sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-1999, 2000, 2001, 2006 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 <stdlib.h>
  48 # include <string.h>
  49 #endif
  50
  51 #if HAVE_FCNTL_H || _LIBC
  52 # include <fcntl.h>
  53 #endif
  54
  55 #if HAVE_SYS_TIME_H || _LIBC
  56 # include <sys/time.h>
  57 #endif
  58
  59 #if HAVE_STDINT_H || _LIBC
  60 # include <stdint.h>
  61 #endif
  62
  63 #if HAVE_UNISTD_H || _LIBC
  64 # include <unistd.h>
  65 #endif
  66
  67 #include <sys/stat.h>
  68 #if STAT_MACROS_BROKEN
  69 # undef S_ISDIR
  70 #endif
  71 #if !defined S_ISDIR && defined S_IFDIR
  72 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  73 #endif
  74 #if !S_IRUSR && S_IREAD
  75 # define S_IRUSR S_IREAD
  76 #endif
  77 #if !S_IRUSR
  78 # define S_IRUSR 00400
  79 #endif
  80 #if !S_IWUSR && S_IWRITE
  81 # define S_IWUSR S_IWRITE
  82 #endif
  83 #if !S_IWUSR
  84 # define S_IWUSR 00200
  85 #endif
  86 #if !S_IXUSR && S_IEXEC
  87 # define S_IXUSR S_IEXEC
  88 #endif
  89 #if !S_IXUSR
  90 # define S_IXUSR 00100
  91 #endif
  92
  93 #if _LIBC
  94 # define struct_stat64 struct stat64
  95 #else
  96 # define struct_stat64 struct stat
  97 # define __getpid getpid
  98 # define __gettimeofday gettimeofday
  99 # define __mkdir mkdir
 100 # define __open open
 101 # define __open64 open
 102 # define __lxstat64(version, path, buf) lstat (path, buf)
 103 # define __xstat64(version, path, buf) stat (path, buf)
 104 #endif
 105
 106 #if ! (HAVE___SECURE_GETENV || _LIBC)
 107 # define __secure_getenv getenv
 108 #endif
 109
 110 #ifdef _LIBC
 111 # include <hp-timing.h>
 112 # if HP_TIMING_AVAIL
 113 #  define RANDOM_BITS(Var) \
 114   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 115     {                                                                         \
 116       /* If this is the first time this function is used initialize           \
 117          the variable we accumulate the value in to some somewhat             \
 118          random value.  If we'd not do this programs at startup time          \
 119          might have a reduced set of possible names, at least on slow         \
 120          machines.  */                                                        \
 121       struct timeval tv;                                                      \
 122       __gettimeofday (&tv, NULL);                                             \
 123       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 124     }                                                                         \
 125   HP_TIMING_NOW (Var)
 126 # endif
 127 #endif
 128
 129 /* Use the widest available unsigned type if uint64_t is not
 130    available.  The algorithm below extracts a number less than 62**6
 131    (approximately 2**35.725) from uint64_t, so ancient hosts where
 132    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 133    which is better than not having mkstemp at all.  */
 134 #if !defined UINT64_MAX && !defined uint64_t
 135 # define uint64_t uintmax_t
 136 #endif
 137
 138 /* Return nonzero if DIR is an existent directory.  */
 139 static int
 140 direxists (const char *dir)
 141 {
 142   struct_stat64 buf;
 143   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 144 }
 145
 146 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 147    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 148    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 149    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 150    doesn't exist, none of the searched dirs exists, or there's not
 151    enough space in TMPL. */
 152 int
 153 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 154                int try_tmpdir)
 155 {
 156   const char *d;
 157   size_t dlen, plen;
 158
 159   if (!pfx || !pfx[0])
 160     {
 161       pfx = "file";
 162       plen = 4;
 163     }
 164   else
 165     {
 166       plen = strlen (pfx);
 167       if (plen > 5)
 168         plen = 5;
 169     }
 170
 171   if (try_tmpdir)
 172     {
 173       d = __secure_getenv ("TMPDIR");
 174       if (d != NULL && direxists (d))
 175         dir = d;
 176       else if (dir != NULL && direxists (dir))
 177         /* nothing */ ;
 178       else
 179         dir = NULL;
 180     }
 181   if (dir == NULL)
 182     {
 183       if (direxists (P_tmpdir))
 184         dir = P_tmpdir;
 185       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 186         dir = "/tmp";
 187       else
 188         {
 189           __set_errno (ENOENT);
 190           return -1;
 191         }
 192     }
 193
 194   dlen = strlen (dir);
 195   while (dlen > 1 && dir[dlen - 1] == '/')
 196     dlen--;                     /* remove trailing slashes */
 197
 198   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 199   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 200     {
 201       __set_errno (EINVAL);
 202       return -1;
 203     }
 204
 205   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 206   return 0;
 207 }
 208
 209 /* These are the characters used in temporary filenames.  */
 210 static const char letters[] =
 211 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 212
 213 /* Generate a temporary file name based on TMPL.  TMPL must match the
 214    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 215    does not exist at the time of the call to __gen_tempname.  TMPL is
 216    overwritten with the result.
 217
 218    KIND may be one of:
 219    __GT_NOCREATE:       simply verify that the name does not exist
 220                         at the time of the call.
 221    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 222                         and return a read-write fd.  The file is mode 0600.
 223    __GT_BIGFILE:        same as __GT_FILE but use open64().
 224    __GT_DIR:            create a directory, which will be mode 0700.
 225
 226    We use a clever algorithm to get hard-to-predict names. */
 227 int
 228 __gen_tempname (char *tmpl, int kind)
 229 {
 230   int len;
 231   char *XXXXXX;
 232   static uint64_t value;
 233   uint64_t random_time_bits;
 234   unsigned int count;
 235   int fd = -1;
 236   int save_errno = errno;
 237   struct_stat64 st;
 238
 239   /* A lower bound on the number of temporary files to attempt to
 240      generate.  The maximum total number of temporary file names that
 241      can exist for a given template is 62**6.  It should never be
 242      necessary to try all these combinations.  Instead if a reasonable
 243      number of names is tried (we define reasonable as 62**3) fail to
 244      give the system administrator the chance to remove the problems.  */
 245 #define ATTEMPTS_MIN (62 * 62 * 62)
 246
 247   /* The number of times to attempt to generate a temporary file.  To
 248      conform to POSIX, this must be no smaller than TMP_MAX.  */
 249 #if ATTEMPTS_MIN < TMP_MAX
 250   unsigned int attempts = TMP_MAX;
 251 #else
 252   unsigned int attempts = ATTEMPTS_MIN;
 253 #endif
 254
 255   len = strlen (tmpl);
 256   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 257     {
 258       __set_errno (EINVAL);
 259       return -1;
 260     }
 261
 262   /* This is where the Xs start.  */
 263   XXXXXX = &tmpl[len - 6];
 264
 265   /* Get some more or less random data.  */
 266 #ifdef RANDOM_BITS
 267   RANDOM_BITS (random_time_bits);
 268 #else
 269 # if HAVE_GETTIMEOFDAY || _LIBC
 270   {
 271     struct timeval tv;
 272     __gettimeofday (&tv, NULL);
 273     random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
 274   }
 275 # else
 276   random_time_bits = time (NULL);
 277 # endif
 278 #endif
 279   value += random_time_bits ^ __getpid ();
 280
 281   for (count = 0; count < attempts; value += 7777, ++count)
 282     {
 283       uint64_t v = value;
 284
 285       /* Fill in the random bits.  */
 286       XXXXXX[0] = letters[v % 62];
 287       v /= 62;
 288       XXXXXX[1] = letters[v % 62];
 289       v /= 62;
 290       XXXXXX[2] = letters[v % 62];
 291       v /= 62;
 292       XXXXXX[3] = letters[v % 62];
 293       v /= 62;
 294       XXXXXX[4] = letters[v % 62];
 295       v /= 62;
 296       XXXXXX[5] = letters[v % 62];
 297
 298       switch (kind)
 299         {
 300         case __GT_FILE:
 301           fd = __open (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 302           break;
 303
 304         case __GT_BIGFILE:
 305           fd = __open64 (tmpl, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 306           break;
 307
 308         case __GT_DIR:
 309           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 310           break;
 311
 312         case __GT_NOCREATE:
 313           /* This case is backward from the other three.  __gen_tempname
 314              succeeds if __xstat fails because the name does not exist.
 315              Note the continue to bypass the common logic at the bottom
 316              of the loop.  */
 317           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 318             {
 319               if (errno == ENOENT)
 320                 {
 321                   __set_errno (save_errno);
 322                   return 0;
 323                 }
 324               else
 325                 /* Give up now. */
 326                 return -1;
 327             }
 328           continue;
 329
 330         default:
 331           assert (! "invalid KIND in __gen_tempname");
 332         }
 333
 334       if (fd >= 0)
 335         {
 336           __set_errno (save_errno);
 337           return fd;
 338         }
 339       else if (errno != EEXIST)
 340         return -1;
 341     }
 342
 343   /* We got out of the loop because we ran out of combinations to try.  */
 344   __set_errno (EEXIST);
 345   return -1;
 346 }