lib/tempname.c

   1 /* Copyright (C) 1991-1999, 2000, 2001 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #if HAVE_CONFIG_H
  20 # include <config.h>
  21 #endif
  22
  23 #include <sys/types.h>
  24 #include <assert.h>
  25
  26 #include <errno.h>
  27 #ifndef __set_errno
  28 # define __set_errno(Val) errno = (Val)
  29 #endif
  30
  31 #include <stdio.h>
  32 #ifndef P_tmpdir
  33 # define P_tmpdir "/tmp"
  34 #endif
  35 #ifndef TMP_MAX
  36 # define TMP_MAX 238328
  37 #endif
  38 #ifndef __GT_FILE
  39 # define __GT_FILE      0
  40 # define __GT_BIGFILE   1
  41 # define __GT_DIR       2
  42 # define __GT_NOCREATE  3
  43 #endif
  44
  45 #if STDC_HEADERS || _LIBC
  46 # include <stddef.h>
  47 # include <string.h>
  48 #endif
  49
  50 #include <stdlib.h>
  51
  52 #if HAVE_FCNTL_H || _LIBC
  53 # include <fcntl.h>
  54 #endif
  55
  56 #if HAVE_SYS_TIME_H || _LIBC
  57 # include <sys/time.h>
  58 #endif
  59
  60 #if HAVE_STDINT_H || _LIBC
  61 # include <stdint.h>
  62 #endif
  63
  64 #if HAVE_UNISTD_H || _LIBC
  65 # include <unistd.h>
  66 #endif
  67
  68 #include <sys/stat.h>
  69 #if STAT_MACROS_BROKEN
  70 # undef S_ISDIR
  71 #endif
  72 #if !defined S_ISDIR && defined S_IFDIR
  73 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  74 #endif
  75 #if !S_IRUSR && S_IREAD
  76 # define S_IRUSR S_IREAD
  77 #endif
  78 #if !S_IRUSR
  79 # define S_IRUSR 00400
  80 #endif
  81 #if !S_IWUSR && S_IWRITE
  82 # define S_IWUSR S_IWRITE
  83 #endif
  84 #if !S_IWUSR
  85 # define S_IWUSR 00200
  86 #endif
  87 #if !S_IXUSR && S_IEXEC
  88 # define S_IXUSR S_IEXEC
  89 #endif
  90 #if !S_IXUSR
  91 # define S_IXUSR 00100
  92 #endif
  93
  94 #if _LIBC
  95 # define struct_stat64 struct stat64
  96 #else
  97 # define struct_stat64 struct stat
  98 # define __getpid getpid
  99 # define __gettimeofday gettimeofday
 100 # define __mkdir mkdir
 101 # define __open open
 102 # define __open64 open
 103 # define __lxstat64(version, path, buf) lstat (path, buf)
 104 # define __xstat64(version, path, buf) stat (path, buf)
 105 #endif
 106
 107 #if ! (HAVE___SECURE_GETENV || _LIBC)
 108 # define __secure_getenv getenv
 109 #endif
 110
 111 #ifdef _LIBC
 112 # include <hp-timing.h>
 113 # if HP_TIMING_AVAIL
 114 #  define RANDOM_BITS(Var) \
 115   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 116     {                                                                         \
 117       /* If this is the first time this function is used initialize           \
 118          the variable we accumulate the value in to some somewhat             \
 119          random value.  If we'd not do this programs at startup time          \
 120          might have a reduced set of possible names, at least on slow         \
 121          machines.  */                                                        \
 122       struct timeval tv;                                                      \
 123       __gettimeofday (&tv, NULL);                                             \
 124       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 125     }                                                                         \
 126   HP_TIMING_NOW (Var)
 127 # endif
 128 #endif
 129
 130 /* Use the widest available unsigned type if uint64_t is not
 131    available.  The algorithm below extracts a number less than 62**6
 132    (approximately 2**35.725) from uint64_t, so ancient hosts where
 133    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 134    which is better than not having mkstemp at all.  */
 135 #if !defined UINT64_MAX && !defined uint64_t
 136 # define uint64_t uintmax_t
 137 #endif
 138
 139 /* Return nonzero if DIR is an existent directory.  */
 140 static int
 141 direxists (const char *dir)
 142 {
 143   struct_stat64 buf;
 144   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 145 }
 146
 147 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 148    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 149    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 150    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 151    doesn't exist, none of the searched dirs exists, or there's not
 152    enough space in TMPL. */
 153 int
 154 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 155                int try_tmpdir)
 156 {
 157   const char *d;
 158   size_t dlen, plen;
 159
 160   if (!pfx || !pfx[0])
 161     {
 162       pfx = "file";
 163       plen = 4;
 164     }
 165   else
 166     {
 167       plen = strlen (pfx);
 168       if (plen > 5)
 169         plen = 5;
 170     }
 171
 172   if (try_tmpdir)
 173     {
 174       d = __secure_getenv ("TMPDIR");
 175       if (d != NULL && direxists (d))
 176         dir = d;
 177       else if (dir != NULL && direxists (dir))
 178         /* nothing */ ;
 179       else
 180         dir = NULL;
 181     }
 182   if (dir == NULL)
 183     {
 184       if (direxists (P_tmpdir))
 185         dir = P_tmpdir;
 186       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 187         dir = "/tmp";
 188       else
 189         {
 190           __set_errno (ENOENT);
 191           return -1;
 192         }
 193     }
 194
 195   dlen = strlen (dir);
 196   while (dlen > 1 && dir[dlen - 1] == '/')
 197     dlen--;                     /* remove trailing slashes */
 198
 199   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 200   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 201     {
 202       __set_errno (EINVAL);
 203       return -1;
 204     }
 205
 206   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 207   return 0;
 208 }
 209
 210 /* These are the characters used in temporary filenames.  */
 211 static const char letters[] =
 212 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 213
 214 /* Generate a temporary file name based on TMPL.  TMPL must match the
 215    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 216    does not exist at the time of the call to __gen_tempname.  TMPL is
 217    overwritten with the result.
 218
 219    KIND may be one of:
 220    __GT_NOCREATE:       simply verify that the name does not exist
 221                         at the time of the call.
 222    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 223                         and return a read-write fd.  The file is mode 0600.
 224    __GT_BIGFILE:        same as __GT_FILE but use open64().
 225    __GT_DIR:            create a directory, which will be mode 0700.
 226
 227    We use a clever algorithm to get hard-to-predict names. */
 228 int
 229 __gen_tempname (char *tmpl, int kind)
 230 {
 231   int len;
 232   char *XXXXXX;
 233   static uint64_t value;
 234   uint64_t random_time_bits;
 235   unsigned int count;
 236   int fd = -1;
 237   int save_errno = errno;
 238   struct_stat64 st;
 239
 240   /* A lower bound on the number of temporary files to attempt to
 241      generate.  The maximum total number of temporary file names that
 242      can exist for a given template is 62**6.  It should never be
 243      necessary to try all these combinations.  Instead if a reasonable
 244      number of names is tried (we define reasonable as 62**3) fail to
 245      give the system administrator the chance to remove the problems.  */
 246   unsigned int attempts_min = 62 * 62 * 62;
 247
 248   /* The number of times to attempt to generate a temporary file.  To
 249      conform to POSIX, this must be no smaller than TMP_MAX.  */
 250   unsigned int attempts = attempts_min < TMP_MAX ? TMP_MAX : attempts_min;
 251
 252   len = strlen (tmpl);
 253   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 254     {
 255       __set_errno (EINVAL);
 256       return -1;
 257     }
 258
 259   /* This is where the Xs start.  */
 260   XXXXXX = &tmpl[len - 6];
 261
 262   /* Get some more or less random data.  */
 263 #ifdef RANDOM_BITS
 264   RANDOM_BITS (random_time_bits);
 265 #else
 266 # if HAVE_GETTIMEOFDAY || _LIBC
 267   {
 268     struct timeval tv;
 269     __gettimeofday (&tv, NULL);
 270     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 271   }
 272 # else
 273   random_time_bits = time (NULL);
 274 # endif
 275 #endif
 276   value += random_time_bits ^ __getpid ();
 277
 278   for (count = 0; count < attempts; value += 7777, ++count)
 279     {
 280       uint64_t v = value;
 281
 282       /* Fill in the random bits.  */
 283       XXXXXX[0] = letters[v % 62];
 284       v /= 62;
 285       XXXXXX[1] = letters[v % 62];
 286       v /= 62;
 287       XXXXXX[2] = letters[v % 62];
 288       v /= 62;
 289       XXXXXX[3] = letters[v % 62];
 290       v /= 62;
 291       XXXXXX[4] = letters[v % 62];
 292       v /= 62;
 293       XXXXXX[5] = letters[v % 62];
 294
 295       switch (kind)
 296         {
 297         case __GT_FILE:
 298           fd = __open (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 299           break;
 300
 301         case __GT_BIGFILE:
 302           fd = __open64 (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 303           break;
 304
 305         case __GT_DIR:
 306           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 307           break;
 308
 309         case __GT_NOCREATE:
 310           /* This case is backward from the other three.  __gen_tempname
 311              succeeds if __xstat fails because the name does not exist.
 312              Note the continue to bypass the common logic at the bottom
 313              of the loop.  */
 314           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 315             {
 316               if (errno == ENOENT)
 317                 {
 318                   __set_errno (save_errno);
 319                   return 0;
 320                 }
 321               else
 322                 /* Give up now. */
 323                 return -1;
 324             }
 325           continue;
 326
 327         default:
 328           assert (! "invalid KIND in __gen_tempname");
 329         }
 330
 331       if (fd >= 0)
 332         {
 333           __set_errno (save_errno);
 334           return fd;
 335         }
 336       else if (errno != EEXIST)
 337         return -1;
 338     }
 339
 340   /* We got out of the loop because we ran out of combinations to try.  */
 341   __set_errno (EEXIST);
 342   return -1;
 343 }