src/shared/time-dst.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Timezone file reading code from glibc 2.16.
   7
   8   Copyright (C) 1991-2012 Free Software Foundation, Inc.
   9   Copyright 2012 Kay Sievers
  10
  11   systemd is free software; you can redistribute it and/or modify it
  12   under the terms of the GNU Lesser General Public License as published by
  13   the Free Software Foundation; either version 2.1 of the License, or
  14   (at your option) any later version.
  15
  16   systemd is distributed in the hope that it will be useful, but
  17   WITHOUT ANY WARRANTY; without even the implied warranty of
  18   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  19   Lesser General Public License for more details.
  20
  21   You should have received a copy of the GNU Lesser General Public License
  22   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  23 ***/
  24 #include <ctype.h>
  25 #include <errno.h>
  26 #include <stddef.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <time.h>
  31 #include <endian.h>
  32 #include <byteswap.h>
  33 #include <assert.h>
  34 #include <limits.h>
  35 #include <unistd.h>
  36 #include <stdint.h>
  37 #include <stdbool.h>
  38 #include <sys/stat.h>
  39
  40 #include "time-dst.h"
  41 #include "util.h"
  42
  43 /*
  44  * If tzh_version is '2' or greater, the above is followed by a second instance
  45  * of tzhead and a second instance of the data in which each coded transition
  46  * time uses 8 rather than 4 chars, then a POSIX-TZ-environment-variable-style
  47  * string for use in handling instants after the last transition time stored in
  48  * the file * (with nothing between the newlines if there is no POSIX
  49  * representation for such instants).
  50  */
  51 #define TZ_MAGIC                "TZif"
  52 struct tzhead {
  53         char tzh_magic[4];      /* TZ_MAGIC */
  54         char tzh_version[1];    /* '\0' or '2' as of 2005 */
  55         char tzh_reserved[15];  /* reserved--must be zero */
  56         char tzh_ttisgmtcnt[4]; /* coded number of trans. time flags */
  57         char tzh_ttisstdcnt[4]; /* coded number of trans. time flags */
  58         char tzh_leapcnt[4];    /* coded number of leap seconds */
  59         char tzh_timecnt[4];    /* coded number of transition times */
  60         char tzh_typecnt[4];    /* coded number of local time types */
  61         char tzh_charcnt[4];    /* coded number of abbr. chars */
  62 };
  63
  64 struct ttinfo {
  65         long int offset;        /* Seconds east of GMT.  */
  66         unsigned char isdst;    /* Used to set tm_isdst.  */
  67         unsigned char idx;      /* Index into `zone_names'.  */
  68         unsigned char isstd;    /* Transition times are in standard time.  */
  69         unsigned char isgmt;    /* Transition times are in GMT.  */
  70 };
  71
  72 struct leap {
  73         time_t transition;      /* Time the transition takes effect.  */
  74         long int change;        /* Seconds of correction to apply.  */
  75 };
  76
  77 static inline int decode(const void *ptr) {
  78         return be32toh(*(int *)ptr);
  79 }
  80
  81 static inline int64_t decode64(const void *ptr) {
  82         return be64toh(*(int64_t *)ptr);
  83 }
  84
  85 int time_get_dst(time_t date, const char *tzfile,
  86                  time_t *switch_cur, char **zone_cur, bool *dst_cur,
  87                  time_t *switch_next, int *delta_next, char **zone_next, bool *dst_next) {
  88         unsigned char *type_idxs = 0;
  89         size_t num_types = 0;
  90         struct ttinfo *types = NULL;
  91         char *zone_names = NULL;
  92         struct stat st;
  93         size_t num_isstd, num_isgmt;
  94         struct tzhead tzhead;
  95         size_t chars;
  96         size_t i;
  97         size_t total_size;
  98         size_t types_idx;
  99         int trans_width = 4;
 100         size_t tzspec_len;
 101         size_t num_leaps;
 102         size_t lo, hi;
 103         size_t num_transitions = 0;
 104         _cleanup_free_ time_t *transitions = NULL;
 105         _cleanup_fclose_ FILE *f;
 106
 107         f = fopen(tzfile, "re");
 108         if (f == NULL)
 109                 return -errno;
 110
 111         if (fstat(fileno(f), &st) < 0)
 112                 return -errno;
 113
 114 read_again:
 115         if (fread((void *)&tzhead, sizeof(tzhead), 1, f) != 1 ||
 116             memcmp(tzhead.tzh_magic, TZ_MAGIC, sizeof(tzhead.tzh_magic)) != 0)
 117                 return -EINVAL;
 118
 119         num_transitions = (size_t)decode(tzhead.tzh_timecnt);
 120         num_types = (size_t)decode(tzhead.tzh_typecnt);
 121         chars = (size_t)decode(tzhead.tzh_charcnt);
 122         num_leaps = (size_t)decode(tzhead.tzh_leapcnt);
 123         num_isstd = (size_t)decode(tzhead.tzh_ttisstdcnt);
 124         num_isgmt = (size_t)decode(tzhead.tzh_ttisgmtcnt);
 125
 126         /* For platforms with 64-bit time_t we use the new format if available.  */
 127         if (sizeof(time_t) == 8 && trans_width == 4 && tzhead.tzh_version[0] != '\0') {
 128                 size_t to_skip;
 129
 130                 /* We use the 8-byte format.  */
 131                 trans_width = 8;
 132
 133                 /* Position the stream before the second header.  */
 134                 to_skip = (num_transitions * (4 + 1)
 135                            + num_types * 6
 136                            + chars
 137                            + num_leaps * 8 + num_isstd + num_isgmt);
 138                 if (fseek(f, to_skip, SEEK_CUR) != 0)
 139                         return -EINVAL;
 140
 141                 goto read_again;
 142         }
 143
 144         if (num_transitions > ((SIZE_MAX - (__alignof__(struct ttinfo) - 1)) / (sizeof(time_t) + 1)))
 145                  return -EINVAL;
 146
 147         total_size = num_transitions * (sizeof(time_t) + 1);
 148         total_size = ((total_size + __alignof__(struct ttinfo) - 1) & ~(__alignof__(struct ttinfo) - 1));
 149         types_idx = total_size;
 150         if (num_leaps > (SIZE_MAX - total_size) / sizeof(struct ttinfo))
 151                 return -EINVAL;
 152
 153         total_size += num_types * sizeof(struct ttinfo);
 154         if (chars > SIZE_MAX - total_size)
 155                 return -EINVAL;
 156
 157         total_size += chars;
 158         if (__alignof__(struct leap) - 1 > SIZE_MAX - total_size)
 159                  return -EINVAL;
 160
 161         total_size = ((total_size + __alignof__(struct leap) - 1) & ~(__alignof__(struct leap) - 1));
 162         if (num_leaps > (SIZE_MAX - total_size) / sizeof(struct leap))
 163                 return -EINVAL;
 164
 165         total_size += num_leaps * sizeof(struct leap);
 166         tzspec_len = 0;
 167         if (sizeof(time_t) == 8 && trans_width == 8) {
 168                 off_t rem = st.st_size - ftello(f);
 169
 170                 if (rem < 0 || (size_t) rem < (num_transitions * (8 + 1) + num_types * 6 + chars))
 171                         return -EINVAL;
 172                 tzspec_len = (size_t) rem - (num_transitions * (8 + 1) + num_types * 6 + chars);
 173                 if (num_leaps > SIZE_MAX / 12 || tzspec_len < num_leaps * 12)
 174                         return -EINVAL;
 175                 tzspec_len -= num_leaps * 12;
 176                 if (tzspec_len < num_isstd)
 177                         return -EINVAL;
 178                 tzspec_len -= num_isstd;
 179                 if (tzspec_len == 0 || tzspec_len - 1 < num_isgmt)
 180                         return -EINVAL;
 181                 tzspec_len -= num_isgmt + 1;
 182                 if (SIZE_MAX - total_size < tzspec_len)
 183                         return -EINVAL;
 184         }
 185
 186         /* leave space for additional zone_names zero terminator */
 187         transitions = malloc0(total_size + tzspec_len + 1);
 188         if (transitions == NULL)
 189                 return -EINVAL;
 190
 191         type_idxs = (unsigned char *)transitions + (num_transitions
 192                                                     * sizeof(time_t));
 193         types = (struct ttinfo *)((char *)transitions + types_idx);
 194         zone_names = (char *)types + num_types * sizeof(struct ttinfo);
 195
 196         if (sizeof(time_t) == 4 || trans_width == 8) {
 197                 if (fread(transitions, trans_width + 1, num_transitions, f) != num_transitions)
 198                         return -EINVAL;
 199         } else {
 200                 if (fread(transitions, 4, num_transitions, f) != num_transitions ||
 201                     fread(type_idxs, 1, num_transitions, f) != num_transitions)
 202                         return -EINVAL;
 203         }
 204
 205         /* Check for bogus indices in the data file, so we can hereafter
 206            safely use type_idxs[T] as indices into `types' and never crash.  */
 207         for (i = 0; i < num_transitions; ++i)
 208                 if (type_idxs[i] >= num_types)
 209                         return -EINVAL;
 210
 211         if (__BYTE_ORDER == __BIG_ENDIAN ? sizeof(time_t) == 8 && trans_width == 4
 212                                          : sizeof(time_t) == 4 || trans_width == 4) {
 213                 /* Decode the transition times, stored as 4-byte integers in
 214                    network (big-endian) byte order.  We work from the end of
 215                    the array so as not to clobber the next element to be
 216                    processed when sizeof (time_t) > 4.  */
 217                 i = num_transitions;
 218                 while (i-- > 0)
 219                         transitions[i] = decode((char *)transitions + i * 4);
 220         } else if (__BYTE_ORDER != __BIG_ENDIAN && sizeof(time_t) == 8) {
 221                 /* Decode the transition times, stored as 8-byte integers in
 222                    network (big-endian) byte order.  */
 223                 for (i = 0; i < num_transitions; ++i)
 224                         transitions[i] = decode64((char *)transitions + i * 8);
 225         }
 226
 227         for (i = 0; i < num_types; ++i) {
 228                 unsigned char x[4];
 229                 int c;
 230
 231                 if (fread(x, 1, sizeof(x), f) != sizeof(x))
 232                         return -EINVAL;
 233                 c = getc(f);
 234                 if ((unsigned int)c > 1u)
 235                         return -EINVAL;
 236                 types[i].isdst = c;
 237                 c = getc(f);
 238                 if ((size_t) c > chars)
 239                         /* Bogus index in data file.  */
 240                         return -EINVAL;
 241                 types[i].idx = c;
 242                 types[i].offset = (long int)decode(x);
 243         }
 244
 245         if (fread(zone_names, 1, chars, f) != chars)
 246                 return -EINVAL;
 247
 248         zone_names[chars] = '\0';
 249
 250         for (i = 0; i < num_isstd; ++i) {
 251                 int c = getc(f);
 252                 if (c == EOF)
 253                         return -EINVAL;
 254                 types[i].isstd = c != 0;
 255         }
 256
 257         while (i < num_types)
 258                 types[i++].isstd = 0;
 259
 260         for (i = 0; i < num_isgmt; ++i) {
 261                 int c = getc(f);
 262                 if (c == EOF)
 263                         return -EINVAL;
 264                 types[i].isgmt = c != 0;
 265         }
 266
 267         while (i < num_types)
 268                 types[i++].isgmt = 0;
 269
 270         if (num_transitions == 0)
 271                return -EINVAL;
 272
 273         if (date < transitions[0] || date >= transitions[num_transitions - 1])
 274                return -EINVAL;
 275
 276         /* Find the first transition after TIMER, and
 277            then pick the type of the transition before it.  */
 278         lo = 0;
 279         hi = num_transitions - 1;
 280
 281         /* Assume that DST is changing twice a year and guess initial
 282            search spot from it.
 283            Half of a gregorian year has on average 365.2425 * 86400 / 2
 284            = 15778476 seconds.  */
 285         i = (transitions[num_transitions - 1] - date) / 15778476;
 286         if (i < num_transitions) {
 287                 i = num_transitions - 1 - i;
 288                 if (date < transitions[i]) {
 289                         if (i < 10 || date >= transitions[i - 10]) {
 290                                 /* Linear search.  */
 291                                 while (date < transitions[i - 1])
 292                                         i--;
 293                                 goto found;
 294                         }
 295                         hi = i - 10;
 296                 } else {
 297                         if (i + 10 >= num_transitions || date < transitions[i + 10]) {
 298                                 /* Linear search.  */
 299                                 while (date >= transitions[i])
 300                                         i++;
 301                                 goto found;
 302                         }
 303                         lo = i + 10;
 304                 }
 305         }
 306
 307         /* Binary search. */
 308         while (lo + 1 < hi) {
 309                 i = (lo + hi) / 2;
 310                 if (date < transitions[i])
 311                         hi = i;
 312                 else
 313                         lo = i;
 314         }
 315         i = hi;
 316
 317 found:
 318         if (switch_cur)
 319                 *switch_cur = transitions[i-1];
 320         if (zone_cur)
 321                 *zone_cur = strdup(&zone_names[types[type_idxs[i - 1]].idx]);
 322         if (dst_cur)
 323                 *dst_cur = types[type_idxs[i-1]].isdst;
 324
 325         if (switch_next)
 326                 *switch_next = transitions[i];
 327         if (delta_next)
 328                 *delta_next = (types[type_idxs[i]].offset - types[type_idxs[i-1]].offset) / 60;
 329         if (zone_next)
 330                 *zone_next = strdup(&zone_names[types[type_idxs[i]].idx]);
 331         if (dst_next)
 332                 *dst_next = types[type_idxs[i]].isdst;
 333
 334         return 0;
 335 }