lib/tempname.c

   1 /* tempname.c - generate the name of a temporary file.
   2
   3    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
   4    2000, 2001, 2002 Free Software Foundation, Inc.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License along
  17    with this program; if not, write to the Free Software Foundation,
  18    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  19
  20 #if HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <sys/types.h>
  25 #include <assert.h>
  26
  27 #include <errno.h>
  28 #ifndef __set_errno
  29 # define __set_errno(Val) errno = (Val)
  30 #endif
  31
  32 #include <stdio.h>
  33 #ifndef P_tmpdir
  34 # define P_tmpdir "/tmp"
  35 #endif
  36 #ifndef TMP_MAX
  37 # define TMP_MAX 238328
  38 #endif
  39 #ifndef __GT_FILE
  40 # define __GT_FILE      0
  41 # define __GT_BIGFILE   1
  42 # define __GT_DIR       2
  43 # define __GT_NOCREATE  3
  44 #endif
  45
  46 #if STDC_HEADERS || _LIBC
  47 # include <stddef.h>
  48 # include <string.h>
  49 #endif
  50
  51 #include <stdlib.h>
  52
  53 #if HAVE_FCNTL_H || _LIBC
  54 # include <fcntl.h>
  55 #endif
  56
  57 #if HAVE_SYS_TIME_H || _LIBC
  58 # include <sys/time.h>
  59 #endif
  60
  61 #if HAVE_STDINT_H || _LIBC
  62 # include <stdint.h>
  63 #endif
  64
  65 #if HAVE_UNISTD_H || _LIBC
  66 # include <unistd.h>
  67 #endif
  68
  69 #include <sys/stat.h>
  70 #if STAT_MACROS_BROKEN
  71 # undef S_ISDIR
  72 #endif
  73 #if !defined S_ISDIR && defined S_IFDIR
  74 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  75 #endif
  76 #if !S_IRUSR && S_IREAD
  77 # define S_IRUSR S_IREAD
  78 #endif
  79 #if !S_IRUSR
  80 # define S_IRUSR 00400
  81 #endif
  82 #if !S_IWUSR && S_IWRITE
  83 # define S_IWUSR S_IWRITE
  84 #endif
  85 #if !S_IWUSR
  86 # define S_IWUSR 00200
  87 #endif
  88 #if !S_IXUSR && S_IEXEC
  89 # define S_IXUSR S_IEXEC
  90 #endif
  91 #if !S_IXUSR
  92 # define S_IXUSR 00100
  93 #endif
  94
  95 #if _LIBC
  96 # define struct_stat64 struct stat64
  97 #else
  98 # define struct_stat64 struct stat
  99 # define __getpid getpid
 100 # define __gettimeofday gettimeofday
 101 # define __mkdir mkdir
 102 # define __open open
 103 # define __open64 open
 104 # define __lxstat64(version, path, buf) lstat (path, buf)
 105 # define __xstat64(version, path, buf) stat (path, buf)
 106 #endif
 107
 108 #if ! (HAVE___SECURE_GETENV || _LIBC)
 109 # define __secure_getenv getenv
 110 #endif
 111
 112 #ifdef _LIBC
 113 # include <hp-timing.h>
 114 # if HP_TIMING_AVAIL
 115 #  define RANDOM_BITS(Var) \
 116   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 117     {                                                                         \
 118       /* If this is the first time this function is used initialize           \
 119          the variable we accumulate the value in to some somewhat             \
 120          random value.  If we'd not do this programs at startup time          \
 121          might have a reduced set of possible names, at least on slow         \
 122          machines.  */                                                        \
 123       struct timeval tv;                                                      \
 124       __gettimeofday (&tv, NULL);                                             \
 125       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 126     }                                                                         \
 127   HP_TIMING_NOW (Var)
 128 # endif
 129 #endif
 130
 131 /* Use the widest available unsigned type if uint64_t is not
 132    available.  The algorithm below extracts a number less than 62**6
 133    (approximately 2**35.725) from uint64_t, so ancient hosts where
 134    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 135    which is better than not having mkstemp at all.  */
 136 #if !defined UINT64_MAX && !defined uint64_t
 137 # define uint64_t uintmax_t
 138 #endif
 139
 140 /* Return nonzero if DIR is an existent directory.  */
 141 static int
 142 direxists (const char *dir)
 143 {
 144   struct_stat64 buf;
 145   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 146 }
 147
 148 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 149    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 150    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 151    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 152    doesn't exist, none of the searched dirs exists, or there's not
 153    enough space in TMPL. */
 154 int
 155 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 156                int try_tmpdir)
 157 {
 158   const char *d;
 159   size_t dlen, plen;
 160
 161   if (!pfx || !pfx[0])
 162     {
 163       pfx = "file";
 164       plen = 4;
 165     }
 166   else
 167     {
 168       plen = strlen (pfx);
 169       if (plen > 5)
 170         plen = 5;
 171     }
 172
 173   if (try_tmpdir)
 174     {
 175       d = __secure_getenv ("TMPDIR");
 176       if (d != NULL && direxists (d))
 177         dir = d;
 178       else if (dir != NULL && direxists (dir))
 179         /* nothing */ ;
 180       else
 181         dir = NULL;
 182     }
 183   if (dir == NULL)
 184     {
 185       if (direxists (P_tmpdir))
 186         dir = P_tmpdir;
 187       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 188         dir = "/tmp";
 189       else
 190         {
 191           __set_errno (ENOENT);
 192           return -1;
 193         }
 194     }
 195
 196   dlen = strlen (dir);
 197   while (dlen > 1 && dir[dlen - 1] == '/')
 198     dlen--;                     /* remove trailing slashes */
 199
 200   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 201   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 202     {
 203       __set_errno (EINVAL);
 204       return -1;
 205     }
 206
 207   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 208   return 0;
 209 }
 210
 211 /* These are the characters used in temporary filenames.  */
 212 static const char letters[] =
 213 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 214
 215 /* Generate a temporary file name based on TMPL.  TMPL must match the
 216    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 217    does not exist at the time of the call to __gen_tempname.  TMPL is
 218    overwritten with the result.
 219
 220    KIND may be one of:
 221    __GT_NOCREATE:       simply verify that the name does not exist
 222                         at the time of the call.
 223    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 224                         and return a read-write fd.  The file is mode 0600.
 225    __GT_BIGFILE:        same as __GT_FILE but use open64().
 226    __GT_DIR:            create a directory, which will be mode 0700.
 227
 228    We use a clever algorithm to get hard-to-predict names. */
 229 int
 230 __gen_tempname (char *tmpl, int kind)
 231 {
 232   int len;
 233   char *XXXXXX;
 234   static uint64_t value;
 235   uint64_t random_time_bits;
 236   unsigned int count;
 237   int fd = -1;
 238   int save_errno = errno;
 239   struct_stat64 st;
 240
 241   /* A lower bound on the number of temporary files to attempt to
 242      generate.  The maximum total number of temporary file names that
 243      can exist for a given template is 62**6.  It should never be
 244      necessary to try all these combinations.  Instead if a reasonable
 245      number of names is tried (we define reasonable as 62**3) fail to
 246      give the system administrator the chance to remove the problems.  */
 247   unsigned int attempts_min = 62 * 62 * 62;
 248
 249   /* The number of times to attempt to generate a temporary file.  To
 250      conform to POSIX, this must be no smaller than TMP_MAX.  */
 251   unsigned int attempts = attempts_min < TMP_MAX ? TMP_MAX : attempts_min;
 252
 253   len = strlen (tmpl);
 254   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 255     {
 256       __set_errno (EINVAL);
 257       return -1;
 258     }
 259
 260   /* This is where the Xs start.  */
 261   XXXXXX = &tmpl[len - 6];
 262
 263   /* Get some more or less random data.  */
 264 #ifdef RANDOM_BITS
 265   RANDOM_BITS (random_time_bits);
 266 #else
 267 # if HAVE_GETTIMEOFDAY || _LIBC
 268   {
 269     struct timeval tv;
 270     __gettimeofday (&tv, NULL);
 271     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 272   }
 273 # else
 274   random_time_bits = time (NULL);
 275 # endif
 276 #endif
 277   value += random_time_bits ^ __getpid ();
 278
 279   for (count = 0; count < attempts; value += 7777, ++count)
 280     {
 281       uint64_t v = value;
 282
 283       /* Fill in the random bits.  */
 284       XXXXXX[0] = letters[v % 62];
 285       v /= 62;
 286       XXXXXX[1] = letters[v % 62];
 287       v /= 62;
 288       XXXXXX[2] = letters[v % 62];
 289       v /= 62;
 290       XXXXXX[3] = letters[v % 62];
 291       v /= 62;
 292       XXXXXX[4] = letters[v % 62];
 293       v /= 62;
 294       XXXXXX[5] = letters[v % 62];
 295
 296       switch (kind)
 297         {
 298         case __GT_FILE:
 299           fd = __open (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 300           break;
 301
 302         case __GT_BIGFILE:
 303           fd = __open64 (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 304           break;
 305
 306         case __GT_DIR:
 307           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 308           break;
 309
 310         case __GT_NOCREATE:
 311           /* This case is backward from the other three.  __gen_tempname
 312              succeeds if __xstat fails because the name does not exist.
 313              Note the continue to bypass the common logic at the bottom
 314              of the loop.  */
 315           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 316             {
 317               if (errno == ENOENT)
 318                 {
 319                   __set_errno (save_errno);
 320                   return 0;
 321                 }
 322               else
 323                 /* Give up now. */
 324                 return -1;
 325             }
 326           continue;
 327
 328         default:
 329           assert (! "invalid KIND in __gen_tempname");
 330         }
 331
 332       if (fd >= 0)
 333         {
 334           __set_errno (save_errno);
 335           return fd;
 336         }
 337       else if (errno != EEXIST)
 338         return -1;
 339     }
 340
 341   /* We got out of the loop because we ran out of combinations to try.  */
 342   __set_errno (EEXIST);
 343   return -1;
 344 }