 if (packet_time < info->daytime_start ||
203 packet_time > info->daytime_stop)
204 return false;
205 } else {
206 if (packet_time < info->daytime_start &&
207 packet_time > info->daytime_stop)
208 return false;
209
210 /** if user asked to ignore 'next day', then e.g.
211 * '1 PM Wed, August 1st' should be treated
212 * like 'Tue 1 PM July 31st'.
213 *
214 * This also causes
215 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
216 * Monday 23:00 to Tuesday 01:00.
217 */
218 if ((info->flags & XT_TIME_CONTIGUOUS) &&
219 packet_time <= info->daytime_stop)
220 stamp -= SECONDS_PER_DAY;
221 }
222
223 localtime_2(¤t_time, stamp);
224
225 if (!(info->weekdays_match & (1U << current_time.weekday)))
226 return false;
227
228 /* Do not spend time computing monthday if all days match anyway */
229 if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
230 localtime_3(¤t_time, stamp);
231 if (!(info->monthdays_match & (1U << current_time.monthday)))
232 return false;
233 }
234
235 return true;
236 }
237
time_mt_check(const struct xt_mtchk_param * par)238 static int time_mt_check(const struct xt_mtchk_param *par)
239 {
240 const struct xt_time_info *info = par->matchinfo;
241
242 if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
243 info->daytime_stop > XT_TIME_MAX_DAYTIME) {
244 pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
245 return -EDOM;
246 }
247
248 if (info->flags & ~XT_TIME_ALL_FLAGS) {
249 pr_info_ratelimited("unknown flags 0x%x\n",
250 info->flags & ~XT_TIME_ALL_FLAGS);
251 return -EINVAL;
252 }
253
254 if ((info->flags & XT_TIME_CONTIGUOUS) &&
255 info->daytime_start < info->daytime_stop)
256 return -EINVAL;
257
258 return 0;
259 }
260
261 static struct xt_match xt_time_mt_reg __read_mostly = {
262 .name = "time",
263 .family = NFPROTO_UNSPEC,
264 .match = time_mt,
265 .checkentry = time_mt_check,
266 .matchsize = sizeof(struct xt_time_info),
267 .me = THIS_MODULE,
268 };
269
time_mt_init(void)270 static int __init time_mt_init(void)
271 {
272 int minutes = sys_tz.tz_minuteswest;
273
274 if (minutes < 0) /* east of Greenwich */
275 pr_info("kernel timezone is +%02d%02d\n",
276 -minutes / 60, -minutes % 60);
277 else /* west of Greenwich */
278 pr_info("kernel timezone is -%02d%02d\n",
279 minutes / 60, minutes % 60);
280
281 return xt_register_match(&xt_time_mt_reg);
282 }
283
time_mt_exit(void)284 static void __exit time_mt_exit(void)
285 {
286 xt_unregister_match(&xt_time_mt_reg);
287 }
288
289 module_init(time_mt_init);
290 module_exit(time_mt_exit);
291 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
292 MODULE_DESCRIPTION("Xtables: time-based matching");
293 MODULE_LICENSE("GPL");
294 MODULE_ALIAS("ipt_time");
295 MODULE_ALIAS("ip6t_time");
296