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/rtc.h>
18 #include <linux/skbuff.h>
19 #include <linux/types.h>
20 #include <linux/netfilter/x_tables.h>
21 #include <linux/netfilter/xt_time.h>
22
23 struct xtm {
24 u_int8_t month; /* (1-12) */
25 u_int8_t monthday; /* (1-31) */
26 u_int8_t weekday; /* (1-7) */
27 u_int8_t hour; /* (0-23) */
28 u_int8_t minute; /* (0-59) */
29 u_int8_t second; /* (0-59) */
30 unsigned int dse;
31 };
32
33 extern struct timezone sys_tz; /* ouch */
34
35 static const u_int16_t days_since_year[] = {
36 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
37 };
38
39 static const u_int16_t days_since_leapyear[] = {
40 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335,
41 };
42
43 /*
44 * Since time progresses forward, it is best to organize this array in reverse,
45 * to minimize lookup time.
46 */
47 enum {
48 DSE_FIRST = 2039,
49 SECONDS_PER_DAY = 86400,
50 };
51 static const u_int16_t days_since_epoch[] = {
52 /* 2039 - 2030 */
53 25202, 24837, 24472, 24106, 23741, 23376, 23011, 22645, 22280, 21915,
54 /* 2029 - 2020 */
55 21550, 21184, 20819, 20454, 20089, 19723, 19358, 18993, 18628, 18262,
56 /* 2019 - 2010 */
57 17897, 17532, 17167, 16801, 16436, 16071, 15706, 15340, 14975, 14610,
58 /* 2009 - 2000 */
59 14245, 13879, 13514, 13149, 12784, 12418, 12053, 11688, 11323, 10957,
60 /* 1999 - 1990 */
61 10592, 10227, 9862, 9496, 9131, 8766, 8401, 8035, 7670, 7305,
62 /* 1989 - 1980 */
63 6940, 6574, 6209, 5844, 5479, 5113, 4748, 4383, 4018, 3652,
64 /* 1979 - 1970 */
65 3287, 2922, 2557, 2191, 1826, 1461, 1096, 730, 365, 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 */
localtime_1(struct xtm * r,time64_t time)76 static inline unsigned int localtime_1(struct xtm *r, time64_t time)
77 {
78 unsigned int v, w;
79
80 /* Each day has 86400s, so finding the hour/minute is actually easy. */
81 div_u64_rem(time, SECONDS_PER_DAY, &v);
82 r->second = v % 60;
83 w = v / 60;
84 r->minute = w % 60;
85 r->hour = w / 60;
86 return v;
87 }
88
localtime_2(struct xtm * r,time64_t time)89 static inline void localtime_2(struct xtm *r, time64_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 = div_u64(time, SECONDS_PER_DAY);
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
localtime_3(struct xtm * r,time64_t time)104 static void localtime_3(struct xtm *r, time64_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(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
time_mt(const struct sk_buff * skb,struct xt_action_param * par)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 time64_t stamp;
160
161 /*
162 * We need real time here, but we can neither use skb->tstamp
163 * nor __net_timestamp().
164 *
165 * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
166 * use different clock types (real vs monotonic).
167 *
168 * Suppose you have two rules:
169 * 1. match before 13:00
170 * 2. match after 13:00
171 *
172 * If you match against processing time (ktime_get_real_seconds) it
173 * may happen that the same packet matches both rules if
174 * it arrived at the right moment before 13:00, so it would be
175 * better to check skb->tstamp and set it via __net_timestamp()
176 * if needed. This however breaks outgoing packets tx timestamp,
177 * and causes them to get delayed forever by fq packet scheduler.
178 */
179 stamp = ktime_get_real_seconds();
180
181 if (info->flags & XT_TIME_LOCAL_TZ)
182 /* Adjust for local timezone */
183 stamp -= 60 * sys_tz.tz_minuteswest;
184
185 /*
186 * xt_time will match when _all_ of the following hold:
187 * - 'now' is in the global time range date_start..date_end
188 * - 'now' is in the monthday mask
189 * - 'now' is in the weekday mask
190 * - 'now' is in the daytime range time_start..time_end
191 * (and by default, libxt_time will set these so as to match)
192 *
193 * note: info->date_start/stop are unsigned 32-bit values that
194 * can hold values beyond y2038, but not after y2106.
195 */
196
197 if (stamp < info->date_start || stamp > info->date_stop)
198 return false;
199
200 packet_time = localtime_1(¤t_time, stamp);
201
202 if (info->daytime_start < info->daytime_stop) {
203 if (packet_time < info->daytime_start ||
204 packet_time > info->daytime_stop)
205 return false;
206 } else {
207 if (packet_time < info->daytime_start &&
208 packet_time > info->daytime_stop)
209 return false;
210
211 /** if user asked to ignore 'next day', then e.g.
212 * '1 PM Wed, August 1st' should be treated
213 * like 'Tue 1 PM July 31st'.
214 *
215 * This also causes
216 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
217 * Monday 23:00 to Tuesday 01:00.
218 */
219 if ((info->flags & XT_TIME_CONTIGUOUS) &&
220 packet_time <= info->daytime_stop)
221 stamp -= SECONDS_PER_DAY;
222 }
223
224 localtime_2(¤t_time, stamp);
225
226 if (!(info->weekdays_match & (1U << current_time.weekday)))
227 return false;
228
229 /* Do not spend time computing monthday if all days match anyway */
230 if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
231 localtime_3(¤t_time, stamp);
232 if (!(info->monthdays_match & (1U << current_time.monthday)))
233 return false;
234 }
235
236 return true;
237 }
238
time_mt_check(const struct xt_mtchk_param * par)239 static int time_mt_check(const struct xt_mtchk_param *par)
240 {
241 const struct xt_time_info *info = par->matchinfo;
242
243 if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
244 info->daytime_stop > XT_TIME_MAX_DAYTIME) {
245 pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
246 return -EDOM;
247 }
248
249 if (info->flags & ~XT_TIME_ALL_FLAGS) {
250 pr_info_ratelimited("unknown flags 0x%x\n",
251 info->flags & ~XT_TIME_ALL_FLAGS);
252 return -EINVAL;
253 }
254
255 if ((info->flags & XT_TIME_CONTIGUOUS) &&
256 info->daytime_start < info->daytime_stop)
257 return -EINVAL;
258
259 return 0;
260 }
261
262 static struct xt_match xt_time_mt_reg __read_mostly = {
263 .name = "time",
264 .family = NFPROTO_UNSPEC,
265 .match = time_mt,
266 .checkentry = time_mt_check,
267 .matchsize = sizeof(struct xt_time_info),
268 .me = THIS_MODULE,
269 };
270
time_mt_init(void)271 static int __init time_mt_init(void)
272 {
273 int minutes = sys_tz.tz_minuteswest;
274
275 if (minutes < 0) /* east of Greenwich */
276 pr_info("kernel timezone is +%02d%02d\n",
277 -minutes / 60, -minutes % 60);
278 else /* west of Greenwich */
279 pr_info("kernel timezone is -%02d%02d\n",
280 minutes / 60, minutes % 60);
281
282 return xt_register_match(&xt_time_mt_reg);
283 }
284
time_mt_exit(void)285 static void __exit time_mt_exit(void)
286 {
287 xt_unregister_match(&xt_time_mt_reg);
288 }
289
290 module_init(time_mt_init);
291 module_exit(time_mt_exit);
292 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
293 MODULE_DESCRIPTION("Xtables: time-based matching");
294 MODULE_LICENSE("GPL");
295 MODULE_ALIAS("ipt_time");
296 MODULE_ALIAS("ip6t_time");
297