1 /* Time zone functions such as tzalloc and localtime_rz
2
3 Copyright 2015-2018 Free Software Foundation, Inc.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3, or (at your option)
8 any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License along
16 with this program; if not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Paul Eggert. */
19
20 /* Although this module is not thread-safe, any races should be fairly
21 rare and reasonably benign. For complete thread-safety, use a C
22 library with a working timezone_t type, so that this module is not
23 needed. */
24
25 #include <config.h>
26
27 #include <time.h>
28
29 #include <errno.h>
30 #include <limits.h>
31 #include <stdbool.h>
32 #include <stddef.h>
33 #include <stdlib.h>
34 #include <string.h>
35
36 #include "flexmember.h"
37 #include "time-internal.h"
38
39 #ifndef SIZE_MAX
40 # define SIZE_MAX ((size_t) -1)
41 #endif
42
43 /* The approximate size to use for small allocation requests. This is
44 the largest "small" request for the GNU C library malloc. */
45 enum { DEFAULT_MXFAST = 64 * sizeof (size_t) / 4 };
46
47 /* Minimum size of the ABBRS member of struct tm_zone. ABBRS is larger
48 only in the unlikely case where an abbreviation longer than this is
49 used. */
50 enum { ABBR_SIZE_MIN = DEFAULT_MXFAST - offsetof (struct tm_zone, abbrs) };
51
52 /* Magic cookie timezone_t value, for local time. It differs from
53 NULL and from all other timezone_t values. Only the address
54 matters; the pointer is never dereferenced. */
55 static timezone_t const local_tz = (timezone_t) 1;
56
57 #if HAVE_TM_ZONE || HAVE_TZNAME
58
59 /* Return true if the values A and B differ according to the rules for
60 tm_isdst: A and B differ if one is zero and the other positive. */
61 static bool
isdst_differ(int a,int b)62 isdst_differ (int a, int b)
63 {
64 return !a != !b && 0 <= a && 0 <= b;
65 }
66
67 /* Return true if A and B are equal. */
68 static int
equal_tm(const struct tm * a,const struct tm * b)69 equal_tm (const struct tm *a, const struct tm *b)
70 {
71 return ! ((a->tm_sec ^ b->tm_sec)
72 | (a->tm_min ^ b->tm_min)
73 | (a->tm_hour ^ b->tm_hour)
74 | (a->tm_mday ^ b->tm_mday)
75 | (a->tm_mon ^ b->tm_mon)
76 | (a->tm_year ^ b->tm_year)
77 | isdst_differ (a->tm_isdst, b->tm_isdst));
78 }
79
80 #endif
81
82 /* Copy to ABBRS the abbreviation at ABBR with size ABBR_SIZE (this
83 includes its trailing null byte). Append an extra null byte to
84 mark the end of ABBRS. */
85 static void
extend_abbrs(char * abbrs,char const * abbr,size_t abbr_size)86 extend_abbrs (char *abbrs, char const *abbr, size_t abbr_size)
87 {
88 memcpy (abbrs, abbr, abbr_size);
89 abbrs[abbr_size] = '\0';
90 }
91
92 /* Return a newly allocated time zone for NAME, or NULL on failure.
93 A null NAME stands for wall clock time (which is like unset TZ). */
94 timezone_t
tzalloc(char const * name)95 tzalloc (char const *name)
96 {
97 size_t name_size = name ? strlen (name) + 1 : 0;
98 size_t abbr_size = name_size < ABBR_SIZE_MIN ? ABBR_SIZE_MIN : name_size + 1;
99 timezone_t tz = malloc (FLEXSIZEOF (struct tm_zone, abbrs, abbr_size));
100 if (tz)
101 {
102 tz->next = NULL;
103 #if HAVE_TZNAME && !HAVE_TM_ZONE
104 tz->tzname_copy[0] = tz->tzname_copy[1] = NULL;
105 #endif
106 tz->tz_is_set = !!name;
107 tz->abbrs[0] = '\0';
108 if (name)
109 extend_abbrs (tz->abbrs, name, name_size);
110 }
111 return tz;
112 }
113
114 /* Save into TZ any nontrivial time zone abbreviation used by TM, and
115 update *TM (if HAVE_TM_ZONE) or *TZ (if !HAVE_TM_ZONE &&
116 HAVE_TZNAME) if they use the abbreviation. Return true if
117 successful, false (setting errno) otherwise. */
118 static bool
save_abbr(timezone_t tz,struct tm * tm)119 save_abbr (timezone_t tz, struct tm *tm)
120 {
121 #if HAVE_TM_ZONE || HAVE_TZNAME
122 char const *zone = NULL;
123 char *zone_copy = (char *) "";
124
125 # if HAVE_TZNAME
126 int tzname_index = -1;
127 # endif
128
129 # if HAVE_TM_ZONE
130 zone = tm->tm_zone;
131 # endif
132
133 # if HAVE_TZNAME
134 if (! (zone && *zone) && 0 <= tm->tm_isdst)
135 {
136 tzname_index = tm->tm_isdst != 0;
137 zone = tzname[tzname_index];
138 }
139 # endif
140
141 /* No need to replace null zones, or zones within the struct tm. */
142 if (!zone || ((char *) tm <= zone && zone < (char *) (tm + 1)))
143 return true;
144
145 if (*zone)
146 {
147 zone_copy = tz->abbrs;
148
149 while (strcmp (zone_copy, zone) != 0)
150 {
151 if (! (*zone_copy || (zone_copy == tz->abbrs && tz->tz_is_set)))
152 {
153 size_t zone_size = strlen (zone) + 1;
154 size_t zone_used = zone_copy - tz->abbrs;
155 if (SIZE_MAX - zone_used < zone_size)
156 {
157 errno = ENOMEM;
158 return false;
159 }
160 if (zone_used + zone_size < ABBR_SIZE_MIN)
161 extend_abbrs (zone_copy, zone, zone_size);
162 else
163 {
164 tz = tz->next = tzalloc (zone);
165 if (!tz)
166 return false;
167 tz->tz_is_set = 0;
168 zone_copy = tz->abbrs;
169 }
170 break;
171 }
172
173 zone_copy += strlen (zone_copy) + 1;
174 if (!*zone_copy && tz->next)
175 {
176 tz = tz->next;
177 zone_copy = tz->abbrs;
178 }
179 }
180 }
181
182 /* Replace the zone name so that its lifetime matches that of TZ. */
183 # if HAVE_TM_ZONE
184 tm->tm_zone = zone_copy;
185 # else
186 if (0 <= tzname_index)
187 tz->tzname_copy[tzname_index] = zone_copy;
188 # endif
189 #endif
190
191 return true;
192 }
193
194 /* Free a time zone. */
195 void
tzfree(timezone_t tz)196 tzfree (timezone_t tz)
197 {
198 if (tz != local_tz)
199 while (tz)
200 {
201 timezone_t next = tz->next;
202 free (tz);
203 tz = next;
204 }
205 }
206
207 /* Get and set the TZ environment variable. These functions can be
208 overridden by programs like Emacs that manage their own environment. */
209
210 #ifndef getenv_TZ
211 static char *
getenv_TZ(void)212 getenv_TZ (void)
213 {
214 return getenv ("TZ");
215 }
216 #endif
217
218 #ifndef setenv_TZ
219 static int
setenv_TZ(char const * tz)220 setenv_TZ (char const *tz)
221 {
222 return tz ? setenv ("TZ", tz, 1) : unsetenv ("TZ");
223 }
224 #endif
225
226 /* Change the environment to match the specified timezone_t value.
227 Return true if successful, false (setting errno) otherwise. */
228 static bool
change_env(timezone_t tz)229 change_env (timezone_t tz)
230 {
231 if (setenv_TZ (tz->tz_is_set ? tz->abbrs : NULL) != 0)
232 return false;
233 tzset ();
234 return true;
235 }
236
237 /* Temporarily set the time zone to TZ, which must not be null.
238 Return LOCAL_TZ if the time zone setting is already correct.
239 Otherwise return a newly allocated time zone representing the old
240 setting, or NULL (setting errno) on failure. */
241 static timezone_t
set_tz(timezone_t tz)242 set_tz (timezone_t tz)
243 {
244 char *env_tz = getenv_TZ ();
245 if (env_tz
246 ? tz->tz_is_set && strcmp (tz->abbrs, env_tz) == 0
247 : !tz->tz_is_set)
248 return local_tz;
249 else
250 {
251 timezone_t old_tz = tzalloc (env_tz);
252 if (!old_tz)
253 return old_tz;
254 if (! change_env (tz))
255 {
256 int saved_errno = errno;
257 tzfree (old_tz);
258 errno = saved_errno;
259 return NULL;
260 }
261 return old_tz;
262 }
263 }
264
265 /* Restore an old setting returned by set_tz. It must not be null.
266 Return true (preserving errno) if successful, false (setting errno)
267 otherwise. */
268 static bool
revert_tz(timezone_t tz)269 revert_tz (timezone_t tz)
270 {
271 if (tz == local_tz)
272 return true;
273 else
274 {
275 int saved_errno = errno;
276 bool ok = change_env (tz);
277 if (!ok)
278 saved_errno = errno;
279 tzfree (tz);
280 errno = saved_errno;
281 return ok;
282 }
283 }
284
285 /* Use time zone TZ to compute localtime_r (T, TM). */
286 struct tm *
localtime_rz(timezone_t tz,time_t const * t,struct tm * tm)287 localtime_rz (timezone_t tz, time_t const *t, struct tm *tm)
288 {
289 #ifdef HAVE_LOCALTIME_INFLOOP_BUG
290 /* The -67768038400665599 comes from:
291 https://lists.gnu.org/r/bug-gnulib/2017-07/msg00142.html
292 On affected platforms the greatest POSIX-compatible time_t value
293 that could return nonnull is 67768036191766798 (when
294 TZ="XXX24:59:59" it resolves to the year 2**31 - 1 + 1900, on
295 12-31 at 23:59:59), so test for that too while we're in the
296 neighborhood. */
297 if (! (-67768038400665599 <= *t && *t <= 67768036191766798))
298 {
299 errno = EOVERFLOW;
300 return NULL;
301 }
302 #endif
303
304 if (!tz)
305 return gmtime_r (t, tm);
306 else
307 {
308 timezone_t old_tz = set_tz (tz);
309 if (old_tz)
310 {
311 bool abbr_saved = localtime_r (t, tm) && save_abbr (tz, tm);
312 if (revert_tz (old_tz) && abbr_saved)
313 return tm;
314 }
315 return NULL;
316 }
317 }
318
319 /* Use time zone TZ to compute mktime (TM). */
320 time_t
mktime_z(timezone_t tz,struct tm * tm)321 mktime_z (timezone_t tz, struct tm *tm)
322 {
323 if (!tz)
324 return timegm (tm);
325 else
326 {
327 timezone_t old_tz = set_tz (tz);
328 if (old_tz)
329 {
330 time_t t = mktime (tm);
331 #if HAVE_TM_ZONE || HAVE_TZNAME
332 time_t badtime = -1;
333 struct tm tm_1;
334 if ((t != badtime
335 || (localtime_r (&t, &tm_1) && equal_tm (tm, &tm_1)))
336 && !save_abbr (tz, tm))
337 t = badtime;
338 #endif
339 if (revert_tz (old_tz))
340 return t;
341 }
342 return -1;
343 }
344 }
345