sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991-2001, 2006, 2007 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_DIR       1
  41 # define __GT_NOCREATE  2
  42 #endif
  43
  44 #if STDC_HEADERS || _LIBC
  45 # include <stddef.h>
  46 # include <stdlib.h>
  47 # include <string.h>
  48 #endif
  49
  50 #if HAVE_FCNTL_H || _LIBC
  51 # include <fcntl.h>
  52 #endif
  53
  54 #if HAVE_SYS_TIME_H || _LIBC
  55 # include <sys/time.h>
  56 #endif
  57
  58 #if HAVE_STDINT_H || _LIBC
  59 # include <stdint.h>
  60 #endif
  61
  62 #if HAVE_UNISTD_H || _LIBC
  63 # include <unistd.h>
  64 #endif
  65
  66 #include <sys/stat.h>
  67 #if STAT_MACROS_BROKEN
  68 # undef S_ISDIR
  69 #endif
  70 #if !defined S_ISDIR && defined S_IFDIR
  71 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
  72 #endif
  73 #if !S_IRUSR && S_IREAD
  74 # define S_IRUSR S_IREAD
  75 #endif
  76 #if !S_IRUSR
  77 # define S_IRUSR 00400
  78 #endif
  79 #if !S_IWUSR && S_IWRITE
  80 # define S_IWUSR S_IWRITE
  81 #endif
  82 #if !S_IWUSR
  83 # define S_IWUSR 00200
  84 #endif
  85 #if !S_IXUSR && S_IEXEC
  86 # define S_IXUSR S_IEXEC
  87 #endif
  88 #if !S_IXUSR
  89 # define S_IXUSR 00100
  90 #endif
  91
  92 #if _LIBC
  93 # define struct_stat64 struct stat64
  94 #else
  95 # define struct_stat64 struct stat
  96 # define __getpid getpid
  97 # define __gettimeofday gettimeofday
  98 # define __mkdir mkdir
  99 # define __open open
 100 # define __open64 open
 101 # define __lxstat64(version, path, buf) lstat (path, buf)
 102 # define __xstat64(version, path, buf) stat (path, buf)
 103 #endif
 104
 105 #if ! (HAVE___SECURE_GETENV || _LIBC)
 106 # define __secure_getenv getenv
 107 #endif
 108
 109 #ifdef _LIBC
 110 # include <hp-timing.h>
 111 # if HP_TIMING_AVAIL
 112 #  define RANDOM_BITS(Var) \
 113   if (__builtin_expect (value == UINT64_C (0), 0))                            \
 114     {                                                                         \
 115       /* If this is the first time this function is used initialize           \
 116          the variable we accumulate the value in to some somewhat             \
 117          random value.  If we'd not do this programs at startup time          \
 118          might have a reduced set of possible names, at least on slow         \
 119          machines.  */                                                        \
 120       struct timeval tv;                                                      \
 121       __gettimeofday (&tv, NULL);                                             \
 122       value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;                      \
 123     }                                                                         \
 124   HP_TIMING_NOW (Var)
 125 # endif
 126 #endif
 127
 128 /* Use the widest available unsigned type if uint64_t is not
 129    available.  The algorithm below extracts a number less than 62**6
 130    (approximately 2**35.725) from uint64_t, so ancient hosts where
 131    uintmax_t is only 32 bits lose about 3.725 bits of randomness,
 132    which is better than not having mkstemp at all.  */
 133 #if !defined UINT64_MAX && !defined uint64_t
 134 # define uint64_t uintmax_t
 135 #endif
 136
 137 /* Return nonzero if DIR is an existent directory.  */
 138 static int
 139 direxists (const char *dir)
 140 {
 141   struct_stat64 buf;
 142   return __xstat64 (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
 143 }
 144
 145 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
 146    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
 147    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
 148    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
 149    doesn't exist, none of the searched dirs exists, or there's not
 150    enough space in TMPL. */
 151 int
 152 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
 153                int try_tmpdir)
 154 {
 155   const char *d;
 156   size_t dlen, plen;
 157
 158   if (!pfx || !pfx[0])
 159     {
 160       pfx = "file";
 161       plen = 4;
 162     }
 163   else
 164     {
 165       plen = strlen (pfx);
 166       if (plen > 5)
 167         plen = 5;
 168     }
 169
 170   if (try_tmpdir)
 171     {
 172       d = __secure_getenv ("TMPDIR");
 173       if (d != NULL && direxists (d))
 174         dir = d;
 175       else if (dir != NULL && direxists (dir))
 176         /* nothing */ ;
 177       else
 178         dir = NULL;
 179     }
 180   if (dir == NULL)
 181     {
 182       if (direxists (P_tmpdir))
 183         dir = P_tmpdir;
 184       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
 185         dir = "/tmp";
 186       else
 187         {
 188           __set_errno (ENOENT);
 189           return -1;
 190         }
 191     }
 192
 193   dlen = strlen (dir);
 194   while (dlen > 1 && dir[dlen - 1] == '/')
 195     dlen--;                     /* remove trailing slashes */
 196
 197   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
 198   if (tmpl_len < dlen + 1 + plen + 6 + 1)
 199     {
 200       __set_errno (EINVAL);
 201       return -1;
 202     }
 203
 204   sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx);
 205   return 0;
 206 }
 207
 208 /* These are the characters used in temporary filenames.  */
 209 static const char letters[] =
 210 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 211
 212 /* Generate a temporary file name based on TMPL.  TMPL must match the
 213    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 214    does not exist at the time of the call to __gen_tempname.  TMPL is
 215    overwritten with the result.
 216
 217    KIND may be one of:
 218    __GT_NOCREATE:       simply verify that the name does not exist
 219                         at the time of the call.
 220    __GT_FILE:           create the file using open(O_CREAT|O_EXCL)
 221                         and return a read-write fd.  The file is mode 0600.
 222    __GT_DIR:            create a directory, which will be mode 0700.
 223
 224    We use a clever algorithm to get hard-to-predict names. */
 225 int
 226 __gen_tempname (char *tmpl, int flags, int kind)
 227 {
 228   int len;
 229   char *XXXXXX;
 230   static uint64_t value;
 231   uint64_t random_time_bits;
 232   unsigned int count;
 233   int fd = -1;
 234   int save_errno = errno;
 235   struct_stat64 st;
 236
 237   /* A lower bound on the number of temporary files to attempt to
 238      generate.  The maximum total number of temporary file names that
 239      can exist for a given template is 62**6.  It should never be
 240      necessary to try all these combinations.  Instead if a reasonable
 241      number of names is tried (we define reasonable as 62**3) fail to
 242      give the system administrator the chance to remove the problems.  */
 243 #define ATTEMPTS_MIN (62 * 62 * 62)
 244
 245   /* The number of times to attempt to generate a temporary file.  To
 246      conform to POSIX, this must be no smaller than TMP_MAX.  */
 247 #if ATTEMPTS_MIN < TMP_MAX
 248   unsigned int attempts = TMP_MAX;
 249 #else
 250   unsigned int attempts = ATTEMPTS_MIN;
 251 #endif
 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,
 300                        (flags & ~O_ACCMODE)
 301                        | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
 302           break;
 303
 304         case __GT_DIR:
 305           fd = __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR);
 306           break;
 307
 308         case __GT_NOCREATE:
 309           /* This case is backward from the other three.  __gen_tempname
 310              succeeds if __xstat fails because the name does not exist.
 311              Note the continue to bypass the common logic at the bottom
 312              of the loop.  */
 313           if (__lxstat64 (_STAT_VER, tmpl, &st) < 0)
 314             {
 315               if (errno == ENOENT)
 316                 {
 317                   __set_errno (save_errno);
 318                   return 0;
 319                 }
 320               else
 321                 /* Give up now. */
 322                 return -1;
 323             }
 324           continue;
 325
 326         default:
 327           assert (! "invalid KIND in __gen_tempname");
 328         }
 329
 330       if (fd >= 0)
 331         {
 332           __set_errno (save_errno);
 333           return fd;
 334         }
 335       else if (errno != EEXIST)
 336         return -1;
 337     }
 338
 339   /* We got out of the loop because we ran out of combinations to try.  */
 340   __set_errno (EEXIST);
 341   return -1;
 342 }